2020
DOI: 10.1029/2019av000132
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Sea‐Ice Induced Southern Ocean Subsurface Warming and Surface Cooling in a Warming Climate

Abstract: Much of the Southern Ocean surface south of 55°S cooled and freshened between at least the early 1980s and the early 2010s. Many processes have been proposed to explain the unexpected cooling, including increased winds or freshwater fluxes. However, these mechanisms so far failed to fully explain the surface trends and the concurrent subsurface warming (100 to 500 m). Here, we argue that these trends are predominantly caused by an increased wind-driven northward sea-ice transport, enhancing the extraction of f… Show more

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Cited by 53 publications
(50 citation statements)
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References 86 publications
(226 reference statements)
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“…Current models and observations indicate that the Southern Ocean is freshening (Haumann et al, 2016(Haumann et al, , 2020. Even though the ML may become shallower as it becomes fresher, it is likely that MLI will persist (Callies & Ferrari, 2018), and the dynamics described here will continue to be relevant.…”
Section: Discussionmentioning
confidence: 78%
“…Current models and observations indicate that the Southern Ocean is freshening (Haumann et al, 2016(Haumann et al, , 2020. Even though the ML may become shallower as it becomes fresher, it is likely that MLI will persist (Callies & Ferrari, 2018), and the dynamics described here will continue to be relevant.…”
Section: Discussionmentioning
confidence: 78%
“…this being suggested to be related to strengthening winds and associated sea ice transport (Haumann et al, 2020). Below this near-surface layer, at the 55-65°S latitudes important for krill, there has been a continuation of the longer term warming since the 1980s, albeit with little change below 200 m (Haumann et al, 2020).…”
Section: Discussionmentioning
confidence: 97%
“…This freshening together with a very small warming ( Figure 12) decreases surface density (Figure 12d) and increases the vertical stratification of the upper water column as expressed by the squared Brunt-Väisälä frequency (Figure 12c). This increase in the stratification reduces the transport and mixing of subsurface waters, which usually carry saltier and warmer waters toward the surface, where they are cooled by the atmosphere and freshened by an excess of freshwater input from the atmosphere and the melting of sea ice (Haumann et al, 2020). Through the reduction in this upward transport and mixing, the increased stratification leads to a buildup of positive anomalies in temperature (up to 1.5°C; Figure 12a) and in salinity (up to 0.1 psu; Figure 12b) below~75 m. These anomalies tend to compensate each other in terms of their effect on subsurface density (Figures 12d-12f).…”
Section: Global Biogeochemical Cyclesmentioning
confidence: 99%