720 sq km Ice Block Falls Off Antarctica

The Pine Island Glacier, in West Antarctica, drains (as ice and water) a measurable percent of the West Antarctic Ice Sheet. It is probably the case that glaciers in this area of the Antarctic contribute more of the ice to water transition than any other glacial region in the world, so how they melt is of great interest. And now, Pine Island Glacier has given birth!

In October 2011 a large crack started to form across the glacier, downstream from its grounding line. Over the last few days, it seems, this crack finally transected the entire glacier, causing the down-stream side of it to become a 720 square kilometer ice berg. That is nothing like the largest ice berg ever (that would be B-15, which calaved in March 2000, at 11,000 square kilometers, and still melting).

Is this important?

The calving of an ice flow like this, in and of itself, is normal. Glaciers in the interior of Antarctica grow because more snow falls than melts/evaporates. The weight of this ice pushes the glaciers downstream in giant frozen rivers. Somewhere along the way, beneath these giant rivers of ice, we often find water for a long distance, then a "grounding line" where the ice touches the surface of the earth. Beyond the grounding line there is an "ice shelf" of floating ice (not the same thing as sea ice) that can extend a pretty good distance into the sea. Every now and then a large piece of one of these shelves breaks off, like just happened in this case, and floats off into the sea.

This is important because the calving of giant ice bergs beyond grounding lines of huge glacial rivers is part of the process of the ice to sea transition that is constantly going on with glaciers. Glaciers also have smaller scale calving of ice bergs, and plain old melting especially during warm months. All these things together make up the melting half of the formula for glaciers, the other half of the formula being the formation of new ice on glacial surfaces.

We assume the worlds' glaciers are all either melting or going to melt to some degree because of increased temperatures due to anthropogenic global warming, and this assumption is born out by the fact that so many glaciers are getting smaller. The balance of new ice and melted ice is generally, but not always, in the direction of overall reduced ice. This contributes additional water to the world's oceans, and is a major (and growing) contributor to global sea level rise. Global sea level rise may be the most important negative outcome of anthropogenic climate change, given that so many people live near the sea, and in fact, a lot of the world's agriculture is carried out at relatively low elevation. Also, storms that flood the coast do more flooding when the sea level rises, with storm surges taking modest (a few inches here, a few inches there) rises in sea level to create much higher levels of inundation.

One problem we have is that modeling of future glacial melt is very difficult, and many feel that we are pretty much in the dark as to how fast glaciers will melt given various warming scenarios.

So, the Pine Island Glacier calving event that just happened is an important data point to add to the other large scale events to try to understand the rate of glacier melt.

There is a serious concern when it comes to Pine Island Glacier and similar systems, like the much larger nearby Thwaites Glacier. The two of these impound about 20% of the water in the West Antarctic Ice Sheet, which in turn is between 8 and 9 meters of sea level rise were it all to melt. This has to do with a complex interaction between glacial geometry, movement, and the presence of water underneath the ice that provides lubrication for this movement. Some time ago one researcher called the Thwaites and Pine Island glaciers the "weak underbelly" of the Antarctic glacial system. Very briefly, and I oversimplify, the shapes of these two glacial basins is such that they are more likely than other glaciers to speed up their march to the sea, to well exceed their growth from fresh precipitation. This problem is summarized in detail HERE, and recent research confirming that we should be concerned about this is to be found HERE.

So, this is an interesting event, and it might be a very important event. I'll report back after digesting reaction and commentary by glacier experts over the next few days.

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