Tropical Pacific sea surface temperatures and upper water column thermal structure during the last glacial maximum

Using two cores from the eastern and western Pacific, we have attempted to better quantify tropical ocean temperatures during the last glacial in order to determine how this climatically-important region responds to large scale changes in climate forcing. By analyzing the oxygen isotopes of surface dwelling (G. sacculifer, G. ruber), thermocline dwelling (N. dutertrei, G. menardii, P. obliquiloculata) and sub-thermodine dwelling (G. inflata) planktonic foraminifera, both relative and absolute estimates of the changes in the temperature gradient over this depth interval have been made. Owing to poor carbonate preservation in the Holocene section of both cores, relative temperature estimates suggest only a slight glacial cooling (similar to 2 degrees C) at these locations, similar to that reported by CLIMAP [1976, 1981]. However, absolute temperature estimates determined from calcite-seawater paleothermometry indicate the eastern equatorial Pacific (EEP) was similar to 3 degrees C cooler during the last glacial maximum (LGM), while the western equatorial Pacific (WEP) was similar to 4 degrees C cooler. The upper water column appears to have been less stratified in the EEP, with a steeper thermocline, interpreted as indicating an increase in upwelling during the LGM. The WEP maintained a well developed mixed layer and deep thermocline, similar to today. These results are consistent with a variety of recent tropical temperature estimates for the LGM.