Antarctic icebergs reorganize ocean circulation during Pleistocene glacials

Aidan Starr (), Ian R. Hall (), Stephen Barker, Thomas Rackow, Xu Zhang, Sidney R. Hemming, H. J. L. van der Lubbe, Gregor Knorr, Melissa A. Berke, Grant R. Bigg, Alejandra Cartagena-Sierra, Francisco J. Jiménez-Espejo, Xun Gong, Jens Gruetzner, Nambiyathodi Lathika, Leah J. LeVay, Rebecca S. Robinson and Martin Ziegler
Additional contact information
Aidan Starr: Cardiff University
Ian R. Hall: Cardiff University
Stephen Barker: Cardiff University
Thomas Rackow: Helmholtz Centre for Polar and Marine Research
Xu Zhang: Lanzhou University
Sidney R. Hemming: Lamont-Doherty Earth Observatory of Columbia University
H. J. L. van der Lubbe: Cardiff University
Gregor Knorr: Helmholtz Centre for Polar and Marine Research
Melissa A. Berke: University of Notre Dame
Grant R. Bigg: University of Sheffield
Alejandra Cartagena-Sierra: University of Notre Dame
Francisco J. Jiménez-Espejo: Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR)
Xun Gong: Helmholtz Centre for Polar and Marine Research
Jens Gruetzner: Helmholtz Centre for Polar and Marine Research
Nambiyathodi Lathika: Ministry of Earth Sciences
Leah J. LeVay: Texas A&M University
Rebecca S. Robinson: University of Rhode Island
Martin Ziegler: Utrecht University

Nature, 2021, vol. 589, issue 7841, 236-241

Abstract: Abstract The dominant feature of large-scale mass transfer in the modern ocean is the Atlantic meridional overturning circulation (AMOC). The geometry and vigour of this circulation influences global climate on various timescales. Palaeoceanographic evidence suggests that during glacial periods of the past 1.5 million years the AMOC had markedly different features from today1; in the Atlantic basin, deep waters of Southern Ocean origin increased in volume while above them the core of the North Atlantic Deep Water (NADW) shoaled2. An absence of evidence on the origin of this phenomenon means that the sequence of events leading to global glacial conditions remains unclear. Here we present multi-proxy evidence showing that northward shifts in Antarctic iceberg melt in the Indian–Atlantic Southern Ocean (0–50° E) systematically preceded deep-water mass reorganizations by one to two thousand years during Pleistocene-era glaciations. With the aid of iceberg-trajectory model experiments, we demonstrate that such a shift in iceberg trajectories during glacial periods can result in a considerable redistribution of freshwater in the Southern Ocean. We suggest that this, 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 NADW. 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.

Date: 2021
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DOI: 10.1038/s41586-020-03094-7

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