Each winter, wide swaths（细长的列） of the Arctic Ocean freeze to form sheets of sea ice that spread over millions of square miles. This ice acts as a massive sun visor（遮阳板） for Earth, reflecting solar radiation and shielding the planet from excessive warming. The Arctic ice cover reaches its peak each year in mid-March, before shrinking with warmer spring temperatures. But over the last three decades, this winter ice cap has shrunk: Its annual maximum reached record lows, according to satellite observations, in 2007 and again in 2011.

 

Understanding the processes that drive sea-ice formation and advancement¹ can help scientists predict the future extent of Arctic ice coverage² -- an essential factor in detecting climate fluctuations³（波动） and change. But existing models vary in their predictions for how sea ice will evolve.

 

Now researchers at MIT have developed a new method for optimally⁴ combining models and observations to accurately⁵ simulate the seasonal⁶ extent of Arctic sea ice and the ocean circulation beneath. The team applied⁷ its synthesis method to produce a simulation of the Labrador Sea, off the southern coast of Greenland, that matched actual satellite and ship-based observations in the area.

 

Through their model, the researchers identified an interaction between sea ice and ocean currents that is important for determining what's called "sea ice extent" -- where, in winter, winds and ocean currents push newly formed ice into warmer waters, growing the ice sheet. Furthermore, springtime ice melt may form a "bath" of fresh seawater more conducive⁸ for ice to survive the following winter.

 

Accounting⁹ for this feedback phenomenon is an important piece in the puzzle to precisely¹⁰ predict sea-ice extent, says Patrick Heimbach, a principal research scientist in MIT's Department of Earth, Atmospheric¹¹ and Planetary Sciences.

 

"Until a few years ago, people thought we might have a seasonal ice-free Arctic by 2050," Heimbach says. "But recent observations of sustained ice loss make scientists wonder whether this ice-free Arctic might occur much sooner than any models predict … and people want to understand what physical processes are implicated¹² in sea-ice growth and decline."

 

Heimbach and former MIT graduate student Ian Fenty, now a postdoc at NASA's Jet Propulsion Laboratory, will publish a paper, "Hydrographic Preconditioning for Seasonal Sea Ice Anomalies in the Labrador Sea," in the Journal of Physical Oceanography.

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