Wednesday, May 27, 2015

Evidence of Reduced Export Productivity Supporting Living or Heterogeneous Ocean Hypotheses for KT/K-Pg mass Extinction

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


Esmeray-Senlet et al


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. These perturbations have been explained by several hypotheses: global collapse of primary productivity (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 vs. 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‰ δ13C decrease in organic carbon, a collapse of the surface to bottom δ13C gradient, and a drop in organic carbon percentage. We interpret an early Danian ~1.0‰ planktonic foraminiferal δ13C gradient, 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) and the Atlantic (Site 1262) oceans as a proxy for changes in export productivity. The interbasinal δ13C gradient was reduced after the mass extinction, suggesting a reduction in global export productivity. Although our data support the Living Ocean hypothesis, evidence from paleo-upwelling zones shows significant export productivity, indicating spatial heterogeneity in the wake of the K/Pg mass extinction (Heterogeneous Ocean).

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