Comparing changes in sea surface and thermocline temperatures between the western and eastern equatorial Pacific since the Last Glacial Maximum

We present sea surface and thermocline temperature reconstructions from two cores in the eastern and two from the western equatorial Pacific (WEP) based on alkenone undersaturation and planktonic foraminiferal Mg/Ca spanning the last 30,000 years. Whereas equatorial Pacific surface waters warmed by about 3 degrees C during the deglaciation, foraminiferal Mg/Ca records from the two WEP cores suggest a steady increase in thermocline temperatures by about 10 degrees C between the Last Glacial Maximum (LGM) and today. These subsurface temperature estimates are based on Mg/Ca records from both Pulleniatina obliquiloculata and two size groups of Neogloboquadrina dutertrei (250-350um and 400-500um), which all yield very similar temperature estimates. In sharp contrast, Mg/Ca data from the larger specimens of N. dutertrei (400-500um) in the eastern equatorial Pacific (EEP) cores suggest almost unchanged habitat (thermocline) temperatures between the LGM and modern with maximal habitat (thermocline) temperatures during the deglaciation. Mg/Ca records from the smaller (250-350um) N. dutertrei specimens, on the other hand, show a steady increase in EEP subsurface temperatures by about 4 degrees. These results suggest that there may be two distinct populations of N. dutertrei in the EEP distinguished in part by shell Mg/Ca content and test size. We will compare our temperature estimates to species-specific isotope records, and discuss oceanographic implications of our results.