From the AGU: Anthropogenically induced changes in winds in the Southern Hemisphere are playing a key role in recent warming of subsurface waters around Antarctica, according to a new study by Spence et al. The warming water increases melting of coastal glaciers and thus could affect sea levels in the future.
Since the 1950s, westerly winds in the Southern Hemisphere have been picking up and shifting poleward, due to anthropogenic global climate warming. The authors combined half a century of atmospheric data with a model of the coastal currents that shuttle water around Antarctic glaciers. Easterly winds create surface currents that pump cool fresh water downward, the authors demonstrated, keeping the temperatures at the bases of glaciers cool and pushing warm water away. But the westerly winds reduce these currents, and as a result, warm water creeps inward and upward toward the shore, where it heats up glaciers. Warm temperatures along grounding lines—where the glacier meets the ocean floor—especially increase melting.
The authors found that the changing westerly winds are responsible for an increase in water temperature of 2.5 °C on the western side of the Antarctic Peninsula, at critical depths of 200–700 meters. They calculated that the total heat increase in that region was enough to cause a sea level rise of 5.5 mm over the past 50 years (assuming that the grounded ice remains stationary). Based on the strong relationship between temperature increases and these winds, the authors think that current projections for sea level rise may be significantly underestimated.
Rapid subsurface warming and circulation changes of Antarctic coastal waters by poleward shifting winds
The southern hemisphere westerly winds have been strengthening and shifting poleward since the 1950s. This wind trend is projected to persist under continued anthropogenic forcing, but the impact of the changing winds on Antarctic coastal heat distribution remains poorly understood. Here we show that a poleward wind shift at the latitudes of the Antarctic Peninsula can produce an intense warming of subsurface coastal waters that exceeds 2°C at 200–700 m depth. The model simulated warming results from a rapid advective heat flux induced by weakened near-shore Ekman pumping and is associated with weakened coastal currents. This analysis shows that anthropogenically induced wind changes can dramatically increase the temperature of ocean water at ice sheet grounding lines and at the base of floating ice shelves around Antarctica, with potentially significant ramifications for global sea level rise.