Edge of the Arctic Shelf
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Daily Update

Dispatch 09 - September 18, 2003
By C. A. Linder

Weather conditions: Overcast skies, snow flurries, 15 kt winds, 1-2 ft seas, air temperature 30°F

Our science operations have continued all day today as we make our way south from last night's farthest north position. The winds have died down, allowing thick layers of fog to form over the water. Every so often a large raft of broken ice will appear on the horizon, but the Healy hardly even slows down -- the floes are easily thrust to the side as we cruise from station to station.

Night cast
CTD operations continue 24 hours a day, 7 days a week. This cast was brought aboard at 1AM.
Click to enlarge
Question from Karen, Grade 6, Morse Pond School: What types of things are you researching while you are there (besides temperature)
Answer: Chief Scientist Rebecca Woodgate answers this important question about "why we're here":

"Our primary aim is to understand how the waters in the Chukchi Sea get into the Arctic. The Chukchi Sea is shallow, only about 50 meters deep. (That's about 50 yards - think of a 50 yard dash or half the length of a football field.) The Arctic Ocean just north of it is over 3000 meters deep. (That's about 2 miles - how far do you come to school?). About 1 million tons of water flow from the Chukchi Sea into the Arctic every second. (That's on average over the year - at any one time it could be more or less. Usually it's more in summer and less in winter.) It's not like a huge waterfall, as there is water in the Arctic already. It's more like turning on a hose into a swimming pool.

We're trying to track the water from the Chukchi as it moves off the shallow shelf (the Chukchi Sea) and into the deep Basin (the Arctic). Hence the name of our project - Shelf-Basin Interactions (visit the SBI Website). Some of the questions we are trying to answer are:

- how much water flows off, where does it flow off the most (see the three branches in our "best guess" at the circulation)

- how does it flow off - in large currents ("rivers in the sea"), or in "eddies" (larger versions of the whirlpools you can make by moving a stick through the water - they are a few inches in size, these are more like 5 miles across!).

We care about these questions for several reasons:

- because the water in the Chukchi Sea is very rich in nutrients (food for all levels of marine life) and so it's important to know how these waters move for the marine ecosystem.

- because these waters (for reasons I won't explain here) help preserve the sea-ice floating in the Arctic, and that's important for the climate of the world

- and also, because we don't understand yet how things flow up here and we are curious to find out!

We try to answer these questions using - temperature and salinity measurements, by investigating the chemistry of the water, by measuring the direction of flow of the water. We do that both from measurements we are taking now with the ship and also by looking at the information collected by the moorings, the instruments that have been out measuring since last summer."

Wind and waves congregate small chunks of ice into neat rows.
Click to enlarge
Linnea from Mrs. Rodgers' class at the Morse Pond School has a question about moorings.
Question: Are the moorings in danger of being hit or damaged by sea animals like whales and/or polar bears?
Answer: David Leech has been working with moorings for 34 years, so I asked him to answer this question:
"Polar Bears? No, these moorings are all subsurface and the tops are deep enough to avoid even the deepest ice keels (we hope).
Whales and seals? Probably not because they navigate with accoustics, sonar, and our flotation buoys are very good reflectors of acoustic signals.
I don't know about walrus who dive down for clams and other amphipods for food. Practically speaking, we have not seen any evidence of our instruments having been bumped by these creatures. They are so big that we would have probably seen broken parts."

To see diagrams of what the moorings look like, visit the instruments page. The ice keels that David mentions are the biggest dangers to the moorings. When pack ice forms it is smooth and uniform. However, winds and currents cause them to smash into each other. This smashing can cause the ice to form "pressure ridges" where the plates meet -- these extend both high into the air and deep below the surface. The underside of the ice can form into sharp jagged edges known as ice keels. That's why the mooring instrumentation is all far below the water surface.

I have received several weather-related questions from Morse Pond School students.
Question from Taylor and Elliot (Mrs. Rodgers' class): Has there been any unexpected weather? Any surprises?
Answer: So far, I am surprised at how uneventful the weather has been. Coming from New England, I'm used to at least three seasons in one day. Out here, the skies have been slate gray overcast for probably 95% of the time. The temperature hasn't changed more than 5 degrees since we left Barrow. That to me is surprising!

Salinity analysis
Christina Courcier measures the amount of dissolved salt in the seawater samples using a salinometer.
Click to enlarge

Question from Mary (Mrs. Werner's class): What is the coldest that it has ever gotten in the Arctic?
Answer: I contacted my friend Rick Krishfield back at Woods Hole Oceanographic Institution for the answer to this one. Rick is a veteran Arctic oceanographer. He deploys buoys in the ice that measure the atmosphere and ocean. He tells me:
"As to the coldest temperatures: our buoys only recorded temperatures down to -40°C (-40°F), and our systems usually saw winter temperatures between -35 and -40°C. On the other hand, I found winter air temperatures in the icepack down to about -56°C (-69°F) at Russian NP-22 drifting station, and -55°C at Ice Island T-3. In fact, the sea ice helps to moderate the cold temperatures, so the coldest temperatures are usually found on land. I did a quick web search and found the coldest temperature in the Northern Hemisphere according to George H. Taylor, Climatologist: February 6th, 1933, -90°F, Verkhoyansk, Siberia."

Rick's answer helps explain why Antarctica is so much colder than the Arctic. Can anyone guess the lowest recorded temperature on Antarctica? I'll provide the answer in the next dispatch.

Virgynia from Mrs. Werner's 6th grade class at the Morse Pond School had this question.
What time do you go to bed?
Answer: I will be going to bed right after I finish this dispatch! Usually that is around midnight or 1AM. Even while I am sleeping, though, science operations are underway. The Healy's Marine Science Technicians and the science party CTD watchstanders work 24 hours a day, seven days a week. The day is divided into different "watches" -- for example our CTD team is broken into three watches. One group works from noon to 8PM, another works from 8PM to 4AM, and a third works from 4AM to noon. That way every minute of the day is covered. Everyone lends a helping hand at sea -- the mooring technicians and even the dispatch writer pitch in to help with CTDs!

Tomorrow the CTDs will continue as we make our way back to the Alaskan coast. Carin Ashjian will also be deploying the Video Plankton Recorder to look at tiny organisms in the water column. Friday the 19th of September is also "Talk Like a Pirate Day" aboard the Healy, so stand by for some humorous photos... Arr!

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