Tag Archives: glacier

Pine Island Glacier Grounding and Unhinging

I can’t get Pine Island Glacier, Antarctica out of my mind. Checking my e-mail over breakfast, I was alerted to the forum post of Dr. King, a geophysicist working at the University of Newcastle in northern England. His post provided a hint and link to data on where all glaciers around Antarctica are grounded. The file at the National Snow and Ice Data Center was too slow to download at home, so I quickly bicycled to work, got the data, wrote a little script , and plotted Pine Island Glacier’s grounding and “coastline”:

Pine Island Glacier, Antarctica as seen Jan.-12, 2012 from MODIS Terra. The blue colors top-left are ocean, red-yellow are ice. Thick black line shows where the glacier is grounded to the bedrock below sea level, that is, all "red" areas to the left (west) of this line are floating on the ocean. The thin black line is the "coastline." Grounding and coastlines are from National Snow and Ice Data Center'. North is to the top.

The image indicates a problem in a rapidly changing world: Both the “coastline” and the “grounding line” change with time, rapidly so. The black lines shown above come from hundreds of cloud-free satellite images from the 2004/05 summer in Antarctica. Dr. Scambos, Lead Scientist for the National Snow and Ice Data Center painstakingly analyzed these data and assembled them into the “Mosaic of Antarctica.” The derived coastline for the Pine Island region suggests, that the glacier advanced over 10 km in 7 years. The crack behind it identifies the next ice island that, I speculate, has already separates from the glacier, as its front is moving 10 times faster than the glacier itself. The grounding line looks different from one that I have seen before, too, e.g.,

Bottom topography under Pine Island Glacier and grounding line. North is to the bottom. (NASA)

Trying to resolve this issue, I google searched “Pine Island Grounding Line” only to find a number of excellent science essays and publications on the impacts that Pine Island Glacier and its streaming ice have on climate change and global sea level rise:

Good science essays hide in strange places: “West-Antarctic Ice: Slip-sliding Away” by Dr. Bruce E. Johansen of the University of Nebraska makes reference to a 2010 publication in the Proceedings of the Royal Society of Dr. Katz, University of Oxford. This theoretical fluid dynamicist modeled “Stability of ice-sheet grounding lines” . It is a very theoretical paper whose results are summarized in The New Scientist. This is where I am now, hoping on my bicycle to visit my BrewHaHa coffee shop to read the paper away from my desk over lunch.

Oh, I also stumbled into a NASA animation of how Pine Island and adjacent ice streams accelerate and become thinner very far inland as a result. The graphics are stunning, the data are free, and the message is scary, yet, the science is exciting and I feel very lucky to be able to study this. Watch it, get hooked on science, and have fun.

Swirling Ice in Coastal Waters off Eastern Greenland

Nature provides us with art that is always changing in time and space. Delicate swirls and vortices give a rare glimpse of how the ocean’s surface looked today off eastern Greenland. The data originate from the MODIS/Terra satellite which from 440 miles above the earth captures light that is reflected from anything below. Here it shows the ice-free ocean (bottom right) and Greenland’s ice-free Scoresby Sound (bottom left) in very dark blues, lightly vegetated lands (left) in light blue, and a highly organized pattern of sea ice (top right) in white. The resolution of this image of light just beyond the visible, just beyond the red is about 300 yards and the swirls and elongated filaments are about 3-5 miles. To me, they vividly show the ocean’s surface circulation.

Swirling surface motion on the continental shelf off eastern Greenland Sept.-12, 2011 as indicated by sea ice. Black lines show contours of bottom depth from 300 to 1200 meters in 300 meter increments.

The physics of these motions are similar to those I was reading into another beautiful work of art to the north of Norway. The postulated physics involve the earth’s rotation as well as differences in density. The density of the ocean relates to its temperature a little and to its salinity a lot. Near the coast and at the surface, ocean waters are much fresher and thus lighter than they are offshore and at depth, because Greenland’s melting glaciers and sea ice are fresher than the waters of the Atlantic Ocean. The thin black lines show bottom depths to distinguish the deep Atlantic Ocean to the right in the image from the shallow continental shelf off eastern Greenland to the left in the image. Note that all the swirls, eddies, and filaments are within 30 kilometers (20 miles) off the coast in water less than 300-m deep. The same physics apply to the algal blooms off Norway which is the reason that the swirls and eddies are of similar size here and there as well.

Incidentally, the same physics also apply the discharges from rivers and estuaries such as the Delaware or Cheasapeake Bay. There, the pattern are not quiet as visible to the naked (satellite) eye as off Norway or Greenland, but if one takes measurements of the ocean, similar patterns of ocean salinity and velocity as, I speculate, they do here for the ice (Greenland) and algae blooms (Norway). While my academic journey of fresh water discharges started with the discharge of the Delaware River into the Atlantic almost 25 years ago, I am still fascinated by the many ways these patterns always come back to me. Physics and oceanography are beautiful in both their many natural manifestations and its unique balance of forces. There is so much more in how the oceans interact with the ice and glaciers off Greenland and elsewhere. To be continued …