Edge of the Arctic Shelf

Nick of Time
We deployed the moorings yesterday in the nick of time! As night fell another arctic gale hit us, bringing our CTD operations to a halt at 2:30AM. The storm increased in intensity through the day, peaking at a sustained wind speed of 50 knots! Standing on deck felt like sticking your head out of a car window driving down the highway -- in winter... Even bundled up, after several minutes on deck my head was throbbing like I had an ice cream headache. Nothing I had to wear could stop that icy wind from cutting through.

Since science operations were canceled, it was a welcome day of rest for most of the science party. Thanks to the marvels of satellite technology, half of the science party was glued to a laptop in the science lounge watching a webcast of the Boston Red Sox vs. Oakland A's game. A crowd also gathered on the bridge to watch Healy meeting the fury of the gale. Every few minutes the ship would hit a particularly large wave at just the right moment, sending spray flying as high as 70 feet in the air. It was an incredible sight, and several crewmembers videotaped the experience from the safety of the bridge. We also gained a new appreciation for how stable the Healy is in rough seas. A smaller vessel would have been lost in the 15 foot wave troughs today, but the Healy cruised along with only minor rolls and pitches.

Another elementary school class has joined our online expedition! These questions come from Mrs. Lyons' 5th grade class at Mt. Alvernia Academy, Chestnut Hill, Massachusetts.

Question from Sam: Why does the water flow from the Chukchi Sea into the Deep Basin?
Answer: I asked Chief Scientist Rebecca Woodgate to answer this question. She has been studying the physical oceanography of the Arctic for over a decade.

"We have some ideas of why water flows north through the Chukchi into the Arctic, and it's to do with the ocean and atmosphere circulation of the whole world. Basically, water evaporates from the Atlantic ocean, is carried over to the Pacific ocean by air currents, and rains back down on the Pacific. So now we have "too much" water in the Pacific and it has to get back somehow, so it flows back through the Chukchi Sea and the Arctic. That's part of it. The ocean currents could be doing the same sort of thing - pushing too much water into the Pacific, so it leaks out at the top into the Arctic. We call these effects "pressure head" effects, because there is more water on one side (the Pacific) than on the other (the Arctic) and so that drives a flow. It's the same effect as causes your toilet to flush - kinda. The winds drive the water in the Chukchi Sea too, but the average wind is actually towards the south, and tries to drive the water back south against this pressure head. The effect of the wind is however less than the pressure head effect, so on average the water still goes north.

SO .. now we have it in the Chukchi headed north and we need to explain how it gets into the Arctic. That is one of the main questions of this whole project. I can give you some ideas. One is again the winds - they push it off the shelf over the deep basin. One is just gravity. As it flows over the shelf, it's denser than the water it flows into and so it flows down. Because the earth is spinning, ocean currents like to turn to the right in the Northern Hemisphere, so quite a lot of the waters flowing out of the Chukchi Sea (past the moorings we picked first in the trip) turn right and flow along the north coast of Alaska (past the moorings we just finished with yesterday). There again the wind can push it off shore and/or the current can "go unstable" and little bits of it break off and form eddies (large [about 5 miles across] rotating blobs of water, big, slow whirlpools if you like) and these can move off into the Arctic. We see the waters from the Chukchi Sea right out in the central Arctic, and even exiting the Arctic in Fram Strait east of Greenland, in a layer about 300-450 feet down in the ocean. I don't think much of the shelf water actually gets down much deeper than this. Some people talk about plumes of really dense water formed on the shelves plunging down the side of the Arctic Ocean to great depths (1/2 a mile or more), but no-one has found them yet."

Question from Victoria: Is this the coldest place you have ever been?
Answer: Hi, Victoria. Believe it or not, the weather actually hasn't been that cold so far on this trip. I can recall some mornings waiting for the bus to take me to high school in Wisconsin that were much colder than out here... And this past winter you surely remember that week (or was it two?) when the temperature in Massachusetts hardly broke out of the teens. I will say this, though - this is the coldest I have ever been in October!

Our latest weather forecast calls for the storm to begin subsiding by tomorrow afternoon. As soon as the weather permits, we will be resuming our high resolution CTD section alongside the mooring array.