NOAA/WDS Paleoclimatology - Patrick and Thunell 1997 Tropical Pacific SST Reconstruction

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-thermocline 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 (∼2°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 ∼3°C cooler during the last glacial maximum (LGM), while the western equatorial Pacific (WEP) was ∼4°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.

本研究选取东太平洋与西太平洋两处岩芯，旨在更精准地量化末次冰期热带海洋温度，以明确这一气候关键区域对气候强迫大规模变化的响应机制。本研究通过分析表层、温跃层及次温跃层栖息浮游有孔虫（planktonic foraminifera）的氧同位素组成，其中表层类群包括G. sacculifer、G. ruber，温跃层类群包括N. dutertrei、G. menardii、P. obliquiloculata，次温跃层类群包括G. inflata，最终对该深度区间内温度梯度的相对与绝对变化量进行了估算。由于两处岩芯的全新世段碳酸盐保存状况较差，相对温度估算结果显示，上述区域仅出现了约2℃的冰期降温，与CLIMAP[1976, 1981]的报道结果一致。然而，通过方解石-海水古温度计法得到的绝对温度估算结果显示，末次冰盛期（Last Glacial Maximum, LGM）期间，东赤道太平洋（Eastern Equatorial Pacific, EEP）较现代低约3℃，西赤道太平洋（Western Equatorial Pacific, WEP）则低约4℃。东赤道太平洋的上层水体层化程度较低，温跃层更陡，这一特征被解读为末次冰盛期上升流增强的信号。西赤道太平洋则维持了发育良好的混合层与较深的温跃层，与现代海洋状态一致。上述结果与近年多项针对末次冰盛期的热带温度估算结果相符。