LOCAL HETEROGENEITY OF MARINE EXPORT PRODUCTIVITY IN THE AFTERMATH OF THE K-PG MASS EXTINCTION

One of the most significant environmental consequences of the K-Pg mass extinction in the marine realm was a long term decline in the efficiency of the biological pump, the mechanism by which organic matter is transported from the photic zone to the deep sea. This is exemplified by a complete collapse of the surface to deep ocean carbon isotope gradient at the K-Pg boundary, which did not return to pre-extinction values until about 1.8 myr later. However, the decline in biological pump efficiency was not uniform, with proxies for export productivity based on marine barite showing a heterogeneous change in local export production on an ocean basin scale. At some sites (principally in the Pacific and Southern Oceans) local export productivity actually increased after the K-Pg boundary. Despite these observations, it is currently uncertain whether these heterogenous trends in export productivity occurred on a local, regional, or global scale. Here, we present new barium abundance data (presented as Ba/Ti and Ba/Fe ratios) from DSDP, ODP, and IODP sites in the Gulf of Mexico and the Caribbean. These sites, covering an area of a few thousand square kilometers, show significant variability in the sign and timing of export productivity change in the aftermath of the K-Pg mass extinction. The observed changes are unlikely to have been caused by changes in terrestrial delivery of non-marine barite because all sites are > 500 km from land and the heterogeneity is independent of distance from land or catchment (i.e., Gulf of Mexico vs. Caribbean). Instead, we suggest that these changes are linked to ecological variability in recovery assemblages, where some localities had a more efficient biological pump due to the perseverance or early recovery of larger organisms which facilitated the removal of carbon from the photic zone, while others did not and thus had an accumulation of nutrients in the photic zone leading to locally high productivity.

This apparent regional-scale heterogeneity confirms that the decline and recovery of the biological pump was primarily moderated by ecological changes in the upper water column in the aftermath of the mass extinction, and that these changes were not solely driven by external factors like distance from shore, water depth, or ocean basin.