Abstract:
A dramatic decrease in planktic-to-benthic carbon isotopic (delta (super 13) C) gradients occurs at open-marine Cretaceous/Tertiary (K/T) sequences world-wide. This suggests that the export of organic carbon from surface to deep waters was drastically reduced following the K/T boundary impact. To reconstruct planktic-to-benthic and interplanktic delta (super 13) C gradients, I picked planktic foraminifera and benthic foraminifera of the latest Cretaceous through early Paleocene interval of South Atlantic Deep Sea Drilling Project Site 528 for detailed carbon and oxygen isotopic analyses. These isotopic data were combined with fine carbonate and benthic foraminiferal data from D'Hondt and Lindinger (1988). These results indicate that in the South Atlantic interplanktic delta (super 13) C gradients collapsed after the K/T impact and did not recover until two million years later. Planktic-to-benthic delta (super 13) C gradients achieved partial recovery about 1 million years after the K/T impact, but, at least in this region, did not fully recover until almost three million years after the event. This suggests that, in the South Atlantic, the post-boundary recovery of the planktic-to-benthic delta (super 13) C gradient took far longer than previous estimates (which ranged from only a few thousand years to about two million years). There is no conclusive evidence for long-term changes in mean temperature after the K/T impact. However, it remains possible that our isotopic records were aliased by fine-scale variations in climate.