Arctic sea ice cover passes winter maximum

The extent of the Arctic sea ice cover reached its maximum winter area on March 15 and is now beginning to shrink as the region enters the warming phase of the year, the National Snow and Ice Data Center, or NSIDC, has reported. The maximum extent of 5.84 million square miles was the sixth lowest recorded since satellite ice observations began in 1979.

An analysis of the average March ice extent each year since 1979 continues to show a long-term decline in the ice cover at a rate of 2.5 percent per decade.

The fact that this year’s maximum ice extent is not at a record low level, despite an extreme, record low extent recorded in September, results from the fastest growth in ice cover ever recorded between the fall ice cover minimum and the late winter ice maximum. However, the ice resulting from this growth spurt is thin, new ice, with some thicker multiyear ice being lost as it drifted out of the Arctic, the NSIDC said. The result is a record extent of first-year sea ice in the Arctic region.

“The boundary between primarily first-year ice and multiyear ice is now near the North Pole, marking the first time since the winter of 2008 that a substantial amount of first-year ice may be covering the pole as we enter the melt season,” the NSIDC said.

Thin first-year ice disappears more rapidly than thick multiyear ice during the summer ice melt, so that high levels of first-year ice in the Arctic Ocean tend to accelerate the melting process.

NSIDC said that in March unusually high air pressure over much of the Arctic Ocean, in a phenomenon known as a negative Arctic oscillation, resulted in wind patterns that have caused fracturing of the ice cover in the Beaufort and Chukchi seas.

—Alan Bailey