Edge of the Arctic Shelf

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Dispatch 04 - July 18, 2002
By C.A. Linder

Weather conditions: clear skies, calm winds and seas, air temperature 55° F

Beyond the Circle
We have now officially entered the Arctic, defined by the Arctic Circle, an imaginary line circling the globe at 66 degrees 32 minutes North. Why such an odd number? It has to do with the tilt of the Earth on its axis relative to the position of the sun. On midsummer’s day (June 21st), if you are north of the Arctic Circle the sun will never set. For more answers about Arctic phenomena, wildlife, and more, check our Images and Facts section.


Marine Science Technician Lee Brittle checks the cable that sends the CTD data back to the deck computer.	The CTD package is recovered after the second test cast.
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A foggy morning gave way to bright sunshine this afternoon, the first we have seen since setting out from Dutch Harbor on July 15th. The weather seemed to reflect our spirits; by the end of the day several equipment problems had been solved. The CTD group narrowed the previous day’s problem to the point where the data cable joins the CTD frame. This point, known as the “termination” of the cable, gets a lot of wear and tear when the CTD is deployed and recovered, and thus frequently requires maintenance. The problem was solved by replacing part of the cable near the termination point. A second test cast brought a sigh of relief - the temperature and salinity data came through beautifully on the shipboard computer.


	Aaron Morello completes final checks on the nutrient analyzer.
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Aaron Morello from the University of Washington also succeeded in getting his nutrient analyzer machine set up and working properly. His job on this cruise is to take the water samples from the Niskin bottles on the CTD package and determine the quantity of dissolved nutrients in the samples. The nutrient analyzer automatically splits the water into four different samples and mixes them with particular combinations of chemicals. Based on the intensity of colors produced in these reactions, the concentration of water nutrients is measured. An example of one of these is silicate (SiO₃). Physical oceanographers are interested in knowing how much silicate is in the deep waters of the Chukchi Shelf because it is a good indication of the presence of Pacific Ocean waters.


Jim Johnson’s current meters will be deployed on a Chukchi Sea mooring.	David Leech works on the acoustic release for his mooring.
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Science begins in earnest tomorrow on the Polar Star. At 0800 we are scheduled to put in the first mooring and the CTD group is hoping to complete a section -- a group of stations aligned in a straight line -- overnight.

Today I received a question via the arcticedge@whoi.edu email address:

Q: I am really enjoying your website - it is very interesting and informative. I have a question: Is there any volcanic activity along the way that would affect the Pacific-origin water as it travels through the Bering Strait, and how would this impact the circulation over the Chukchi Sea and Beaufort/Chukchi slope? Thank you. I hope that Bob Pickart has gotten over his “jellylegs.” Sincerely, George

A: Chief Scientist Tom Weingartner answers: This is a great question! There is a lot of volcanic activity along the Aleutian Island Arc and the Aleutian Trench of the North Pacific Ocean. (These regions are 600 or more miles south of Bering Strait). Undoubtedly this will influence the chemical composition and the circulation of the waters near the volcanoes. However, the volcanic activity is very deep (greater than 1000 meters for the most part I think) and likely to be in the form of hydrothermal vents. In contrast the water flowing through Bering Strait is either of shelf origin or from the upper layers of the Bering Sea basin. In either case these waters are of comparatively shallow origin and generally not much deeper than 150 meters or so.

Keep those questions “flowing!”

And yes, Bob Pickart has finally recovered from his mountain run in Dutch Harbor; although something tells me he won’t be jumping on the ship’s stairmaster anytime on this cruise...

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