Edge of the Arctic Shelf

Eddy Chasing
This morning we entered a different phase of our research expedition. Instead of sampling at predetermined locations, our goal is to locate an oceanographic feature and then study it intensively using all of the scientific tools we have onboard. The feature we are looking for is called an eddy.

Eddies are large, circular (10-15 miles across), rotating parcels of water that tend to migrate from the shallow shelf water to the deep Arctic basin. There are many different ways to find eddies. Since they are rotating, we can often see them in our measurements of currents (speed and direction). Another way is by measuring the water temperature--these eddies are made up of shelf water, and depending on the time of year they can either be colder or warmer than the surrounding water. In fact, since shelf water is so different from deep water, almost every property of water that we measure will reveal the eddy.

Last night as we steamed south from the ice, Andreas Münchow found our first eddy. "We crossed three eddies already" he exclaimed, carrying several plots into the main lab. Andreas monitors the shipboard acoustic doppler current profiler. This instrument records the strength and direction of the ocean currents directly beneath the ship. However, since we are more interested in where the eddies are first formed, we continued on our way to the edge of the shelf and have now commenced a methodical "eddy reconnaissance mission".

Throughout the day today, we have been dropping an expendable instrument called an XBT, which stands for "Expendable Bathythermograph." Shaped like a tiny torpedo, the XBT is launched over the side while the ship is still moving. The data is fed back to the ship via a thin wire. When the probe hits the bottom, we break the wire. The probe is not recovered (hence the term "expendable"). In order to cover our area as thoroughly as possible, we are sampling along five parallel lines spaced 25 kilometers apart. This will provide us with a three-dimensional view of the temperature in this large box. Not only will we be able to confirm the presence of eddies, but also their approximate location. What's next? Well, as soon as the XBT survey is complete we will select the most promising looking eddy and begin a more intensive survey. Check back tomorrow to see how the chase is progressing!

These questions about polar bears are from Linda Werner's sixth grade class at the Morse Pond School in Falmouth, Massachusetts. Thanks for your questions!

Question: Have you seen any polar bears or walruses?
Answer: On September 8th, Anna and the morning watch team saw a mother and baby walrus. They swam around the ship while we were stopped for a science station. Since then, we have seen only two more lone walrusese and one swimming polar bear. Although we saw polar bear tracks, we saw no bears during our two days transiting along the ice edge. This surprised all of us--we had expected to encounter at least one bear hunting for seals on the ice.

Question: Is polar bear fur clear or white?
Answer: Polar bear fur is white with a somewhat yellowish tint. Polar bears actually have two sets of fur--an inner coat and an outer coat. The inner coat is soft and fluffy, and works just like a fleece jacket, trapping the bear's body heat. The outer coat is composed of long, waterproof guard hairs, functioning like a shell jacket.

Question: Do you know how much polar bears weigh and how long they live?
Answer: Male polar bears stand about eight and a half feet tall and weigh around 1000 pounds. Females are typically half the size of the males. They live for about 20 years.

If you want to read more about these kings of the arctic ice, check out the book Polar Bears by Ian Stirling and Dan Guravich. Have a question for the science team? Send your email to us here in the Arctic at arcticedge@whoi.edu.