Vigorous lateral export of the meltwater outflow from beneath an Antarctic ice shelf

Naveira Garabato, Alberto C.; Forryan, Alexander; Dutrieux, Pierre ORCID: https://orcid.org/0000-0002-8066-934X; Brannigan, Liam; Biddle, Louise C.; Heywood, Karen J.; Jenkins, Adrian ORCID: https://orcid.org/0000-0002-9117-0616; Firing, Yvonne L. ORCID: https://orcid.org/0000-0002-3640-3974; Kimura, Satoshi ORCID: https://orcid.org/0000-0003-1689-1605. 2017 Vigorous lateral export of the meltwater outflow from beneath an Antarctic ice shelf. Nature, 542 (7640). 219-222. 10.1038/nature20825

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© 2017 Nature Publishing Group This is the author’s version of a work that was accepted for publication in Nature. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version will be published in Nature doi:10.1038/nature20825
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Official URL: http://dx.doi.org/10.1038/nature20825

Abstract/Summary

The instability and accelerated melting of the Antarctic Ice Sheet are among the foremost elements of contemporary global climate change1, 2. The increased freshwater output from Antarctica is important in determining sea level rise1, the fate of Antarctic sea ice and its effect on the Earth’s albedo4, 5, ongoing changes in global deep-ocean ventilation6, and the evolution of Southern Ocean ecosystems and carbon cycling7, 8. A key uncertainty in assessing and predicting the impacts of Antarctic Ice Sheet melting concerns the vertical distribution of the exported meltwater. This is usually represented by climate-scale models3–5, 9 as a near-surface freshwater input to the ocean, yet measurements around Antarctica reveal the meltwater to be concentrated at deeper levels10, 11, 12, 13, 14. Here we use observations of the turbulent properties of the meltwater outflows from beneath a rapidly melting Antarctic ice shelf to identify the mechanism responsible for the depth of the meltwater. We show that the initial ascent of the meltwater outflow from the ice shelf cavity triggers a centrifugal overturning instability that grows by extracting kinetic energy from the lateral shear of the background oceanic flow. The instability promotes vigorous lateral export, rapid dilution by turbulent mixing, and finally settling of meltwater at depth. We use an idealized ocean circulation model to show that this mechanism is relevant to a broad spectrum of Antarctic ice shelves. Our findings demonstrate that the mechanism producing meltwater at depth is a dynamically robust feature of Antarctic melting that should be incorporated into climate-scale models.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	10.1038/nature20825
Programmes:	BAS Programmes > BAS Programmes 2015 > Polar Oceans
ISSN:	0028-0836
Date made live:	06 Feb 2017 14:35 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/516122

Item Type:

Publication - Article

Digital Object Identifier (DOI):

10.1038/nature20825

Programmes:

BAS Programmes > BAS Programmes 2015 > Polar Oceans

ISSN:

0028-0836

Date made live:

06 Feb 2017 14:35 +0 (UTC)

URI:

https://nora.nerc.ac.uk/id/eprint/516122