Vertical ocean heat redistribution sustaining sea-ice concentration trends in the Ross Sea

Abstract

Several processes have been hypothesized to explain the slight overall expansion of Antarctic sea ice over the satellite observation era, including externally forced changes in local winds or in the Southern Ocean’s hydrological cycle, as well as internal climate variability. Here, we show the critical influence of an ocean–sea-ice feedback. Once initiated by an external perturbation, it may be sufficient to sustain the observed sea-ice expansion in the Ross Sea, the region with the largest and most significant expansion. We quantify the heat trapped at the base of the ocean mixed layer and demonstrate that it is of the same order of magnitude as the latent heat storage due to the long-term changes in sea-ice volume. The evidence thus suggests that the recent ice coverage increase in the Ross Sea could have been achieved through a reorganization of energy within the near-surface ice-ocean system.

Tropical Teleconnections to Antarctic Sea Ice During Austral Spring 2016 in Coupled Pacemaker Experiments

“…The positive ice ocean feedback involving the vertical redistribution of heat and salt between the surface and subsurface proposed by Lecomte et al (2017) raises the possibility that it may be necessary to simulate the multidecadal increase in sea ice around Antarctica to capture the magnitude of the abrupt 2016 decline.…”

Southern Ocean Warming

“…In addition, ocean warming accelerates melt of Antarctic ice shelves (Schmidtko et al, 2014), threatening the stability of the Antarctic ice sheet (Paolo et al, 2015), with global implications in terms of sea level rise (Hellmer et al, 2012). Melt of the ice sheet also means that freshwater input onto the ocean surface is increased, which stabilizes the ocean surface and can feed back on heat uptake (Lecomte et al, 2017).…”

“…Surface water conditions are therefore associated with a cooling of the surface layer, and a circumpolar-scale increase in sea ice extent (Cavalieri and Parkinson, 2008;Comiso, 2010;Vaughan et al, 2013). In addition, the reduced entrainment and mixing of surface waters with underlying warmer waters causes heat to accumulate beneath the surface layer (Schmidtko et al, 2014;Lecomte et al, 2017). Near the continental slope and shelf, observations also suggest that the surface layer shoals, allowing the relatively warm CDW to reach the continental shelves (Schmidtko et al, 2014;process [5] in Figure 1).…”

“…The weak warming of the southernmost surface region of the Southern Ocean is consistent with the observed and concomitant increase of Antarctic sea ice area (Vaughan et al, 2013). South of the Antarctic Circumpolar Current, the paucity of observations under the surface layer discourages any comment on longterm change, but there is some suggestion that heat might have accumulated right below the surface layer (Lecomte et al, 2017). Close to the Antarctic continent, over the continental shelf and slope, there are indications that the old and relatively warm waters (CDW; see Figure 1) have slightly warmed over the past decades, associated with a shoaling of the upper layer, which allowed CDW greater access to continental shelves (Schmidtko et al, 2014).…”

“…Near-surface stratification has increased due to a decrease in surface salinity south of the Antarctic Circumpolar Current at the circumpolar scale (de Lavergne et al, 2014;Lecomte et al, 2017), associated with ice shelf melt and/ or a sea ice regime change that releases freshwater in the surface layer (Jacobs, 2006;Haumann et al, 2016). Increased near-surface stratification (process [1] in Figure 1) reduces intrusion of the relatively warm CDW into the surface layer.…”