Christopher Michael Lowery, Timothy J Bralower

The global heterogeneity in export productivity after the Cretaceous-Paleogene (K-Pg) mass extinction is well documented, with some sites showing no change on geologic timescales, some demonstrating sustained decline, and a few showing a somewhat surprising increase. However, observational data come from sites so widespread that a key outstanding question is the geographic scale of changes in export productivity, and whether similar environments (e.g., open ocean gyres) responded similarly or whether heterogeneity is unrelated to environment. To address this, we developed three new Ba/Ti export productivity records from sites in the Gulf of Mexico and Caribbean which, combined with published data from a fourth site in the Chicxulub Crater itself, allow us to reconstruct regional changes in post K-Pg export productivity for the first time. We find that, on a regional scale, export productivity change was homogenous, with all four sites showing a ~300 kyr period of elevated export production just after the boundary, followed by a longer period of decline. Interestingly, this interval of elevated export production appears to coincide with the post K-Pg global micrite layer, which is thought to at least partially have been produced by blooms of carbonate-producing cyanobacteria and other picophytoplankton. Global comparison of sites shows that elevated export productivity appears to have been most common in oligotrophic gyres, which suggests that changing plankton ecology evidenced by the micrite layer altered the biological pump, leading to a temporary increase in export production in these settings.