Author(s): Vernon Squire
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Abstract: The polar oceans continue to change, especially at the surface where air, sea and ice exchange heat and momentum. The mediterraneus Arctic sea-ice cover has thinned, adjusted from mostly perennial to seasonal ice, and reduced in extent to nearly 30% less at the end of a longer summer melt period when it now resembles a marginal ice zone (MIZ). Sea-ice is also more deformed, primary productivity has increased alongside ecosystem shifts, and swings in atmospheric circulation and northern hemisphere weather patterns have been observed. The dwindling ice cover has experienced heightened storm activity, such as arose during August 2012. Unquestionably, severe events now occur more often, but the combination of fiercer winds and increased (aggregated) open water fetches produces larger waves throughout the region as well, which then feed ice albedo-feedback by breaking up the sea-ice and bringing warm water into contact with ice floes. Antarctica, on the other hand, is a continent with 98% of its land blanketed by ice, encircled by an ocean that has almost its entire surface covered by seasonal sea-ice. While Antarctic terrestrial ice decreases at an accelerating rate – an average rate of 70 Gt/year, the continent’s surrounding sea-ice is actually increasing in extent despite the Southern Ocean warming faster than the rest of the world’s oceans (0.17°C per decade as opposed to 0.1°C). Undoubtedly complex, one probable cause is increased rain, snowfall and continental freshwater runoff freshening and stabilizing the surface waters so that mixing is undermined and less heat is transported upwards from the warmer deeper ocean to melt the sea-ice. Pervasive Southern Ocean waves supplement the ice growth, by breaking the floes up so that they are more mobile and the ensuing areas of open water can freeze over. Evidently global climate change helps ocean waves to exert a much greater contribution in all of the polar seas than ever before. Yet their impact is absent in contemporary ice/ocean models and OGCMs, just as a sea-ice parameterization is omitted from wave forecasting models such as Wavewatch III (R).
Year: 2014