Phytoplankton community disruption caused by latest Cretaceous global warming

Abstract. Phytoplankton responses to a ~ 350 kiloyear long phase of gradual late Maastrichtian (latest-Cretaceous) global warming starting at ~ 66.4 Ma can provide valuable insights into the long-term influences of global change on marine ecosystems. Here we perform micropaleontological analyses on three cores from the New Jersey paleoshelf, to assess the response of phytoplankton using cyst-forming dinoflagellates and benthic ecosystems using benthic foraminifera. Our records show that this Latest Maastrichtian Warming Event (LMWE), characterized by a 4.0 ± 1.3 ⁰C warming of sea-surface waters on the New Jersey paleoshelf, resulted in a succession of nearly monospecific dinoflagellate cyst assemblages, dominated by the species Palynodinium grallator. This response, likely triggered by the combination of warmer and seasonally thermally-stratified seas, appears to have been more intense at offshore sites than at nearshore sites. The LMWE, and related dinoflagellate response, is associated with an impoverished benthic ecosystem. A wider geographic survey of literature data reveals that the dominance of P. grallator is a marker for the LMWE throughout the northern mid-latitudes. While the dinocyst assemblage returned to a stable, normal marine community in the last tens of thousands of years of the Maastrichtian, benthic foraminiferal diversity remained slightly suppressed. Increased ecosystem stress during the latest Maastrichtian potentially primed global ecosystems for the subsequent mass extinction following the K-Pg boundary Chicxulub impact.