Arctic sea ice may have started rebuilding after reaching a record low, according to the US National Snow and Ice Data Centre.
Arctic ice now covers 1.61 million square miles, the agency said, up from 1.59 million on September 16, which appears to have been the minimum.
Some variability could still occur, however, the agency cautioned.
The previous record low for Arctic sea ice was 2.1 million square miles set on September 20-21, 2005, and the average low at the end of a summer melt is 2.6 million square miles.
The Northwest Passage between the Atlantic and Pacific oceans along the coasts of Canada and Alaska remains open but is starting to re-freeze, the centre said.
The Northeast Passage along the coast of Siberia is closed by ice, according to the research cooperative.