Ice-ocean interactions and climate dynamics across the Middle Weichselian (~90-60ka)

In the Nordic seas, major warm and cold phases are thought to be related to a variable advection of warm surface waters and the occurrence or absence of deepwater formation, icebergs, sea-ice, and meltwater. The onset of the last glaciation – after the peak of MIS5e but well before MIS5d - was already accompanied by widespread ice drift, conditions which persisted almost continuously into the Holocene (~10 ka).

In this study we focused on the time period MIS5b into MIS3 (~90-60ka). With respect to the concept of a 100ky glacial-interglacial periodicity, this Middle Weichselian interval stands out in the arctic-subarctic ocean as it commenced with a deglacial phase that led to an intermittent but rather pronounced warming after ~85ka (MIS5a). By using benthic and planktic foraminiferal indicator species combined with stable isotope analyses, our data suggest that brief but intense warming episodes were responsible for ice growth and associated large sea-level drop recognized globally for glacial MIS4 (~70-65ka). Although occurring during times of decreasing summer insolation the massive size increase of surrounding ice sheets must have been facilitated through high moisture supply transferred into the polar region. MIS4 terminates in a major deglaciation (~H6) implying that the transition into MIS3 was again forced by a major warming. While this warming is difficult to verify in the Nordic seas through conventional proxies, the world-wide decrease in foraminiferal carbon isotopes at this time may indicate the involvement of the carbon system.