Edge of the Arctic Shelf

1,427 Meters of Wire
This morning the main lab was strangely quiet - the calm before the storm. The preparations were finished, now it was show time. Over the next few days John Kemp, Ryan Schrawder, Dan Torres, and the Healy boatswain's mates will be doing a marathon redeployment operation - eight moorings taken out, eight put back in. Almost the entire WHOI team will be involved in the Beaufort Slope mooring array in some way. Marshall Swartz will be calibrating the profiling CTD instruments. Sarah Zimmermann wil be analyzing the past year's moored profiler CTD data. Dan Torres will be helping with the recovery and deployment and analyzing the ADCP data. The action started after breakfast with the deepest mooring.

Last year this mooring was particularly difficult to deploy because of the shifting brash ice (read more about it in 2002 Dispatch 14). This year not a trace of ice was to be seen - just gray waves. This took a load off of John Kemp's mind. The topmost buoy had been outfitted with an avalanche beacon last year, so that we could find it even if it popped up under the ice. He was extremely pleased to not have to use it. Once we hooked the top buoy with a line through our A-frame, it was just a matter of pulling it all in... All 1,400 meters of line - that's nearly a mile! It took over two hours to bring it all on deck. The primary instrument on the WHOI moorings is a moored profiler, a small robotic instrument that climbs up and down the mooring wire twice a day. When this instrument was retrieved it was immediately wheeled into the main lab, where a waiting crew took it apart and began checking the data. After several tense minutes, Ryan Schrawder made the diagnosis - 2,500 files - it worked perfectly! The little yellow profiler made its last trip up the wire just 10 days ago! Bob Pickart was smiling ear to ear, exclaiming "now that's what I call a mooring deployment!" His elation was even more complete when the team brought the second mooring in just before dinner and discovered that this moored profiler had made its last profile as we released the anchor today - two for two!

Mrs. Werner's class at the Morse Pond School came up with these great questions about moorings. The leader of the WHOI mooring team, John Kemp, helped me with the answers.

Question: How deep down do the moorings go?
Answer: Since the moorings are spanning a submerged "cliff," the depths vary. The deepest mooring is in 1,400 meters (4,593 ft) of water, and the shallowest is in a mere 57 meters (188 ft) of water. The moorings are about 2-4 kilometers apart. Click here to see a diagram of what the moorings look like when they are all deployed.

Question: How much do the moorings weigh?
Answer: This is a great question, since it has two answers! Do you want to know how much it weighs when it's on land, or in the water? It weighs a lot less when it's in the water, due to the upward force of buoyancy from the floats. Since the mooring is designed to operate in the water, all of the calculations are made for water weight. The net upward force on the anchor is 1,000 pounds. The anchor has a water weight of 3,000 pounds. So, if you were to weigh the mooring underwater, it would be 2,000 pounds.

Question: How much do the moorings cost?
Answer: Since the moorings vary in size, they also vary in cost. The smallest ones are the cheapest, and cost around $50,000. The biggest one - the one we recovered today, costs around $150,000. The grand total for the eight moorings is around $1,000,000. This is one reason why we all have our fingers crossed when the mooring release is activated. The other reason is the data. To Bob Pickart, the data is worth more than the hardware. Hardware can be replaced, but the data is priceless.

Question: Were they especially built for your research?
Answer: Yes, these moorings were built specifically for this project. John Kemp designed all of the moorings. The critical instrument is a moored profiler (the yellow pill-shaped device shown above left). WHOI scientists and engineers invented this instrument; it is manufactured by McLane Instruments, Inc. It measures temperature, salinity, and the currents. For the shallower moorings, a modification was made to the moored profiler, making it much smaller and cheaper. This "coastal moored profiler" only measures temperature, salinity, and depth. This instrument was entirely designed and constructed at WHOI.

Question: Do you attach a computer to the mooring to get data or how do you get the data?
Answer: The data from the moored profilers is stored on a tiny hard drive built into a PCMCIA card. It's about the size of a credit card, and plugs directly into a laptop. It can hold 440 megabytes of data.

Tomorrow the marathon continues. If the moorings and weather cooperate we could have three or even four more moorings on deck, hopefully brimming with data.