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Modeling the interplay between sea ice formation and the oceanic mixed layer: Limitations of simple brine rejection parameterizations

Modeling the interplay between sea ice formation and the oceanic mixed layer: Limitations of simple brine rejection parameterizations
Modeling the interplay between sea ice formation and the oceanic mixed layer: Limitations of simple brine rejection parameterizations
The subtle interplay between sea ice formation and ocean vertical mixing is hardly represented in current large-scale models designed for climate studies. Convective mixing caused by the brine release when ice forms is likely to prevail in leads and thin ice areas, while it occurs in models at the much larger horizontal grid cell scale. Subgrid-scale parameterizations have hence been developed to mimic the effects of small-scale convection using a vertical distribution of the salt rejected by sea ice within the mixed layer, instead of releasing it in the top ocean layer. Such a brine rejection parameterization is included in the global ocean–sea ice model NEMO-LIM3. Impacts on the simulated mixed layers and ocean temperature and salinity profiles, along with feedbacks on the sea ice cover, are then investigated in both hemispheres. The changes are overall relatively weak, except for mixed layer depths, which are in general excessively reduced compared to observation-based estimates. While potential model biases prevent a definitive attribution of this vertical mixing underestimation to the brine rejection parameterization, it is unlikely that the latter can be applied in all conditions. In that case, salt rejections do not play any role in mixed layer deepening, which is unrealistic. Applying the parameterization only for low ice–ocean relative velocities improves model results, but introduces additional parameters that are not well constrained by observations.
Model, Brine rejection, Parameterization, Ocean mixed layer, Arctic, Antarctic
1463-5003
141-152
Barthélemy, Antoine
e063bff5-5482-41fe-8abd-674a4a161502
Fichefet, Thierry
7b3028c8-1af9-4671-b041-51022a13bf73
Goosse, Hugues
33c33c55-356b-48ec-be78-3e9eb5d04f29
Madec, Gurvan
ffb28deb-4bbd-4a4c-914f-492f813e4864
Barthélemy, Antoine
e063bff5-5482-41fe-8abd-674a4a161502
Fichefet, Thierry
7b3028c8-1af9-4671-b041-51022a13bf73
Goosse, Hugues
33c33c55-356b-48ec-be78-3e9eb5d04f29
Madec, Gurvan
ffb28deb-4bbd-4a4c-914f-492f813e4864

Barthélemy, Antoine, Fichefet, Thierry, Goosse, Hugues and Madec, Gurvan (2015) Modeling the interplay between sea ice formation and the oceanic mixed layer: Limitations of simple brine rejection parameterizations. Ocean Modelling, 86, 141-152. (doi:10.1016/j.ocemod.2014.12.009).

Record type: Article

Abstract

The subtle interplay between sea ice formation and ocean vertical mixing is hardly represented in current large-scale models designed for climate studies. Convective mixing caused by the brine release when ice forms is likely to prevail in leads and thin ice areas, while it occurs in models at the much larger horizontal grid cell scale. Subgrid-scale parameterizations have hence been developed to mimic the effects of small-scale convection using a vertical distribution of the salt rejected by sea ice within the mixed layer, instead of releasing it in the top ocean layer. Such a brine rejection parameterization is included in the global ocean–sea ice model NEMO-LIM3. Impacts on the simulated mixed layers and ocean temperature and salinity profiles, along with feedbacks on the sea ice cover, are then investigated in both hemispheres. The changes are overall relatively weak, except for mixed layer depths, which are in general excessively reduced compared to observation-based estimates. While potential model biases prevent a definitive attribution of this vertical mixing underestimation to the brine rejection parameterization, it is unlikely that the latter can be applied in all conditions. In that case, salt rejections do not play any role in mixed layer deepening, which is unrealistic. Applying the parameterization only for low ice–ocean relative velocities improves model results, but introduces additional parameters that are not well constrained by observations.

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More information

Published date: February 2015
Keywords: Model, Brine rejection, Parameterization, Ocean mixed layer, Arctic, Antarctic
Organisations: Marine Systems Modelling

Identifiers

Local EPrints ID: 374890
URI: https://eprints.soton.ac.uk/id/eprint/374890
ISSN: 1463-5003
PURE UUID: 6f500bb5-4ff8-4e58-b77d-12a28af93d2a

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Date deposited: 04 Mar 2015 17:01
Last modified: 17 Jul 2017 21:22

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Contributors

Author: Antoine Barthélemy
Author: Thierry Fichefet
Author: Hugues Goosse
Author: Gurvan Madec

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