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| Stef Lhermitte image published in Washington Post 9-25-17 |
Where are the pines on the Pine Island Glacier in West Antarctica? Of course, there aren’t any. The name comes from the US Navy ship Pine Island, which surveyed near this region during Operation High Jump in 1946.
What the Pine Island Glacier (PIG) does have is cracks in its seaward floating ice shelf. These cracks have become more frequently observed and have spawned large icebergs including one spotted in late September that amounts to one hundred square miles, dubbed B-44. Now, compared to the immense size of the Antarctic ice sheets, that’s puny. Don’t think that’s the issue. Rather it’s the role these ice shelves play as a throttle to the discharge of ice from the continent, and therefore how they affect sea level.
What’s the news about this? First some background. The PIG drains a significant portion of the West Antarctic Ice Sheet. A Wikipedia page gives all the details, but the amount of ice staged to flow from the PIG drainage is enough to raise global sea level an average of over one meter (4 feet). I have blogged about this region previously [May 20, 2014], reporting research that showed there are good reasons to believe the PIG system is nearly unstable or in fact unstable. What does stable/unstable mean? Simply, it means that the rate of discharge of ice from the glacial drainage equals the rate of input of ice and snow to the drainage area. Unstable means there is more rapid input than discharging output, or in the case we worry about, more rapid discharge than the input. That would mean rapid flow of ice off West Antarctica that will raise sea level.
One of the several means that control the discharge rate is the size of the floating ice shelves in front of the glacier. They serve to buttress the glacier and regulate the speed of advance, hence its discharge rate. What’s in fact happening is the PIG ice shelf front is retreating. One of the several means that control the discharge rate is the size of the floating ice shelves in front of the glacier. They serve to buttress the glacier and regulate the speed of advance, hence its discharge rate. What’s in fact happening is the PIG ice shelf front is retreating. Stef Lhermitte, at Delft University of Technology in the Netherlands, who noticed the latest calving or break-off in satellite images told the Washington Post; “It’s the fifth large calving event since 2000. This one and 2015, they were much further inland than the previous ones. So there has been a retreat of the calving front, specifically between 2011 and 2015.” With the ice shelf retreating, we can expect an increase in discharge.
But what about the Larsen ice shelf in the Antarctic Peninsula? That’s been breaking off also, and apparently at a high rate with bigger bergs. We’ve been reading about this over the past decade, most recently in July 2017 when Larsen C broke apart. Both ice shelves buttress the glaciers and ice sheets behind them but the Larsen blocks a small ice sheet on the Peninsula while the PIG throttles a significant portion, like ten percent, of the immense West Antarctic Ice Sheet.
Back in 2014, when I alerted followers to reports of the unstable condition of the PIG, it was acknowledged as a “looks like it” moment. Now, only three years later, it seems more certain that the drainage system of the PIG is in collapse. That’s bad news—a potential outcome worse than the damage we’ve seen for storm surges due to the monster hurricanes this summer (2017). Sea level rise is a permanent problem of our times. I hope some clever coastal engineers are on the job, figuring out how to face this challenge for the twenty-first century. But before they begin to build dikes and sea walls, it will be important to put a finer point on what to expect; sea level rise will differ from place to place. The California Ocean Protection Council recently published a good model for how to approach the science of sea level rise for that state. The April 2017 report for California is available from a link on their website.