Over the past three decades, the depths of the Antarctic Weddell Sea have warmed five times faster than the rest of the ocean at depths exceeding 2,000 meters. This was the main finding of an article just published by oceanographers from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI). In the article, they analyze an unprecedented oceanographic time series from the Weddell Sea and show that the warming of the polar depths is chiefly due to changed winds and currents above and in the Southern Ocean. In addition, the experts warn that the warming of the Weddell Sea could permanently weaken the overturning of tremendous water masses that takes place there—with far-reaching consequences for global ocean circulation. Their study was just released on the online portal of the Journal of Climate.

Only the water below 700 meters is growing warmer

Their findings are surprising. “Our data shows a clear division in the water column of the Weddell Sea. While the water in the upper 700 meters has hardly warmed at all, in the deeper regions we’re seeing a consistent temperature rise of 0.0021 to 0.0024 degrees Celsius per year,” says Dr. Volker Strass, an AWI oceanographer and the study’s first author.

These values may seem minuscule at first glance. But, as Strass explains, “Since the ocean has roughly 1,000 times the heat capacity of the atmosphere, these numbers represent an enormous scale of heat absorption. By using the temperature rise to calculate the warming rate in watts per square meter, you can see that over the past 30 years, at depths of over 2,000 meters the Weddell Sea has absorbed five times as much heat as the rest of the ocean on average.” Through the formation of bottom water in the Weddell Sea, this heat is then distributed to the deep basins of the world’s oceans.