Assessment of Southern Ocean water mass circulation and characteristics in CMIP5 models: Historical bias and forcing response

Sallee, J.-B.; Shuckburgh, E. ORCID: https://orcid.org/0000-0001-9206-3444; Bruneau, N.; Meijers, AJ.S. ORCID: https://orcid.org/0000-0003-3876-7736; Bracegirdle, T.J. ORCID: https://orcid.org/0000-0002-8868-4739; Wang, Z.; Roy, T.. 2013 Assessment of Southern Ocean water mass circulation and characteristics in CMIP5 models: Historical bias and forcing response. Journal of Geophysical Research: Oceans, 118 (4). 1830-1844. 10.1002/jgrc.20135

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Abstract/Summary

The ability of the models contributing to the fifth Coupled Models Intercomparison Project (CMIP5) to represent the Southern Ocean hydrological properties and its overturning is investigated in a water mass framework. Models have a consistent warm and light bias spread over the entire water column. The greatest bias occurs in the ventilated layers, which are volumetrically dominated by mode and intermediate layers. The ventilated layers have been observed to have a strong fingerprint of climate change and to impact climate by sequestrating a significant amount of heat and carbon dioxide. The mode water layer is poorly represented in the models and both mode and intermediate water have a significant fresh bias. Under increased radiative forcing, models simulate a warming and lightening of the entire water column, which is again greatest in the ventilated layers, highlighting the importance of these layers for propagating the climate signal into the deep ocean. While the intensity of the water mass overturning is relatively consistent between models, when compared to observation-based reconstructions, they exhibit a slightly larger rate of overturning at shallow to intermediate depths, and a slower rate of overturning deeper in the water column. Under increased radiative forcing, atmospheric fluxes increase the rate of simulated upper cell overturning, but this increase is counterbalanced by diapycnal fluxes, including mixed-layer horizontal mixing, and mostly vanishes.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	10.1002/jgrc.20135
Programmes:	BAS Programmes > Polar Science for Planet Earth (2009 - ) > Climate BAS Programmes > Polar Science for Planet Earth (2009 - ) > Polar Oceans
ISSN:	21699275
Additional Keywords:	Southern Ocean, water mass, overturning, CMIP5
Date made live:	22 May 2013 11:09 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/502031

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