Surface Heat Fluxes Drive a Two‐Phase Response in Southern Ocean Mode Water Stratification

Pimm, Ciara ORCID: 0009-0002-5591-0709, Williams, Richard G ORCID: 0000-0002-3180-7558, Jones, Dani ORCID: 0000-0002-8701-4506 and Meijers, Andrew JS ORCID: 0000-0003-3876-7736 (2024) Surface Heat Fluxes Drive a Two‐Phase Response in Southern Ocean Mode Water Stratification. Journal of Geophysical Research: Oceans, 129 (3).

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Official URL: http://dx.doi.org/10.1029/2023jc020795

Abstract

<jats:title>Abstract</jats:title><jats:p>Subantarctic mode waters have low stratification and are formed through subduction from thick winter mixed layers in the Southern Ocean. To investigate how surface forcing affects the stratification in mode water formation regions in the Southern Ocean, a set of adjoint sensitivity experiments are conducted. The objective function is the annual‐average stratification over the mode water formation region, which is evaluated from potential temperature and salinity adjoint sensitivity experiments. The analysis of impacts, from the product of sensitivities and forcing variability, identifies the separate effects of the wind stress, heat flux, and freshwater flux, revealing that the dominant control on stratification is from surface heat fluxes, as well as a smaller effect from zonal wind stress. The adjoint sensitivities of stratification to surface heat flux reveal a surprising change in sign over 2 years lead time: surface cooling leads to the expected initial local decrease in stratification, but there is a delayed response leading to an increase in stratification. This delayed response in stratification involves effective atmospheric damping of the surface thermal contribution, so that eventually the oppositely‐signed advective haline contribution dominates. This two‐phase response of stratification is found to hold over mode water formation regions in the South Indian and Southeast Pacific sectors of the Southern Ocean, where there are strong advective flows linked to the Antarctic Circumpolar Current.</jats:p>

Item Type:	Article
Divisions:	Faculty of Science and Engineering > School of Environmental Sciences
Depositing User:	Symplectic Admin
Date Deposited:	15 Mar 2024 17:43
Last Modified:	15 Mar 2024 17:43
DOI:	10.1029/2023jc020795
Open Access URL:	https://agupubs.onlinelibrary.wiley.com/doi/epdf/1...
Related URLs:	Publisher
URI:	https://livrepository.liverpool.ac.uk/id/eprint/3179440