NOAA: Multi Year Ice Disappearing
October 11, 2011
I’ve been using Jim Maslanik’s animation on this for several years. Now, he’s updated it.
Watch several decades worth of ice thickness data, as the oldest, thickest ice – the whitest shade, is steadily broken down and flushed out of the arctic, to disappear in the open ocean. The pulsing of the winter to summer cycle is like the beating of a cold polar heart.
The Arctic Ocean is virtually surrounded by land. The blanket of sea ice that forms there during the winter isn’t completely free to drift away into warmer, southern waters. Because of that geography, it’s common for sea ice to linger for many years at high latitudes, growing thicker and stronger, which makes it more likely to survive the summer melt. Or at least, itused to be common.
The animation above shows how dramatically the amount of multi-year ice (ice that has survived at least one summer melt season) in the Arctic has decreased over the past two decades. Based on satellite tracking of ice parcels over time, the maps show the estimated age of sea ice once a week from January 1987 through mid-summer 2011. Ice age increases from darkest blue (1 year old) to white (9 or more years old).
At the outermost edges of the ocean basin, the ice is seasonal: it forms every winter and melts every summer. Off the northeast coast of Greenland, a river of old ice continually flows out of the Arctic through the Fram Strait into warmer waters. Natural climate patterns accelerate the loss in some years and slow it down in others.
Historically, that ice river was the major route by which the Arctic lost its very old ice. The export was balanced by ocean currents and wind patterns on the other side of the Arctic. Young sea ice gets caught up in the giant loop current called the Beaufort Gyre. The ice could remain in the gyre for years, circling around and around the central Arctic through the Beaufort and Chuchki Seas, growing thicker. The Beaufort Gyre was an incubator for growing multi-year ice.
Since the late 1990s, however, the ice traveling through the southern part of the gyre rarely survives the summer melt. In other words, sea ice gets far less time in the incubator. In the mid-1980s, roughly 75 percent of the Arctic ice pack at the yearly maximum in March had survived at least one summer melt season; today only 45 percent has. Since the record low sea ice extent that occurred in summer 2007, no very old ice (9 or more years old) is left in the central Arctic basin. Only a thin ribbon remains tucked up against the islands of the Canadian Arctic.
The loss of the multi-year ice is both a result of climate change and, ultimately, an accelerator of it. The less old ice there is in the ice pack, the more easily the ice melts in the summer. The more ice that melts, the more of the ocean that’s exposed to the 24-hour summer Sun. Bright white ice reflects incoming sunlight, but dark ocean water absorbs it, heating the ocean and accelerating warming.