Evidence for reduced export productivity following the Cretaceous/Paleogene mass extinction

Abstract The Cretaceous/Paleogene (K/Pg) mass extinction was associated with a collapse in the carbon isotopic (δ13C) gradient between planktonic and benthic foraminifera and a decrease in bulk carbonate δ13C values. Theseperturbationshavebeenexplainedbyseveralhypotheses: global collapseofprimaryproductivity (Strangelove Ocean), greatly reduced export but not primary productivity (Living Ocean), little or no reduction in export productivity (Resilient Ocean), and geographic heterogeneity in the change of export productivity (Heterogeneous Ocean). We tested primary versus export productivity changes in the paleoshelf of New Jersey, where δ13C values and organic carbon accumulation rates can distinguish among different ocean responses. On the shelf, the K/Pg boundary is associated with a ~2.5 ‰ δ13C decrease in bulk carbonate, a~0.8‰δ13Cdecrease inorganic carbon,a collapseof thesurface tobottomδ13Cgradient, andadrop inorganic carbonaccumulation rates.We interpretanearlyDanian~1.0‰planktonic foraminiferalδ13Cgradient, a ~0.75 ‰ cross-shelf benthic foraminiferal δ13C gradient, and a drop in carbon accumulation rates to reflect the presence of active primary but limited export productivity, consistent with the Living Ocean hypothesis. We evaluated interbasinal deep-sea benthic foraminiferal δ13C gradients between the Pacific (Site 1210) andAtlantic (Site 1262) oceans as a proxy for changes in export productivity. The interbasinal δ13C gradient was reduced after themass extinction, suggesting a reduction in global export productivity. Although our data support the Living Ocean hypothesis, evidence from paleoupwelling zones shows significant export productivity, indicating spatial heterogeneity in the wake of the K/Pgmass extinction (Heterogeneous Ocean). 1