Strong westerly winds around the South Pole account for an 80 percent increase in sea ice volume over the past three decades.
The Arctic’s melting sea ice has received much attention of late, but less clear is the situation occurring in Antarctica. Despite increasing air and ocean temperatures, Antarctica’s current sea ice situation is set to hit a record high this year – a fact emphasized by global warming skeptics.
Weather changes have likely played a large role in some of the recent, short-term changes in sea ice. However, new research from the University of Washington suggests that wind changes have led to an upward sea ice trend. The new modeling study, set to be published in the Journal of Climate, reveals that stronger polar winds result in an increase in Antarctic sea ice, in spite of a warming climate.
Jinlun Zhang, an oceanographer at the UW Applied Physics Laboratory, led the study, which shows that strong westerly winds around the South Pole account for an 80 percent increase in sea ice volume over the past three decades.
The polar vortex is not only stronger than it was in the 1970s, it also has more convergence. This results in ridging, as the sea ice is shoved together. Stronger winds are also responsible for driving ice faster, further contributing to more deformation and ridging, and creating thicker, longer-lasting ice. The surrounding water and thin ice is exposed to blistering cold winds, which in turn causes more ice growth.
A computer simulation detailing interactions between the wind and sea reveals that the ice has increased at a rate of about one percent per year from 1979 to 2010. The amount of thin ice, on the other hand, has stayed relatively constant. The end result is a thicker, larger ice pack, which lasts long into the summer.
When polar winds were held at a constant level, increases in sea ice were a fifth of what they were. Previous studies indicate that the remaining increase could be explained by changes in water density.
Funded by the National Science Foundation, this is the first model experiment that confirms the possible link between wind and the expansion of Antarctic sea ice.
It is still unknown why the southern winds have been getting stronger. Some researchers have hypothesized that it’s a result of global warming, while others suggest that ozone depletion or natural variability is responsible.
Differences between the two poles could explain the variations in behavior. The Arctic appears to be experiencing more uniform surface air warming, and its northern water is in a fairly protected basin. Meanwhile, Antarctic sea ice is exposed in open oceans, where it can freely expand in the winter and melt away in the summer.
Eventually, if warmer temperatures continue, this apparent contradiction will be resolved.