Oceanographic and climatic implications of the Palaeocene carbon isotope maximum

We have compared detailed planktonic and benthonic foraminiferal carbon and oxygen isotope records from the Palaeocene and early Eocene successions at DSDP Site 577 (Shatsky Rise, North Pacific), a composite section derived from DSDP Leg 74 sites (Walvis Ridge, South Atlantic) and a composite section from ODP Leg 113 sites (Maud Rise, Weddell Sea). The δ¹³C records of Palaeocene and early Eocene Foraminifera at Site 577 and the Leg 74 sites show that an increase in δ¹³C values in surface waters at 64 Ma (end of Zone P1) resulted in increased vertical carbon isotope gradients (δ¹³C) between surface and deeper dwelling planktonic foraminifera, and between surface-dwelling planktonics and benthonic foraminifera which became progressively steeper until the iniddle Late Palaeocene (Zone P4). This steepening also occurs in the latest Palaeocene of the composite Leg 113 section and can be explained by an increase in surface ocean productivity. This increase in productivity probably resulted in an expansion of the oxygen minimum zone (OMZ). Benthonic δ¹³C values increased during the late Palaeocene in Site 577 and the composite Leg 74 section, suggesting that the Palaeocene carbon isotope maximum was composed of both within-ocean reservoir (increased surface water productivity) and between-reservoir (organic carbon burial) ftactionation effects. The benthonic δ¹³C increase lags the surface ocean δ¹³C increase in the early Palaeocene (63–64 Ma) suggesting that surface water productivity increase probably led an increase in the burial rate of organic carbon relative to carbonate sedimentation. Moreover, inter-site δ¹³C comparisons suggest that the locus of deep to intermediate water formation for the majority of the Palaeocene and the earliest Eocene was more likely to have been in the high southern latitudes than in the lower latitudes. Oxygen isotope data show a decline in deeper water temperatures in the early and early late Palaeocene, followed by a temperature increase in the late Palaeocene and across the PalaeoceneEocene boundary. We speculate that these changes in deeper water temperatures were related to the flux of CO₂ between the oceans and the atmosphere through a mechanism operating at the high southern latitudes.