Recent water mass changes reveal mechanisms of ocean warming

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Authors

Jan Zika , Jonathan Gregory, Elaine McDonagh, Alice Marzocchi, Louis Clement

Abstract

Over 90% of the build up of additional heat in the earth system over recent decades is contained in the ocean. Since 2006 new observational programs have revealed heterogeneous patterns of ocean heat content change. It is unclear how much of this heterogeneity is due to heat being added to and mixed within the ocean leading to material changes in water mass properties or due to changes in circulation which redistribute existing water masses. Here we present a novel diagnosis of the ‘material’ and ‘redistributed’ contributions to regional heat content change between 2006 and 2017 based on water mass theory. We show that material warming has large spatial coherence. The material change tends to be smaller than the redistributed change at any geographical location, however it sums globally to the net warming of the ocean, while the redistributed component sums, by design, to zero. Material warming is robust over the time period of this analysis, whereas the redistributed signal only emerges from the variability in a few regions. In the North Atlantic, water mass changes indicate substantial material warming while redistribution cools the subpolar region due to a slowdown in the Meridional Overturning Circulation. Warming in the Southern Ocean is explained by material warming and by anomalous southward heat transport of 118 +/- 50 PW due to redistribution. Our results suggest near term projections of ocean heat content change and therefore sea level change will hinge on understanding and predicting changes in ocean redistribution.

DOI

https://doi.org/10.31223/osf.io/npxkb

Subjects

Climate, Oceanography, Oceanography and Atmospheric Sciences and Meteorology, Physical Sciences and Mathematics

Keywords

climate change, Decadal variability, Ocean heat uptake, Ocean temperature change, Water masses, water mass transformation

Dates

Published: 2020-05-19 18:35

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License

GNU Lesser General Public License (LGPL) 2.1

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