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

Vigorous lateral export of the meltwater outflow from beneath an Antarctic ice shelf
Vigorous lateral export of the meltwater outflow from beneath an Antarctic ice shelf
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.
0028-0836
219-222
Naveira Garabato, Alberto C.
97c0e923-f076-4b38-b89b-938e11cea7a6
Forryan, Alexander
4e753ae9-7f12-495f-933a-2c5a1f554a0e
Dutrieux, Pierre
366b1813-3d70-4202-aabb-0e314e3d99b7
Brannigan, Liam
6093fdb8-8cae-42ee-8a10-9ee87288fed3
Biddle, Louise C.
1fb7ece5-4374-4bb3-9f14-e82bb4b63890
Heywood, Karen J.
83d91436-76bc-4d55-ae41-9af6a6fc8869
Jenkins, Adrian
ae892509-d8d8-4176-99b2-66cc717ef376
Firing, Yvonne L.
2518c141-9864-4b97-a9ed-adbab90dca66
Kimura, Satoshi
c2d72821-b5a4-4407-95f8-d2204e771007
Naveira Garabato, Alberto C.
97c0e923-f076-4b38-b89b-938e11cea7a6
Forryan, Alexander
4e753ae9-7f12-495f-933a-2c5a1f554a0e
Dutrieux, Pierre
366b1813-3d70-4202-aabb-0e314e3d99b7
Brannigan, Liam
6093fdb8-8cae-42ee-8a10-9ee87288fed3
Biddle, Louise C.
1fb7ece5-4374-4bb3-9f14-e82bb4b63890
Heywood, Karen J.
83d91436-76bc-4d55-ae41-9af6a6fc8869
Jenkins, Adrian
ae892509-d8d8-4176-99b2-66cc717ef376
Firing, Yvonne L.
2518c141-9864-4b97-a9ed-adbab90dca66
Kimura, Satoshi
c2d72821-b5a4-4407-95f8-d2204e771007

Naveira Garabato, Alberto C., Forryan, Alexander, Dutrieux, Pierre, Brannigan, Liam, Biddle, Louise C., Heywood, Karen J., Jenkins, Adrian, Firing, Yvonne L. and Kimura, Satoshi (2017) Vigorous lateral export of the meltwater outflow from beneath an Antarctic ice shelf. Nature, 542 (7640), 219-222. (doi:10.1038/nature20825).

Record type: Article

Abstract

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.

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Accepted/In Press date: 10 November 2016
e-pub ahead of print date: 30 January 2017
Published date: 9 February 2017
Organisations: Ocean and Earth Science, Physical Oceanography, National Oceanography Centre, Marine Physics and Ocean Climate

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Local EPrints ID: 405581
URI: http://eprints.soton.ac.uk/id/eprint/405581
ISSN: 0028-0836
PURE UUID: 498d3584-b111-4b04-8b02-823ec34e6f04

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Date deposited: 06 Feb 2017 15:25
Last modified: 08 Jan 2022 07:14

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Contributors

Author: Alexander Forryan
Author: Pierre Dutrieux
Author: Liam Brannigan
Author: Louise C. Biddle
Author: Karen J. Heywood
Author: Adrian Jenkins
Author: Yvonne L. Firing
Author: Satoshi Kimura

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