Washington, Oct 7 (IANS): The extent of sea ice covering the Arctic Ocean has dipped to the second-lowest level, narrowly missing a new record low, said satellite data from NASA.

The Arctic ice cap grows each winter as the sun sets for several months and shrinks each summer as the sun rises higher.

Each year it reaches its annual minimum extent in September. It hit a record low in 2007.

The near-record ice-melt followed higher-than-average summer temperatures, but without the unusual weather conditions that contributed to the extreme melt of 2007.

Sea ice "area" differs from the extent in that it equals the actual surface area covered by ice, while extent includes any area where ice covers at least 15 percent of the ocean.

Arctic sea ice extent Sep 9, the lowest point this year, was 4.33 million square km. Averaged over the month of September, ice extent was 4.61 million square km.

"Atmospheric and oceanic conditions were not as conducive to ice loss this year, but the melt still neared 2007 levels," said Walt Meier of the National Snow and Ice Data Center (NSIDC), University of Colorado, Boulder.

"This probably reflects loss of multi-year ice in the Beaufort and Chukchi seas as well as other factors that are making the ice more vulnerable," added Meier.

The continued low minimum sea ice levels fit into the large-scale decline pattern that scientists have watched unfold over the past three decades, according to an NSIDC statement.

"The sea ice is not only declining, the pace of the decline is becoming more drastic. The older, thicker ice is declining faster than the rest, making for a more vulnerable perennial ice cover," said Joey Comiso, senior scientist at NASA's Goddard Space Flight Centre.

This places 2011 as the second lowest ice extent both for the daily minimum extent and the monthly average. Ice extent was 2.43 million square km below the 1979 to 2000 average.