Understanding TEX86H Temperature Estimates in the Eastern Equatorial Pacific over the Last Deglacial

Abstract:

An index based on the relative abundance of glycerol dialkyl glycerol tetraethers (TEX₈₆) has been gaining support for use as a sea surface temperature proxy. It has had limited application in the Eastern Equatorial Pacific (EEP) and, prior to this study, has not been applied to a high-resolution record within this region. Here, we utilize the TEX₈₆^H temperature index to calculate a North-South temperature gradient in the EEP over the last ~25 kyr using two sediment cores, MV1014-02-17JC (located within the equatorial upwelling zone on the Carnegie Ridge) and MV1014-01-08JC (located North of the seasonal upwelling region on the Cocos Ridge). During the Late Holocene, the Cocos Ridge exhibited warmer TEX₈₆^H temperatures as compared to the Carnegie Ridge. The TEX₈₆^H calculated temperatures are within analytical error of both modern annual sea surface temperatures at each site and Mg/Ca-based SST estimates derived from Globigerinoides ruber. From 5.6 kyr to 8.5 kyr there is an abrupt ~3°C decrease in the TEX₈₆^H temperatures at the Cocos Ridge, marking a breakdown in the N-S temperature gradient. Then, similar TEX₈₆^H temperatures are calculated through the Early Holocene and into the deglacial as both sites cool into the Last Glacial Maximum (LGM). Interestingly, the temperature gradient switches during the LGM, with the Carnegie Ridge yielding temperatures 1-2°C warmer than the Cocos Ridge. This gradient reversal, in contrast, is not seen in the limited Mg/Ca temperatures measured during the LGM in the same core intervals. Instead, the calculated TEX₈₆^H temperatures from both sites are cooler than calculated Mg/Ca–SSTs from the near-surface dwelling planktonic foraminifera G. ruber. Additional foraminiferal Mg/Ca and stable isotope analyses will also be presented in an effort to better constrain deglacial changes in upper water column hydrography at both sites.