Warming, acidification, and calcification feedback during the first hyperthermal of the Cenozoic—The Latest Danian Event

The Latest Danian Event (LDE; ca. 62.15 Ma) is a major double-spiked eccentricity-driven transient warming event and carbon cycle perturbation (hyperthermal) in the early Paleocene, which has received significantly less attention compared to the larger events of the late Paleocene−early Eocene. A better understanding of the nature of the LDE may broaden our understanding of hyperthermals more generally and improve our knowledge of Earth system responses to extreme climate states. We present planktic and benthic foraminiferal Mg/Ca and B/Ca records that shed new light on changes in South Atlantic temperature and carbonate chemistry during the LDE. Our planktic Mg/Ca record reveals a pulsed increase in sea-surface temperature of at least ∼1.5 °C during the older carbon isotope excursion, and ∼0.5 °C during the younger isotope excursion. We observe drops in planktic and benthic B/Ca, synchronous with pronounced negative excursions in benthic δ¹³C, which suggest a shift in the carbonate system toward more acidic, dissolved inorganic carbon−rich conditions, in both the surface and deep ocean. Conditions remained more acidic following the LDE, which we suggest may be linked to an enhanced ocean alkalinity sink due to changes in the makeup of planktic calcifiers, hinting at a novel feedback between calcifier ecology and ocean-atmosphere CO₂.