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The glacial mid-depth radiocarbon bulge and its implications for the overturning circulation

Burke, Andrea and Stewart, Andrew L. and Adkins, Jess F. and Ferrari, Raffaele and Jansen, Malte F. and Thompson, Andrew F. (2015) The glacial mid-depth radiocarbon bulge and its implications for the overturning circulation. Paleoceanography, 30 (7). pp. 1021-1039. ISSN 0883-8305.

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Published reconstructions of radiocarbon in the Atlantic sector of the Southern Ocean indicate that there is a mid-depth maximum in radiocarbon age during the Last Glacial Maximum (LGM). This is in contrast to the modern ocean where intense mixing between water masses results in a relatively homogenous radiocarbon profile. Ferrari et al. (2014) suggested that the extended Antarctic sea ice cover during the LGM necessitated a shallower boundary between the upper and lower branches of the meridional overturning circulation. This shoaled boundary lay above major topographic features associated with strong diapycnal mixing, isolating dense southern sourced water in the lower branch of the overturning circulation. This isolation would have allowed radiocarbon to decay and thus provides a possible explanation for the mid-depth radiocarbon age bulge. We test this hypothesis using an idealized, 2-D, residual-mean dynamical model of the global overturning circulation. Concentration distributions of a decaying tracer that is advected by the simulated overturning are compared to published radiocarbon data. We find that a 600 km (~5° of latitude) increase in sea ice extent shoals the boundary between the upper and lower branches of the overturning circulation at 45°S by 600 m and shoals the depth of North Atlantic Deep Water convection at 50°N by 2500 m. This change in circulation configuration alone decreases the radiocarbon content in the mid-depth South Atlantic at 45°S by 40‰, even without an increase in surface radiocarbon age in the source region of deep waters during the LGM.

Item Type:Article
Related URLs:
URLURL TypeDescription
Burke, Andrea0000-0002-3754-1498
Stewart, Andrew L.0000-0001-5861-4070
Adkins, Jess F.0000-0002-3174-5190
Ferrari, Raffaele0000-0003-1895-4294
Thompson, Andrew F.0000-0003-0322-4811
Additional Information:© 2015 American Geophysical Union. Received 7 JAN 2015; Accepted 27 MAY 2015; Accepted article online 2 JUN 2015; Published online 28 JUL 2015. This work was supported by a Foster and Coco Stanback Postdoctoral Fellowship and a Marie Curie Career Integration grant (CIG14-631752) awarded to A.B., and an NSF grant awarded to A.F.T. (OPP-1246460). All radiocarbon data presented in this paper can be found in supplemental tables from previous publications (,, and or from the GLODAP database ( [Key et al., 2004]. Model results are available by request to ALS ( Andrea Burke and Andrew L. Stewart contributed equally to this work.
Funding AgencyGrant Number
Foster and Coco Stanback Postdoctoral FellowshipUNSPECIFIED
Marie Curie FellowshipCIG14-631752
Subject Keywords:radiocarbon; overturning circulation; Last Glacial Maximum
Issue or Number:7
Record Number:CaltechAUTHORS:20150910-140031548
Persistent URL:
Official Citation:Burke, A., A. L. Stewart, J. F. Adkins, R. Ferrari, M. F. Jansen, and A. F. Thompson (2015), The glacial mid-depth radiocarbon bulge and its implications for the overturning circulation, Paleoceanography, 30, 1021–1039, doi:10.1002/2015PA002778
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:60176
Deposited By: Tony Diaz
Deposited On:11 Sep 2015 04:14
Last Modified:09 Oct 2019 20:33

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