NOAA/WDS Paleoclimatology - Eastern Pacific Ocean TEX86 and Mg/Ca SST Reconstructions during the Holocene and Last Glacial Maximum

The use of the TEX86 temperature proxy has thus far come to differing results as to whether TEX86 temperatures are representative of surface or subsurface conditions. In addition, although TEX86 temperatures might reflect sea surface temperatures based on core-top (Holocene) values, this relationship might not hold further back in time. Here, we investigate the TEX86 temperature proxy by comparing TEX86 temperatures to Mg/Ca temperatures of multiple species of planktonic foraminifera for two sites in the eastern tropical Pacific (on the Cocos and Carnegie Ridges) across the Holocene and Last Glacial Maximum. Core-top and Holocene TEXH86 temperatures at both study regions agree well, within error, with the Mg/Ca temperatures of Globigerinoides ruber, a surface dwelling planktonic foraminifera. However, during the Last Glacial Maximum, TEXH86 temperatures are more representative of upper thermocline temperatures, and are offset from G. ruber Mg/Ca temperatures by 5.8◦C and 2.9◦C on the Cocos Ridge and Carnegie Ridge, respectively. This offset between proxies cannot be reconciled by using different TEX86 temperature calibrations, and instead, we suggest that the offset is due to a deeper export depth of GDGTs at the LGM. We also compare the degree of glacial cooling at bothsites based on both temperature proxies, and find that TEXH86 temperatures greatly overestimate glacial cooling, especially on the Cocos Ridge. This study has important implications for applying the TEX86 paleothermometer in the eastern tropical Pacific.