Abstract

The past few years have seen an increase in the search and validation of clean label antimicrobials for their application in ready-to-eat meat products. Essential oils (EOs) from plants have been found to be effective against foodborne pathogenic bacteria such as Salmonella and Listeria under laboratory conditions. In the present study, the effect of thyme EO, pH, and isolated soy protein (ISP), and their interactions on the inactivation of either a Listeria or Salmonella cocktail were studied through a Box–Behnken experimental design. It was observed that as the amount of ISP decreased and thyme EO concentration increased, the number of microorganisms declined; furthermore, at higher ISP concentrations, a higher concentration of thyme EO was needed. This suggests an interaction between ISP and thyme EO that reduces bacterial inactivation. The results obtained from this research are a first step to establish appropriate thyme essential oil concentrations for its application as an antimicrobial on ready-to-eat meat products depending on their pH and protein content.

Keywords: thyme essential oil, antimicrobials, model system

#### 1. Introduction

Ready-to-eat meat products such as cold cuts and deli style ham or sausages have been implicated in the risk of foodborne diseases caused by the ingestion of pathogenic bacteria such as Salmonella and Listeria [1], especially when sliced at retail points [2]. Antimicrobial compounds used as ingredients in the product formulation have helped diminish foodborne disease cases, but the consumers' demand for "clean label" products has led to the search and validation of alternative compounds such as plant essential oils [3] since they not only possess generally recognized as safe (GRAS) status and wide acceptance from consumers [4] but, as plant secondary metabolites, they also contain antimicrobial components, which are important for plant defense [5], and nowadays as potential antimicrobial ingredients for food application.

Oregano and thyme have been reported as among the most effective essential oils as antimicrobials, suggesting that low concentrations of them may be needed to achieve the desired effect. This, in turn, is an advantage since high concentrations of an EO can have a negative impact on the sensory acceptability of food products [4]. Although some studies have shown the efficacy of EOs as antimicrobials in meat products, others have reported very low antimicrobial activity and the need for high concentrations of the EO to accomplish the desired effect [3].

In this context, there is a need to evaluate EOs directly in food products or in model systems that simulate food composition [4]. The use of food model media before food application is important since conditions can be controlled in order to determine the interactions between EOs and food components that could influence their antimicrobial activity.

In this regard, the main objective of this work was to, by means of a Box-Behnken design (BBD) of response surface methodology, evaluate the effects of pH, protein, and thyme essential oil concentration on the log of colony-forming units (CFU)/mL obtained after either a Salmonella or Listeria cocktail was subjected to the selected factors in model culture media.

(Autoplate 4000, Spiral Biotech, Norwood, MA) for each concentration of thyme

NutriOmics group

Laboratory collection Salmonella spp. Benemérita Universidad Autónoma de Puebla (BUAP) Food

Looking for the Killer Combination: pH, Protein, and Thyme Essential Oil Interactions that…

Salmonella typhi (ATCC ® 19,430) BUAP Chemical Sciences Faculty Food Microbiology

by Dra. María Lorena Luna Guevara

Universidad de las Américas Puebla Food Microbiology

Microbiology Laboratory collection, isolated from tomatoes

Instituto Tecnológico de Estudios Superiores de Monterrey

MIC was considered as the lowest concentration of EO at which no bacterial growth was observed after 24 h of incubation at 35°C and MBC as the lowest concentration, which resulted in no visible growth on the plate and no growth on trypticase soy broth after streaking the plate surface and further incubated under

Plate preparation and inoculation: The media for plates were prepared by mixing isolated soy protein (ISP) adjusted to the desired concentration, trypticase soy broth as the nutrient provider, bacteriological agar as solidifying media, NaCl to adjust water activity to 0.98, and distilled water. The mixture was heated until boiling under continuous agitation and sterilized by autoclaving for 5 min at 17 lb./

. After the media cooled down to 45°C, pH was adjusted with citric acid (10%), and EO to the desired tested concentration was added during continuous agitation with a magnetic stirrer. The media was poured in Petri dishes and left to cool for at least 2 h prior to inoculation. Plates at room temperature were inoculated with 30 μL (in three drops of 10 μL) of the cocktail dilution which, by previous determination,

Experimental design: A Box-Behnken design (BBD) of response surface methodology was applied using Minitab 18.1. (Minitab, Inc., State College, PA) to study the effect of medium pH, isolated soy protein (ISP) concentration (% w/w), and EO concentration (% w/w), as well as their interactions on the growth of Salmonella or Listeria cocktails measured as fraction of surviving microorganisms when compared

Each factor was investigated at three different levels (1, 0, +1) shown in Table 2. The experimental design included 15 sets of test conditions, including 3

A Isolated soy protein (% weight/weight) 10.0 11.5 13.0 B pH 5.5 6.0 6.5 C Essential oil (% weight/weight) 0.19 0.22 0.25

1 0 +1

Factor Independent variable Coded level

replicated center points as randomized experiments to avoid bias.

Studied independent variables and their levels for tested box-Behnken design.

EO tested, 0.065–0.093% (w/w).

Salmonella Typhimurium (ATCC®

Studied bacterial strains and providers.

13,311)

Table 1.

Strain Provider

DOI: http://dx.doi.org/10.5772/intechopen.90099

Laboratory collection Listeria monocytogenes (CDBB-B-1426)

L. monocytogenes (Scott A) Salmonella typhimurium (ATCC ® 14028)

allowed the count of 20–70 CFU in each drop.

to CFU/mL found in each cocktail.

optimal conditions [10].

in2

Table 2.

95


*2.6. Data Analysis*

#### 2.6.1. Loss Rate

Several approaches for determining quantitative losses have been developed. The counting and weighing methods were used to assess the rates of maize loss during storage. This method is the most used in studies and produces better results.

The formula used by Pantenius [17] is as follows:

$$\%Losses = \frac{(E\*B) - (C\*D)}{(E\*A)} \* 100\tag{1}$$

where *A* is the total number of grains, *B* is the number of damaged grains, *C* is the number of healthy grains, *D* is the weight of damaged grains and E is the weight of healthy grains.

#### 2.6.2. Storage Costs

The cost of the maize storage encompassed both fixed and variable costs. Thus, the total cost of maize storage was obtained by summing up the fixed and variable costs. The fixed costs included the costs of the storage structures and small storage equipment, such as basins and baskets. Following Arouna et al. [20] the average monthly cost was calculated as:

$$E(j) = \frac{\mathbb{C} - R}{n} + [(\mathbb{C} - R) \* f + R] \* (q - 1) + \mathbb{C} \* r \tag{2}$$

where *j* is the type of storage structure or storage small equipment, *E*(*j*) is the monthly cost of the storage structure or small storage equipment *j*, *C* is the storage structure construction cost or purchase price, *R* is the residual value of the storage structure or small storage equipment, *n* is its useful lifespan, (*q* − 1) is the interest rate, *f* is the capital asset factor, and *r* is the repair or maintenance cost factor (coefficient). The capital asset factor is estimated using the formula as follows:

$$Capital asset factor = (Interestrate/100) \* maizeselling price \tag{3}$$

In the study area, the small equipment was mostly not repaired and used until it was thrown away. Thus *R* = 0 and *r* = 0 and Equation (2) is written as follows:

$$E(j) = \frac{\mathbb{C}}{n} + \mathbb{C} \* f \* (q - 1) \tag{4}$$

The variable costs of maize storage encompassed the costs associated with storage losses and other variable costs. The storage loss in monetary value, also called financial loss, represented the quantified sum of the quantitative losses occurring during storage with a given treatment. Thus, to calculate the quantitative loss, the quantity stored was multiplied by the loss rate. The financial loss was obtained by multiplying the quantitative loss by the average monthly maize selling price. The other variable costs comprised the labor costs associated with maize storage operations—including the dispatching and shelling costs of maize before storage in storage structures, the cost of loading and unloading the maize from the storage structure, the cost of the application of the conservation measure Actellic® Super and interest on the capital asset of the maize stock.

#### 2.6.3. Benefit–Cost Ratio (BCR)

The benefit–cost ratio (BCR) was estimated for each treatment.

It was obtained by dividing the flow of the present value of the benefits (benefits) by that of the present value of the cost following the formula of Gittinger [18].

$$\frac{B}{C} = \sum\_{t=1}^{n} \frac{B\_t}{(1+i)^{t-1}} \Big/ \sum\_{t=1}^{n} \frac{C\_t}{(1+i)^{t-1}} \tag{5}$$

where *Bt* is the monthly benefits, *Ct* is the monthly costs, *n* is the storage duration (in months), *i* is the interest rate (expected) and *t* is a given month.

#### 2.6.4. Break-Even Quantity

The break-even quantity was estimated for each treatment, and thus, the break-even quantity of the turnover and the break-even ratio were determined.

The break-even quantity in turnover (BREQ) was calculated using the following formula:

$$BREQ = \left( Fixedcosts\* \frac{Revenue}{Grossmargin} \right) \* 100 \tag{6}$$

The percentage of capacity used, also called the break-even ratio, indicates the percentage of production for which the gross margin covers the fixed costs. The risk increases as the capacity percentage increases; a low percentage (maximum = 1) gives a level of security

against unpredictable operating difficulties. Therefore, when the value of this capacity tends towards 1, there is a risk in which the producer may no longer be able to pay for the equipment used. This percentage is computed by the following formula:

$$\%capparity used = \left(\frac{BREQ}{Revenue}\right) \ast 100\tag{7}$$

The break-even quantity of maize to be stored in each storage and preservation technology to make the investment profitable is given by the following formula:

$$\text{Break} - \text{evenquality} = \% \text{capacity} \,\text{used} \,\ast \,\text{chemical capacity} \tag{8}$$

#### 2.6.5. Statistical Analysis

The Student–Newman–Keuls (SNK) ANOVA statistical test was used to test the difference between the paired means between the different storage and conservation technologies using SPSS Statistics software. These paired multiple comparison tests captured the difference between paired means and generated a matrix that informed the means of groups of significantly different storage and conservation technologies [21].

#### 2.6.6. Sensitivity Analysis

The sensitivity analysis consisted of varying the fixed costs and the selling prices of maize to assess the effect of the change in certain parameters (fixed costs and selling prices of maize) on the benefit–cost ratio and the threshold quantity for each of the technologies. This assessment allowed the impact of the different treatments implemented on the economic profitability of maize storage to be observed when these parameters changed for any reason.

#### **3. Results**

#### *3.1. Average Loss Rate Recorded for the Different Treatments Implemented*

The PICS bag with grain treatment and the PICS bag without grain treatment recorded fewer losses in the two communes during storage (Tables 1 and 2).

**Table 1.** Evolution of the average loss rates of the different treatments during storage in Savalou.

*p* > F probabilities are indicated by symbols: ns = no significant differences; \*\* significant differences at *p* < 0.05; \*\*\* significant differences at *p* < 0.01. For each column, values with the same letter indicate no significant differences at 5%; Source: Experimentation data, 2015, 2016 and 2017 (− ctrol means: without chemical conservation measure; + ctrol means: with chemical conservation measure).

*p* > F probabilities are indicated by symbols: ns = no significant differences; \*\* significant differences at *p* < 0.05; \*\*\* significant differences at *p* < 0.01. For each column, values with the same letter indicate no significant differences at 5%; Source: Experimentation data, 2015, 2016 and 2017 (− ctrol means: without chemical conservation measure; + ctrol means: with chemical conservation measure).

The statistical differences observed showed that a significant increase in the loss of dry matter was observed at the level of each treatment throughout the six months of storage in Boukoumbé (*p* < 0.0001). In Savalou, significant variations were observed during the first two months. However, in the last month of storage, in the commune of Savalou, the PICS bag with a chemical conservation measure (9.42 ± 4.64%), the polypropylene bag with a chemical conservation measure (10.56 ± 2.80%) and the PICS bag without a chemical conservation measure (11.71 ± 2.78%) were the three treatments that recorded fewer losses, while the improved clay granary (22.64 ± 7.21%) recorded the highest loss rate (Table 2). In Boukoumbé, the PICS bag with a chemical conservation measure (2.69 ± 0.77%), the polypropylene bag with a chemical conservation measure (4.02 ± 1.23%) and the metal silo with a chemical conservation measure (4.92 ± 1.36%) were the treatments that recorded significantly fewer losses in order of priority, while the improved clay granary without a chemical conservation measure (12.57 ± 3.68%) was the treatment that recorded the most maize loss during storage (F = 3.093, *p* < 0.0001) (Table 2).


**3. Sociodemographic contexts**

#### **3.1. Araraiana community**

The first phase of research was performed in the Araraiana community that belongs to the county of Ponta de Pedras, Marajó Island, PA. The county area is approximately 3,365.30 km², with a population of 20,067 inhabitants. Araraiana is a community geographically isolated from urban centers, with an absence of medical and social assistance see [19].

The Araraiana community, during data collection, consisted of 22 families with 125 inhabitants who lived in stilt houses on the margins of the river. Overall, the houses had three rooms (e.g., living room, bedroom, and kitchen) and were made of wood and straw collected from the forest adjacent to the houses. The houses were distributed along the river with an approximate minimum distance of 300 m from each other. The houses had no furniture, such as sofas, chairs, wardrobes, or beds. In several houses, it was common to sit and have guests sit on the floor made of wood boards or on benches made of wood close to the walls, typically in the living room and kitchen. The few appliances were wood-burning stoves, radios, and televisions. Because of the absence of local electricity, televisions and radios functioned with batteries for limited periods of time, mainly at night. The houses were essentially occupied by the family, in which the number varied as a function of family type (i.e., nuclear families with one to six residents or extended families with six to 10 residents), whereas multigenerational families were characterized by a higher density (i.e., eight to 12 residents).

The principal occupation of the men was extraction activities, followed by fishing. Women were housewives or artisans. The river and forest provided food and products for local extraction activities, such as fish, shrimp, game animals, and açaí.

With regard to the availability of health services, no assistance was provided by the state, in addition to the lack of treated water, trash and sewer services, and complex health problems of the population (e.g., stomach and intestinal problems and malnutrition). Similar to the lack of health services, no investments were made in education. The only school in the community was located in the house of a local resident who provided only first-year elementary school education.

### **3.2. Piriquitaquara community**

repetitive periods and guided by the dynamics of nature, distinct senses and meanings are generated in these populations, in which their routine tasks and social relationships develop

Based on interest in recognizing parenthood within the context such different development, the objective of the present study was to understand parental practices based on the descrip‐ tions of the routines of two riverine families and provide evidence of the relationships between cultural activities and the Amazonian context. We highlight the social activities during weekdays and weekends, with parenthood considered based on the daily activities that reflect

This study comprised two periods of data collection, between 2006 and 2010, when visits and interviews were performed in two Amazonia riverine communities that have different geographies and social dynamics. The Araraiana community is located in Ponta de Pedras city in the Marajó archipelago, and the Piriquitaquara community is on Combu Island and belongs to the insular area of Belém. The data form the database of the Laboratory of Ecology of Human Development, which has been conducting scientific studies on the development of Amazonia

The first phase of research was performed in the Araraiana community that belongs to the county of Ponta de Pedras, Marajó Island, PA. The county area is approximately 3,365.30 km², with a population of 20,067 inhabitants. Araraiana is a community geographically isolated

The Araraiana community, during data collection, consisted of 22 families with 125 inhabitants who lived in stilt houses on the margins of the river. Overall, the houses had three rooms (e.g., living room, bedroom, and kitchen) and were made of wood and straw collected from the forest adjacent to the houses. The houses were distributed along the river with an approximate minimum distance of 300 m from each other. The houses had no furniture, such as sofas, chairs, wardrobes, or beds. In several houses, it was common to sit and have guests sit on the floor made of wood boards or on benches made of wood close to the walls, typically in the living room and kitchen. The few appliances were wood-burning stoves, radios, and televisions. Because of the absence of local electricity, televisions and radios functioned with batteries for limited periods of time, mainly at night. The houses were essentially occupied by the family, in which the number varied as a function of family type (i.e., nuclear families with one to six residents or extended families with six to 10 residents), whereas multigenerational families

from urban centers, with an absence of medical and social assistance see [19].

were characterized by a higher density (i.e., eight to 12 residents).

more slowly [18].

100 Parenting in South American and African Contexts

these families' beliefs.

**2. Method**

riverine families.

**3. Sociodemographic contexts**

**3.1. Araraiana community**

This community belongs to Combu Island, Belém county, Pará state. It has an approximate territorial size of 15 km² and is approximately 1.5 km from the capital Belém via waterway. It is characterized by floodplain forest with diversified flower composition in addition to enormous tourist and commercial attractions.

Considered the fourth largest island of Belém county, Combu Island is located at the margins of Guamá River. In this area, approximately 375 families or 1,700 residents live in and are clustered in four communities: Igarapé of the Combu, Igarapé of the Piriquitaquara, "Furo da Paciência," and the margin of Guamá River. The houses are predominantly made of wood and distributed along the margins of the waterways. The social and production structure is organized as a function of local natural resources, such as açaí and cacau harvesting, palm heart extraction, shrimping, fishing, and raising chickens, ducks, and pigs, which constituted the principal local activities.

Access to Combu Island is via waterway on boats that leave daily from different Belém harbors. Such waterways play a strategic role in the transportation of goods and people. Work is performed with activities in the riverine area. Other services, including the marketing of plant and gathering products, health services, schools, shops, and amenities, occur in the urban context.

The houses were made of wood and covered with clay tiles or asbestos. They were built on stilts and located approximately 30 m from each other. Electricity was not available during data collection, but it became available in July 2011. Treated water was not yet available. Drinking water was obtained from a public tap in Belém and carried in bulk or plastic bottles to the community.

With regard to infrastructure, the community had a health center that was having difficulty with functioning because it was closed for some months due to a lack of physicians, equipment, and medicine. Aside from this health center, a municipal school was located in the igarapé itself, characterized by a typical Amazonia riverine style and made of wood on stilts. The school had two classrooms, a courtyard, a pantry, restrooms, a coordination room, and an external area available for recreation when the river level was low. In this community, almost all of the residents received benefits from the federal program "Bolsa Família" (family grant), a program that directly provides income to families depending on health conditions and school attend‐ ance.

The inventories were applied with the parents on previously scheduled days. During the interviews, we asked questions, and the participants were free to respond. The responses were recorded and transcribed. The tabulation of responses into categories of activities was based on discussions and agreement of two of the three researchers who collected the data. In case

Parenting in Amazonian Riverside Context http://dx.doi.org/10.5772/57056 103

We divided the activities into eight categorical clusters: Economic Subsistence (ES; which refers to all activities that are aimed at obtaining financial resources), Food subsistence (FS; which includes all activities involved in food acquisition and preparation), Domestic tasks (DT; which refers to tasks performed in the house, excluding the kitchen; e.g., sweeping, dish washing, gathering firewood, and fixing the house), Physical care (PC; which refers to tasks related to other people, typically the children; e.g., feeding, bathing, and putting them to sleep), Leisure (L; which refers to activities performed in their free time, including activities for having fun, entertainment, or distraction; e.g., social interaction/talking, watching television, and playing soccer), Play (which represents playful activities with children), and Study (which comprises

To facilitate data visualization, we made Diagrams of Family Activities (DFAs) that consisted of forms that allowed descriptions of intrafamilial subsystems in activity performance. The DFAs were composed of a genealogy tree of the groups who shared a house, and the activity subsystems in which the family members were inserted were delineated with lines of different thicknesses, which allowed distinguishing activity categories. Such categories were identified by complementary descriptions around the figure. The DFA allowed knowledge of the tasks and who performed them, the time of the meeting, whether there was close interaction or isolation, and useful reflections on the nature and characteristics of family gatherings [20].

The contexts investigated here had similarities and differences that represented peculiar lifestyles in the Amazon river region. Both presented forest vegetation and delimitations from regional rivers, contextual aspects that characterize the disposition of the houses where lands

The authors [21, 22, 23]indicated that this disposition of geographic isolation, marked by the presence of rivers, reveals an important contextual characteristic that is necessary to under‐ stand the composition of relationships established in the Amazon river communities. To reach out to neighbors, one must go through natural barriers that restrict exiting from the domestic environment. Therefore, the groups of river families turn to themselves, intensely sharing

are flooded and promote isolation although they are close to each other.

of discordance, we consulted the project mentors.

learning activities in addition to formal teaching).

**7. Results and discussion**

**7.1. Contextual characteristics**

**6. Data compilation**

In the present study, we used two representative families, one from each context (focal families), and the choice was made by considering accessibility and availability.


**1. Introduction**

Photosynthesis is a vital process in which plants convert light energy into chemical energy [1,2]. In higher plants, chlorophyll *a* and *b* are the two major pigments located in the thylakoid membrane of photosynthetic organisms [2]. These chlorophyll molecules play essential roles in harvesting light energy and transferring that energy to reaction centers of the photosystem [2,3]. In the past few decades, tremendous research has been conducted on chlorophyll-deficient mutants in model plants, but the molecular genetic mechanisms underlying these soybean chlorophyll-deficiency mutations are not well understood.

For soybean, 15 chlorophyll-deficient mutant genes were reported to be mapped to chromosomes [4]. Of these genes, six lethal yellow mutant genes, including *Y11*, *Y18*/*Y18\_1*, *Y18\_2*, *YL\_PR350*, *PsbP*, and *CD-5*, were mapped to chromosomes 13, 14, 17, 15, 3 and 15, respectively [5–9]. The other nine viable yellow mutant genes, including *Y9*, *Y10*, *Y12*, *Y13*, *Y17*, *Y20*, *Y23*, *Tic110*, and *Cd1*, were mapped to chromosomes 15, 3, 6, 13, 15, 12, 13, 2, and 10, respectively [8,10–16]. However, only the function of *Y11* and *Y9* genes in yellow foliage was validated by complementary analysis [6,9].

RNA editing is a post-transcriptional modification process that changes the sequence of RNA molecules so that the information in the mature RNA differs from that defined in the genome [17]. In land plants, RNA editing occurs in transcripts of chloroplasts and mitochondria. There are 20–60 chloroplasts and over 300 RNA mitochondrial editing sites in most flowering plants [17,18]. RNA editing is

performed by an editosome that is assembled via protein-protein/RNA interactions [19]. Several organelle RNA recognition motif-containing (ORRM) proteins are known to be essential RNA editing factors. ORRM1 controls 62% of chloroplast editing sites in *Arabidopsis* and 81% of editing sites in maize, with the *Zm-orrm1* mutant exhibiting a pale green phenotype [20]. ORRM6 is primarily required for editing *psbF*-C77 and *accD*-C794 sites in *Arabidopsis* chloroplasts [21]. In addition, ORRM2, ORRM3, ORRM4 and ORRM5 are mitochondrial RNA editing factors [22–24]. Moreover, pentatricopeptide repeat (PPR) proteins, multiple organellar RNA editing factor (MORF)/RNA editing factor interacting proteins (RIPs), organelle zinc finger 1 (OZ1), protoporphyrinogen oxidase 1 (PPO1), and genomes uncoupled 1 (GUN1) have been identified as components of the plant RNA editosome [19,25–30].

Here, we report the characterization of a soybean *yellow leaf* (*yl*) mutant with chlorophyll deficiency and impaired photosynthesis. Fine mapping and DNA sequencing showed that *YL* encodes a GmORRM1. We showed that multiple chloroplast RNA editing sites were changed in *yl* mutants. Our findings provide new insight into the function of YL in soybean photosynthesis.


*Pinus* is the main component of temperate mixed deciduous and coniferous forest, whereas *Quercus* D is the constructive taxa of the broadleaved deciduous forest (Li et al., 2001; Zhao, 1980). In addition, the mountains within 5 km of the Lake Xiaolongwan, which ranges from ~500 to ~1000 m asl, are covered by temperate broadleaved forest, temperate mixed deciduous and coniferous forest, and their ecotone. Thus, the antiphase fluctuations between *Pinus* and *Quercus* D represent the ratio changes between coniferous and broadleaved plants in the forest community (Li et al., 2008; Sun et al., 2003) and dynamics of vertical vegetation belt in Changbai Mountain region (Herzschuh et al., 2006; Körner, 1998) (Figure 2).

Figure 3. Characteristic PCA F1 periodicities.

A high abundance of *Pinus* and low PCA F1 scores suggest downward of temperate mixed deciduous and coniferous forest and thus cool climatic conditions, whereas a high proportion of *Quercus* D and high PCA F1 imply upward of temperate deciduous forest and thus a warm conditions.

The decreases of *Quercus* D component and PCA F1 (increases of *Pinus* component) indicated the cooling trend during the past 5350 years (Figure 2). In addition, the most striking feature is a series of multicentennial oscillations among *Pinus*, *Quercus* D, and PCA F1 during the cooling trend (Figure 2). *Pinus* component reaches its higher value, while *Quercus* D ratio and PCA F1 value drop to a low level around 2700 BC, 2200 BC, 1600 BC, 1200 BC, 900 BC, 600 BC, 300 BC, 200 AD, 700 AD, 1200 AD, and 1800 AD. Each PCA F1 and *Quercus* D ratio's lower value (*Pinus* higher value) interval is about 500 year. The regular 11 antiphase coupled fluctuations between *Pinus* and *Quercus* D existed throughout the past 5350 years. Furthermore, these oscillations seem rather regular during the past 5350 years.

We performed spectral and wavelet analysis on PCA F1 and spectral analysis on the percentage of *Pinus* and *Quercus* D (Figure 3) to determine their periods and periodic stabilities (Schulz and Mudelsee, 2002; Torrence and Compo, 1998). The spectra of PCA F1 reveal peaks at ~500-year period, significant at the 99% confidence level. The result of the wavelet analysis shows that 500-year quasi-periodic oscillations of PCA F1 are almost completely stable and dominant during the last 5350 years.

Figure 4. A comparison of climate proxy records from core Lake Xiaolongwan with other proxy records for Total Solar Irradiance and Greenland (GISP2) oxygen isotope (δ18O).

During the last millennia, two warm (800 ~ 1100 AD and 1830 ~ 2005 AD) and one cold (1550 ~ 1830 AD) periods (Figure 4) inferred from PCA F1 are almost in phase with the well-known Medieval Warm Period (MWP), Modern Warm Period (MCP), and Little Ice Age (LIA), respectively (Lamb, 1977). In the MCP, the abrupt rebound of PCA F1 is nearly synchronous with Greenland temperature (Stuiver et al., 1995) and TSI (Steinhilber et al., 2012; Stuiver and Braziunas, 1993) changes, and this warming phase lasts nearly 170 years (Figure 3). This recurrent warm phase would be ended within several decades according to the cyclic climate change in East Asia, if anthropogenic forcing were unconcerned. Thus, the coming of natural-forced ~250-year cooling phase could reduce the anthropogenic warming according to prediction of cyclic climate change in East Asia.

Thus, our study provides evidence for the influence of ~500-year solar variability on climate in East Asia. The solar variability associated with amplified AO/NAO and NADW anomaly could regulate land temperature variation over East Asia and trigger periodic vertical zonal vegetation change in Northeast Asia.

#### 5. Conclusion

Our pollen record shows ~500-year cyclic vegetation and temperature oscillation in East Asia during the last five millennia. This result indicates that ~500-year cyclic climate change over East Asian still exists under anthropogenic forcing during the last century. Recent warm phase, which has lasted about 170 years, is most likely finished in several decades without regard to anthropogenic factors. In addition, this periodic climate change could reduce the man-made warming trend in the next two centennials in East Asia.

#### Acknowledgments

This study was supported by NSFC (41471166) and NBRPC (2015CB953801).

Changbai Mountain, Northeast China and their relations to the modern vegetation. Acta Botanica Sinica 45, 910–916.

### **Geochemical Signatures of the Pinglin Tuff, Western Foothills, Central Taiwan: Constraints on Thinning of Continental Lithosphere before South China Sea Spreading**

Mengming Yu1,2,\*, Chi-Yue Huang1,3, Yi Yan1 , and Qing Lan4

1 *Key Laboratory of Marginal Sea Geology, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China*

2 *University of Chinese Academy of Sciences, Beijing, China* 3

*Department of Earth Sciences, National Cheng Kung University, Tainan, Taiwan, Republic of China 4*

*State Key Laboratory of Ore Deposits Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, China* \*Corresponding author E-mail<EMAIL_ADDRESS>
**Keywords:** continental extension, initial seafloor spreading, South China Sea

The South China continental margin (SCCM) were progressively attenuated by developing series of pre-Oligocene rift basins, such as the Sanshui, Lianping, Heyuan, and Pearl River Mouth, and eventually seafloor spreading of the South China Sea (SCS) during the Oligocene and Early Miocene (Holloway, 1982; Taylor and Hayes, 1983). This attenuated process has also been witnessed by Cenozoic intraplate volcanism in the SCCM, which characteized by the Eocene IAT-like volcanic rocks had been nearly replaced by the pervading Miocene to Pliocene OIB-like basalts (Zhu et al., 2004; Wang et al., 2012; Huang et al., 2013c). Since there was an Oligocene magmatic quiescence in the SCCM (Zhu et al., 2004; Huang et al., 2013c), the SCS seafloor spreading during ~32–16 Ma probably have drained mantle melts of ancient metasomatized mantle origin that formed those Eocene IAT-like volcanic rocks (Huang et al., 2013c). However, until now lifespan of this ancient metasomatized mantle and especially its contribution to magma that crystallized ocean crust of the SCS is unclear. Since the Site U1435 of the IODP Expedition 349 failed to core old lavas of the SCS, volcanisms developed near the continentocean transition zone and erupted during the transition from rifting to early seafloor spreading stage of the SCS, which could act as great candidates.

The Pinglin tuff, which originally deposited on the continental slope basin and currently outcropped in the Western Foothills of central Taiwan, is uncomfortably overlain by the postrift sedimentary units of the SCS (Huang et al., 2012, 2013a, b; Lan et al., 2014). It may record a last volcanism before initial seafloor spreading. Here we report major trace elements and Sr-Nd-Pb isotopes data of tuff samples from the top of the Pinglin tuff layer, and then compare them with Eocene IAT-like intraplate volcanic rocks outcropped in Guangdong (Huang et al., 2013c), Taiwan Strait, and western Taiwan (Wang et al., 2012) to discuss mantle evolution

Taiwan: Constraints on Thinning of Continental Lithosphere Before South China Sea Spreading

before seafloor spreading of the SCS. The Pinglin tuff is grayish green and reddish brown in color, it shows fine-grained porphyritic texture, and contains glauconite grains. In the TAS plot, the PL-1 and PL-2 locate in the andesite area, whereas the PL-4 and PL-5 fall in dacite region after LOI corrected due to high LOI contents (5.67–9.81 wt.%). All show LREEs enrichment ((La/Sm)N = 1.8–4.3) and flat HREE pattern ((Gd/Yb)N = 1.0–1.2) after Chondrite is normalized. However, later two dacites display negative Eu abnormality, and the PL-2 apparently has low content REEs than others. In the incompatible elements pattern, all show LILEs enrichment and obviously negative Nb, Ta, and Ti abnormalities, and exhibit typical arc-like characteristics. Moreover, though part of them show distinct major and trace elements characteristics, Sr-Nd-Pb isotopes of all are relatively uniform with 87Sr/86Sr = 0.70620–0.70851, 143Nd/144 Nd = 0.51261–0.51277, 206Pb/204Pb = 18.430–18.446, 207Pb/204Pb = 15.607–15.614, and 208Pb/204Pb = 38.634–38.661. Comparatively, Pb isotopic compositions are more uniform than Sr and Nd isotopes, which indicate the Pinglin tuff in this study share the same mantle source (Figure 1).

When comparing the Pinglin tuff with the Eocene IAT-like intraplate volcanic rocks exposed in Guangdong (Huang et al., 2013c), Taiwan Strait, and western Taiwan (Wang et al., 2012), it shows that they have the same trace element signatures. Moreover, Sr-Nd-Pb isotopes of the Pinglin tuff locate in the mantle evolution trend line defined by Eocene IAT-like and Miocene OIB-like intraplate volcanic rocks end members of the SCCM (Figure 1). All these features show the Pinglin tuff are congenic with Eocene IAT-like intraplate volcanic rocks exposed along the SCCM, which are generated by ancient metasomatized mantle source (Wang et al., 2012; Huang et al., 2013c). Since the Pinglin tuff is uncomfortably overlain by the SCS breakupunconformity that represents initial seafloor

spreading (Huang et al., 2012, 2013a, b; Lan et al., 2014), it recorded magma characters of thinning of continental lithosphere nearly at initial seafloor spreading. Thus, we propose the ancient metasomatized mantle source beneath the SCCM was still alive nearly at initial seafloor spreading. And the SCS ocean crust crystallized during initial seafloor spreading stage may inherit IAT-like geochemical signatures.

Figure 1. (a) Variation of 87Sr/86Sr - εNd(t); (b) 207Pb/204Pb and 208Pb/204Pb versus 206Pb/204Pb for the Pinglin tuff from central Taiwan. Data for the Jieyang volcanic rocks are from Huang et al. (2013c), the Taiwan basalts data cite from Wang et al. (2012) and Chung et al. (1995), and the SCS seamount basalts data are from Tu et al. (1992). The EM1, EM2, and NHRL are from Hart (1984).

#### Acknowledgments

This work is financially support by the National Natural Science Foundation of China (grant 41472093, U1505231, 41476036).

### **Characterizing and Tracing the Dust Sources of Lakes Sihailongwan and Huguang Maar in NE and SE China Over the Past 80 ka**

Shikma Zaarur1,\*, Mordechai Stein1,2, and Yigal Erel1

1 *Institute of Earth Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel 2 Geological Survey of Israel, Jerusalem, Israel*

\*Corresponding author E-mail<EMAIL_ADDRESS>
**Keywords:** maar lakes*,* dust, paleo-synoptics, Nd-Sr radiogenic isotopes

Desert dust is an important component of the global environmental-climate system; it travels long distances in the atmosphere and settles on Earths' surface. Arid continental regions (e.g., Sahara-Arabia desert belt, Gobi desert), referred to as accumulation basins, are the source of desert dust comprised of fine mineral particles. This dust can be lifted and blown by strong winds and circulate the atmosphere before settling in destination basins. The isotopic signature (e.g., 87Sr/86Sr, εNd) of the dust source rocks is preserved in the particle and hence can be used to trace the source of the dust (accumulation basin). Because the dust is windblown and circulates the atmosphere, tracing the source provides means to studying past climate and hydrological conditions in the source basin and the paleo-synoptic conditions of dust transport (e.g., Grousset and Biscaye 2005). Deep-sea and lacustrine sediments serve as important archives for dust.

In this study, we analyze sediments from lakes Sihailongwan and Huguang Maar to establish the paleo-synoptic conditions that controlled dust transport from the central Asia deserts to the areas of NE and SE China during the MIS 5/4 transition (~80–70 ka BP), during MIS2 (~30–14ka BP), and during Termination T1 and the MIS2/1 transition (14–9 ka BP).

Sediment cores from the Sihailongwan and Huguang Maar lakes were obtained by the German-Chinese drilling project (Mingram et al. 2004; Zhu et al. 2013), and sediments were collected from around, and the vicinity of Lake Huguang Maar. The cores of these two lakes have been previously dated and their general composition had been characterized (Mingram et al. 2004; Zhu et al. 2013). In this study, we focus on the chemical and isotopic composition of the dust size particles (<70 µm) of the core sediments; our goal is to trace the dust sources.

The grain size distribution of each sediment sample is measured, and the different grain-size fractions are separated accordingly. We measure the chemical and isotopic compositions of the different

Huguang Maar in NE And SE China Over The Past 80 Ka

fractions, as well as analyze their mineralogical composition.

Basalt, tuff, soils, and paleosols from the vicinity of Lake Huguang Maar are used to characterize the local signature and input into the lake sediments. In a previous study, Zhou et al. (2009) published isotopic values for bulk sediments in Lake Huguang Maar; based on their results, they estimated up to ~20% dust input into the lake. We compare the results of our measurements, to the values published by Zhou et al. (2009) (Figure 1). We find an overlap of the values in some of the materials and a hint to a mixing of two end members in the lake sediments; one is the composition of the local volcanic deposits, and the other has higher εNd and 87Sr/86Sr values. We additionally identify another distinct group of soils that has an isotopic signature that hints to a loess-like source from the Chinese Loess Plateau and the Tibetan Plateau (Yang et al. 2009).

Figure 1. εNd versus 87Sr/86Sr of our bulk samples (diamonds) and from Zhou et al. (2009) (circles). The colors correspond to different materials, listed in the legend. Our samples overlap with those of Zhou et al. (2009). Three soil samples collected ~2 km from the lake have isotopic values that are distinct from the rest and might point to an additional endmember. The gray + and – symbols are materials from the Chines Loess Plateau (CLP) and the Tibetan Plateau (TP) (Yang et al. 2009).

Grain size analysis of these samples revealed that while the tuffs and paleosols are bimodal, the soils and lake surface sediment samples have on average finer particles, and exhibit an additional particle size group at 0.2 µm. We separate these different fractions to characterize the mineralogy, chemistry, and isotopic composition of each group. Characterizing the fractions separately allows us to identify the dust fractions independently from the bulk sediment.

Our isotopic results suggest that there is an aeolian loess component to soils around Lake Huguang Maar. Ultimately, our goal is to use these chemical and isotopic signals on the core sediments to identify the dust sources to these lakes and use it as a tracer to study the paleo-synoptic evolution of the region.

#### Acknowledgments

We thank Jens Mingram and the GFZ team for their assistance and for providing us the core samples. We thank ISF-CAS 2235/15 for funding this study. We thank J. Liu, G. Chu, J. T. Han, J. Liu, and J. Wu for their help in sampling and discussing the research concept.

### **Magma-Derived CO2 Emissions in the Tengchong Volcanic Field, SE Tibet: Implications for Deep Carbon Cycle at Intracontinent Subduction Zone**

Maoliang Zhang1,2,\*, Zhengfu Guo1 , Yuji Sano3 , Lihong Zhang1 , Yutao Sun1,2, Zhihui Cheng1,2, and Tsanyao Frank Yang4

Emissions in the Tengchong Volcanic Field, SE Tibet: Implications for Deep Carbon Cycle at Intracontinent Subduction

1 *Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China*

*Department of Geosciences, National Taiwan University, Taipei, Taiwan*

**Keywords:** soil CO2 flux, deep carbon cycle, continental subduction zone

Active volcanoes at oceanic subduction zone have long been regard as important pathways for deep carbon degassed from Earth's interior, whereas those at continental subduction zone are poorly constrained. Large-scale active volcanoes, together with significant modern hydrothermal activities, are widely distributed in the Tengchong volcanic field (TVF) on convergent boundary between the Indian and Eurasian plates. They provide an important opportunity for studying deep carbon cycle at the ongoing intracontinent subduction zone. Soil microseepage survey based on accumulation chamber method reveals an average soil CO2 flux of ca. 280 g m-2 d-1 in wet season for the Rehai geothermal park (RGP). Combined with average soil CO2 flux in dry season (ca. 875 g m-2 d-1 ), total soil CO2 output of the RGP, and adjacent region (ca. 3 km2 ) would be about 6.30 × 105 t a-1 . Additionally, we conclude that total flux of outgassing CO2 from the TVF would range in (4.48−7.05) × 106 t a-1 , if CO2 fluxes from hot springs and soil in literature are taken into account. Both hot spring and soil gases from the TVF exhibit enrichment in CO2 (>85%) and remarkable contribution from mantle components, as indicated by their elevated 3He/4He ratios (1.85−5.30 RA) and δ13C-CO2 values

Derived CO2

Zone

(−9.00% to −2.07%). He-C isotope coupling model suggests involvement of recycled organic metasediments and limestones from subducted Indian continental lithosphere in formation of the enriched mantle wedge (EMW), which has been recognized as source region of the TVF parental magmas. Contamination by crustal limestone is the first-order control on variations in He-CO2 systematics of volatiles released by the EMWderived melts. Depleted mantle and recycled crustal materials from subducted Indian continental lithosphere contribute about 45−85% of the total carbon inventory, while the rest of the carbon (about 15−55%) is accounted by limestones in continental crust. As indicated by origin and evolution of the TVF volatiles, mantle-derived magmas at continental subduction zone can act as important triggers for liberation of carbon stored in crustal carbonate rocks, which has the potential to be a complement to volatile recycling mechanism at subduction zones. Variations in He-Nd-Sr isotopes of magmas and volatiles from different types of plate boundaries suggests higher amounts of recycled materials for mantle wedge enrichment of continental subduction zone relative to that of oceanic subduction zone.

*2 University of Chinese Academy of Sciences, Beijing, China*

*3 Atmosphere and Ocean Research Institute, University of Tokyo, Chiba, Japan* 4

\*Corresponding author E-mail<EMAIL_ADDRESS>
### **New Evidence for the Yellow River Intrusion into the Huaihe River**

Lei Zhang1,2,\* , Xiaoguang Qin1 , and Jiaqi Liu1

1 *Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China 2 University of Chinese Academy of Sciences, Beijing, China* \*Corresponding author E-mail<EMAIL_ADDRESS>
**Keywords:** geochemical, provenance, intrusion, Yellow River, Huaibei Plain

The sediments of the Huaibei Plain in semihumid mid-eastern China represent valuable geological records with respect to eolian–fluvial interactions, depositional environments, and climate change in this region (Figure 1). Provenance is often reconstructed using sedimentary geochemistry methods. In this study, an 8-m core from Huainan and a set of loess samples from northern and southern China were analyzed for major, trace, and rare earth elements (REEs). Results were compared to determine the samples' provenance and to discuss the Yellow River intrusion into Huaihe River. The major, trace, rare earth elements contents, and grain size distribution were found to fluctuate widely in the 2–8 m section of the Huainan core and more narrowly closer to the surface (0–2 m). This suggests a provenance shift at a depth of 2 m. The TiO2/Al2O3, SiO2/Al2O3, Th/Nb, La/Nb values, and REE patterns in the upper core (0–2 m) are similar to those found in samples from the Chinese Loess Plateau (CLP) (Figure 2). These results suggest that the CLP in northern China is likely to be the primary origin of the upper part (0–2 m) of the Huainan core. The sediments may have been transported from the CLP to Huainan as Yellow River flood events, probably during the last deglaciation (13.2 ka) as a result of increased precipitation, along with glacier and snow melt in the upper reaches of the Yellow River catchment during this period. This suggests that the Yellow River may have migrated into the Huaihe River catchment much earlier than the earliest historical records (361 BCE) suggest. This result demonstrates that the influence of the Yellow River in the formation and shaping of the Huaibei Plain has been underestimated.

The implications of this would be profound with respect to the Chinese history.

Figure 1. Digital elevation model of the Huaibei Plain. The solid black triangle indicates the core location. LC means Luochuan, XC means Xuancheng.

Figure 2. Cross-plots of K2O/Al2O3 versus TiO2/Al2O3 of Huainan core sediments from the Huaibei Plain, and loess from northern and southern China. Data for the Luochuan loess are from Gallet et al. (1996) and Xuancheng and Lingtai loess are from Qiao et al. (2011). Those for the Xining, Xifeng, and Jixian loess are from Jahn et al. (2001).

#### Acknowledgments

Financial support for this study was provided by the National Scientific Foundation of China (Grant Nos. 41372187, 41172158, 40472094 and 40024202), the Key Consultation Program of the Chinese Academy of Engineering (Study of Environment and Development of the Huaihe River Watershed), 973 Program (Grant No.2010CB950200), the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA05120502) and the Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No. KZCX2-YW-Q1-03).

### **Study on C14 Age of Dawengquan Volcano in Longgang Volcano Area**

Bo Zhao1,\*, Zhida Bai2 , Debin Xu2 , Hongmei Yu1 , Jiandong Xu1 , and Bo Pan1

*1 Institute of Geology, China Earthquake Administration, Beijing<EMAIL_ADDRESS>*2 China University of Geoscience, Beijing, China*

\*Corresponding author E-mail<EMAIL_ADDRESS>
**Keywords:** Dawengquan Maar volcano, C14 age, Longgang volcano area

Longgang volcano area is one of the typical monogenetic volcanic fields of Quaternary in China (Wei et al., 1999). Volcanic activities started in Neogene, and got its peak in Pleistocene (Fan et al., 2002; Bai et al., 2006). In AD 460, there was a basaltic explosive eruption (Liu et al., 2009). There are many Maar volcanoes and base-surge deposits, such as Dalongwan (DALW), Erlongwan (ELW), Sanjiaolongwan (SJLW), Sihailongwan (SHLW), Nanlongwan (NLW), Donglongwan (DLW), Longquanlongwan (LQLW), and Dawengquan (DWQ). This paper mainly presents our study of strata and chronology in DWQ volcano.

Figure 1. Distribution of Maar volcano in Longgang.

### **1. Strata of DWQ volcano**

Longgang Volcano Area

DWQ is a low rimmed volcano, which is located in the northeast of Jinchuan town. Characteristics of the volcanic strata near the crater are interlaying with coarse massive layer and fine thin layer in section Lg-11. There are lenticular structure, sag structure, and dune-like structure in base-surge deposits.

Under the base-surge deposits there are scoria. Median diameters (MdФ) are –2.53. Sorting (σФ) parameters are 0.95. Characteristics of grain size are moderately sorted. The origin of scoria is still not understood.

### **2. C14 age of DWQ volcano**

Carbonized woods were found in both the basesurge deposits and scoria deposits. One age is 15,560 ± 50 BP in the base-surge deposits from DWQ which was tested by Beta laboratory in the United States. The result is close to the age of 15,965 ± 145 BP (Bai et al., 2006; Liu et al., 2009).

The other is 17,120 ± 145 BP in the scoria which was tested by C14 laboratory in the institute of Geology, China Earthquake Administration. There are two tephra layers in ELW lake (Liu et al., 2009), which is about 7.6 km away from DWQ. One layer's age is near the 16,997 BP, which is good fit to the age of carbonized woods in scoria.

According to the C14 dating result and strata among these volcanoes, volcano activity of this area is frequency in the Late Pleistocene. There are many volcanoes around the DWQ volcano, such as Dalongwan volcano, Sanjiaolongwan volcano, and Jilongdingzi volcano. It may be helpful for building the volcanic succession in this area.

### **Cenozoic K-Rich Adakitic Volcanic Rocks in the Hohxil Area: Lower-Crust Partial Melting in an Intracontinental Setting**

Weigui Zhou\* , Yu Guo, Jinwei Feng, Jingzhou Yang, and Baorong Luo

*College of Earth Sciences, Chengdu University of Technology, Chengdu, China* \*Corresponding author E-mail<EMAIL_ADDRESS>
**Keywords:** potassic volcanic rocks, lower crust, partial melting, Cenozoic

It is generally accepted that the Cenozoic potassic volcanic rocks of northern Tibet were derived from a lithospheric mantle source. Cenozoic rocks reported in Gangdisi (south Tibetan Plateau) have received attention because of the apparent absence of a contemporaneous proximal subduction zone. The Gangdisi area was in an arc setting from the Mesozoic to the early Tertiary, and an active collision zone between the Indian and Asian continents exists nearby, others have argued that these adakitic magmas could have originated by partial melting of subducted oceanic crust, involving incorporation of melts from sediments and mantlewedge components (Qu et al., 2004). Thus, the origin of Cenozoic adakites in southern Tibet remains controversial.

Our study deals with a new adakite locality within the Tibetan Plateau and presents new geochemical and isotopic data to clarify the issue. Unlike the adakitic rocks in the Gangdisi region referred to here, the Cenozoic K-rich adakitic volcanic rocks in the Hohxil area of northern Tibet occur within an intracontinental setting, far removed from an active collision zone or an island-arc zone during the Cenozoic Era. They are geochemically similar to adakites produced by slab melting in subduction zones, except for their high K contents and other geochemical peculiarities discussed herein. A critical issue therefore is whether these Cenozoic rocks represent nonarc adakites, derived by partial melting of amphibolebearing eclogitic rocks in the lower crust. If so, they would be the first documented occurrence of adakitic magmatism not directly associated with subduction of oceanic crust and so would have important implications for models of adakite genesis.

The Tibetan Plateau constitutes a tectonic collage of continental blocks (terranes). From north to south, the three main east-trending continental blocks are Kunlun (Qaidam), Songpan-Ganzi (SG), and Qiangtang, all within the north-central Tibetan region (Figure 1A) (Yin and Harrison, 2000). The SG block, containing the Hohxil area, is bounded by the Anyimaqen-Kunlun-Muztagh suture to the north, and the Jinshajiang suture to the south (Yin and

Hohxil Area: Lower-Crust Partial Melting in an Intracontinental Setting

Harrison, 2000). It is generally accepted that suturing of the SG-Kunlun and SG-Qiangtang blocks occurred in pre-Jurassic time (Tapponnier et al., 2001), and consequently the SG and Kunlun blocks have been in an intracontinental setting since the Jurassic. Although volumetrically minor, Cenozoic volcanic rocks are widely distributed in the SG block (Figure 1A). Previous studies indicated that most are potassic to ultrapotassic in composition, and their eruption ages range from ca. 17–15 to 1 Ma (Turner et al., 1996; Zheng et al., 1996; Deng, 1998; Cooperet al., 2002). The K-rich adakitic volcanic rocks discussed here occur in the Hohxil area near the center of the SG block in northern Tibet (Figures 1A and B), and the available data indicate that intermediate to acidic volcanic rocks are dominant in the Hohxil area (Deng, 1998), whereas mafic volcanic rocks are common in the western SG block (Deng, 1998; Cooper et al., 2002).

Figure 1. (A) Map of Tibetan Plateau showing major blocks and temporal-spatial distribution of Cenozoic volcanic rocks. (B) Simplified geologic map showing outcrops of magmatic rocks in Hohxil area, Songpan-Ganzi block, northern Tibet.

Our investigations and published data indicate that samples with adakitic compositional features (such as high Sr/Y ratios, high Sr concentrations, and low Y and heavy rare earth element [REE] contents) are confined to three sites (Hongshuihe, Wuxuefeng, and Damaoshan), all in the Hohxil area (Figure 1B). These Cenozoic adakitic volcanic rocks are exposed either as large-scale lava flows or as small-volume lava domes. The Hongshuihe volcanic dome, for example, has an outcrop area of 2 km2 , whereas the Wuxuefeng and Damaoshan flows crop out over areas of 190 and 150 km2 , respectively. Individual lava flows and domes are typically 30– 100 m thick. No Cenozoic basaltic rocks occur in association with the adakitic rocks in the Hohxil area (Figure 1B), but in the southern Hohxil Lake area (Figure 1A), small-volume (<1 km2 ) olivine-bearing leucite foidites (SiO2 = 43–45 wt%) have been discovered (Zheng et al., 1996; Data Repository Table DR21 ), and dated to ca. 16.47 Ma (40Ar/39Ar plateau age; Table DR1; see footnote 1).

Here, we report new chronological, geochemical, and isotopic data for the Miocene (ca. 18–15 Ma) Krich adakitic volcanic rocks from the Hohxil area of the Songpan-Ganzi block in northern Tibet. We contend that these rocks were generated by partial melting of the mafic lower crust, in an intracontinental setting unrelated to subduction of oceanic crust.

The Hohxil rocks exhibit high Sr/Y and La/Yb ratios, high Sr and La contents, but low Yb and Y concentrations, similar to adakites formed by slab melting associated with subduction. However, their relatively low εNd values (22.09–24.58); high 87Sr/86Sr (0.7072–0.7075), Th/U, Th/Ba, and Rb/Ba ratios; and distinctive potassium enrichments (K2O > Na2O) are very different from the composition of typical adakites. In addition, those K-rich adakitic rocks with the highest SiO2 contents (>61 wt%) exhibit the lowest 87Sr/86Sr ratios and highest εNd values and are the oldest Cenozoic volcanic rocks exposed in the Songpan-Ganzi block, suggesting that they were derived neither directly from a mantle source nor by differentiation of a shoshonitic magma. Taking into account the composition of lowercrustal mafic xenoliths in Tibet, as well as the tectonic and geophysical evidence, we conclude that the Hohxil adakitic magmas were produced by partial melting of amphibole-bearing eclogites with a K-rich mafic bulk composition, in the lower part (>55 km) of the thickened northern Tibetan crust. Partial melting of the lower crust may have been triggered by dehydration release of fluids from sedimentary materials in the southward-subducted continental lithosphere.

### **Maar Lake Sediments and Their Potential for Environmental and Climate Reconstruction: A Global Review**

Bernd Zolitschka

*Institute of Geography, GEOPOLAR – Geomorphology and Polar Research, University of Bremen, Celsiusstr. Bremen, Germany,*<EMAIL_ADDRESS>
**Keywords:** lacustrine sediments, crater lakes, maars, varves

During the last 50 years lacustrine sediment records have established as environmental and climatic archives throughout the continents. Although they are present in many different environmental settings, they are distributed irregularly on Earth and mainly occur in landscapes formed by two processes: crater lakes exist in volcanic and tectonically active zones, while glacial lakes predominate in areas under recent or Pleistocene glacial influence. Morphologically, both types of lakes have much in common: they can be rather deep and often are hydrologically closed, i.e., they are terminal lakes. However, differences exist: crater lakes are smaller with a round perimeter and a central deep basin, while glacial lakes are often larger with a complicated morphology and many tributaries. As influences of the (shorter) shoreline and the (smaller) catchment area are reduced, crater lakes provide a simpler depositional basin, which allows for an easier and more straightforward interpretation of their sediment record. Of all crater lakes, the monogenetic "maar" type is the most promising candidate for environmental and climatic reconstruction. Protected by steep and forested crater-wall slopes, these lakes tend to be sheltered against the influence of wind and thus often establish a stable stratification of the water column.

Selected maar lakes with prominent environmental and climatic records are introduced from such diverse regions as western Germany, southern Italy, northeastern China, the North Island of New Zealand, and southern Argentina.

If a maar lake has a rather small surface area with a considerable depth and if the protection from surrounding winds by the crater walls and a closed forest in combination with at least mesotrophic nutrient conditions exists, then the formation of a stratified water column is strongly supported. At least seasonal (holomixis) or even perennial (meromixis) anoxic conditions may establish at the sediment/water interface. Such lakes are ideal candidates for the development of annually laminated sediments (Zolitschka et al., 2015). These varved sediments enable unique and highresolution analyses to be carried out, because the seasonal depositional signal is not destroyed by bioturbation. Moreover, preservation of varved sediments provides the opportunity to develop a varve chronology. Based on incremental dating it provides ages in calendar years. This internal time control is one of the best dating methods and makes a high-resolution and continuous age/depth relationship available. Finally, such a dataset provides easy access to sedimentation rates and, in combination with dry bulk density, sediment accumulation or flux rates can be calculated.

Today, the meaning of "varve" has expanded to include all annually deposited laminae in terrestrial, i.e., lacustrine (Zolitschka et al., 2015), and marine settings (Schimmelmann et al., 2016). Individual (sub)laminae in varved sediments typically express contrasting colors, differ in terms of their organic (Figure 1), chemical and/or mineralogical composition, and often also with regard to their grainsize. The various climatic and depositional conditions result in clastic, biogenic (Figure 1), and endogenic (evaporitic) varved sediments and their mixtures.

To establish a varve chronology, the annual character of laminations needs to be determined and verified in a multidisciplinary fashion. Sources and influences of possible errors in the varve chronology are best determined and constrained by repeated varve counts and the multiple dating approach, including radioisotopes, combination with tephrochronology (Lane et al., 2015; Wutke et al., 2015), and correlation with historically documented events (Kienel et al., 2013). A wellestablished varve chronology greatly enhances the scientific value of annually laminated archives by securely anchoring the wealth of multiproxy paleoenvironmental information in the form of a time series in calendar years for reliable multidisciplinary interpretations.

Varved sediment records provide accurate time control for a multitude of environmentally relevant sedimentary parameters and document the frequency and rates of change of annual to millennial climatic and environmental oscillations. Monitoring approaches like sediment trapping additionally provide detailed characterization of modern sedimentary processes to enhance the reliability of mechanistic models of varve formation. Furthermore, the increasing availability of modern instrumental environmental and meteorological time series aids in rigorous calibration of environmental proxies from a local varve record, assesses statistical error margins, and enhances the validity of interpretations.

Figure 1. Biogenic varves from Holzmaar, Germany. Macroscopic (A) and microscopic (B) photographies of pale diatom-bloom layers (white bars) and dark organicrich detritus (black bars). The macroscopic image covers 5 years and the microscopic image covers 2 years (Zolitschka et al., 2015).

Due to their exceptional high temporal resolution and in combination with their accurate "internal" time scale in calendar years, varved sediments are regarded as one of the most precious environmental archives. Records that are necessary to extend temporally limited instrumental climate records back in time and make available highresolution reconstructions. Such data are necessary to better understand natural climate variations, like, e.g., temperature variations (Chu et al., 2012), the East Asian summer monsoon (Stebich et al., 2015), or the rising level of human impact on environmental systems during the Anthropocene as documented by, e.g., cultural eutrophication (Jenny et al., 2016) and soil erosion (Su et al., 2015).

#### References

Chu, G., Sun, Q., Wang, X., Liu, M., Lin, Y., Xie, M., Shang, W., Liu, J., 2012. Seasonal temperature variability during the past 1600 years recorded in historical documents and varved lake sediment profiles from northeastern China. The Holocene 22: 785−792.

http://dx.doi.org/10.1177/0959683611430413

http://dx.doi.org/10.1016/j.earscirev.2016.04.009

Stebich, M., Rehfeld, K., Schlütz, F., Tarasov, P.E., Liu, J., Mingram, J., 2015. Holocene vegetation and climate dynamics of NE China based on the pollen record from Sihailongwan Maar Lake. Quaternary Science Reviews 124: 275–289.

http://dx.doi.org/10.1016/j.quascirev.2015.07.021

### **Volcanic, Climatic, and Anthropogenic Forcing Recorded in the Holocene Crater-Lake Sediments of Laguna Azul (Patagonia, Argentina)**

Bernd Zolitschka1,\*, Michael Fey1 , Stephanie Janssen2 , Nora I. Maidana3 , Christoph Mayr4,5, Sabine Wulf6,7,8, Torsten Haberzettl9 , Hugo Corbella10, Andreas Lücke11, Christian Ohlendorf1 , and Frank Schäbitz2

1 *Universität Bremen, Institut für Geographie, GEOPOLAR – Geomorphologie und Polarforschung, Bremen 2*

*Universität zu Köln, Institute for Geography Education, Köln, Germany*

*3 Universidad Nacional de Buenos Aires, Departamento de Biodiversidad y Biología Experimental, IBBEA (CONICET-UBA), Buenos Aires, Argentina*

**Corbella, Andreas Lücke, Christian Ohlendorf and Frank Schäbitz:** Volcanic, Climatic and Anthropogenic Forcing Recorded in

*4 Ludwig-Maximilians-Universität München, GeoBio-CenterLMU und Department für Geo- und Umweltwissenschaften, München, Germany 5*

*Friedrich-Alexander-Universität Erlangen-Nürnberg, Institut für Geographie, Erlangen, Germany 6 Helmholtz Zentrum Potsdam, Deutsches GeoForschungsZentrum,*

*Potsdam, Germany*

*7 Senckenberg Gesellschaft für Naturforschung, Biodiversität und Klima Forschungszentrum (BiK-F), Frankfurt/Main, Germany*

*8 Institut für Geowissenschaften, Ruprecht-Karls-Universität Heidelberg, Heidelberg, Germany*

*9*

*Friedrich-Schiller-Universität Jena, Institut für Geographie, Physische Geographie, Jena, Germany 10Museo Argentino de Ciencias Naturales Bernardino Rivadavia, Buenos Aires, Argentina 11Forschungszentrum Jülich, Institut für Bio- und Geowissenschaften, Jülich, Germany*

*\*Corresponding author E-mail<EMAIL_ADDRESS>
**Keywords:** Southern Hemispheric Westerlies, lake-level fluctuations, tephra layers

Laguna Azul (Figure 1) is located 25 km N of the Strait of Magellan and 60 km W of the Atlantic Ocean in extra-Andean Southeastern Patagonia, Argentina (52°05' S, 69°35' W). This crater lake is part of the Pliocene to Late Quaternary Pali Aike Volcanic Field. Its volcanism is characterized by the eruption of alkali basaltic and basanitic magmas deposited on molasse-type sediments of the Late-Miocene Santa Cruz Formation and Plio-Pleistocene glaciofluvial sediments (Zolitschka et al., 2006; Ross et al., 2011; Coronato et al., 2013). The main crater exhibits a complex eruptive history of explosive and effusive volcanism with a pyroclastic ring wall of 850 m in diameter. The central depression (Figure 1) of the crater formed by gravitational collapse after phreatomagmatic explosions during an early (maar) stage of the eruption. Later a lava lake filled the depression and extensive magma production caused an overflow through a 30-m wide channel to the N creating proximal "pahoehoe" and distal "aa" lava (Corbella et al., 2009). Dating of the basalt flow related to the overflow of the lava lake resulted in a 40Ar/39Ar age of 0.01 ± 0.02 Ma (Corbella, 2002).

In the deepest part of the depression related to the Laguna Azul crater, a lake developed at the Pleistocene/Holocene transition with a maximum present-day water depth of 56 m (Figure 1). It is one of the very few permanent water bodies in the semiarid grass steppe of southeastern Patagonia.

the Holocene Crater-Lake Sediments of Laguna Azul (Patagonia, Argentina)

Figure 1. Aerial photography of Laguna Azul in southeastern Patagonia (Province of Santa Cruz, Argentina) with bathymetry, coring, and sampling locations.

Here we present a radiocarbon-dated sediment record from Laguna Azul including sedimentological, physical, and geochemical as well as pollen, diatom, and stable isotope data. The focus is directed to processes of sediment formation and their volcanic, climatic, and anthropogenic forcing factors.

Temperature, precipitation, and wind intensity of southern South America respond to the airpressure gradient between polar and subtropical southern latitudes, to sea-surface temperatures of adjacent oceans, sea-ice and continental ice masses, as well as the pathway of the Southern Hemispheric Westerlies (SHW, Garreaud et al., 2009; Mayr et al., 2013). The resulting variations of the regional hydrological balance are recorded especially in sediments of closed lakes (Piovano et al., 2009) like Laguna Azul.

Multiproxy limnogeological investigations of the Holocene sediment record from Laguna Azul document a superior climatic control on the lacustrine system, i.e., position and intensity of the SHW. These climatic conditions influence local evaporation, precipitation, and insolation with impacts on the type of stratification of the water column and lake-level fluctuations. Altogether, these climatic influences lead to internal feedbacks on wave erosion along the lakeshore, algal communities, and trophic conditions as well as on authigenic mineral formation. Based on a gravity core with a millennial-long record (Mayr et al., 2005), we continue this interdisciplinary research approach and present a detailed environmental reconstruction documenting hydrological variability during the entire Holocene.

Volcanic influences on the sediments are evidenced by radiocarbon ages that are significantly older than their stratigraphical position would demand. They probably suffer from 14C-depleted carbon as the result of volcanic CO2 exhalations during the Lateglacial and the early Holocene. Human impact is restricted to the last ca. 150 years when it obscures the climatic signal. Additionally, two volcanic ash layers were detected, geochemically characterized, and identified. Their sources are Mt. Burney and a so far unknown volcano in the Northern Andean Volcanic Zone (NAVZ). These well-documented and well-dated events provide useful knowledge for updating the tephrostratigraphic framework in South America.

### Acknowledgments

This is a contribution to the project "South Argentinean Lake Sediment Archives and modeling" (SALSA) funded within the framework of the German Climate Research Program (DEKLIM grants 01 LD 0034 and 0035) of the German Federal Ministry of Education and Research (BMBF). Additional financial support was provided by the German Science Foundation (DFG) in the framework of the Priority Program 'ICDP' (grants ZO 102/5-1, 2, 3).

## *Edited by Jiaqi Liu*

This Book of Abstracts covers the abstracts presented at the 6th International Maar Conference (6IMC) in Changchun (China). The 6IMC conference sessions are focused on Maar and Environment Change, covering a wide spectrum of topics including: characteristics, mechanism, modeling and geological background of Monogenetic volcanic activities; volcanic evolution and spatial distribution regulation, resources, disaster, detecting, monitoring and societal responses of volcanic activity.

6th International

Maar Conference

Abstracts

*Edited by Jiaqi Liu*

ISBN 978-953-51-2540-2

ISBN 978-953-51-7301-4

6th International Maar Conference - Abstracts

Photo by onlyyouqj / iStock