19.04.2021: Online Ocean Circulation and Climate Dynamics Colloquium

Aidan Starr, School of Earth and Environmental Sciences, Cardiff University, Cardiff (UK): "Antarctic icebergs reorganize ocean circulation during Pleistocene glacials"

When?      Monday, 19 April 2021 at 11am
Where?    ZOOM meeting room: https://geomar-de.zoom.us/j/88504244923?pwd=dkJGUG9HcUZBNDNpeCtlNktLbFVWUT09
Meeting-ID: 885 0424 4923
Kenncode: 768841

The geometry and vigour of the Atlantic Meridional Overturning Circulation (AMOC) influences global climate on various timescales. Palaeoceanographic evidence suggests that during glacial periods of the past 1.5 million years the AMOC was markedly different from today, however an absence of evidence on the origin of this phenomenon means that the sequence of events leading to global glacial conditions remains unclear. In this seminar, I will show multi-proxy evidence and iceberg trajectory model results demonstrating that northward shifts in Antarctic iceberg melt in the Indian–Atlantic Southern Ocean (0–50° E) systematically preceded deep-water mass reorganizations during Pleistocene-era glaciations. Such a shift in iceberg trajectories during glacial periods can result in a considerable redistribution of freshwater in the Southern Ocean which, in concert with increased sea-ice cover, enabled positive buoyancy anomalies to ‘escape’ into the upper limb of the AMOC, providing a teleconnection between surface Southern Ocean conditions and the formation of deep water in the North Atlantic. The magnitude and pacing of this mechanism evolved substantially across the mid-Pleistocene transition, and the coeval increase in magnitude of the ‘southern escape’ and deep circulation perturbations implicate this mechanism as a key feedback in the transition to the ‘100-kyr world’, in which glacial–interglacial cycles occur at roughly 100,000-year periods.


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