The Northern Passage has succeeded in its goal of sailing through the Northeast and Northwest Passages in the same summer season. The trip took a few days longer than planned, but reached Baffin Bay with at least two weeks to spare, as Arctic ice extent is almost the lowest it has ever been.
The journey is not over for the Northern Passage. It will be dodging icebergs for the next three days at it sails the length of Baffin Bay. It may then face the largest waves of its journey as it crosses from Greenland to Iceland and from there to the North Sea. This part of the trip may require quite a bit of sailing skill, but it is at least familiar territory for sailors.
The fall equinox happened a few days ago, and with it comes much shorter days and longer nights, which will eventually lead to new ice cover forming across the Arctic Ocean. First, though, the surface water temperatures have to decline. At this point, ice forms at night, but melts out completely during the day, at least on the warmer days. The melting process cools the ocean. Eventually, the daylight will not last long enough to melt the ice that forms at night, but with warmer ocean water, this may happen later this year than ever before.
This year’s summer ice extent was similar to the pattern of 2007, when the record low occurred, and 2008. The ice was thinner to begin with this season, and there was favorable weather for ice melt in the late spring. In particular, winds pushed most of the thickest ice toward the southernmost areas of the Arctic Ocean, near Alaska and Chukotka, where it melted out despite its thickness. This also means that next spring’s melt may again start with unusually thin ice. Large areas of the ocean were ice-free all summer, and surface water temperatures warmed to Pacific-like temperatures. This suggests that the Arctic Ocean stays cold in summer only because of melting ice, so that after the ice disappears, the ocean can take on properties similar to the neighboring areas of the Pacific Ocean.
One interesting thing to note is that this year’s September ice map has been more favorable for shipping than the record low extent map of September 2007. Indeed, the Northeast Passage was comfortably open for most of August and all of September this year, and freight traffic passed through routinely, though I don’t know how much cargo was carried. The Northwest Passage has been similarly open for about a month. Both passages are apparently still navigable for heavy ships. The scarcity of September ice in the southern Arctic could indicate that it is not so easy for the thinner ice now on the Arctic Ocean to drift south and clog shipping lanes.