NASA published a stunningly crisp image of Pine Island Glacier (PIG), Antarctica yesterday that is already out of date, because the PIG is on the move. Glaciers change rapidly these days and the speed of the PIG is anything but glacial. The image below from Nov.-13, 2011 shows a massive crack that will develop into an ice island about 3-4 times larger than the one formed from Petermann Glacier, Greenland in 2010. While the image indicates that the part seaward of the crack is still attached, I am convinced that it is already moving independently of the glacier.
The same Terra space craft that provides the very crisp and high-resolution ASTER image also has sensors that image a larger area at slightly coarser 250 meter resolution. And monday was again an exceptionally clear day over Pine Island Glacier that revealed this (false color) image of radiation received at a “color” that is out of range of our eyes, the near infrared (865 nanometers):
The glacier has advanced a fair amount, the crack breaking off is a perfectly normal event. This is what tidewater glaciers do, they move out to sea and break off icebergs and ice islands. Subtracting the January-30, 2012 image from a Nov.-3, 2011, I think that the thick red line below shows how far and fast the new ice island has moved the last 3 months. Its speed is at least ten times that of the glacier behind the crack:
Lets leave the boring crack alone, nothing to worry there. What is important at Pine Island Glacier is the retreat of the grounding line, the location where ice, ocean, and bedrock meet. All ice located seaward of the grounding line is floating and does not add to rising global sea level. [Actually, it does raise sea level a tiny amount on account of subtle nonlinearity on how volume of water and ice are influenced by temperature, salinity, and pressure, but lets neglect this detail for now as everyone else does for a good reason).
It is the ice landward of the grounding line that will raise sea level as it passes the grounding line and becomes floating ice. And the thickness of this part of the glacier is decreasing at a rapid and alarming rate, because the glacier is melting from below by the ocean and much of the bedrock landward is below sea level, thus allowing the PIG to become “unhinged.”
The problem with this process is that we cannot see it as easy from space, as we can see changes at the surface. The ocean melting does not give the stunning images that portray drama, concern, and excitement the same way that new ice islands do. Yet, for most large glaciers like Pine Island, Antarctic and Petermann, Greenland, the oceans are eroding and melting these glaciers from below. It is the physics on how this works that we scientists do not yet know and understand very well. It is one thing to have a theory and perhaps a model, but only hard data from the ice and the ocean will give us the confidence and understanding to make smart decisions that balance our energy use contributing to global warming with the need to economically develop. Smart development allows us to live better lives and cope with calamities, some of which may be caused by global warming and the sea level rise it brings.
You say, “The ocean melting does not give the stunning images that portray drama, concern, and excitement the same way that new ice islands do.” but I like to think this image does convey that: http://kenmankoff.com/2012/01/31/pine-island-glacier-and-pine-island-bay
It sure does and I am delighted that you shared it here. So perhaps we should look more closely at the MODIS channels 31 and 32? How well do you know that the thermal signatures actually correspond to plumes of freshwater other than local melt?
The problems I see with ocean sea surface temperature (SST) estimates is that it is always hard to relate remotely sensed skin temperatures (fraction of a mm) to mixed layer temperatures (1-10 m) and then relate those to physical processes at 500 m depth in a salinity stratified ocean. Furthermore, SST from space is a very noisy measurement at the time and space scales that matter dynamically. Blowing the wind just a tad will potentially change the SST distribution dramatically.
That image is Landsat TIR. We tie the thermal signature with sub-shelf melt-water thanks to in-situ oceanographic measurements taken shortly after that satellite image. More details in the (soon to be published) paper.
And I agree, that image is mostly illustrative. There is a connection to the mixed layer and sub-shelf waters hundreds of meters down and kilometers away, but not a strong quantitative one, and it only exists because of near-coincident in-situ measurements.