A 60 Myr Sea Surface Temperature Record of the Northern Atlantic Ocean Using a Multi-proxy Approach

Abstract:

The extrapolation of sea surface temperature calibrations used for proxies into deep time is inherently problematic. On geological time scales, differences in ocean chemistry, source organism evolution and non-analogue processes all affect application of calibrations based on present day proxy relationships. Here we present a multi-proxy (Mg/Ca, δ¹⁸O and TEX₈₆) paleotemperature reconstruction for the North Atlantic American shelf using ODP Leg 174AX Site Bass River (New Jersey Shelf). This record extends from the Cenomanian to the Pliocene and provides an excellent archive for comparing proxies on long time scales, because the sediments yield well-preserved organic biomarkers as well as foraminiferal calcite, suitable for geochemical analysis. Nine sub-sets of high-resolution series were analyzed to gain insight both in the long-term evolution as well as the internal proxy consistency on shorter time scales. Trends in TEX₈₆, δ¹⁸O and Mg/Ca show very good mutual agreement and are consistent with stacked global benthic oxygen isotope records. This implies that the New Jersey shelf record captures the long-term trends in the global oceanic temperature signal. However, TEX₈₆ sea surface temperatures range between ~20 and 35 ⁰C, whereas bottom water temperatures inferred from Mg/Ca (corrected for modeled past changes in sea water Mg/Ca) and δ¹⁸O (corrected for ice volume changes) range between ~15 and 25 ⁰C, and 10 and 20 ⁰C, respectively. These offsets, which increase further back in time, suggest that difference in the isotopic and elemental composition of seawater, or changes in the TEX₈₆ calibration in deep time, affect temperature proxies. Deep time re-calibration based on clumped isotope thermometry will be used to reconcile these proxies also on geological time scales.