Today, we’re going to talk about ice tongues, and why they are critical in our warming climate. Petermann glacier ends in an ice tongue, and this is why us oceanographers are going on that cruise. I apologise before you read – I’m quite tired, so the quality of today’s post will probably not be great (this is also why it is only written today, and not a few days ago). Anyway, first of all: what is an ice tongue?
An ice tongue is a relatively long and narrow strip of ice that comes from a glacier when it flows out. Note that it is not sea ice, which is frozen ocean water. The ice tongue is made of old snow, compacted into ice with time, which travelled from the Greenland continent to end up floating above the ocean.
Petermann ice tongue is 70 km long for 15 km wide (which apparently gives an area slightly larger than that of Berlin), and its thickness varies from 600 m at the grounding line to 80 km at the end. The grounding line is where the ice tongue starts floating, see schematic below:
Ice tongues are being studied because they suffer from global warming. They are sensitive to the heat from above (atmosphere) and below (ocean), so if any of these increases, the ice tongues melt or calve. By going to Petermann this summer, we will be able to tell what the ocean and atmosphere are doing to the ice tongue, and that could explain why Petermann’s has shortened so much over the last years.
This is actually how I ended up on that cruise. In fact, I am not working on the high Arctic. I am interested in the Labrador Sea, that lies at the southern tip of Greenland. But in 2010, about 25% of Petermann ice tongue broke off into a single ice island, which then travelled all the way south to the Labrador Sea (you should read Andreas’s post about it). Another large ice island broke off again in 2012, and again last year. And that, dear reader, is a problem. The ice tongue is already floating on the ocean, so breaking it in bits is not going to raise the sea level. Melting said bits does worsen sea level rise though, because fresh water takes more room than salty water. And melting said bits in the Labrador Sea results in increased risks (flooding and sea ice) for the people who live and work there, be it for the fishing industry, marine transport or off-shore platforms. But worse: by melting there, it could potentially stop, or at least totally modify, the whole global ocean circulation, and hence seriously disturb our climate. That’s what I am meant to work out in the next three years, so I’ll have plenty of opportunities to tell you more about it!
I will probably not write until I am packing for the cruise. Which in fact is very soon, just over a week now. I’ve gone shopping for the tools I was missing today, but any last minute thought about what I must not forget to take is welcome…