Seals and Pressure Ridges!
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Yesterday we went to an area near Scott Base (a New Zealand station) that has pressure ridges.
The pressure ridges are formed by tidal forces and glacial pressure – there is a thick sheet of sea ice that meets the land, and tidal forces (ocean tides) cause the ice to buckle. Two winters of thick sea ice grinds and heaves when the ocean pushes it against the much larger Ross Ice Shelf (normally the ice here breaks up each year, but last year was too cold and that didn't happen – so this sea ice is two years old). The effect is beautiful...and dangerous!
What are all of those flags in the snow all about?
There are flags to map out a safe route. Black means danger – usually crevasses. A crevasse is a dangerous and deep crack in the glacier or ice shelf that can be covered over by blowing snow. There were black flags EVERYWHERE in this area! But, as long as we stayed on the path that had been checked out to be safe, we were pretty confident and comfortable. We had poles (for probing the consistency of the ice and looking for crevasses and voids under the surface) and ice axes to help with climbing. The red and green flags indicate an area is safe (why red means "safety" was a surprise to me and seems counter-intuitive). Most of the established ice roads are marked with red flags. Red and green can also be used just to mark the location of something that you might need to find after it gets buried in snow. In our case, it would be the battery boxes of our Automatic Weather Stations. Blue flags indicate fuel caches, fuel lines and occasionally things that might be necessary for survival, like a survival bag).
Seals are common in this area. These are specifically Weddell seals.
Since this ice is floating on the ocean it is affected by the tidal movement of the water below. It is also being pushed against by the ice shelf. The sea ice and the ice shelf are different. The sea ice is "temporary" and usually breaks up in January (the warmest part of the Antarctic summer). The ice shelf is a glacier that is drifting off of the continent and has pushed hundreds of miles into the sea. Where those two types of ice meet (and where they each touch solid ground – like here on Ross Island) you can expect to see pressure ridges. Where there are pressure ridges there are cracks in the ice that lead into the ocean below...and that means...seals!
Since the seals are mammals, they need to breathe air. They can hold their breath for close to an hour, but at some point, they need to breathe and this is just the place. They also rest and have their pups on the surface! We did see a few pups but since they were born two months ago they are getting big. Some of the members of our party could tell the difference, but they all looked about the same to me!
For more on Weddell seals, I'll refer you to my friend Bridget Ward's Expedition.
Here is a brief description of the Weddell seals from her expedition's page: "Weddell seals are one of the best-studied seals and a classic example of adaptation to the extreme Antarctic environment. A large body size and thick blubber layer help them to stay warm both on and under the ice. Their streamlined shape, body oxygen stores, and collapsible lungs allow them to reach dive depths of 600 meters (almost 2,000 feet!) and remain underwater for over an hour. However, they do not begin life with these advantages. Weddell seal pups are born on the sea ice with a small body size and almost no blubber."