The National Snow and Ice Data Center (NSIDC) says the minimum, reached on 9 September, was 4.33 million sq km.
That value is 36% lower than the average minimum for 1979-2000.
NSIDC said the figure was preliminary, and that "changing winds could still push the ice extent lower" before final numbers are published in early October.
The preliminary value is 160,000 sq km - or 4% - above the record minimum seen in 2007.
"While the record low year of 2007 was marked by a combination of weather conditions that favoured ice loss - including clearer skies, favourable wind patterns and warm temperatures - this year has shown more typical weather patterns but continued warmth over the Arctic," they wrote.
"This supports the idea that the Arctic sea ice cover is continuing to thin."... Read more »