The warm water around canyons may host more krill and fish, happy hunting grounds for seals and penguins.
By DR. JOSEPH TORRES
© St. Petersburg Times, published May 23, 2001
MARGUERITE BAY, Antarctica -- Our last few days have been spent in the southeastern corner of the bay in a small inlet called George VI Sound. It marks the end -- or as near to the end as we can get -- of a deep canyon that runs from the edge of the continental shelf all the way to the shoreline of the bay.
We think the canyon is important to the animals that live here for a number of reasons. I'll explain after a brief weather report.
The days are short. There is no light until 10:30 a.m. It's dark by 2:30 p.m. In another week at this latitude -- 69 degrees, 30 minutes -- the sun will sink below the horizon and won't rise again for two months.
The air temperature is 31 degrees Fahrenheit -- about 10 degrees above the monthly average -- but the ocean is 29 degrees. At 28 degrees, pack ice will begin to form.
That the ocean can be colder than the air is a wee bit complicated. The ocean tends to lose heat quickly when the days get short and there is little radiation from the sun to warm it.
All of us on the boat want the ocean to hurry up and freeze because we don't want to contend with the 20-foot seas that accompany the high winds we've been getting almost every day.
Once the sea is frozen, of course, all water motion ceases. Most of us who come down to the Antarctic greatly prefer "hard water sailing" to the big seas we've been seeing.
We'll be coming down for a second cruise in July to August -- the dead of winter. George VI Sound will be frozen so solid it will be difficult to get in here. But back to the canyons and why they are important. It's heat. In my first report, I told you about the continental shelf: what it is and why it is especially deep in the Antarctic. Let me embellish a little.
The biggest current in the world flows around Antarctica like a doughnut, rotating clockwise from west to east.
The funny thing about the current is that the deeper parts of it are warmer than it is at the surface. With most places in the ocean, the deeper you go the colder it gets. Why? Because cold water sinks. In the Antarctic, the warmer water is saltier, so it sinks.
What does this have to do with the canyons? I'm getting to that.
The current crashes into the peninsula where we are conducting our study. Most of the flow is diverted around the peninsula, but some of the warm deep water flows up the canyons and spreads over the continental shelf. As a result, the deep water on the continental shelf of the peninsula -- below 600 feet -- is warmer than any of the other coastal areas around the Antarctic continent.
Not exactly balmy, mind you -- 35 or 36 degrees -- but maybe just balmy enough. From a biologist's perspective, the canyons also may be richer in krill and fish: better places for seals and penguins to hunt.
Whether the canyons really are richer is one of the primary questions we are trying to answer on the cruise.
Besides looking for where the krill are most numerous, another of our tasks on the fall and winter cruises is find out how a basically vegetarian species such as krill can survive over the winter when there is no algae to eat. Why no algae? That's an easy one: No sunlight.
There are a few different ways that animals deal with a lack of food, and in my next article, I'll tell you a little bit more about how krill, fish and penguins survive winter.