Sea surface temperature variations in the Eastern Equatorial Pacific (ODP Site 1240) over the last 160 kyr from three lipid paleothermometers (UK'37, TEXH86 and LDI)

The Pacific Ocean equatorial upwelling region is of great interest to understand climate dynamics within the context of current global change. It plays a key role in global biogeochemical cycles, especially in the carbon cycle, as it stands for being one of the areas with largest CO₂ fluxes from the ocean to the atmosphere. Moreover, tropical regions play a key role in regulating global climate, since they control the transfer of thermal energy from low to high latitudes. In this context, and with the aim of reconstructing paleoclimate conditions at glacial-interglacial time scales in this region, we analysed selected molecular biomarkers in the marine sediment core ODP 1240, at the easternmost region of the Eastern Equatorial Pacific (EEP), covering the last 160 kyr. We focused on long-chain alkenones, glycerol dialkyl glycerol tetraethers (GDGTs) and long-chain alkyl diols (LCDs). Upon quantification of these lipids, we calculated the U^K'₃₇, TEX^H₈₆ and LDI indices, and discussed their suitability as paleotemperature proxies to reconstruct sea surface conditions in the study region. We found that U^K'₃₇ and TEX^H₈₆ derived-temperatures track the warming and cooling trends typical of glacial-interglacial variations. However, while they provide similar temperatures during the last two interglacial maxima, they disagree during glacial periods, when the TEX^H₈₆-based estimations display significantly cooler temperatures. The LDI-derived record also shows similar temperatures to those from the U^K'₃₇ and TEX^H₈₆during the more recent interglacial but, for the last glacial-interglacial period, LDI-derived temperatures remain colder than those of the U^K’₃₇ and even colder than those of the TEX^H₈₆ at some periods. Multiple factors could be behind this variability and disagreement between the three paleothermometers: depth dwelling, production or exportation of the different biological producers of each lipid, seasonality, diagenetic processes and changes in biogeochemistry conditions of the studied marine region, amongst others. In this presentation, the factors that we believe are most important in the study region will be presented and discussed, to improve our understanding of the biological dynamics of the precursors of each proxy and of their reconstructed marine temperatures in the EEP.