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The Chicxulub impact caused a crash in productivity in the world''s oceans which contributed to the extinction of ~75% of marine species. In the immediate aftermath of the extinction, export productivity was locally highly variable, with some sites, including the Chicxulub crater, recording elevated export production. The long-term transition back to more stable export productivity regimes has been poorly documented. Here, we present elemental abundances, foraminifer and calcareous nannoplankton assemblage counts, total organic carbon, and bulk carbonate carbon isotope data from the Chicxulub crater to reconstruct changes in export productivity during the first 3 Myr of the Paleocene. We show that export production was elevated for the first 320 kyr of the Paleocene, declined from 320 kyr to 1.2 Myr, and then remained low thereafter. A key interval in this long decline occurred 900 kyr to 1.2 Myr post impact, as calcareous nannoplankton assemblages began to diversify. This interval is associated with fluctuations in water column stratification and terrigenous flux, but these variables are uncorrelated to export productivity. Instead, we postulate that the turnover in the phytoplankton community from a post-extinction assemblage dominated by picoplankton (which promoted nutrient recycling in the euphotic zone) to a Paleocene pelagic community dominated by relatively larger primary producers like calcareous nannoplankton (which more efficiently removed nutrients from surface waters, leading to oligotrophy) is responsible for the decline in export production in the southern Gulf of Mexico. © 2021. American Geophysical Union. All Rights Reserved.

The Campanian-Maastrichtian (83-66 Ma) was a period of global climate cooling, featuring significant negative carbon-isotope (d13C) anomalies, such as the Late Campanian Event (LCE) and the Campanian-Maastrichtian Boundary Event (CMBE). A variety of factors, including changes in temperature, oceanic circulation and gateway opening, have been invoked to explain these d13C perturbations, but no precise mechanism has yet been well constrained. In order to improve our understanding of these events, we measured stable carbon and oxygen isotopes of hemipelagic sediments from the Shuqualak-Evans cored borehole (Mississippi, USA) and compared the data with previously published sea-surface temperature (SST) estimates from the same core. We found that the CMBE can be recognised, unambiguously, in the Shuqualak- Evans core, and that it is associated with an interval of cooler SSTs suggesting a possible mechanistic link between palaeotemperature change and this event. Determining the precise position of the LCE in the Shuqualak-Evans core is more problematic, but it may also be associated with cooler SSTs. Our combined records of carbon cycling and SSTs compare well with other studies and provide evidence that cooling during the CMBE (and possibly LCE) was global in nature and affected surface waters, in addition to the deep-ocean. We suggest that short-term cooling drove intensification of high-latitude deep-water formation, which in turn led to changes in the ratio of carbonate to organic carbon burial that led to a negative d13C excursion. Critically, the absence of warming during these intervals implies that the Late Cretaceous events must not have been associated with an appreciable increase in atmospheric pCO2, and was likely associated with decreased pCO2.

The Late Cretaceous ‘greenhouse’ world witnessed a transition from one of the warmest climates of the past 140 million years to cooler conditions, yet still without significant continental ice. Low-latitude sea surface temperature (SST) records are a vital piece of evidence required to unravel the cause of Late Cretaceous cooling, but high-quality data remain illusive. Here, using an organic geochemical palaeothermometer (TEX86), we present a record of SSTs for the Campanian–Maastrichtian interval (~83–66¿Ma) from hemipelagic sediments deposited on the western North Atlantic shelf. Our record reveals that the North Atlantic at 35¿°N was relatively warm in the earliest Campanian, with maximum SSTs of ~35¿°C, but experienced significant cooling (~7¿°C) after this to

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