Changing climate in a pre-impact world: a multi-proxy paleotemperature reconstruction across the last million years of the Cretaceous

Abstract:

Climate instability during the last million years of the Cretaceous (67-66 Ma) is still poorly documented and not well understood. One of the reasons for this is that in deep time, different proxies are likely to yield different temperatures. This is because the application of calibrations based on present day temperature proxy relationships is affected by source organism evolution, differences in ocean chemistry and non-analogue processes. Only by combining temperature estimates derived from different, independent proxies, the problems with individual proxies can be cancelled out. A quantitative, multi-proxy temperature record from the latest Cretaceous therefore may provide a better insight in climate changes across this time interval. For such a multi-proxy research, sediments are required that yield both well-preserved foraminiferal calcite as well as organic biomarkers. Very few sites are known to provide such sedimentary records, but ODP Leg 174AX Site Bass River (New Jersey Shelf) has proven to be an excellent archive for paleotemperature reconstructions for the Cretaceous and Paleogene. We here present a multi-proxy, quantitative paleotemperature reconstruction of the last million years of the Cretaceous of the Bass River core. Benthic and planktic foraminiferal Mg/Ca and δ¹⁸O were determined, as well as the organic geochemical sea surface temperature proxy TEX₈₆. This resulted in a unique coupled surface and bottom water temperature record of the latest Cretaceous. Our data suggest a ~2-6 ˚C bottom water warming and a ~4-6 ˚C surface water warming approximately 300 kyr before the Cretaceous-Paleogene boundary, followed by a cooling trend across the boundary. This warming event appears to coincide with the main phase of the Deccan Traps eruptions and therefore probably represents a global event.