While the world’s oceans warmed, the Southern Ocean around Antarctica cooled between 1982 and 2005 — an anomaly that intrigued climatologists. A new modeling study published in Geophysical Research Letters reveals the unexpected culprit: the hole in the ozone layer, which modified the winds and cooled the ocean from the stratosphere.
An unexplained climate anomaly for decades
While almost all of the planet’s surface oceans were warming under the effect of greenhouse gases, the waters surrounding Antarctica showed a tendency to cool between the late 20th and early 21st centuries. This period even coincided with an expansion of the Antarctic sea ice — against the current of all other global trends.
A new study by Shouwei Li of Princeton University, published in Geophysical Research Letters, identifies a key mechanism behind this anomaly: the depletion of the stratospheric ozone layer over Antarctica, caused by human-made chemicals released in the 20th century.
From the stratosphere to the surface of the ocean
The hole in the ozone layer cools the lower stratosphere and modifies the temperature difference between the poles and the tropics. These temperature variations reinforce the powerful westerly winds that encircle Antarctica and bring them closer to the continent.
This strengthening of the winds is not confined to the atmosphere. It modifies the transport of Ekman – a phenomenon where surface water is pushed by the wind and slightly defleted by the rotation of the Earth. In the southern hemisphere, stronger westerly winds push surface waters northward, moving cold waters away from Antarctica and dispersing them further. Result: the surface of the Southern Ocean cools.
source : science post
