One sure sign of Spring is the start of the annual sea ice melt in the Arctic Ocean.
The National Snow and Ice Data Center (NSIDC; http://nsidc.org/arcticseaicenews/) reported this week that the Arctic Ocean Sea Ice melt is now underway. Or, at least, that it looks like we've reached maximum sea ice extent. Next stop? Summer!
I love maps and graphs - data rock! Here is a map from the NSIDC showing maximum sea ice cover this winter.
The orange lines show the average extent of sea ice cover for the years 1979-2000. The white area shows the current sea ice extent with at least 15% sea ice cover.
This was an interesting sea ice year. If you look at the map you'll see that we have much more sea ice than average in the Bering Sea, west of Alaska and north of the Aleutians. At the same time there was not as much ice as usual in the Barents Sea north of Scandinavia and Russia. Remember the tough time ships had reaching Nome, AK, this year? That's because of all the sea ice.
So, how does this winter's maximum extent stack up against recent years?
2011-12 sea ice cover is shown in light blue in the graph above.
The maximum sea ice extent for this winter didn't reach historical averages...again. But this year it got within about 600,000 square kilometers of the 1979-2000 average sea ice maximum. Even so, the NSIDC reports that this year's sea ice extent is the 9th lowest sea ice extent reported since 1979. You might also be interested to know that all of the past nine years, 2004-2012, are the nine lowest sea ice maximum extents on record.
Here's what this means. First, less ice is forming now than it used to. Second, this means that the edges of the sea ice melts away from coastlines sooner, This makes it tougher for animals that need the pack ice to get there - like polar bears. This is especially tough on females and their young cubs. Mothers and cubs often aren't able to move far from the den and move out onto the ice until the ice melt is well underway. By this time bears often can't reach the ice pack unless they do a LOT of swimming. In recent years polar bears have been been seen swimming across huge stretches of open water. Bears have reportedly been spotted 100s of miles from land or ice...but this takes a toll, especially on cubs. Sadly, increasing numbers of cubs aren't making it...they fatigue and drown. It's even getting tougher for adults to make this kind of swim.
Photo - Eric LefrancPolar bear - Ursus maritimus - Olga Strait, Svalbard, Norway - Mother and cub trapped on a little ice floe drifting 12 miles from the nearest coast in Olga Strait. Polar bears are usually good swimmers however the cubs can not swim for so long and will probably not make it. (http://www.poyi.org/67/01/ae01.php)
"DISTRESSED POLAR BEARS"
"DISTRESSED POLAR BEARS"
Polar bears need to pack ice to hunt for their main prey - seals. The seals live on the ice year round and give birth to their pups in dens under the surface snow. This is what bears are looking for. But if the ice is too thin or short-lived both bears and seals have a hard time. And that's just the effect on these animals. A bigger effect is the role that sea ice plays in something called the albedo.
The albedo of an object refers to its ability to absorb or reflect light.
A perfectly black body will absorb all light that strikes it, and we see black. If it is perfectly white it will reflect all light and it looks brilliant white.
When the Arctic Ocean is covered by sea ice it is closer to white and reflects most of the light that strikes it. This keeps the Arctic colder than it would otherwise be, but, as the ice melts dark seawater is exposed, and because it is so dark it absorbs most of the light that strikes it. This can warm the water, melt more ice, and - worse case scenario, eventually warm the Arctic Ocean seafloor.
Why is this such a bid deal? Scientists have discovered that some areas of the Arctic Oceans sea floor is actually permafrost - frozen sediment - that contains methane hydrate. Methane hydrate is methane trapped in ice. Methane is a greenhouse gas. If the Arctic seafloor warms enough the methane will be released and the Arctic Ocean will "burp" methane into the atmosphere, accelerating warming even more.
This is a model of methane hydrate. The methane is the green and gray molecule in the middle, and the red and white molecules are water frozen into ice, trapping the methane inside.
Methane hydrate is really interesting stuff. It can, for example, burn...
The white stuff is ice, and the methane is released and burns as the ice melts. Similarly, methane will be released by sediments in the Arctic Ocean sea floor if the sediment warms enough for the ice to melt. This photo shows methane being released underwater.
Bears and ice and methane, oh my!