Evidence for the Living Ocean following the Cretaceous/Paleogene Mass Extinction

Abstract:

The Cretaceous/Paleogene (K/Pg) mass extinction (~66 Ma) was associated with a collapse in the carbon isotopic (δ¹³C) gradient between planktonic and benthic foraminifera and a decrease in bulk carbonate δ¹³C values. These perturbations have been attributed to three hypotheses: the Strangelove Ocean, with global collapse of primary productivity; the Living Ocean, with greatly reduced export but not primary productivity; and the Resilient Ocean, with persistent export productivity. While previous studies have focused on deep-sea locations, we tested the hypotheses in the paleo-continental shelf of New Jersey, USA, where δ¹³C values and organic carbon accumulation rates can distinguish among the hypotheses. We also evaluated interbasinal deep-sea δ¹³C differences between Ocean Drilling Program (ODP) Sites 1210 (Shatsky Rise, North Pacific) and 1262 (Walvis Ridge, South Atlantic). New Jersey shelf shows that a ~2.5 ‰ δ¹³C drop in bulk carbonate, a collapse of the vertical δ¹³C gradient between planktonic and benthic foraminifera, and a significant decrease in organic carbon mass accumulation rates occurred across the K/Pg boundary. We interpret a ~1.0 ‰ water column δ¹³C gradient and cross-shelf benthic foraminiferal δ¹³C gradient in the early Danian to reflect the presence of active primary productivity, strongly supporting the Living Ocean hypothesis. Deep-sea δ¹³C differences between ODP Sites 1210 and 1262 show that the interbasinal deep-sea benthic foraminiferal δ¹³C gradient collapsed immediately after the mass extinction, which is consistent with a strong reduction in the export productivity after the K/Pg boundary. However, the ocean floor in highly productive regions like the equatorial Pacific may have continued to receive significant export productivity.