Ice

The vast expanse of ice that makes up the Ross Ice Shelf

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I've much to blog about but we've been so busy, and the network so slow, that I've fallen behind.  Today, though, I'm writing a relatively dry blog about something wet--ice.

We are surrounded by ice, much of McMurdo's research is about ice, and many of the injuries we see in clinic, also involve ice.  It's the central component of life here.   In the last week, my life seems to have revolved around ice.  Tuesday, I toured the pressure ridges in front of Scott Base.  After that, at the Ross Island Yacht club meeting, a McMurdian presented his experiences working on the Nathaniel B. Parker, a ship studying the sea ice.  Then, Wednesday, we went to a lecture about the disappearing ice shelves around Greenland.  Fortunately, Rebecca gave me her field guide to ice.  So is what I've gleaned.

Ross Island is separated from the mainland of Antarctica by the Ross Ice Shelf, a floating mass of ice the size of Texas (or France, depending on whether you favor BBQ or paté).   Hundreds of meters thick, the Ross Ice Shelf is basically an enormous piece of floating ice.  Like all ice shelves, it formed from ice flowing off adjacent glaciers.  The precise location of its ocean edge can wax and wane and large ice chunks can occasionally break off, or "calve", to form icebergs. Although from a distance, it looks flat, cracks can form into deep, frequently snow-hidden and deadly crevasses.  Pressure ridges up to 30 feet high can make travel with vehicles (now) and dog sleds (during the time of the Great Explorers) slow going.  And don't forget, they have a long way to go on it; they're crossing a frozen Texas (or France).

Pistenbully with ground-penetrating radar to look for crevasses. GPR leads convoys across the ice
to prevent tragic accidents like those of the Mawson expedition (sled dog team and driver lost)

At our lecture yesterday, we learned that the few remaining ice shelves in Greenland are thinning and calving due to the warming of the air.  The snow melts through the glacier and pours into the sea under the shelf, causing turbulence in the seawater and allowing warmer water to erode the undersurface of the ice.  As it thins, ice calves the three times the size of San Francisco (or the size of Barbados depending on whether you favor Dungeness crab or gumbo--, clearly, I'm missing good food) have broken off.  Soon, all the ice shelves in Greenland will be gone.  The Ross Ice Shelf has not been this unstable.   

Although the ice shelf separates Ross Island, where we are, from the mainland, for all intents and purposes, it serves as land.   Our two airfields--Phoenix and Willy--are both on the Shelf.  The Terra Nova and Discovery expeditions of Scott and the Aurora portion of Shackleton's expedition began on the Ross Ice Shelf.  The first "land" they crossed was the ice shelf and, when they died--as Scott and four others of his party and three of the Aurora party did--it was on the ice shelf struggling to get back to the base camps.  Because they could not retrieve the bodies from the Scott party quickly enough (and two of the Aurora party were never found), they eventually became part of the ice shelf, and will eventually, in hundreds of years, float out to sea in icebergs.

Sea Ice is the floating ice that forms on the sea (duh).   Sea ice begins as crystals called frazil that coalesce to form sludge-like grease ice. Eventually, the grease ice forms sheets called nilas that, in the right current and wind conditions, get pushed together to form pancake ice--large, thin "lily pads" of ice that dot the ocean.  Wind and currents push the pancakes together to form larger ice floes.  These, in turn, merge to form enormous fields of pack ice.  

Pancake ice (picture taken from the web but similar to that shown to us in the lecture about the ice breaker)

Shackleton's ship--and indeed most Antarctic explorer ships--become stuck in pack ice for the winter. When Shackelton's ship was crushed by the pack ice, his crew then built their camps on the ice, moving when cracks or ridges forced them to evacuate camp.  Throughout their months of travail, their pack ice was blown or moved by currents over the ocean, permitting them to ultimately make it to Elephant Island, hundreds of miles from their original starting point.   

Sea ice that attaches to the ice shelf, land or the seafloor is called fast ice.  A storm this winter broke up the fast ice near McMurdo and blew it out to sea.  The fast ice that has reformed since then is thin and soft with hazardous cracks.  This poor ice limits the ability of scientists to get out to their usual sites to do experiments.  The weak ice also prohibits the creation of the ice pier used to unload the ships that come to supply the base in January.  So it's a bad year ice-wise for the NSF enterprise.

Flags on the ice showing us where it is safe to walk.   Other flags mark
routes for vehicles, going to the airfields and research sites.  Black flags mean "do not go here".

When portions of pack ice slam into either fixed ice or the ice shelf, or when two large pieces of pack ice or two ice floes are pushed together by wind or current, pressure ridges are formed.   Later in the week, I'll post pictures of the pressure ridges, but for now, here's a picture of my group out on the fast ice.

Panorama with the Ross ice shelf is the left three quarters of the picture. 
Water will eventually open up around and beyond Ob Hill on the right, forming the southernmost port in the world.