Dinoflagellate-based sea surface temperature reconstructions across the Cretaceous–Tertiary boundary

Quantitative analysis of organic-walled dinoflagellate cyst (dinocyst) assemblages from closely spaced samples across the Cretaceous–Tertiary boundary (KTB) at El Kef (NW Tunisia), Caravaca (SE Spain) and Stevns Klint (E Denmark) allows for reconstructions of sea surface temperature (SST) trends. The combined dinocyst-based SST curves indicate relatively stable warm conditions during the latest Maastrichtian in contrast to strongly fluctuating and on average cooler conditions during the earliest Danian. In detail, the results indicate cooling across the KTB, immediately followed by an interval of pronounced warming, the latter recorded in all studied sections. Two more cooling pulses may be recognized in the overlying interval followed by a gradual return to stable, relatively warm conditions. Our data furthermore show that these KTB-related climatic changes invoked distinct migration among organic-walled cyst-producing dinoflagellates, a group not pushed to extinction at the KTB, recordable in both hemispheres. Recent models predict periods varying between several months to 8–13 yr of global cooling (`impact winterʹ) and reduced solar transmission as a direct result of the Chicxulub KTB impact, followed by relatively long-term, excess CO2-related global warming. Our results are in line with such models, but suggest that the impact-related cooling phase may have lasted longer, and that marked climatic instability continued to some 100,000 yrs following the KTB event(s).