Sea surface temperature variability in the eastern equatorial Pacific during the last deglaciation: Multiproxy geochemical reconstructions

The role of tropical Pacific sea surface temperature (SST) variability in the global-scale climate reorganization that occurred during the last deglaciation is investigated, using multiproxy geochemical SST reconstructions in sediment cores from the eastern equatorial Pacific (EEP).; A detailed view of deglacial and Holocene SST history is reconstructed from a site near the center of the EEP cold tongue. Based on Mg/Ca paleothermometry and dated extensively by radiocarbon, this record reveals modest surface cooling of ∼1.2°C during the Last Glacial Maximum (LGM). When compared with LGM temperature anomalies of ∼3°C from warmer tropical waters to the north and west it suggests a reduction of zonal and meridional SST gradients in the glacial tropical Pacific, indicative of an El Niño-like time-averaged SST pattern. The record also constrains the timing of the last deglaciation at ∼20,000 years before present, and reveals cooler mid-Holocene SSTs, indicative of an intensified, La Niña-like upwelling response.; δ18O_calcite measured in the planktonic foraminifera Globigerinoides sacculifer and Globigerinoides ruber in a number of EEP cores is used as a tracer of hydrographic variability in the cross-equatorial frontal zone between the cold tongue and the Intertropical Convergence Zone. The meridional δ18O _calcite gradient, reflecting the gradients in temperature and salinity, is found to have been weaker by about 50% during the LGM. Since this gradient is maintained by upwelling-favorable southeast trade winds across the equator, it is suggested that the equatorial trades were weaker in glacial times.; Evidence is presented in support of an intermediate water link between the Southern Ocean and the EEP during deglaciation. It is based on comparison of two radiocarbon-dated climate records from the Subantarctic and the EEP, which demonstrate low- and high-latitude synchrony of surface warming and δ 13C variability. It is proposed that the two regions are linked through temperature variability of southern source intermediate waters upwelling in the EEP.; Finally, downcore SST reconstructions based on alkenone paleothermometry are used to evaluate this method's potential for paleoceanographic studies in this region. Similarities and differences with existing records from other proxies are highlighted, and it is concluded that additional steps are needed for reliable climatic interpretation of alkenone data, including 14 C dating of the alkenones.