Study projects major decline of Antarctic sea ice

Meltdown likely to have serious impacts on marine life

How long will Antarctic sea ice persist? bberwyn photo.

Staff Report

*Adapted from a Virginia Institute of Marine Science press release. More Summit Voice stories on sea ice here.

FRISCO — While global warming deniers try to divert attention from the building climate crisis by pointing at record-high Antarctic sea ice extent, a new study suggests much of that ice will soon melt away.

Plugging projected increases in Antarctic air temperatures into finely scaled models, the scientists said the Ross Sea could lose more than half its summer ice by 2050 and more than 75 percent by 2100.

The changes likely will take a toll on marine life in one of the world’s most productive and unspoiled ecosystems, according to Professor Walker Smith of the Virginia Institute of Marine Science.

The recent increase in Antarctic sea ice extent is probably the result of shifting wind patterns in the southern hemisphere. Some recent studies have shown that, while sea ice extent has increased around parts of Antarctica — including the Ross Sea — it has dwindled in other areas. Other factors include changes in precipitation, salinity, ocean currents, and air and water temperature.

But as air temperatures in the region warm, the end result will be a meltdown of sea ice, according to the new model projects. The ice-free season is also projected to lengthen, with the mean day of retreat in 2100 occurring 11 days earlier and the advance occurring 16 days later than now.

Smith, who has been conducting ship-based fieldwork in the Ross Sea since the 1980s, collaborated on the study with colleagues at Old Dominion University. Their paper, “The effects of changing winds and temperatures on the oceanography of the Ross Sea in the 21st century,” appears in the Feb. 26 issue of Geophysical Research Letters. Smith’s co-authors are Mike Dinniman, Eileen Hofmann, and John Klinck.

“The Ross Sea is critically important in regulating the production of Antarctica’s sea ice overall and is biologically very productive, which makes changes in its physical environment of global concern,” Smith said.

“Our study predicts that it will soon reverse its present trend and experience major drops in ice cover in summer, which, along with decreased mixing of the vertical column, will extend the season of phytoplankton growth. These changes will substantially alter the area’s pristine food web.”

The projected changes will affect the zone where most phytoplankton live.

“Our model projects that the shallow mixed layer will persist for about a week longer in 2050, and almost three weeks longer in 2100 than now,” Smith said. “The depth of the shallow mixed layer will also decrease significantly, with its bottom 12 percent shallower in 2050, and 44 percent shallower in 2100 than now.”

The drop in ice cover will negatively affect several other important species that are ice-dependent, including crystal krill and Antarctic silverfish. A decrease in krill would be particularly troublesome, as these are the major food source for the Ross Sea’s top predators — minke whales, Adélie and Emperor penguins, and crabeater seals.

The decrease in ice cover could also help spur production of phytoplankton, potentially increasing bioproductivity.

“Our results suggest that phytoplankton production will increase and become more diatomaceous,” Smith said. “Other components of the Ross Sea food web will likely be severely disrupted, creating significant but unpredictable impacts on the ocean’s most pristine ecosystem.”


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