Orbitally driven bottom-water dynamics during the Maastrichtian

The long-term global cooling trend during the latest Cretaceous was interrupted by an intense global warming episode at ~69 Ma known as the mid-Maastrichtian event (MME). The MME is characterised by two positive ¹³C excursions with an overall magnitude of 0.6‰ to 1.5‰, separated by a negative inflection. The ¹³C excursions are accompanied by the extinction of inoceramid bivalves, an abrupt increase in deep-sea and sea-surface temperatures as well as high terrestrial mean annual temperatures between 21 and 23 °C at a paleolatitude of ~35° N. Changes in oceanic circulation, particularly a change in thermohaline circulation patterns, have been suggested to be one of the main drivers of the MME. In this study, we aim to test this hypothesis by the generation of new high-resolution d¹³C and d¹⁸O analyses, Mg/Ca-derived bottom-water temperatures and CaCO₃ wt% records from IODP Site U1403 (J-Anomaly Ridge, North Atlantic). Rhythmic variations in these geochemical records reflect an imprint of Earth´s astronomical parameters. Our results point towards a combination of Large Igneous Province (LIP) volcanism and simultaneous changes in deep-ocean circulation as triggers for the MME. For the North Atlantic, we observe an interplay between warmer and colder bottom-waters in combination with CaCO₃ dissolution events. This hints toward a switch in bottom-water source regions between a high- and a low-latitude source region, likely controlled by orbital forcing. With the termination of the MME, bottom-water temperatures started to decrease, and the d¹³C record indicates an abrupt reorganization of the ocean circulation system towards a solely high-latitude North Atlantic source region for bottom-water.