Southern Ocean Heat Uptake, Redistribution, and Storage in a Warming Climate: The Role of Meridional Overturning Circulation

Journal Article · Fri Jun 01 00:00:00 EDT 2018 · Journal of Climate

DOI:https://doi.org/10.1175/JCLI-D-17-0761.1· OSTI ID:1437880

Liu, Wei ^[1]; Lu, Jian ^[2]; Xie, Shang-Ping ^[3]; Fedorov, Alexey ^[4]

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1. Department of Earth Sciences, University of California, Riverside, Riverside, and Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, and Department of Geology and Geophysics, Yale University, New Haven, Connecticut
2. Pacific Northwest National Laboratory, Richland, Washington
3. Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California
4. Department of Geology and Geophysics, Yale University, New Haven, Connecticut

Climate models show that most of the anthropogenic heat resulting from increased atmospheric CO ₂ enters the Southern Ocean near 60°S and is stored around 45°S. This heat is transported to the ocean interior by the meridional overturning circulation (MOC) with wind changes playing an important role in the process. To isolate and quantify the latter effect, we apply an overriding technique to a climate model and decompose the total ocean response to CO ₂ increase into two major components: one due to wind changes and the other due to direct CO ₂ effect. We find that the poleward-intensified zonal surface winds tend to shift and strengthen the ocean Deacon cell and hence the residual MOC, leading to anomalous divergence of ocean meridional heat transport around 60°S coupled to a surface heat flux increase. In contrast, at 45°S we see anomalous convergence of ocean heat transport and heat loss at the surface. As a result, the wind-induced ocean heat storage (OHS) peaks at 46°S at a rate of 0.07 ZJ yr ⁻¹ (° lat) ⁻¹ (1 ZJ = 10 ²¹ J), contributing 20% to the total OHS maximum. The direct CO ₂ effect, on the other hand, very slightly alters the residual MOC but primarily warms the ocean. It induces a small but nonnegligible change in eddy heat transport and causes OHS to peak at 42°S at a rate of 0.30 ZJ yr ⁻¹ (° lat) ⁻¹ , accounting for 80% of the OHS maximum. We also find that the eddy-induced MOC weakens, primarily caused by a buoyancy flux change as a result of the direct CO ₂ effect, and does not compensate the intensified Deacon cell.

• Sponsoring Organization: USDOE
• Grant/Contract Number: SC0016538
• OSTI ID: 1437880
• Journal Information: Journal of Climate, Journal Name: Journal of Climate Vol. 31 Journal Issue: 12; ISSN 0894-8755
• Publisher: American Meteorological Society
• Country of Publication: United States
• Language: English