Mapping the Stable Isotopes to Understand the Geo-Structural Control of Groundwater Recharge and Flow Mechanisms (Case Study From the Northeastern Basin of the West Bank)

*Saed Khayat, Amer Marei and Zaher Barghouthi*

## **Abstract**

Conventional stable isotopic technique was used to differentiate between the potential recharge sources and mixing and flow mechanisms in the Northeastern basin of the West Bank. The isotopic signatures from deep wells show two main fingerprints with respect to recharge sources and mechanisms. These are wells located in the upper part of the Faria fault system and along the Rujeib Moncline which are fed by triggered water in-line the fault system in the south and deep wells surrounded by the Anabta anticline to the west which are fed by the exposed Jerusalem-Hebron formations. This suggests a mixing process with freshwater sources that mainly flow to the system from southern mountains. The isotopic signatures from the shallow well in Marj Sanoor wells and Nassariyeh in the upper Faria well suggest a kind of partial recharge from the Marj Sanoor Lake leaking to the upper Faria Graben area and participating in the recharge process of these wells. The whole finding out of this project might be used for tuning and revision of the groundwater model that has been built by the Palestinian Water Authority.

**Keywords:** isotope hydrology, Palestine, Northeastern aquifer, recharge mechanism, groundwater salinity

## **1. Introduction**

Providing the Palestinian people with their water needs is the main concern for the Palestinian Water Authority, Ministry of Agriculture, as well as for water service providers. During the last 20 years, the annual average water consumption from the Northeastern aquifer reached 25 MCM [1]; this is due to improvement of water infrastructure including drilling new domestic deep wells, improvement of water institutions, and increase in the public awareness.

Tapping of groundwater, using spring water, purchase of water from Mekerot Israeli Company, and collection of rainwater are the sources for domestic and agricultural water in the West Bank. In this context, groundwater is the main one which covers about 70% of the total water supply which is about 100–145 MCM/a from the three water basins in the West Bank, namely, Eastern, Western, and Northeastern (the study area) [1]. During the last two decades, many domestic deep wells were drilled in the Mountain Aquifer in order to improve domestic water supply, where hundreds of illegal groundwater boreholes are drilled in the shallow aquifer systems mainly in Jenin and Jericho districts.

The Mountain Aquifer system with its three groundwater basins, namely, Western, Eastern, and Northeastern basins, covers most of the West Bank area (**Figure 1a**). The Western and Eastern basins cover the western and eastern parts of the West Bank and extend from Hebron in the south to Jerusalem and Ramallah in the north, while the Northeastern locates in the northern part of the West Bank, within the boundary of Nablus-Beit Qad syncline. About 410,000 Palestinians are living in three main districts (Nablus, Jenin, and Tubas), within the surface catchment area of this basin. These districts include large cities such as Nablus, Jenin, Tubas, and Tammon, beside many small municipalities, villages, and refugee camps [2].

Due to the fact that groundwater is the main source of water in the West Bank, management of this source is a high priority by line ministries, so solid and advance scientific knowledge is essential for sustainable management of the water resources [4]. Identification of recharge-discharge zones, groundwater flow regimes, connection between sub-basins, as well as shallow and deep aquifer systems are vectors for better management process. Applying environmental stable isotopic is a method in hydrogeology that is used to help in identification of these vectors, so we use O18 [SMOW] ‰ and D in the Northeastern Basin (NE Basin). We also combined the isotope analysis method, with the geological and hydrogeological setting of the sub-catchment areas [5]. High attention is given to the role of the main structural features of the groundwater flow regimes.

Recharge mechanisms, flow direction, and groundwater resident time are generally quite difficult to measure directly. Measurement of recharge flow can be exacerbated by preferential flow (i.e., macropore flow) in the unsaturated zone, although preferential flow paths are of greatest concern as potential conduits for rapid contamination of aquifers. The above factors, in addition to

**65**

**Figure 2.**

*(a and b) Geological map of the West Bank and NE Basin.*

*Mapping the Stable Isotopes to Understand the Geo-Structural Control of Groundwater Recharge…*

temporal and spatial variability, greatly complicate the estimation of basin-wide recharge rates and flow mechanisms. Estimation methods include use of water budgets, tracers, geophysics, and simulation models. Because of the inherent uncertainties in any method, it is often advisable to apply multiple techniques for

Isotopes as tracer's isotopes for mapping the groundwater recharge and flow mechanisms are important tools in groundwater research and in sustainable

management of groundwater resources. Important applications in shallow and deep groundwater include estimation of groundwater recharge and evaluation of the fate of contaminants, because meaningful groundwater deviation from the local meteoric water line LMWL gives the possibility to determine the residence time of

Sedimentary rocks of the Upper Cretaceous to Quaternary ages cover most of the surface areas of the West Bank. Old rock formation exposed deep eroded area at the top of the anticlines or in deep wades and along some structural features (**Figure 2a**). The development of the structural features took place during the Late Upper Cretaceous-Tartary ages, where many structural features are still active. In the study area, two anticlines and one syncline in addition to the Faria Graben are main structural features. The Anabta anticline with northwest direction, parallel to the Faria anticline with northeast axis direction, borders the study area from the west and east, respectively, where the lines at the top of booths consider as surface/ sub-surface water divide. Nablus-Beit Qad syncline with northeast axis direction locates between the two anticlines [9]. Due to the erosion process, the top of the anticlines is eroded, where rock formation of Cenomanian age crops out at the top of Faria and Anabta anticline, where carbonate rock of Eocene to Quaternary ages

*DOI: http://dx.doi.org/10.5772/intechopen.90449*

groundwater and the dissolved contaminants [6–8].

**2. Hydrogeological settings in NE Basin of the West Bank**

covers the central part of Nablus-Beit Qad syncline (**Figure 2b**).

any study.

**Figure 1.** *(a) Location of the Northeastern Basin and (b) urban zones in the NE basin catchment area [3].*

*Mapping the Stable Isotopes to Understand the Geo-Structural Control of Groundwater Recharge… DOI: http://dx.doi.org/10.5772/intechopen.90449*

temporal and spatial variability, greatly complicate the estimation of basin-wide recharge rates and flow mechanisms. Estimation methods include use of water budgets, tracers, geophysics, and simulation models. Because of the inherent uncertainties in any method, it is often advisable to apply multiple techniques for any study.

Isotopes as tracer's isotopes for mapping the groundwater recharge and flow mechanisms are important tools in groundwater research and in sustainable management of groundwater resources. Important applications in shallow and deep groundwater include estimation of groundwater recharge and evaluation of the fate of contaminants, because meaningful groundwater deviation from the local meteoric water line LMWL gives the possibility to determine the residence time of groundwater and the dissolved contaminants [6–8].

## **2. Hydrogeological settings in NE Basin of the West Bank**

Sedimentary rocks of the Upper Cretaceous to Quaternary ages cover most of the surface areas of the West Bank. Old rock formation exposed deep eroded area at the top of the anticlines or in deep wades and along some structural features (**Figure 2a**). The development of the structural features took place during the Late Upper Cretaceous-Tartary ages, where many structural features are still active. In the study area, two anticlines and one syncline in addition to the Faria Graben are main structural features. The Anabta anticline with northwest direction, parallel to the Faria anticline with northeast axis direction, borders the study area from the west and east, respectively, where the lines at the top of booths consider as surface/ sub-surface water divide. Nablus-Beit Qad syncline with northeast axis direction locates between the two anticlines [9]. Due to the erosion process, the top of the anticlines is eroded, where rock formation of Cenomanian age crops out at the top of Faria and Anabta anticline, where carbonate rock of Eocene to Quaternary ages covers the central part of Nablus-Beit Qad syncline (**Figure 2b**).

**Figure 2.** *(a and b) Geological map of the West Bank and NE Basin.*

*Isotopes Applications in Earth Sciences*

mainly in Jenin and Jericho districts.

municipalities, villages, and refugee camps [2].

features of the groundwater flow regimes.

covers about 70% of the total water supply which is about 100–145 MCM/a from the three water basins in the West Bank, namely, Eastern, Western, and Northeastern (the study area) [1]. During the last two decades, many domestic deep wells were drilled in the Mountain Aquifer in order to improve domestic water supply, where hundreds of illegal groundwater boreholes are drilled in the shallow aquifer systems

The Mountain Aquifer system with its three groundwater basins, namely, Western, Eastern, and Northeastern basins, covers most of the West Bank area (**Figure 1a**). The Western and Eastern basins cover the western and eastern parts of the West Bank and extend from Hebron in the south to Jerusalem and Ramallah in the north, while the Northeastern locates in the northern part of the West Bank, within the boundary of Nablus-Beit Qad syncline. About 410,000 Palestinians are living in three main districts (Nablus, Jenin, and Tubas), within the surface catchment area of this basin. These districts include large cities such as Nablus, Jenin, Tubas, and Tammon, beside many small

Due to the fact that groundwater is the main source of water in the West Bank, management of this source is a high priority by line ministries, so solid and advance scientific knowledge is essential for sustainable management of the water resources [4]. Identification of recharge-discharge zones, groundwater flow regimes, connection between sub-basins, as well as shallow and deep aquifer systems are vectors for better management process. Applying environmental stable isotopic is a method in hydrogeology that is used to help in identification of these vectors, so we use

[SMOW] ‰ and D in the Northeastern Basin (NE Basin). We also combined the isotope analysis method, with the geological and hydrogeological setting of the sub-catchment areas [5]. High attention is given to the role of the main structural

Recharge mechanisms, flow direction, and groundwater resident time are generally quite difficult to measure directly. Measurement of recharge flow can be exacerbated by preferential flow (i.e., macropore flow) in the unsaturated zone, although preferential flow paths are of greatest concern as potential conduits for rapid contamination of aquifers. The above factors, in addition to

*(a) Location of the Northeastern Basin and (b) urban zones in the NE basin catchment area [3].*

**64**

**Figure 1.**

O18

## **2.1 Stratigraphy**

The stratigraphy sequences of the sedimentary rocks are the following from youngest to the oldest (**Figure 1b**) [10]:

### *2.1.1 Alluvial deposits (Quaternary to recent age)*

It consists of alluvial deposits, mainly sand and gravel in flat and depression areas within the syncline. Brown earth Rendzina is the dominant soil type. The alluvial deposits cover an area of about 215 km2 and normally overlay the Jenin subseries formation (**Figure 2b**).

#### *2.1.2 Jenin subseries (Eocene age)*

It consists of six members: relief limestone, nummulitic limestone, karstified limestone, limestone, and chalky limestone. The thickness of this subseries varies from one site to another depending on the location within the syncline but generally range between 100 and 300 m. The series is considered as a local shallow aquifer system that is used mostly in the agricultural sector. The majority of the springs in the NE Basin drain water from this aquifer; in addition to that, most of the groundwater boreholes (up to 350 m depth) in Jenin governorate are tapping water from this system. This rock formation covers an area of about 378 km2 (**Figure 2b**). This formation overlays the Abu Dis formation in the central part of the syncline, where the Jerzim Group crop outs in the southern part of Nablus city.

#### *2.1.3 Jerzim group (Maastrichtian age)*

This group crops out in Jerzim Mountain 832 m above sea level within the southern part of the syncline to the south of Nablus city. It consists of chert nodules, chalk, and chalky limestone. The thickness is about 400 m. This group is considered as a local aquifer, where many springs in Nablus city drain water from this formation along the contact line between this layer and the underlying Abu Dis chalk unit.

### *2.1.4 Abu Dis unit (Senonian age)*

It is composed of a massive thick hard chalk unit, interbedded with two bands of highly fractured cherty layers with a distance of 2–5 m between the two bands; the material of the upper part of unit l becomes soft and unclear in bedding. The unit exposes to the surface over the anticline flanks (**Figure 2b**) with a thickness range between 100 m at the edges and 500 m in the middle of the syncline. This unit is considered as an impermeable layer that separates the shallow Eocene aquifer from the underlying Jerusalem formation that is considered as the upper part of the Upper Mountain Aquifer system. The chalky units cover an area of about 153 km2 .

#### *2.1.5 Jerusalem formation (Turonian age)*

This formation consists of thin-bedded highly fractured limestone and dolomitic limestone. The lower part consists mainly of rosy limestone, where oyster fossil could be found at the top of this formation with variable thickness range between 70 and 150 m thick. This formation is cropped out mainly over the anticline and considered as recharge zone, where below the central part of the syncline consider as good aquifer. This formation overlays the Bethlehem formation (**Figure 2b**, Upper Aquifer).

**67**

Faria Graben.

**2.2 Hydrology**

*Mapping the Stable Isotopes to Understand the Geo-Structural Control of Groundwater Recharge…*

This formation consists of 50–120 m of thin-bedded limestone and marly limestone which is highly karstified. Large caves and voids are common phenomena within this formation. This formation outcrop also covers the anticline flanks, and considers as the Jerusalem formation as good aquifer in the central and western part

It consists of 105–250 m of thick bedded limestone and dolomite; it is highly fractured and karstified. This formation is cropped out also over the anticlines flanks and in deep eroded Wadis like Wadi Al Faria (**Figure 2b**), in these sites; it considers are recharge zone, where within the syncline consider as a target layer for

It is composed mainly of marl and marly limestone; this formation is considered as an aquiclude in the southern part of the West Bank and separates the Upper from the Lower Aquifer system, but in the study area, this formation is more of limestone than marl and crops out at the flank of the anticline and is considered as part of the

The catchment area of the Upper Aquifer system (Jerusalem, Bethlehem, and

Aquifer system of the Mountain Aquifer system and are separated from the Lower Aquifer system through impermeable marl layer of Yatta formation of Lower Cenomanian age. Older formations such as Upper and Lower Beit Kahel do not out

. Together, Jerusalem, Bethlehem, and Hebron formation build up the Upper

It consists of a 160–190-m-thick well-bedded limestone and dolomite. The lower part of this formation is made up of limestone with thin layers of porous dolomite interchanging with marly limestone and calcite massive limestone near the base.

It consists of gray limestone layers alternating with layers of shale and marl in the lower part, whereas the upper part is made up of gray to brown dolomite with

Both formations are considered as Lower Aquifer system of the Mountain Aquifer in the southern part of the West Bank, but in the northern part of the Upper and Lower Aquifer system, they are considered as one hydrological system.

crop out also in deep eroded streams within the Faria anticline as well as within the

Rainy months extend from October to May, where 70% of the rainfall takes place between December and February. **Figure 3** shows the rain fall distribution during

The outcrop area of the deep aquifer system is about 33 km2

, where the area of Yatta formation is about

. The two formations

*DOI: http://dx.doi.org/10.5772/intechopen.90449*

of the basin (**Figure 2b**, Upper Aquifer).

groundwater subtraction.

Upper Aquifer system.

crop in the study area.

21 km2

Hebron formation) is about 148 km2

*2.1.9 Upper Bet Kahel formation (Albian)*

*2.1.10 Lower Bet Kahel Formation (Albian)*

clayey and marly limestone.

*2.1.7 Hebron formations (Upper Cenomanian age)*

*2.1.8 Yatta formation (Lower Cenomanian age)*

*2.1.6 Bethlehem formations (Upper Cenomanian age)*

*Mapping the Stable Isotopes to Understand the Geo-Structural Control of Groundwater Recharge… DOI: http://dx.doi.org/10.5772/intechopen.90449*

#### *2.1.6 Bethlehem formations (Upper Cenomanian age)*

*Isotopes Applications in Earth Sciences*

youngest to the oldest (**Figure 1b**) [10]:

subseries formation (**Figure 2b**).

*2.1.2 Jenin subseries (Eocene age)*

*2.1.3 Jerzim group (Maastrichtian age)*

*2.1.4 Abu Dis unit (Senonian age)*

*2.1.5 Jerusalem formation (Turonian age)*

*2.1.1 Alluvial deposits (Quaternary to recent age)*

alluvial deposits cover an area of about 215 km2

The stratigraphy sequences of the sedimentary rocks are the following from

It consists of alluvial deposits, mainly sand and gravel in flat and depression areas within the syncline. Brown earth Rendzina is the dominant soil type. The

It consists of six members: relief limestone, nummulitic limestone, karstified limestone, limestone, and chalky limestone. The thickness of this subseries varies from one site to another depending on the location within the syncline but generally range between 100 and 300 m. The series is considered as a local shallow aquifer system that is used mostly in the agricultural sector. The majority of the springs in the NE Basin drain water from this aquifer; in addition to that, most of the groundwater boreholes (up to 350 m depth) in Jenin governorate are tapping water from

formation overlays the Abu Dis formation in the central part of the syncline, where

This group crops out in Jerzim Mountain 832 m above sea level within the southern part of the syncline to the south of Nablus city. It consists of chert nodules, chalk, and chalky limestone. The thickness is about 400 m. This group is considered as a local aquifer, where many springs in Nablus city drain water from this formation along the contact line between this layer and the underlying Abu Dis chalk unit.

It is composed of a massive thick hard chalk unit, interbedded with two bands of highly fractured cherty layers with a distance of 2–5 m between the two bands; the material of the upper part of unit l becomes soft and unclear in bedding. The unit exposes to the surface over the anticline flanks (**Figure 2b**) with a thickness range between 100 m at the edges and 500 m in the middle of the syncline. This unit is considered as an impermeable layer that separates the shallow Eocene aquifer from the underlying Jerusalem formation that is considered as the upper part of the Upper Mountain Aquifer system. The chalky units cover an area of about 153 km2

This formation consists of thin-bedded highly fractured limestone and dolomitic

limestone. The lower part consists mainly of rosy limestone, where oyster fossil could be found at the top of this formation with variable thickness range between 70 and 150 m thick. This formation is cropped out mainly over the anticline and considered as recharge zone, where below the central part of the syncline consider as good aquifer. This formation overlays the Bethlehem formation (**Figure 2b**,

this system. This rock formation covers an area of about 378 km2

the Jerzim Group crop outs in the southern part of Nablus city.

and normally overlay the Jenin

(**Figure 2b**). This

.

**2.1 Stratigraphy**

**66**

Upper Aquifer).

This formation consists of 50–120 m of thin-bedded limestone and marly limestone which is highly karstified. Large caves and voids are common phenomena within this formation. This formation outcrop also covers the anticline flanks, and considers as the Jerusalem formation as good aquifer in the central and western part of the basin (**Figure 2b**, Upper Aquifer).

#### *2.1.7 Hebron formations (Upper Cenomanian age)*

It consists of 105–250 m of thick bedded limestone and dolomite; it is highly fractured and karstified. This formation is cropped out also over the anticlines flanks and in deep eroded Wadis like Wadi Al Faria (**Figure 2b**), in these sites; it considers are recharge zone, where within the syncline consider as a target layer for groundwater subtraction.

#### *2.1.8 Yatta formation (Lower Cenomanian age)*

It is composed mainly of marl and marly limestone; this formation is considered as an aquiclude in the southern part of the West Bank and separates the Upper from the Lower Aquifer system, but in the study area, this formation is more of limestone than marl and crops out at the flank of the anticline and is considered as part of the Upper Aquifer system.

The catchment area of the Upper Aquifer system (Jerusalem, Bethlehem, and Hebron formation) is about 148 km2 , where the area of Yatta formation is about 21 km2 . Together, Jerusalem, Bethlehem, and Hebron formation build up the Upper Aquifer system of the Mountain Aquifer system and are separated from the Lower Aquifer system through impermeable marl layer of Yatta formation of Lower Cenomanian age. Older formations such as Upper and Lower Beit Kahel do not out crop in the study area.

#### *2.1.9 Upper Bet Kahel formation (Albian)*

It consists of a 160–190-m-thick well-bedded limestone and dolomite. The lower part of this formation is made up of limestone with thin layers of porous dolomite interchanging with marly limestone and calcite massive limestone near the base.

#### *2.1.10 Lower Bet Kahel Formation (Albian)*

It consists of gray limestone layers alternating with layers of shale and marl in the lower part, whereas the upper part is made up of gray to brown dolomite with clayey and marly limestone.

Both formations are considered as Lower Aquifer system of the Mountain Aquifer in the southern part of the West Bank, but in the northern part of the Upper and Lower Aquifer system, they are considered as one hydrological system. The outcrop area of the deep aquifer system is about 33 km2 . The two formations crop out also in deep eroded streams within the Faria anticline as well as within the Faria Graben.

#### **2.2 Hydrology**

Rainy months extend from October to May, where 70% of the rainfall takes place between December and February. **Figure 3** shows the rain fall distribution during

**Figure 3.** *Actual average rainfall in the West Bank in the hydrological year 2010/2011.*

the hydrological year 2015/2016, where three high rainfall zones are identified namely within the boundary of the basin, these are north of Nablus, Selet al Thaher with 600 and 800 mm/a respectively [11]. It's also noticed that rainfall decreases in the eastward direction of the Faria Graben which locates more within the rainfall shadow site (**Figure 3**). The average monthly temperature during December, January, and February is 11, 14, 17o C. respectively; this indicate that the losses of water through evapotranspiration is relatively low during these months which improve the groundwater recharge rate [12].

### **2.3 Groundwater aquifer systems**

The Northeastern Basin covers 959 km2 of surface area (**Figure 1b**), depending on surface water shed divide; within the basin, two aquifer systems are identified; Mountain Aquifer with rock layers related to the Upper Cretaceous age, and shallow aquifer with rock layers related to the Tertiary-Quaternary eras (Eocene-Miocene age). Both systems are hydraulically separated from each other in most of the basin especially in the central part but seems to be connected where deep structural features strike the rock layers of both systems, such as in Al Faria Graben [13].

Recharge process for both aquifer systems takes place wherever the rock formation is outcropped and exposed directly to the rainfall or underlying thin soil layers. Marei et al. estimate the groundwater recharge rate, by using chloride mass balance method for the study area, of about 95.2 and 269.7 mm/year, with a total average recharge volume of 138.5 MCM/year (**Figure 4**) [14], while the total calculated recharge rate by the previous study of the authors is 107.1 MCM/a [14]. Recharge rate can be higher than estimated when karstic and high fractured rock layers are cropped out at the surface such as the formation of the Upper and Lower Mountain aquifer system at the two anticline flanks in the west and in the east, in the other hand ground recharge decrease to about zero from Abu Dis formation "Chalky Unit". The formation of shallow aquifer system is exposed mainly in the central part of the basin, and water body responds quickly to rainfall.

**69**

**Figure 4.**

km2

**Table 1.**

Outcrop area with

Total recharge in MCM/a

*Recharge volume of NE Basin.*

*Mapping the Stable Isotopes to Understand the Geo-Structural Control of Groundwater Recharge…*

**Table 1** summarized the recharge volume of the deep and shallow aquifer

Recharge rate 210 mm/year 210 mm/year 200 mm/year Recharge volume 12.6 MCM 19.9 MCM 75.6 MCM

**Mountain Aquifer "Cretaceous age" Shallow Aquifer**

**Western flank of "Al Faria anticline"**

60 95 378

32.5 MCM 75.6 MCM

**"Eocene"**

**Nablus-Beit Qad "syncline"**

Two main groundwater flow regimes are assumed to present in the study area. These are as follows: a SW-NE main groundwater flow direction parallel to

systems depending on the chloride mass balance method [14].

*Recharge rate over the West Bank including the NE Basin (Marei et al., 2011).*

**Eastern flank of "Anabta anticline"**

**2.4 Groundwater flow regimes**

*DOI: http://dx.doi.org/10.5772/intechopen.90449*

*Mapping the Stable Isotopes to Understand the Geo-Structural Control of Groundwater Recharge… DOI: http://dx.doi.org/10.5772/intechopen.90449*

#### **Figure 4.**

*Isotopes Applications in Earth Sciences*

January, and February is 11, 14, 17o

**2.3 Groundwater aquifer systems**

improve the groundwater recharge rate [12].

*Actual average rainfall in the West Bank in the hydrological year 2010/2011.*

The Northeastern Basin covers 959 km2

of the basin, and water body responds quickly to rainfall.

the hydrological year 2015/2016, where three high rainfall zones are identified namely within the boundary of the basin, these are north of Nablus, Selet al Thaher with 600 and 800 mm/a respectively [11]. It's also noticed that rainfall decreases in the eastward direction of the Faria Graben which locates more within the rainfall shadow site (**Figure 3**). The average monthly temperature during December,

water through evapotranspiration is relatively low during these months which

ing on surface water shed divide; within the basin, two aquifer systems are identified; Mountain Aquifer with rock layers related to the Upper Cretaceous age, and shallow aquifer with rock layers related to the Tertiary-Quaternary eras (Eocene-Miocene age). Both systems are hydraulically separated from each other in most of the basin especially in the central part but seems to be connected where deep structural features strike the rock layers of both systems, such as in Al Faria

Recharge process for both aquifer systems takes place wherever the rock formation is outcropped and exposed directly to the rainfall or underlying thin soil layers. Marei et al. estimate the groundwater recharge rate, by using chloride mass balance method for the study area, of about 95.2 and 269.7 mm/year, with a total average recharge volume of 138.5 MCM/year (**Figure 4**) [14], while the total calculated recharge rate by the previous study of the authors is 107.1 MCM/a [14]. Recharge rate can be higher than estimated when karstic and high fractured rock layers are cropped out at the surface such as the formation of the Upper and Lower Mountain aquifer system at the two anticline flanks in the west and in the east, in the other hand ground recharge decrease to about zero from Abu Dis formation "Chalky Unit". The formation of shallow aquifer system is exposed mainly in the central part

C. respectively; this indicate that the losses of

of surface area (**Figure 1b**), depend-

**68**

Graben [13].

**Figure 3.**

*Recharge rate over the West Bank including the NE Basin (Marei et al., 2011).*

#### **Table 1.**

*Recharge volume of NE Basin.*

**Table 1** summarized the recharge volume of the deep and shallow aquifer systems depending on the chloride mass balance method [14].

#### **2.4 Groundwater flow regimes**

Two main groundwater flow regimes are assumed to present in the study area. These are as follows: a SW-NE main groundwater flow direction parallel to Nablus-Beit Qad syncline axis with historical discharge site in Hiteen and Ein Jaloot spring and a flow direction from both anticline flanks (Anabtaa, and Al Faria) to the center of the syncline which joins the NE flow direction; these flow directions take place within the Mountain Aquifer system [15, 16]. Addition flow direction to the southeast is governed through Al Faria fault system "Graben" that diverted groundwater to flow in this direction [17].

## **3. Methodology**

Integrated isotopic tools were used to investigate the effect of complex geologic structure on the groundwater residence times and respective potential sources, mixing, and recharge mechanisms [18]. In order to achieve the abovementioned objectives, 82 groundwater samples were obtained from different areas in the Northeastern basins. The samples represent 8 springs, 20 wells from shallow Eocene aquifer in the plain zone of the study area, 7 wells in Sanoor swamp area, 10 shallow wells in Nassariyeh area in the upper part of Wadi Faria stream, 20 wells from the lower part of Faria stream, and 17 deep aquifer wells within and near the flanks of the NE basin (**Figure 5**). All samples were taken in the hydrological year 2017/2018. Several rainwater samples were obtained from rain gauges' stations that were constructed on the roofs of some schools all over the study area.

Groundwater samples for deuterium and δ18O isotopes have been taken from the mentioned wells and spring. Samples for deuterium and δ18O isotopes were collected with 25 ml bottles and sent to the Al-Quds University research lab for analysis. Samples were analyzed using laser spectroscopy for deuterium and δ18O in ‰ in respect to Vienna Standard Mean Ocean Water (V-SMOW) standard; the precision of δ18O[SMOW] ‰ measurements is ±0.1‰; the precision of δD values is ±2‰ [19].

**71**

**Figure 6.**

*Mapping the Stable Isotopes to Understand the Geo-Structural Control of Groundwater Recharge…*

The local meteoric water line shows the same slope for the Mediterranean Meteoric Water Line but with more enriched deuterium excess. This might refer to the formation of a large swamp lake in Sanoor area which resulted from the inundation from the runoff drained to the area from the surrounded mountains causing

**Figure 5** shows the distribution of sampled wells and different geological structures that control the hydrology of the region. As it is mentioned above, the structural geology is highly controlling the hydrological flow system in the region. The main structure that might play an important role in this regard is the Faria fault system which might control the groundwater flow regime in the eastern part of the

Spring systems in both locations (Bathan in the east and Nablus in the north west) show closed signatures to the local meteorological line, which indicate rapid freshwater input; the other end member of shallow wells within the middle of the

Other wells, which show signatures in between, have different recharge mechanisms which need to be separated in details with respect to isotopic signature from

The following sections illustrate the relations between different aquifers as well

The isotopic signatures from deep wells show two main fingerprints with respect

First, the deep wells that are located within the area of the Faria fault system, southern part of the syncline and upper part of Faria fault system, show depleted signatures that are more or less closed to springs and LMWL, while other deep wells reflect high variation in isotopic enrichment with respect to its depth and location

with respect to recharge mechanisms and groundwater flow directions.

The data show a wide range of isotopic signatures, which reflects wide variations

*DOI: http://dx.doi.org/10.5772/intechopen.90449*

high humid conditions in the area (**Figure 6**).

syncline shows the most enriched signatures (**Figure 6**).

*Deuterium vs. δ18O[SMOW] ‰ for the whole wells and springs in the study area.*

as the recharge mechanism for each system.

to recharge sources and mechanisms.

**4. Results and discussion**

**4.1 Results overview**

NE Basin.

each group.

**4.2 Deep wells**

*Mapping the Stable Isotopes to Understand the Geo-Structural Control of Groundwater Recharge… DOI: http://dx.doi.org/10.5772/intechopen.90449*

## **4. Results and discussion**

### **4.1 Results overview**

*Isotopes Applications in Earth Sciences*

**3. Methodology**

values is ±2‰ [19].

groundwater to flow in this direction [17].

Nablus-Beit Qad syncline axis with historical discharge site in Hiteen and Ein Jaloot spring and a flow direction from both anticline flanks (Anabtaa, and Al Faria) to the center of the syncline which joins the NE flow direction; these flow directions take place within the Mountain Aquifer system [15, 16]. Addition flow direction to the southeast is governed through Al Faria fault system "Graben" that diverted

Integrated isotopic tools were used to investigate the effect of complex geologic structure on the groundwater residence times and respective potential sources, mixing, and recharge mechanisms [18]. In order to achieve the abovementioned objectives, 82 groundwater samples were obtained from different areas in the Northeastern basins. The samples represent 8 springs, 20 wells from shallow Eocene aquifer in the plain zone of the study area, 7 wells in Sanoor swamp area, 10 shallow wells in Nassariyeh area in the upper part of Wadi Faria stream, 20 wells from the lower part of Faria stream, and 17 deep aquifer wells within and near the flanks of the NE basin (**Figure 5**). All samples were taken in the hydrological year 2017/2018. Several rainwater samples were obtained from rain gauges' stations that were

Groundwater samples for deuterium and δ18O isotopes have been taken from the mentioned wells and spring. Samples for deuterium and δ18O isotopes were collected with 25 ml bottles and sent to the Al-Quds University research lab for analysis. Samples were analyzed using laser spectroscopy for deuterium and δ18O in ‰ in respect to Vienna Standard Mean Ocean Water (V-SMOW) standard; the precision of δ18O[SMOW] ‰ measurements is ±0.1‰; the precision of δD

*The study area including all the sampled wells and springs, including rock formations and structure.*

constructed on the roofs of some schools all over the study area.

**70**

**Figure 5.**

The local meteoric water line shows the same slope for the Mediterranean Meteoric Water Line but with more enriched deuterium excess. This might refer to the formation of a large swamp lake in Sanoor area which resulted from the inundation from the runoff drained to the area from the surrounded mountains causing high humid conditions in the area (**Figure 6**).

The data show a wide range of isotopic signatures, which reflects wide variations with respect to recharge mechanisms and groundwater flow directions.

**Figure 5** shows the distribution of sampled wells and different geological structures that control the hydrology of the region. As it is mentioned above, the structural geology is highly controlling the hydrological flow system in the region. The main structure that might play an important role in this regard is the Faria fault system which might control the groundwater flow regime in the eastern part of the NE Basin.

Spring systems in both locations (Bathan in the east and Nablus in the north west) show closed signatures to the local meteorological line, which indicate rapid freshwater input; the other end member of shallow wells within the middle of the syncline shows the most enriched signatures (**Figure 6**).

Other wells, which show signatures in between, have different recharge mechanisms which need to be separated in details with respect to isotopic signature from each group.

The following sections illustrate the relations between different aquifers as well as the recharge mechanism for each system.

#### **4.2 Deep wells**

The isotopic signatures from deep wells show two main fingerprints with respect to recharge sources and mechanisms.

First, the deep wells that are located within the area of the Faria fault system, southern part of the syncline and upper part of Faria fault system, show depleted signatures that are more or less closed to springs and LMWL, while other deep wells reflect high variation in isotopic enrichment with respect to its depth and location

**Figure 7.**

*Relation between δ18O[SMOW] ‰ and deuterium for the groundwater from deep aquifer shows different recharge mechanisms for each cluster.*

(**Figures 6** and **7**). Some of the deep wells show obvious close relation to the recharge that feeds the aquifer layers through the exposed Jerusalem-Hebron formations on Anabta anticline (**Figure 7**), where the wells within this area show more enriched δ 18O signatures than those near the upper Faria fault system (**Figure 7**).

The isotopic signatures of deuterium show clear differences between each deep well cluster with an average shifting of 4‰. These differences are more or less related to the recharge locations with different altitudes [20].

The deep wells in the south and upper part of Faria show relatively more depleted deuterium than those deep wells that receive direct recharge from the western Anabta anticline outcrops. The elevation of Anabta anticline in the western part of the basin has an average altitude of 300 m above sea level, while the southern elevation over the mountains in Nablus and Salfit areas to the south, from where the recharge for deep Faria well cluster is expected, reaches an average of 500 m above sea level.

However, the δ 18O[SMOW] ‰ signatures show slight shifting between both clusters, with more slight enrichment for the wells near to the western Anabta anticline that reach around −1‰. This also reflect different recharge mechanisms and different hydrological flow conditions from each source [21].

**Figure 8** shows the suggested recharge zones and flow mechanisms for each of deep well cluster.

#### **4.3 Shallow wells**

This group of wells can be divided into three major categories according to its locations: shallow Eocene wells that are distributed in the plain area of syncline, Sanoor wells which are belonging to the same previous area but located directly within the area of surface water swamp, and upper Faria (Bathan) shallow wells in Nassariyeh area and lower Faria shallow wells to the southeast.

**73**

*Mapping the Stable Isotopes to Understand the Geo-Structural Control of Groundwater Recharge…*

According to isotopic signatures from these shallow wells, different recharge mechanisms for each group can be indicated. Also the isotope data reflect some hydrological connections between some groups. The hydrological relations as well

This includes the shallow wells that are dug in the Eocene and Quaternary alluvial areas in the northwest of Nablus-Bet Qad syncline (**Figure 5**). Those wells show

deuterium values for the shallow wells in the Al Jalameh (north) indicate relatively enrichment deviation from the LMWL due to fractionation with the thick soil layer

(**Figure 6**). The deviation from LMWL with the slope of 4 indicates an evaporation trend that increases toward the north of the study area where those wells tapped

In general, the problem of water deterioration in this group seems to be connected with the heavy abstraction rate from these wells. The slow replenishment, with such heavy abstraction, increases the evaporite salinity problem [22].

In general, Marj Sanoor wells show relatively enriched δ18O signatures but less than the rest of shallow wells in the north (**Figure 6**). This might be due to the fact that the aquifer is located beneath the water swamp that is collected in the winter time and infiltrated slowly to the aquifer layers. The integration of the results with the results of other locations shows a connection between the infiltrated surface water from this group with some wells to the southeast as it will be described below.

The shallow wells in Nassariyeh that are located at the beginning of Faria structural faults show the same stable isotopic signatures as Marj Sanoor wells. This

18O[SMOW] ‰ and

18O[SMOW] ‰ values reach −3.5‰

as recharge mechanisms can be described with respect to each group.

*Suggested recharge zones and flow mechanisms for each of deep well cluster.*

high evaporation inputs with relatively high TDS content. The δ

*4.3.1 Shallow wells within the Eocene plain area*

during slow infiltration. For these wells, the δ

their water from (**Figure 6**).

**Figure 8.**

*4.3.2 Shallow wells in Nassariyeh*

*DOI: http://dx.doi.org/10.5772/intechopen.90449*

*Mapping the Stable Isotopes to Understand the Geo-Structural Control of Groundwater Recharge… DOI: http://dx.doi.org/10.5772/intechopen.90449*

**Figure 8.** *Suggested recharge zones and flow mechanisms for each of deep well cluster.*

According to isotopic signatures from these shallow wells, different recharge mechanisms for each group can be indicated. Also the isotope data reflect some hydrological connections between some groups. The hydrological relations as well as recharge mechanisms can be described with respect to each group.

#### *4.3.1 Shallow wells within the Eocene plain area*

This includes the shallow wells that are dug in the Eocene and Quaternary alluvial areas in the northwest of Nablus-Bet Qad syncline (**Figure 5**). Those wells show high evaporation inputs with relatively high TDS content. The δ 18O[SMOW] ‰ and deuterium values for the shallow wells in the Al Jalameh (north) indicate relatively enrichment deviation from the LMWL due to fractionation with the thick soil layer during slow infiltration. For these wells, the δ 18O[SMOW] ‰ values reach −3.5‰ (**Figure 6**). The deviation from LMWL with the slope of 4 indicates an evaporation trend that increases toward the north of the study area where those wells tapped their water from (**Figure 6**).

In general, the problem of water deterioration in this group seems to be connected with the heavy abstraction rate from these wells. The slow replenishment, with such heavy abstraction, increases the evaporite salinity problem [22].

In general, Marj Sanoor wells show relatively enriched δ18O signatures but less than the rest of shallow wells in the north (**Figure 6**). This might be due to the fact that the aquifer is located beneath the water swamp that is collected in the winter time and infiltrated slowly to the aquifer layers. The integration of the results with the results of other locations shows a connection between the infiltrated surface water from this group with some wells to the southeast as it will be described below.

#### *4.3.2 Shallow wells in Nassariyeh*

The shallow wells in Nassariyeh that are located at the beginning of Faria structural faults show the same stable isotopic signatures as Marj Sanoor wells. This

*Isotopes Applications in Earth Sciences*

(**Figures 6** and **7**). Some of the deep wells show obvious close relation to the

The deep wells in the south and upper part of Faria show relatively more depleted deuterium than those deep wells that receive direct recharge from the western Anabta anticline outcrops. The elevation of Anabta anticline in the western part of the basin has an average altitude of 300 m above sea level, while the southern elevation over the mountains in Nablus and Salfit areas to the south, from where the recharge for deep Faria well cluster is expected, reaches an average of 500 m

clusters, with more slight enrichment for the wells near to the western Anabta anticline that reach around −1‰. This also reflect different recharge mechanisms

**Figure 8** shows the suggested recharge zones and flow mechanisms for each of

This group of wells can be divided into three major categories according to its locations: shallow Eocene wells that are distributed in the plain area of syncline, Sanoor wells which are belonging to the same previous area but located directly within the area of surface water swamp, and upper Faria (Bathan) shallow wells in

and different hydrological flow conditions from each source [21].

Nassariyeh area and lower Faria shallow wells to the southeast.

18O[SMOW] ‰ signatures show slight shifting between both

related to the recharge locations with different altitudes [20].

recharge that feeds the aquifer layers through the exposed Jerusalem-Hebron formations on Anabta anticline (**Figure 7**), where the wells within this area show more enriched δ18O signatures than those near the upper Faria fault system (**Figure 7**). The isotopic signatures of deuterium show clear differences between each deep well cluster with an average shifting of 4‰. These differences are more or less

*Relation between δ18O[SMOW] ‰ and deuterium for the groundwater from deep aquifer shows different recharge*

**72**

above sea level. However, the δ

**Figure 7.**

*mechanisms for each cluster.*

deep well cluster.

**4.3 Shallow wells**

**Figure 9.** *Relation between δ18O[SMOW] ‰ and deuterium for the groundwater from Nassariyeh and Sanoor shallow wells.*

#### **Figure 10.**

*Suggested groundwater model for the water leakage from Marj Sanoor Lake to the Nassaria and upper Faria wells.*

strongly suggests a connection between seeping water from the seasonal Marj Sanoor Lake, which forms by the collected runoff from surrounding mountains in the late winter season to the wells that are located within the upper Faria and Bathan area (**Figure 9**).

The isotopes signatures suggest that the recharge mechanism for these wells is a mixing between water seepage from Marj Sanoor surface water and fresh water that

**75**

**Figure 12.**

**Figure 11.**

*wells.*

*Mapping the Stable Isotopes to Understand the Geo-Structural Control of Groundwater Recharge…*

*Relation between δ18O[SMOW] ‰ and deuterium for the groundwater from deep wells and lower Faria shallow*

inline the Faria Fault that triggered from deeper Jerusalem formation, and seeping

*Model of groundwater recharge and flow mechanisms for the lower Faria wells from different sources.*

This finding can be used to efficiently utilize the surface water in the syncline area to artificially feed the wells further to the east, keeping the groundwater level in good standing all over the summer season. On the other hand, heavy abstraction from the shallow and deep wells within the syncline area might affect the produc-

along the area of Faria Graben (**Figure 10**).

tivity of Bathan and upper Faria wells.

*DOI: http://dx.doi.org/10.5772/intechopen.90449*

*Mapping the Stable Isotopes to Understand the Geo-Structural Control of Groundwater Recharge… DOI: http://dx.doi.org/10.5772/intechopen.90449*

#### **Figure 11.**

*Isotopes Applications in Earth Sciences*

**74**

**Figure 10.**

**Figure 9.**

(**Figure 9**).

*wells.*

*Suggested groundwater model for the water leakage from Marj Sanoor Lake to the Nassaria and upper Faria*

*Relation between δ18O[SMOW] ‰ and deuterium for the groundwater from Nassariyeh and Sanoor shallow wells.*

strongly suggests a connection between seeping water from the seasonal Marj Sanoor Lake, which forms by the collected runoff from surrounding mountains in the late winter season to the wells that are located within the upper Faria and Bathan area

The isotopes signatures suggest that the recharge mechanism for these wells is a mixing between water seepage from Marj Sanoor surface water and fresh water that

*Relation between δ18O[SMOW] ‰ and deuterium for the groundwater from deep wells and lower Faria shallow wells.*

**Figure 12.** *Model of groundwater recharge and flow mechanisms for the lower Faria wells from different sources.*

inline the Faria Fault that triggered from deeper Jerusalem formation, and seeping along the area of Faria Graben (**Figure 10**).

This finding can be used to efficiently utilize the surface water in the syncline area to artificially feed the wells further to the east, keeping the groundwater level in good standing all over the summer season. On the other hand, heavy abstraction from the shallow and deep wells within the syncline area might affect the productivity of Bathan and upper Faria wells.

#### *4.3.3 Lower Faria shallow wells*

The isotopic signatures from lower Faria shallow wells suggest strong correlation with the recharge of the deep well in the upper Faria part. Most of the shallow lower Faria wells show the same δ18O and deuterium signatures for the deep wells of Bathan, Faria, Tubas, and Tammoun. This similarity emphasizes the unity of recharge mechanism for both locations which mainly come from Jerusalem formation of Turonian age, that triggered along the northern Faria fault and seeping to the wells drilled within lower Faria plain (**Figures 11** and **12**).

However, the isotopic signatures show enrichment trend with respect to distance from the fault to the middle and the south of the Wadi (**Figure 13**). This emphasizes that the main recharge source for the wells in the lower Faria is coming mainly from the northwest, in-line the Fault system (**Figure 12**).

This also can be an indicator about the limitation of the water recharge from the southern part of the Fault, which suggests in role that most of the recharge in the southern area is drain surfacely and sub-surfacely to the area constrains between the southern Faria Fault and Bet Forik Fault, where the mentioned area must be a good potential for freshwater production with sufficiently high amount.

#### **5. Conclusion and recommendations**

The isotopic signatures from deep wells show two main fingerprints with respect to recharge sources and mechanisms. Those are wells located in the upper part of Faria fault system and along the Rujeib Moncline which are fed by triggered water in-line the Fault system in the south and deep wells surrounded by Anabta anticline to the West which are fed by the exposed Jerusalem-Hebron formations. This suggests a mixing process with freshwater sources that mainly flow to the system from southern mountains. However, the impermeability of the southern part of Faria fault system makes this water diverted to the area constrain between the southern

#### **Figure 13.**

*Spatial distribution of δ18O[SMOW] ‰ for the shallow wells in lower Faria shows relatively depleted signatures along the fault and more enriched to the center of the Graben.*

**77**

*Mapping the Stable Isotopes to Understand the Geo-Structural Control of Groundwater Recharge…*

Faria fault and Bet Forik faults, where the mentioned area must be a good potential

The whole finding of this project might be used for tuning and revision of the groundwater model that has been built by the Palestinian Water Authority. The suggested new flow mechanisms and potential recharge zones can help the Palestinian

We thank the International Atomic Agency for funding this work through the national project PAL7005. Special thanks should go to Gerald Reys, the Section Head of Asia and the Pacific in the Department of Technical Cooperation, for her follow-up and continuous administrative and technical support. Also many thanks go to Mr. Ismael Hroub, the NLO in the Palestinian Ministry of Health for his

and Zaher Barghouthi3

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

1 Palestine Technical University/Kadoorie (PTUK), Tulkarm, Palestine

3 NARC—National Agricultural Research Centre, Jenin, Palestine

\*Address all correspondence to<EMAIL_ADDRESS>
stakeholders in good planning for the whole Northeastern aquifer system.

The isotopic signatures from the shallow well in Marj Sanoor wells and Nassariyeh in the upper Faria well suggest a kind of partial recharge from the Marj Sanoor Lake that leaks to the upper Faria Graben area and participates in the recharge process of these wells. This finding can be used to efficiently utilize the surface water in the syncline area to artificially feed the wells further to the east, keeping the groundwater level in good standing all over the summer season. On the other hand, heavy abstraction from the shallow and deep wells within the syncline area might affect the productivity of Bathan and upper Faria wells. The northern part of the Faria Graben fault which shows a good ability for freshwater transmission from different sources is extended further to the northwest, reaching the syncline area. The area of fault extension can be a good potential

for freshwater production with sufficiently high amount (**Figure 13**).

*DOI: http://dx.doi.org/10.5772/intechopen.90449*

source for drilling new wells in the future.

follow-up and administration support.

\*, Amer Marei2

provided the original work is properly cited.

2 Al-Quds University, East Jerusalem, Palestine

**Acknowledgements**

**Author details**

Saed Khayat1

#### *Mapping the Stable Isotopes to Understand the Geo-Structural Control of Groundwater Recharge… DOI: http://dx.doi.org/10.5772/intechopen.90449*

Faria fault and Bet Forik faults, where the mentioned area must be a good potential for freshwater production with sufficiently high amount (**Figure 13**).

The isotopic signatures from the shallow well in Marj Sanoor wells and Nassariyeh in the upper Faria well suggest a kind of partial recharge from the Marj Sanoor Lake that leaks to the upper Faria Graben area and participates in the recharge process of these wells. This finding can be used to efficiently utilize the surface water in the syncline area to artificially feed the wells further to the east, keeping the groundwater level in good standing all over the summer season. On the other hand, heavy abstraction from the shallow and deep wells within the syncline area might affect the productivity of Bathan and upper Faria wells.

The northern part of the Faria Graben fault which shows a good ability for freshwater transmission from different sources is extended further to the northwest, reaching the syncline area. The area of fault extension can be a good potential source for drilling new wells in the future.

The whole finding of this project might be used for tuning and revision of the groundwater model that has been built by the Palestinian Water Authority. The suggested new flow mechanisms and potential recharge zones can help the Palestinian stakeholders in good planning for the whole Northeastern aquifer system.

## **Acknowledgements**

*Isotopes Applications in Earth Sciences*

*4.3.3 Lower Faria shallow wells*

The isotopic signatures from lower Faria shallow wells suggest strong correlation with the recharge of the deep well in the upper Faria part. Most of the shallow lower Faria wells show the same δ18O and deuterium signatures for the deep wells of Bathan, Faria, Tubas, and Tammoun. This similarity emphasizes the unity of recharge mechanism for both locations which mainly come from Jerusalem formation of Turonian age, that triggered along the northern Faria fault and seeping to

However, the isotopic signatures show enrichment trend with respect to distance from the fault to the middle and the south of the Wadi (**Figure 13**). This emphasizes that the main recharge source for the wells in the lower Faria is coming mainly from

This also can be an indicator about the limitation of the water recharge from the southern part of the Fault, which suggests in role that most of the recharge in the southern area is drain surfacely and sub-surfacely to the area constrains between the southern Faria Fault and Bet Forik Fault, where the mentioned area must be a good potential for freshwater production with sufficiently high

The isotopic signatures from deep wells show two main fingerprints with respect to recharge sources and mechanisms. Those are wells located in the upper part of Faria fault system and along the Rujeib Moncline which are fed by triggered water in-line the Fault system in the south and deep wells surrounded by Anabta anticline to the West which are fed by the exposed Jerusalem-Hebron formations. This suggests a mixing process with freshwater sources that mainly flow to the system from southern mountains. However, the impermeability of the southern part of Faria fault system makes this water diverted to the area constrain between the southern

the wells drilled within lower Faria plain (**Figures 11** and **12**).

the northwest, in-line the Fault system (**Figure 12**).

**5. Conclusion and recommendations**

**76**

**Figure 13.**

amount.

*Spatial distribution of δ18O[SMOW] ‰ for the shallow wells in lower Faria shows relatively depleted signatures*

*along the fault and more enriched to the center of the Graben.*

We thank the International Atomic Agency for funding this work through the national project PAL7005. Special thanks should go to Gerald Reys, the Section Head of Asia and the Pacific in the Department of Technical Cooperation, for her follow-up and continuous administrative and technical support. Also many thanks go to Mr. Ismael Hroub, the NLO in the Palestinian Ministry of Health for his follow-up and administration support.

## **Author details**

Saed Khayat1 \*, Amer Marei2 and Zaher Barghouthi3

1 Palestine Technical University/Kadoorie (PTUK), Tulkarm, Palestine

\*Address all correspondence to<EMAIL_ADDRESS>
© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

## **References**

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[6] Böhlke J, Denver J. Combined use of groundwater dating, chemical, and isotopic analyses to resolve the history and fate of nitrate contamination in two agricultural watersheds, Atlantic coastal plain, Maryland. Water Resources Research. 1995;**31**(9):2319-2339

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[11] Gunkel A et al. Model signatures and aridity indices enhance the accuracy of water balance estimations in a data-scarce Eastern Mediterranean catchment. Journal of Hydrology: Regional Studies. 2015;**4**(Part B): 487-501

[12] Saleh YFK. Artificial Groundwater Recharge in Faria Catchment A Hydrogeological Study, in Faculty of Graduate Studies. Faculty of Graduate Studies, An-Najah National University: 2009

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[18] Gat JR. Oxygen and hydrogen isotopes in the hydrologic cycle. Annual

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[20] Araguás-Araguás L, Froehlich K, Rozanski K. Deuterium and oxygen-18 isotope composition of precipitation and atmospheric moisture. Hydrological Processes. 2000;**14**(8):1341-1355

[21] Barnes CJ, Allison GB. Tracing of water movement in the unsaturated zone using stable isotopes of hydrogen and oxygen. Journal of Hydrology. 1988;**100**(1-3, 143):-176

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2000. p. 529

2000;**84**(7):997-1014

Westminster; 1963

*Isotopes Applications in Earth Sciences*

[1] Authority-PWA PW. Annual Water Status Report. Yearly Report, 2017.

[11] Gunkel A et al. Model signatures and aridity indices enhance the accuracy of water balance estimations in a data-scarce Eastern Mediterranean catchment. Journal of Hydrology: Regional Studies. 2015;**4**(Part B):

[12] Saleh YFK. Artificial Groundwater

[13] Rofe & Raffety 1965. West Bank hydrology 1963-1965: Analysis. Rofe & Rafferty Consulting Engineers Ltd., A., Report for Central Water Authority, Amman, Hashemite Kingdom of Jordan., West Bank

hydrology 1963-1965. Report for Central Water Authority. Amman, Hashemite

Kingdom of Jordan; 1965

[14] Marei A et al. Estimating groundwater recharge using the chloride mass-balance method in the West Bank, Palestine. Hydrological Sciences Journal-Journal Des Sciences Hydrologiques. 2010;**55**(5):780-791

[15] Najem AAI. Modeling Nitrate Contamination of the Eocene

University; 2008

2012;**66**(4):1071-1082

Palestine. 2003

Aquifer, Palestine. An-Najah National

[16] Rosenthal E, Meiler M, Flexer A. Structure-controlled groundwater flow and salinization paths in the Bet She'an and Harod Valleys, Israel. Environmental Earth Sciences.

[17] Tubeileh HMSR. Groundwater Flow Modeling-Case Study of the EoceneAquifer in the West Bank,

[18] Gat JR. Oxygen and hydrogen isotopes in the hydrologic cycle. Annual

Recharge in Faria Catchment A Hydrogeological Study, in Faculty of Graduate Studies. Faculty of Graduate Studies, An-Najah National University:

487-501

2009

[2] Statistics-PCBS PCBo. Preliminary Estimates of Quarterly National Accounts (First Quarter 2018). 2018

[3] Arij A. Status of the Environment in the Occupied Palestinian Territory. Jerusalem Applied Research Institute

[5] Sidle WC. Environmental isotopes for resolution of hydrology problems. Environmental Monitoring and Assessment. 1998;**52**(3):389-410

[6] Böhlke J, Denver J. Combined use of groundwater dating, chemical, and isotopic analyses to resolve the history and fate of nitrate contamination in two agricultural watersheds, Atlantic coastal plain, Maryland. Water Resources Research. 1995;**31**(9):2319-2339

[7] Clark I, Fritz P. Environmental Isotopes in Hydrogeology. New York: CRC Lewis Publishers, Inc; 1997. p. 328

[8] Cook P, Herczeg AL. Environmental Tracers in Subsurface Hydrology. Norwell: Kluwer Academic Publishers;

[9] Rosenthal E et al. Late cretaceousearly tertiary development of depositional basins in Samaria as a reflection of eastern Mediterranean tectonic evolution. AAPG Bulletin.

[10] Rofe and Raffety, West Bank. Hashemite Kingdom of Jordan. Central Water Authority. London: Rofe and Raffety Consulting Engineers

[4] Abu Zahra BAA. Water crisis in Palestine. Desalination.

2001;**136**(1-3):93-99

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(Arij), 2007.

2018

**81**

thellate corals.

**Chapter 5**

**Abstract**

*Anne Juillet-Leclerc*

model of a coral proxy.

**1. Introduction**

conditions, temperature, light, organic matrix

covering an area of about 284,300 km2

similar oxygen isotopic composition (δ

following thermodynamic laws.

Could Coral Skeleton Oxygen

Isotopic Fractionation be

During 1970s, coral skeleton oxygen isotope composition (δ

the isotopic thermometer following thermodynamic rules. Recently, coral aragonite oxygen isotopic fractionation could appear to be controlled by biology, its rate being accelerated by an enzyme (carbonic anhydrase or CA). Such a new concept results of an original approach involving coral culture in controlled conditions. Environmental factors, temperature and also light have been tested on macrosize scale samples (some mg), and δ18O revealed vital effects, anomalies compared with chemical and isotopic equilibrium, related to metabolic activity. δ18O analyses at microsize scale (some μm), using ion microprobe, could display the mechanism of crystallisation, δ18O fractionation responding to biological kinetic effects. The understanding of coral aragonite δ18O is the absolute prerequisite to develop the first

**Keywords:** oxygen isotopic fractionation, coral skeleton, culture, controlled

Coral colonies built the most important bioconstruction made of calcium carbonate (CaCO3) of the world, with a calcification of about 2–6 kgCaCO3 m−2

results from the work of multiple small colonial organisms. The reefs, the biotic mound structure essentially made of corals as the Great Barrier Reef in Australia, are of major importance for marine ecosystems and biodiversity because they are

Corals are marine animals forming an aragonite (a polymorph of CaCO3) skeleton. They are developed in two distinct ecosystems, essentially zooxanthellate corals or symbiotic ones living in shallow water and solitary colonies or integrated in elaborate reef framework in deeper depth than 50 until 2000 m. More than 793 coral species are spread over marine tropical zone [2]. Branched corals *Acropora* and massive corals *Porites* are ubiquitous genera [3]. We restricted this study to zooxan-

Epstein [4, 5] demonstrated that skeletal carbonates of marine shells display

ganic calcium carbonate (CaCO3) deposited from seawater at the same temperature,

the most productive and they host almost a third of all world fishes.

[1]. This construction built from Jurassic

18OCaCO3) relationship versus SST than inor-

18O) was regarded as

year−1

Controlled by Biology?

## **Chapter 5**

## Could Coral Skeleton Oxygen Isotopic Fractionation be Controlled by Biology?

*Anne Juillet-Leclerc*

## **Abstract**

During 1970s, coral skeleton oxygen isotope composition (δ 18O) was regarded as the isotopic thermometer following thermodynamic rules. Recently, coral aragonite oxygen isotopic fractionation could appear to be controlled by biology, its rate being accelerated by an enzyme (carbonic anhydrase or CA). Such a new concept results of an original approach involving coral culture in controlled conditions. Environmental factors, temperature and also light have been tested on macrosize scale samples (some mg), and δ18O revealed vital effects, anomalies compared with chemical and isotopic equilibrium, related to metabolic activity. δ18O analyses at microsize scale (some μm), using ion microprobe, could display the mechanism of crystallisation, δ18O fractionation responding to biological kinetic effects. The understanding of coral aragonite δ18O is the absolute prerequisite to develop the first model of a coral proxy.

**Keywords:** oxygen isotopic fractionation, coral skeleton, culture, controlled conditions, temperature, light, organic matrix

### **1. Introduction**

Coral colonies built the most important bioconstruction made of calcium carbonate (CaCO3) of the world, with a calcification of about 2–6 kgCaCO3 m−2 year−1 covering an area of about 284,300 km2 [1]. This construction built from Jurassic results from the work of multiple small colonial organisms. The reefs, the biotic mound structure essentially made of corals as the Great Barrier Reef in Australia, are of major importance for marine ecosystems and biodiversity because they are the most productive and they host almost a third of all world fishes.

Corals are marine animals forming an aragonite (a polymorph of CaCO3) skeleton. They are developed in two distinct ecosystems, essentially zooxanthellate corals or symbiotic ones living in shallow water and solitary colonies or integrated in elaborate reef framework in deeper depth than 50 until 2000 m. More than 793 coral species are spread over marine tropical zone [2]. Branched corals *Acropora* and massive corals *Porites* are ubiquitous genera [3]. We restricted this study to zooxanthellate corals.

Epstein [4, 5] demonstrated that skeletal carbonates of marine shells display similar oxygen isotopic composition (δ 18OCaCO3) relationship versus SST than inorganic calcium carbonate (CaCO3) deposited from seawater at the same temperature, following thermodynamic laws.

$$\mathbf{S}^{18}\mathbf{O} = \left\{ \left[ \left( ^{18}\mathbf{O} / ^{16}\mathbf{O} \right)\_{\text{sample}} / \left( ^{18}\mathbf{O} / ^{16}\mathbf{O} \right)\_{\text{standard}} \right] \mathbf{-1} \right\} \ast \mathbf{10}^{-3}$$

The relationship was expressed as:

$$\text{LSTP}"\text{C}=\text{16.5}-4.3 \left( \text{\ $}^{18}\text{O}\_{\text{CaCO}3} - \text{\$ }^{18}\text{O}\_{\text{жачат}} \right) \\ + \text{0.14} \left( \text{\ $}^{18}\text{O}\_{\text{CaCO}3} - \text{\$ }^{18}\text{O}\_{\text{жачат}} \right)^{2} \\ \text{\text{\textdegree C}}$$

from [5] with sea surface temperature (SST) being sea surface temperature and δ 18Oseawater seawater isotopic composition. The authors underlined that coral skeleton presented poor interest [4].

However, after preliminary studies [6], Weber and Woodhead deduced, despite apparent isotopic disequilibrium between coral skeletal carbonate and ambient seawater, that δ 18Ocoral was temperature dependent. To support this assumption [2], the authors conducted isotopic analyses of coral skeleton collected over wide range of temperatures. This data series still constitutes the most exhaustive oxygen isotopic database existing for corals. Weber and Woodhead concluded that the calibration between annual δ 18O and annual SST differed following each coral genus, and the isotopic disequilibrium was attributed to vital effect, anomalies compared with chemical and isotopic equilibrium, related to metabolic activity. Several models of mineralisation were proposed to explain the geochemical specificities of coral skeletons based on kinetic fractionation [7–9] disturbed by "vital effects". Other models, based on precipitation efficiency [10] or Rayleigh fractionation [11–13], were suggested.

We developed drastically different approach considering that corals are animals living in symbiosis with algae, building aragonitic skeleton intimately related to biological activity. In collaboration with biologists from CSM (Centre Scientific de Monaco), Stéphanie Reynaud and Christine Ferrier-Pagès, and Claire Rollion-Bard geochemist from IPGP (Institut Physique du Globe de Paris), we developed an innovative strategy on cultured *Acropora* to identify what was hidden under the term of vital effect of coral skeleton and to highlight the isotopic fractionation involved in. We focused our study on the stable oxygen isotopic ratio δ 18O. Branched coral *Acropora* and massive ones *Porites* belong to different genera but responses to environmental forcing in terms of biological parameters and isotopic signatures are regarded as similar.

Our demonstration is structured as followed: first, the main coral features are highlighted; second, we describe coral culture proceeding; third, temperature and light test results are presented at microscopic size scale; and finally, we display the stable oxygen isotopic ratio δ 18O as indicator of deposit mechanism.

#### **2. Main coral features**

Shallow corals, because they are leaving in symbiosis with micro algae need light to benefit from photosynthetic activity.

#### **2.1 Notions of coral morphology and biological activity**

Coral skeleton is extracellular, located at the base of coral tissue, constituted of similar units, the polyps. Each polyp looks like a bag made by two layers of cells (**Figure 1**). Polyps are linked together by the coenosarc. Most of zooxanthellae are located within an internal layer (**Figure 1**).

Biological activity might be quantified. Photosynthesis and respiration were measured using the respirometry technique, which measured the changes in oxygen concentration at different light levels. Rates of net photosynthesis and respiration

**83**

**Figure 1.**

light impinging on the zooxanthellae.

*Could Coral Skeleton Oxygen Isotopic Fractionation be Controlled by Biology?*

were estimated using a linear regression of O2 against time [15]. By using two light intensities, at three temperatures (**Figure 2**), it appeared that increasing temperature enhanced photosynthetic activity, the effect arising with light intensity (**Figure 2a**) [15]. Additionally, coral growth rates might be estimated. Corals were weighed regularly using the buoyant weight technique and the surface expansion of the new skeleton formed was estimated [15]. It was generally accepted that calcification was light-enhanced (LEC or light enhanced calcification) during the day [16]. Zooxanthellae density and pigment concentration were determined under the light microscope using a counting chamber [15]. Coral symbiont distribution was not homogeneous on the skeleton and it differed following different coral genera, different depths in the fields. For example, tips of coral branches or other exposed surfaces were sun-adapted while most of the lowest parts were shade-adapted [15]. Iluz and Dubinsky [17] listed all the strategies developed by coral to optimise the

*Organisation of the coral adapted from [14]. The colour polyp is the living organism, an animal building the white skeleton. The animal lives in symbiosis with algae, the zooxanthellae, located in the internal layer (the left side high corner). A detail of mesoscale skeletal architecture figures on the left side bottom corner.*

*DOI: http://dx.doi.org/10.5772/intechopen.89146*

*Could Coral Skeleton Oxygen Isotopic Fractionation be Controlled by Biology? DOI: http://dx.doi.org/10.5772/intechopen.89146*

#### **Figure 1.**

*Isotopes Applications in Earth Sciences*

δ18O = {[(18O/

eton presented poor interest [4].

δ

seawater, that δ

between annual δ

regarded as similar.

stable oxygen isotopic ratio δ

to benefit from photosynthetic activity.

located within an internal layer (**Figure 1**).

**2.1 Notions of coral morphology and biological activity**

**2. Main coral features**

The relationship was expressed as:

16O)sample/

(18O/

SST°C = 16.5–4.3 (δ18 OCaCO3 − δ18 Oseawater) + 0.14 (δ18 OCaCO3 − δ18 Oseawater)

18Oseawater seawater isotopic composition. The authors underlined that coral skel-

the authors conducted isotopic analyses of coral skeleton collected over wide range of temperatures. This data series still constitutes the most exhaustive oxygen isotopic database existing for corals. Weber and Woodhead concluded that the calibration

topic disequilibrium was attributed to vital effect, anomalies compared with chemical and isotopic equilibrium, related to metabolic activity. Several models of mineralisation were proposed to explain the geochemical specificities of coral skeletons based on kinetic fractionation [7–9] disturbed by "vital effects". Other models, based on precipitation efficiency [10] or Rayleigh fractionation [11–13], were suggested.

We developed drastically different approach considering that corals are animals living in symbiosis with algae, building aragonitic skeleton intimately related to biological activity. In collaboration with biologists from CSM (Centre Scientific de Monaco), Stéphanie Reynaud and Christine Ferrier-Pagès, and Claire Rollion-Bard geochemist from IPGP (Institut Physique du Globe de Paris), we developed an innovative strategy on cultured *Acropora* to identify what was hidden under the term of vital effect of coral skeleton and to highlight the isotopic fractionation

coral *Acropora* and massive ones *Porites* belong to different genera but responses to environmental forcing in terms of biological parameters and isotopic signatures are

Our demonstration is structured as followed: first, the main coral features are highlighted; second, we describe coral culture proceeding; third, temperature and light test results are presented at microscopic size scale; and finally, we display the

Shallow corals, because they are leaving in symbiosis with micro algae need light

Coral skeleton is extracellular, located at the base of coral tissue, constituted of similar units, the polyps. Each polyp looks like a bag made by two layers of cells (**Figure 1**). Polyps are linked together by the coenosarc. Most of zooxanthellae are

Biological activity might be quantified. Photosynthesis and respiration were measured using the respirometry technique, which measured the changes in oxygen concentration at different light levels. Rates of net photosynthesis and respiration

18O as indicator of deposit mechanism.

involved in. We focused our study on the stable oxygen isotopic ratio δ

from [5] with sea surface temperature (SST) being sea surface temperature and

However, after preliminary studies [6], Weber and Woodhead deduced, despite apparent isotopic disequilibrium between coral skeletal carbonate and ambient

18Ocoral was temperature dependent. To support this assumption [2],

18O and annual SST differed following each coral genus, and the iso-

16O)standard]–1} ∗ 10−3

2 (1)

18O. Branched

**82**

*Organisation of the coral adapted from [14]. The colour polyp is the living organism, an animal building the white skeleton. The animal lives in symbiosis with algae, the zooxanthellae, located in the internal layer (the left side high corner). A detail of mesoscale skeletal architecture figures on the left side bottom corner.*

were estimated using a linear regression of O2 against time [15]. By using two light intensities, at three temperatures (**Figure 2**), it appeared that increasing temperature enhanced photosynthetic activity, the effect arising with light intensity (**Figure 2a**) [15]. Additionally, coral growth rates might be estimated. Corals were weighed regularly using the buoyant weight technique and the surface expansion of the new skeleton formed was estimated [15]. It was generally accepted that calcification was light-enhanced (LEC or light enhanced calcification) during the day [16]. Zooxanthellae density and pigment concentration were determined under the light microscope using a counting chamber [15]. Coral symbiont distribution was not homogeneous on the skeleton and it differed following different coral genera, different depths in the fields. For example, tips of coral branches or other exposed surfaces were sun-adapted while most of the lowest parts were shade-adapted [15]. Iluz and Dubinsky [17] listed all the strategies developed by coral to optimise the light impinging on the zooxanthellae.

#### **Figure 2.**

*Test using a factorial design of three temperatures (22, 25, and 28°C) and two light intensities (200 and 400 μmol photon m−2 s−1 ) of cultured* Acropora*. Biologic response of net productivity (a), zooxanthellae density according to net productivity (b) and averaged δ18O-temperature calibration under high light (HL) and low light (LL) (c).*

#### **2.2 Microstructures of coral skeletal**

It was admitted that the coral skeleton such as coral *Acropora* (**Figure 3a** and **b**) or coral *Porites* presented composite mineral microstructures: centres of calcification (COC) and fibres, embedded in a few organic matter as a network [18]. COC were massive randomly oriented crystals called fusiform crystals (**Figure 3c, h** and **i**) [19], and numerous needle-like crystals projecting in many directions from the fusiform crystals were called the fibres gathered into bundles (**Figure 3e, f** and **g**) [19] oriented perpendicularly to the growth axis (**Figure 3e**) [19].

Skeletogenesis could be the result of two different processes: the deposition of fusiform crystals and the progressive thickening of the initial framework by needle like crystals (**Figure 3f**) [19].

These crystalline elements were differently distributed according to morphology [19–21]. Each microstructure is preferentially present in some morphological parts, which were more or less developed following the genus [22]. However, we know that they are composed by identical microstructures and only differ by their relative amounts.

**85**

culture tests.

**2.3 Consequences on δ18O**

**Figure 3.**

scale by using ion microprobe.

The oxygen isotopic composition of coral skeleton was measured on conventional spectrometer at mm size scale and might be also measured at micrometre

*Identification of mineralisation mechanism of microstructures COCs and fibres using microscopic δ18O analyses. SEM observations of cultured* Acropora *microstructures (a–i). microstructure identification and*

*isotopic signatures (j). COC and fibre location on theca and septa from cultured* Acropora *(k).*

Coral skeleton δ18O was impacted by biology, which was essentially responsible of the vital effect. Most of the models proposed by geochemists neglect biology effects on δ18O, isotopic fractionation only depending on seasurface temperature and isotopic composition, δ18Oseawater following Eq. (1). All climate reconstructions are derived according to this rule, including the estimate of both temperature and salinity based on the use of paired δ18O and Sr/Ca measured on the same sample [23–25]. Salinity values deduced by this method are systematically misleading, d18O and Sr/Ca SST calibrations being based on classical thermodynamics. Whereas consequences of temperature and light on coral growth rates is well known by biologists [26], light effect is ignored by geochemists because the demonstration of this influence cannot be established from field data and needs

*Could Coral Skeleton Oxygen Isotopic Fractionation be Controlled by Biology?*

*DOI: http://dx.doi.org/10.5772/intechopen.89146*

*Could Coral Skeleton Oxygen Isotopic Fractionation be Controlled by Biology? DOI: http://dx.doi.org/10.5772/intechopen.89146*

#### **Figure 3.**

*Isotopes Applications in Earth Sciences*

**2.2 Microstructures of coral skeletal**

 *s−1*

like crystals (**Figure 3f**) [19].

It was admitted that the coral skeleton such as coral *Acropora* (**Figure 3a** and **b**) or coral *Porites* presented composite mineral microstructures: centres of calcification (COC) and fibres, embedded in a few organic matter as a network [18]. COC were massive randomly oriented crystals called fusiform crystals (**Figure 3c, h** and **i**) [19], and numerous needle-like crystals projecting in many directions from the fusiform crystals were called the fibres gathered into bundles (**Figure 3e, f** and **g**) [19] oriented perpendicularly to the growth axis (**Figure 3e**) [19].

*Test using a factorial design of three temperatures (22, 25, and 28°C) and two light intensities (200 and 400*

*according to net productivity (b) and averaged δ18O-temperature calibration under high light (HL) and low*

*) of cultured* Acropora*. Biologic response of net productivity (a), zooxanthellae density*

Skeletogenesis could be the result of two different processes: the deposition of fusiform crystals and the progressive thickening of the initial framework by needle

These crystalline elements were differently distributed according to morphology [19–21]. Each microstructure is preferentially present in some morphological parts, which were more or less developed following the genus [22]. However, we know that they are composed by identical microstructures and only differ by their relative

**84**

amounts.

**Figure 2.**

*μmol photon m−2*

*light (LL) (c).*

*Identification of mineralisation mechanism of microstructures COCs and fibres using microscopic δ18O analyses. SEM observations of cultured* Acropora *microstructures (a–i). microstructure identification and isotopic signatures (j). COC and fibre location on theca and septa from cultured* Acropora *(k).*

## **2.3 Consequences on δ18O**

The oxygen isotopic composition of coral skeleton was measured on conventional spectrometer at mm size scale and might be also measured at micrometre scale by using ion microprobe.

Coral skeleton δ18O was impacted by biology, which was essentially responsible of the vital effect. Most of the models proposed by geochemists neglect biology effects on δ18O, isotopic fractionation only depending on seasurface temperature and isotopic composition, δ18Oseawater following Eq. (1). All climate reconstructions are derived according to this rule, including the estimate of both temperature and salinity based on the use of paired δ18O and Sr/Ca measured on the same sample [23–25]. Salinity values deduced by this method are systematically misleading, d18O and Sr/Ca SST calibrations being based on classical thermodynamics. Whereas consequences of temperature and light on coral growth rates is well known by biologists [26], light effect is ignored by geochemists because the demonstration of this influence cannot be established from field data and needs culture tests.

δ 18O differed following microstructures at microscopic size scale (**Figure 3j** and **k**) [27]. This was confirmed later on [28, 29]. COC δ 18O was lower, while fibre δ 18O was higher and variable between equilibrium and COC value (**Figure 3j** and **k**) [29].

## **3. Calibrations of annual and monthly δ18O***-***temperature**

### **3.1 Weber and Woodhead (1972) data set and annual calibrations revisited**

Weber and Woodhead [3] established a formula able to predict past SST following the isotopic thermometer concept [30], expressed as:

$$\mathbf{SST^{o}C = a \times \delta^{18}O \text{ (}\%\text{)} + b} \tag{2}$$

(a) and (b) being constants (instead of A and B in [3]).

Because *Acropora* and *Porites* are ubiquitous genera, *Acropora* and *Porites* δ 18O calibration deriving from 835 and 421 sample, respectively, calibrations (**Figure 4a** and **b**) might be regarded as statistically significant. Moreover, isotopic analyses were conducted on annual samples, identified by X-ray growth bands, a pair of clear and dark bands corresponding to the annual growth [31]. Each temperature

#### **Figure 4.**

*Annual coral δ18O measures performed on several genera from revisited dataset of [3] (a–e). Location of the 29 sites where coral samples were collected, prescribing temperature values (a). Calibrations of 44 coral genera following δ18O(‰) = a × SST°C + B (b). The colours highlight genera sharing identical temperature and isotopic ranges, underlining the convergence of the groups including* Acropora *and* Porites*. Calibrations of some coral genera* Acropora*,* Porites*,* Platygira*,* Montipora *or* Pavona *following δ18Ocarbonate – δ18Oseawater = a × δ18O(‰) + b (c). The colours of the calibrations correspond with colours from (c). strongly significant linear relationship linking constants a and b, of annual δ18O-annual temperature calibrations for 44 coral genera (d). Strongly significant linear relationship linking constant of annual δ18O-annual temperature calibrations for groups highlighted on (c and e).*

**87**

*Could Coral Skeleton Oxygen Isotopic Fractionation be Controlled by Biology?*

value, corresponding to one island, as associated to the averaged δ

including *Acropora* or *Porites* displayed strong convergence.

corals of the same species, all receiving identical local irradiation. Groups of genera

The dataset [3] did not take into account δ18Oseawater. Juillet-Leclerc and Schmidt [32] included annual δ18Oseawater values assessed in the calibration established for

However, the correlation linking δ18O directly to temperature showed a higher

A similar procedure was conducted for *Acropora*, using the same δ18Oseawater. We

δ18 Ocarbonate– δ18 Oseawater = −0.20 × SST (°C) + 0.45 (3)

δ18 Ocarbonate = −0.27 × SST (°C) + 2.24 (4)

= 0.83, N = 22, p < 0.001, only significant over the SST range from 24 to

= 0.91, N = 24, p < 0.001 including the lowest temperatures neglected in

δ18 Ocarbonate– δ18 Oseawater = −0.21 × SST (°C) + 1.26 (5)

δ18 Ocarbonate = −0.28 × SST (°C) + 3.34 (6)

18O directly to temperature showed a higher coefficient [3]:

18Oseawater exhibited a slope value close to

18O is constant, regardless of temperature

= 0.87, N = 24, p < 0.001, significant over the temperature range from 21

= 0.98, N = 27, p < 0.001, significant over the temperature range from 21

Slopes (a) shown by *Porites* and *Acropora* temperature calibrations including δ18Oseawater , −0.20 and −0.21‰/°C, respectively, differed from those deriving only

After introducing δ18Oseawater into dataset [3], for *Porites* and *Acropora* genera*,* the usual thermodynamic equation is significant but to a lower degree, compared to

In the calibrations depending only on temperature, temperature might act first, according to thermodynamic law [5, 15] and second, through the photosynthetic process [34] (**Figure 2a**), which was enhanced by a temperature increase.

process while the second mechanism caused a rise in δ18O, confusing the global isotopic effect. Temperature influences δ18O twice, explaining that temperature is

isotopic equilibrium of inorganic aragonite with water, suggesting that under quasi-

(**Figure 4c**). Eqs. (3) and (4) confirm that, to a lesser degree than temperature,

Eqs. (4) and (6). For example, by taking into account only temperature, R2

and 0.98 instead of 0.87 and 0.93 for *Porites* and *Acropora* respectively.

Therefore, an increase in temperature induced a decrease in δ

the main factor, which does not exclude the role of δ18Oseawater.

Calibrations taking into account δ

uniform light, the isotopic offset of coral δ

δ18Oseawater may be included in a calibration.

18Ocarbonate (referred as δ18O in the following) and temperature. They were close to the slope of −0.19‰/°C assessed for inorganic aragonite calibration [33]. Slopes have been also obtained from other genera such as *Platygira*, *Montipora* or

18O measured for

= 0.91

18O following the first

*DOI: http://dx.doi.org/10.5772/intechopen.89146*

*Porites* following the formula:

with R2

coefficient [3]:

with R2

with R2

with R2

to 30°C.

from δ

to 30°C (**Figure 4e**).

*Pavona* (**Figure 4e**) [3].

the correlation linking δ

Eq. (5) [32].

obtained:

30°C [32].

*Could Coral Skeleton Oxygen Isotopic Fractionation be Controlled by Biology? DOI: http://dx.doi.org/10.5772/intechopen.89146*

value, corresponding to one island, as associated to the averaged δ 18O measured for corals of the same species, all receiving identical local irradiation. Groups of genera including *Acropora* or *Porites* displayed strong convergence.

The dataset [3] did not take into account δ18Oseawater. Juillet-Leclerc and Schmidt [32] included annual δ18Oseawater values assessed in the calibration established for *Porites* following the formula:

$$\text{-}\,\text{\textdegree O}\_{\text{carbonate}} - \text{\textdegree O}^{18}\text{O}\_{\text{separator}} = -0.20 \times \text{SST (\text{\textdegree C}} + \text{0.45} \tag{3}$$

with R2 = 0.83, N = 22, p < 0.001, only significant over the SST range from 24 to 30°C [32].

However, the correlation linking δ18O directly to temperature showed a higher coefficient [3]:

$$\text{\\$}^{18}\text{O}\_{\text{carbonate}} = -0.27 \times \text{SST (\text{\textdegree C}} \text{)} \text{+ 2.24} \tag{4}$$

with R2 = 0.91, N = 24, p < 0.001 including the lowest temperatures neglected in Eq. (5) [32].

A similar procedure was conducted for *Acropora*, using the same δ18Oseawater. We obtained:

$$\left\|\delta^{18}\mathcal{O}\_{\text{carbonate}} - \delta^{18}\mathcal{O}\_{\text{exact}}\right\| = -0.21 \times \text{SST (\text{\textdegree C}}) + 1.26\tag{5}$$

with R2 = 0.87, N = 24, p < 0.001, significant over the temperature range from 21 to 30°C (**Figure 4e**).

the correlation linking δ 18O directly to temperature showed a higher coefficient [3]:

$$\text{\\$}^{18}\text{O}\_{\text{carbonate}} = -0.28 \times \text{SST (\text{\textdegree C}} \text{)} + \text{\textdegree 3.34} \tag{6}$$

with R2 = 0.98, N = 27, p < 0.001, significant over the temperature range from 21 to 30°C.

Slopes (a) shown by *Porites* and *Acropora* temperature calibrations including δ18Oseawater , −0.20 and −0.21‰/°C, respectively, differed from those deriving only from δ 18Ocarbonate (referred as δ18O in the following) and temperature. They were close to the slope of −0.19‰/°C assessed for inorganic aragonite calibration [33]. Slopes have been also obtained from other genera such as *Platygira*, *Montipora* or *Pavona* (**Figure 4e**) [3].

After introducing δ18Oseawater into dataset [3], for *Porites* and *Acropora* genera*,* the usual thermodynamic equation is significant but to a lower degree, compared to Eqs. (4) and (6). For example, by taking into account only temperature, R2 = 0.91 and 0.98 instead of 0.87 and 0.93 for *Porites* and *Acropora* respectively.

In the calibrations depending only on temperature, temperature might act first, according to thermodynamic law [5, 15] and second, through the photosynthetic process [34] (**Figure 2a**), which was enhanced by a temperature increase. Therefore, an increase in temperature induced a decrease in δ 18O following the first process while the second mechanism caused a rise in δ18O, confusing the global isotopic effect. Temperature influences δ18O twice, explaining that temperature is the main factor, which does not exclude the role of δ18Oseawater.

Calibrations taking into account δ 18Oseawater exhibited a slope value close to isotopic equilibrium of inorganic aragonite with water, suggesting that under quasiuniform light, the isotopic offset of coral δ 18O is constant, regardless of temperature (**Figure 4c**). Eqs. (3) and (4) confirm that, to a lesser degree than temperature, δ18Oseawater may be included in a calibration.

*Isotopes Applications in Earth Sciences*

[27]. This was confirmed later on [28, 29]. COC δ

18O differed following microstructures at microscopic size scale (**Figure 3j** and **k**)

higher and variable between equilibrium and COC value (**Figure 3j** and **k**) [29].

**3.1 Weber and Woodhead (1972) data set and annual calibrations revisited**

Because *Acropora* and *Porites* are ubiquitous genera, *Acropora* and *Porites* δ

(**Figure 4a** and **b**) might be regarded as statistically significant. Moreover, isotopic analyses were conducted on annual samples, identified by X-ray growth bands, a pair of clear and dark bands corresponding to the annual growth [31]. Each temperature

*Annual coral δ18O measures performed on several genera from revisited dataset of [3] (a–e). Location of the 29 sites where coral samples were collected, prescribing temperature values (a). Calibrations of 44 coral genera following δ18O(‰) = a × SST°C + B (b). The colours highlight genera sharing identical temperature and isotopic ranges, underlining the convergence of the groups including* Acropora *and* Porites*. Calibrations of some coral genera* Acropora*,* Porites*,* Platygira*,* Montipora *or* Pavona *following δ18Ocarbonate – δ18Oseawater = a × δ18O(‰) + b (c). The colours of the calibrations correspond with colours from (c). strongly significant linear relationship linking constants a and b, of annual δ18O-annual temperature calibrations for 44 coral genera (d). Strongly significant linear relationship linking constant of annual δ18O-annual temperature calibrations for*

calibration deriving from 835 and 421 sample, respectively, calibrations

Weber and Woodhead [3] established a formula able to predict past SST follow-

**3. Calibrations of annual and monthly δ18O***-***temperature**

ing the isotopic thermometer concept [30], expressed as:

(a) and (b) being constants (instead of A and B in [3]).

18O was lower, while fibre δ

SST°C = a × δ18O (‰) + b (2)

18O was

18O

δ

**86**

**Figure 4.**

*groups highlighted on (c and e).*

When comparing constants (a) and (b) of Eq. (2) from data series [3], for all genera annual δ 18O-annual temperature calibrations (**Figure 4d**), we obtained a strongly significant linear relationship:

$$\mathbf{b} = -2\mathbf{9}.07 \times \mathbf{a} - 5.13 \tag{7}$$

with R2 = 0.95, N = 37 and p < 0.001. (a) corresponds to a disequilibrium indicator compared to −0.19, the slope value derived from the theoretical δ18O at equilibrium [34]. Such a relationship was not hazardous, but reflected inherent features of annual δ18O-annual SST calibrations. Linear calibrations determined from single genus deduced from figures or table of [3], showed strong correlation coefficients: R2 = 0.99 (**Figure 4e**).

This suggests that the δ 18O SST dependence is based on a unique rationale according to taxonomy, in turn inherent to the coral skeleton.

Dataset [3] revealed unique relationship between annual δ18O-annual temperature calibrations of each genus, because coral taxonomy is based on morphology. Land et al. [22] stressed the high δ18O variability following the longitudinal section on the calices of some species or the septa dentations of another one, inducing that according to coral morphology, some skeleton portions might be more or less developed, implying a large isotopic variability.

We underlined the relationship existing between the annual δ18O-annual SST calibration constants. However, identical feature was highlighted for annual Sr/ Ca-annual temperature calibrations [35–37]. The link existing between δ18O and Sr/Ca is not straightforward, oxygen being a component of CaCO3 and Sr/Ca an impurity included in the skeleton. However, it is possible to recognise common δ 18O and Sr/Ca behaviour relative to their microstructure distribution in the coral and the concept of taxonomy.

Coral skeleton presents composite mineral microstructures: centres of calcification (COC) and fibres, embedded in a few organic matter as a network [18], differently distributed according to morphology [19–21]. Latter authors show that COC and fibres are essentially present in morphological parts, more or less developed following the genus. On the one hand, δ 18O signature differs according to the microstructures [19–21], COC δ 18O being lower than fibre δ 18O [29] (**Figure 3j** and **k**). On the other hand, Sr/Ca ratios measured on COCs are higher than those of fibres [9]. Cohen et al. [37] examined synchronously deposited microstructures on *Porites lutea* over a year, exhibiting COC elemental ratios systematically higher compared to those of fibres developed over an identical period. Thus, it is the proof that annual COC Sr/Ca value is higher than the annual fibre Sr/Ca signature [37]. Therefore, we suggested that discrepancies of morphology existing between coral genera are due to differences of microstructure proportions [22], explaining common features between the annual trace element ratio- and annual δ18O-annual temperature calibrations.

#### **3.2 Identification of microstructures and their isotopic signatures using microsensor**

Several small colonies of *Acropora verweyi* (Archaeocoeniina) were cultured following the procedure described by Reynaud-Vaganay et al. [38] under constant and controlled conditions, in Centre Scientific of Monaco (CSM) (**Figure 5**). Such colonies grew glued onto glass slides (**Figure 5**). Morphology of the microstructures, using on a scanning electron microscope (SEM Philips 505) was similar to observations performed by Cuif and Dauphin [19] (**Figure 3a–i**).

**89**

**Figure 5.**

*following potential photosynthetic response of colonies (d).*

*Could Coral Skeleton Oxygen Isotopic Fractionation be Controlled by Biology?*

The new skeleton, formed under unique controlled condition, was grown on the glass slide, and sampled for the calibration of the growth units (**Figure 3j**). COC- and fibre-enriched zones were identified using SEM [29]. To characterise separately the isotopic signature of fibres and COC, analyses were focused on the microstructures earlier identified on the newly formed skeleton on two zones (**Figure 3a–c**; **Figure 3j**). We then focused our measurements around the theca of the newly formed skeleton (**Figure 3k**) where Gladfelter [39] recognised large amounts of "fusiform crystals" (**Figure 3e**). The sampling of the septae aimed

*Culture experiment (a and b) to test δ18O variability caused separately by temperature (c) and by light (d). Aquarium in CSM (a) coral* Acropora *glued on glass slide showing new formed aragonite both on the colony surface and on the glass slide (b). δ18O-temperature calibration derived from averaged isotopic measures (c). Relationship between Pnet and linear extension, revealing the partition of colonies into two populations,*

*DOI: http://dx.doi.org/10.5772/intechopen.89146*

*Could Coral Skeleton Oxygen Isotopic Fractionation be Controlled by Biology? DOI: http://dx.doi.org/10.5772/intechopen.89146*

#### **Figure 5.**

*Isotopes Applications in Earth Sciences*

strongly significant linear relationship:

genera annual δ

with R2

 = 0.99 (**Figure 4e**). This suggests that the δ

the concept of taxonomy.

structures [19–21], COC δ

calibrations.

**microsensor**

(**Figure 3a–i**).

following the genus. On the one hand, δ

R2

When comparing constants (a) and (b) of Eq. (2) from data series [3], for all

tor compared to −0.19, the slope value derived from the theoretical δ18O at equilibrium [34]. Such a relationship was not hazardous, but reflected inherent features of annual δ18O-annual SST calibrations. Linear calibrations determined from single genus deduced from figures or table of [3], showed strong correlation coefficients:

Dataset [3] revealed unique relationship between annual δ18O-annual temperature calibrations of each genus, because coral taxonomy is based on morphology. Land et al. [22] stressed the high δ18O variability following the longitudinal section on the calices of some species or the septa dentations of another one, inducing that according to coral morphology, some skeleton portions might be more or less

We underlined the relationship existing between the annual δ18O-annual SST calibration constants. However, identical feature was highlighted for annual Sr/ Ca-annual temperature calibrations [35–37]. The link existing between δ18O and Sr/Ca is not straightforward, oxygen being a component of CaCO3 and Sr/Ca an impurity included in the skeleton. However, it is possible to recognise common δ

and Sr/Ca behaviour relative to their microstructure distribution in the coral and

18O being lower than fibre δ

**3.2 Identification of microstructures and their isotopic signatures using**

of the microstructures, using on a scanning electron microscope (SEM Philips 505) was similar to observations performed by Cuif and Dauphin [19]

Several small colonies of *Acropora verweyi* (Archaeocoeniina) were cultured following the procedure described by Reynaud-Vaganay et al. [38] under constant and controlled conditions, in Centre Scientific of Monaco (CSM) (**Figure 5**). Such colonies grew glued onto glass slides (**Figure 5**). Morphology

the other hand, Sr/Ca ratios measured on COCs are higher than those of fibres [9]. Cohen et al. [37] examined synchronously deposited microstructures on *Porites lutea* over a year, exhibiting COC elemental ratios systematically higher compared to those of fibres developed over an identical period. Thus, it is the proof that annual COC Sr/Ca value is higher than the annual fibre Sr/Ca signature [37]. Therefore, we suggested that discrepancies of morphology existing between coral genera are due to differences of microstructure proportions [22], explaining common features between the annual trace element ratio- and annual δ18O-annual temperature

Coral skeleton presents composite mineral microstructures: centres of calcification (COC) and fibres, embedded in a few organic matter as a network [18], differently distributed according to morphology [19–21]. Latter authors show that COC and fibres are essentially present in morphological parts, more or less developed

according to taxonomy, in turn inherent to the coral skeleton.

developed, implying a large isotopic variability.

18O-annual temperature calibrations (**Figure 4d**), we obtained a

= 0.95, N = 37 and p < 0.001. (a) corresponds to a disequilibrium indica-

18O SST dependence is based on a unique rationale

b = −29.07 × a–5.13 (7)

18O signature differs according to the micro-

18O [29] (**Figure 3j** and **k**). On

18O

**88**

*Culture experiment (a and b) to test δ18O variability caused separately by temperature (c) and by light (d). Aquarium in CSM (a) coral* Acropora *glued on glass slide showing new formed aragonite both on the colony surface and on the glass slide (b). δ18O-temperature calibration derived from averaged isotopic measures (c). Relationship between Pnet and linear extension, revealing the partition of colonies into two populations, following potential photosynthetic response of colonies (d).*

The new skeleton, formed under unique controlled condition, was grown on the glass slide, and sampled for the calibration of the growth units (**Figure 3j**). COC- and fibre-enriched zones were identified using SEM [29]. To characterise separately the isotopic signature of fibres and COC, analyses were focused on the microstructures earlier identified on the newly formed skeleton on two zones (**Figure 3a–c**; **Figure 3j**). We then focused our measurements around the theca of the newly formed skeleton (**Figure 3k**) where Gladfelter [39] recognised large amounts of "fusiform crystals" (**Figure 3e**). The sampling of the septae aimed

at confirming the presence of both COC and fibres as they have been identified from SEM observations [26].

The present study, confirmed that there was a strong relationship between isotopic value, crystal shape and skeleton morphology [29]. Crystals called "fusiform" by Gladfelter [39], according to their shape, show the same isotopic values as COC. We distinguished in septa both COC and fibres (**Figure 3k**). This confirmed microscopic observations of septa [21] showing discontinuous COC surrounded by fibres.

Isotopic fractionation was likely of kinetic origin, the rate changing according to microstructure. Skeleton microstructures δ18O shed in light how chemical and/ or physical processes might be adapted by biology to form crystals characterised by specific shapes and distributed following a hierarchical arrangement. The present study demonstrated that the presence of organic molecules (the organic matrix located at the interface tissue-mineral (**Figure 1**) had the capability to control the mineral deposition mechanism. Probably, the influence of external factors should be superimposed on the chemical signature of coral biomineral genetically determined).

#### **3.3 Monthly calibrations on coral** *Porites*

The preliminary step of climatic reconstruction using *Porites* skeleton, the genus more often analysed in this context, consisted of the assessment of seasonal δ18Oseasonal temperature calibration based on monthly instrumental temperatures over the last decades covered by the core. Sampling was conducted along the coral's growth through time, following the maximal growth rate perpendicular to the annual density bands shown by X-ray [40].

At millimetre size scale, it was also possible to highlight the strongly significant linear relationship between the constants of seasonal δ 18O-seasonal temperature calibrations and to relate behaviour of the constants of the seasonal-δ 18O- and Sr/Ca-seasonal temperature calibrations to the presence of two crystallographic units. Following DeLong et al. [40], fibres insuring the thickening of a colony should be preferentially deposited during a less active photosynthesis, whereas COC insuring axial growth should be formed during high photosynthetic activity. Juillet-Leclerc and Reynaud agreed, however, they demonstrated that growth mode was not so simple [34].

In order to test seasonal δ18O-seasonal temperature calibration variability including the seasonal light effect, calculated for several coral cores collected on a given site, at different temperature ranges, we considered studies conducted on several *Porites* colonies from three sites. The mean annual temperature offshore Amédée Island, New Caledonia (22°29′ S, 166°28′ E) was 24.72°C, over the period 1968–1992 [41, 42], while at Clipperton Atoll (10°18′ N, 109°13′ W) the mean annual temperature was 28.5°C, over the period 1985–1995 [43] and in the Flores Sea, Indonesia (6°32′ S, 121°13′ E) the mean annual temperature was above 28°C, over the period 1979–1985 [44].

We assumed that calibrations measured on different coral colonies grown at a given site (New Caledonia, Clipperton or Indonesia) differed according to various light sensitivities due to depth or light incidence or acclimation because seasonality strongly affected light variations, and was likely different following site location (**Figure 6a**). However, calibration constants calculated from monthly data for *Porites* remained strongly correlated (**Figure 6b**) as we previously observed for annual δ 18O-annual temperature calibrations.

As seasonal δ 18O-seasonal temperature calibrations presented similar behaviours, even in different sites characterised by distinct δ18Oseawater , they did not reflect classical thermodynamics.

**91**

*Could Coral Skeleton Oxygen Isotopic Fractionation be Controlled by Biology?*

**4. Coral cultures simulating different environmental conditions**

Porites *monthly δ18O from [41–44] (a and b). Monthly δ18O-monthly temperature calibrations for coral*  Porites *and annual δ18O-annual temperature for* Porites *group as defined in Figure 4c (a) and associated*

New technique of culture was developed to calculate δ18O-temperature calibration for *Acropora sp*. The experiment was conducted in Centre Scientific of Monaco (CSM) using colonies of the branching zooxanthellate scleractinian coral, *Acropora sp*. (**Figure 5a** and **b**), in the Gulf of Aqaba (1 m depth) [38]. The nubbins (new colony fragments) were collected from unique parent colony. The specimens were glued on glass slides. Chemical conditions were kept constant during the experiment, as δ18Oseawater (1.29 ± 0.01‰ vs. SMOW) measured in the aquaria under light

on six coral fragments. The skeletal powder was treated following the method

The calibration given by the experiment (**Figure 5c**) might be expressed as:

As δ18Oseawater = 1.29 vs. SMOW = 1.02 vs. PDB was constant, the calibration

Heterotrophy and photosynthesis were linked and were difficult to separate in field experiments. Coral cultures enabled the investigation of each parameter at a

Tips from 24 branches were sampled from a single parent colony of *Acropora sp*.

s−1

 s−1 .

, and their isotopic composition

All colonies were cultured for 6 weeks under a light intensity of 130 μmol m−2

The ring skeleton deposited on the glass slide was then removed with a scalpel [38] dried overnight at room temperature and stored in glass containers pending isotopic analyses. Thereafter, colonies were cultured for an additional period of

δ18 Ocoral = −0.27 × SST(°C) + 5.41 (9)

) on a 12:12 h photoperiod [38]. Five temperatures were tested

δ18 Ocoral– δ18 Oseawater = −0.27 × SST(°C) + 3.22 (8)

*DOI: http://dx.doi.org/10.5772/intechopen.89146*

**4.1 Test of temperature**

*constant relationship (b).*

**Figure 6.**

(260 μmol m−2

s−1

with N = 5 and R2

might be expressed as:

**4.2 Test of light intensity**

time [34, 46].

described by Boiseau and Juillet-Leclerc [45].

= 0.96.

6 weeks under a light intensity of 260 μmol m−2

*Could Coral Skeleton Oxygen Isotopic Fractionation be Controlled by Biology? DOI: http://dx.doi.org/10.5772/intechopen.89146*

**Figure 6.**

*Isotopes Applications in Earth Sciences*

from SEM observations [26].

fibres.

determined).

**3.3 Monthly calibrations on coral** *Porites*

annual density bands shown by X-ray [40].

ear relationship between the constants of seasonal δ

18O-annual temperature calibrations.

tions and to relate behaviour of the constants of the seasonal-δ

at confirming the presence of both COC and fibres as they have been identified

The present study, confirmed that there was a strong relationship between isotopic value, crystal shape and skeleton morphology [29]. Crystals called "fusiform" by Gladfelter [39], according to their shape, show the same isotopic values as COC. We distinguished in septa both COC and fibres (**Figure 3k**). This confirmed microscopic observations of septa [21] showing discontinuous COC surrounded by

Isotopic fractionation was likely of kinetic origin, the rate changing according to microstructure. Skeleton microstructures δ18O shed in light how chemical and/ or physical processes might be adapted by biology to form crystals characterised by specific shapes and distributed following a hierarchical arrangement. The present study demonstrated that the presence of organic molecules (the organic matrix located at the interface tissue-mineral (**Figure 1**) had the capability to control the mineral deposition mechanism. Probably, the influence of external factors should be superimposed on the chemical signature of coral biomineral genetically

The preliminary step of climatic reconstruction using *Porites* skeleton, the genus more often analysed in this context, consisted of the assessment of seasonal δ18Oseasonal temperature calibration based on monthly instrumental temperatures over the last decades covered by the core. Sampling was conducted along the coral's growth through time, following the maximal growth rate perpendicular to the

At millimetre size scale, it was also possible to highlight the strongly significant lin-

In order to test seasonal δ18O-seasonal temperature calibration variability including the seasonal light effect, calculated for several coral cores collected on a given site, at different temperature ranges, we considered studies conducted on several *Porites* colonies from three sites. The mean annual temperature offshore Amédée Island, New Caledonia (22°29′ S, 166°28′ E) was 24.72°C, over the period 1968–1992 [41, 42], while at Clipperton Atoll (10°18′ N, 109°13′ W) the mean annual temperature was 28.5°C, over the period 1985–1995 [43] and in the Flores Sea, Indonesia (6°32′ S, 121°13′ E) the mean annual temperature was above 28°C, over the period

We assumed that calibrations measured on different coral colonies grown at a given site (New Caledonia, Clipperton or Indonesia) differed according to various light sensitivities due to depth or light incidence or acclimation because seasonality strongly affected light variations, and was likely different following site location (**Figure 6a**). However, calibration constants calculated from monthly data for *Porites* remained strongly correlated (**Figure 6b**) as we previously observed for

iours, even in different sites characterised by distinct δ18Oseawater , they did not reflect

18O-seasonal temperature calibrations presented similar behav-

temperature calibrations to the presence of two crystallographic units. Following DeLong et al. [40], fibres insuring the thickening of a colony should be preferentially deposited during a less active photosynthesis, whereas COC insuring axial growth should be formed during high photosynthetic activity. Juillet-Leclerc and Reynaud agreed, however, they demonstrated that growth mode was not so simple [34].

18O-seasonal temperature calibra-

18O- and Sr/Ca-seasonal

**90**

annual δ

As seasonal δ

classical thermodynamics.

1979–1985 [44].

Porites *monthly δ18O from [41–44] (a and b). Monthly δ18O-monthly temperature calibrations for coral*  Porites *and annual δ18O-annual temperature for* Porites *group as defined in Figure 4c (a) and associated constant relationship (b).*

## **4. Coral cultures simulating different environmental conditions**

#### **4.1 Test of temperature**

New technique of culture was developed to calculate δ18O-temperature calibration for *Acropora sp*. The experiment was conducted in Centre Scientific of Monaco (CSM) using colonies of the branching zooxanthellate scleractinian coral, *Acropora sp*. (**Figure 5a** and **b**), in the Gulf of Aqaba (1 m depth) [38]. The nubbins (new colony fragments) were collected from unique parent colony. The specimens were glued on glass slides. Chemical conditions were kept constant during the experiment, as δ18Oseawater (1.29 ± 0.01‰ vs. SMOW) measured in the aquaria under light (260 μmol m−2 s−1 ) on a 12:12 h photoperiod [38]. Five temperatures were tested on six coral fragments. The skeletal powder was treated following the method described by Boiseau and Juillet-Leclerc [45].

The calibration given by the experiment (**Figure 5c**) might be expressed as:

$$\rm{^{18}O\_{\rm{coral}} - \rm{6}^{18}O\_{\rm{seawater}} = -0.27 \times \rm{SST(^{\circ}C)} + 3.22} \tag{8}$$

with N = 5 and R2 = 0.96.

As δ18Oseawater = 1.29 vs. SMOW = 1.02 vs. PDB was constant, the calibration might be expressed as:

$$\\$\,^{18}\text{O}\_{\text{coral}} = -0.27 \times \text{SST} \text{(°C)} + 5.41 \tag{9}$$

#### **4.2 Test of light intensity**

Heterotrophy and photosynthesis were linked and were difficult to separate in field experiments. Coral cultures enabled the investigation of each parameter at a time [34, 46].

Tips from 24 branches were sampled from a single parent colony of *Acropora sp*. All colonies were cultured for 6 weeks under a light intensity of 130 μmol m−2 s−1 . The ring skeleton deposited on the glass slide was then removed with a scalpel [38] dried overnight at room temperature and stored in glass containers pending isotopic analyses. Thereafter, colonies were cultured for an additional period of 6 weeks under a light intensity of 260 μmol m−2 s−1 , and their isotopic composition

was determined (**Figure 5d**). The extension of new aragonite on the glass slide was assimilated to linear extension.

In the first time [46], the averaged results showed that daily calcification, net photosynthesis significantly increased with increasing light and skeletal δ18Ocoral were more negative under low light than high light, −4.2 versus −3.8.

Another interpretation, considering each colony was later published [34]. Following the evolution, δ13Ccoral increasing or decreasing, two populations appeared: one responding to light with increasing net photosynthesis associated to low linear extension and the other characterised by poor net photosynthesis associated to high linear extension (**Figure 5d**).

We suggested that different behaviours were due to different zooxanthellae amounts contained by colonies.

#### **4.3 Factorial design of three temperatures and two light intensities**

Conditions applied to each tank were referred in the following as (light in μmol photons m−2 s−1 , temperature in °C): (200, 22), (200, 25), (200, 28), (400, 22), (400, 25) and (400, 28) [15, 48].

Culture procedures are similar to what was described in **Figure 5a** and **b**. Responses of photosynthesis and zooxanthellae density are displayed in **Figure 2**.

Calibrations calculated from the mean δ 18O values for each temperature regime were consistent with those previously published (**Figure 2c**) [49, 50]. δ 18O *versus* temperature calibrations of nubbins cultured under LL and HL were both highly significant (R2 = 0.94, N = 18, P = 0.001 and R = 0.96, N = 18, P = 0.001, respectively). The slope value was in good agreement with Eq. (2) commonly used for *Porites* corals with b = −0.20‰/°C [37, 51, 52]. However, the values obtained at 22, 25 and 28°C showed a large scattering both at LL and HL, from 0.5 to 1.25‰ or the equivalent of 2 to 5°C.

By comparing our results with other culture experiments [51–53], differences appeared between various δ 18O-temperature (°C) calibrations regarding both the slopes and the intercepts with the temperature scale. We suggested that this could be due to inter-species or inter-colony δ18O differences. Even two calibrations obtained on cultured *Acropora* exhibited differences (the present study and that of Reynaud et al.) [52].

Mean δ18O values calculated for each temperature did not vary with light, which contradicted observations made of mean physiological parameters, in contrast with other proxies (δ 13C, Sr/Ca and Mg/Ca). By changing the light intensity from low to moderate, Juillet-Leclerc and Reynaud [47] recorded a δ18O increase associated with skeletal infilling following a kinetic process. The present experiment, conducted under high light intensities, did not show a similar behaviour. We suggested that temperature and light effects on isotopic composition were competing. The results of the present experiment indicated that, under the chosen conditions, the temperature effect was more important than the light effect. This was illustrated by the weak discrepancy in the mean δ18O recorded at 28°C.

Previous culture experiments have been conducted to test the temperature effect on δ18O [38, 51–54]. Due to the sensitivity of the photosynthesis to temperature, δ18O-temperature calibrations will always include temperaturedependent photosynthetic changes, enabling the vital effect due to temperature only to be deconvolved from the total signature. Therefore, all calibrations, even established on a single coral head or from cultured nubbins, are impacted by photosynthetic activity linked to zooxanthellae density. The universal calibration does not exist.

**93**

*Could Coral Skeleton Oxygen Isotopic Fractionation be Controlled by Biology?*

**5. A new paradigm for δ18O in coral skeleton oxygen isotope fractionation response to biological kinetic effects**

−

from the initial branch to the rim of the expanded tissue (**Figure 7a**).

measurements were made using data from [29, 48].

During the last experiment, we failed understanding the light effect on δ18O. We kept one colony cultured in each of six light and temperature conditions previously discussed. Knowing that standard error obtained in the first step of the experiment for six samples cultured in the same condition was between 0.02 and 0.12, we consider that values measured on one colony by using SIMS were representative for

We discussed our results after listing all biological and biological advances, such as (i) conclusions derived from inorganic CaCO3 precipitation disturbed by biology, biased by non-realistic models [8, 55, 56]; (ii) the potential role of the calicoblastic layer composed of proteins, sugars and water [57, 58] and (iii) the role of carbonic anhydrase (CA), ubiquitous enzymes known to act as catalysts for the

[59, 60].

The random SIMS measurements were made exclusively on the newly formed skeleton coenosteum (the skeleton portion separating corallites), avoiding newly formed corallites and spines [21]. Samples were distributed along the growth axis