Since the deep sea cores became available in the 1960s, paleoclimatic indices of planktonic foraminifera from marine sediments have been used for paleoclimatic reconstruction. Among the early pioneers to apply foraminifera latitudinal abundances, Ericson and Wollin (1968) succeeded in establishing the Pleistocene glacial and interglacial cycles based on the ratios of cold and warm water species in tropical sediments. Similar work was extended to subantarctic region by Kennett (1970), who, based on subpolar cold and warm water planktonic foraminferal species, reconstructed paleoclimatic changes in the Pleistocene, consistent in trends with those established in the tropical region.
When drilling cores, which recovered longer sediment columns than piston cores, came along, paleoclimatic reconstruction investigations were pushed back further in geological times. A climatic curve in the Oligocene was constructed in the Gulf of Mexico by using warm water indicators (Turborotalia pseudoampliapertura, Globoquadrina tripartita, Dentoglobigerina globularis, Dentoglobigerina baroemoenensis, “Globigerina” ciperoensis and Globigerinoides groups, and Cassigerinella chipolensis) and cold water indicators (Catapsydrax spp., Globorotaloides spp., Subbotina angiporoides group, Globigerina s. str., and the tenuitellids). A more extensive geographic coverage was investigated by Spezzaferri in 1995, who analyzed samples from drilling cores in the Atlantic, Indian and South Pacific Oceans and identified and grouped foraminifera into warmer, cooler, warm-temperate and cool-temperate indices. A paleoclimatic curve in the Oligocene and Miocene transition period was established and the curve was supported by the isotope data.
A more sophisticated approach to reconstruct paleoclimate involves using factor analysis. Thompson (1981) was able to relate six foraminiferal assemblages from core top samples to present water masses in the western North Pacific. A transfer function was generated to link the assemblages to sea surface temperatures. A paleotemperature curve for the past 150,000 years was reconstructed by applying this transfer function to old sediments in the cores.
Similar technique has been applied to the Eocene and Oligocene sediments and the forams have been categorized in surface, intermediate and deep water-mass groups. Thus water-mass stratification, in addition to paleotemperature fluctuation has been reconstructed.