Saturday, August 8, 2015

The Pink Hard Hat Makes a Comeback

We have now finished our biggest job out here, which was to deploy a mooring called the Distributed Vertical Line Array (DVLA).  This DVLA is an basically a long wire with hydrophones clamped onto it, which is anchored to the bottom of the ocean and held upright by a buoy that sits below the water surface.  Since it was a big day out on the deck of the Sikuliaq, with cranes operating and heavy equipment being moved around, I had to bust out my signature pink hardhat.  Deploying an array like this is a big job and there were a lot of people involved as you can see from all the orange float coats out on deck (they are nice and warm and have built-in flotation). 

Photo credit: Bruce Thayer

Photo credit: Scott Carey
Photo credit: Scott Carey
Another photo here shows Peter Worcester, our chief scientist, driving the winch, Bern, the Sikuliaq’s resident technician with the magnificent beard overseeing things, and that’s me with the clipboard.  It was my job to record everything that got put on the mooring and make sure it was attached in the right place.
We deployed a similar mooring in the Philippine Sea Experiment, but because we are now surrounded by ice, we had to do things a little bit differently up here in the Arctic.  In the Philippine Sea, we first put the buoy over and then strung out a bunch of wire rope and instruments that all floated at the surface in a big line strung out behind the ship until we and finally dropped the anchor and the whole thing followed the anchor down as it sank.  Well, we can’t string out several kilometers of wire rope and instruments up here because we are surrounded by ice!  This time, we had to put the anchor in first and slowly lower the wire in after it, clamping on all the instruments as we went, and then we finished up with the buoy. The DVLA was already mostly vertical and in the correct orientation so it just sunk straight down when we dropped the buoy.  Basically we did it just backwards of the way that we did it in the Philippine Sea.

The water depth was about 3850 meters (approximately 2.4 miles) and the buoy is about 50 meters below the surface, so the mooring itself was about 3800 meters long.  We attached 60 hydrophone modules (see HM post from PhilSea) as well as 24 MicroCAT instruments.  The CAT in MicroCAT stands for Conductivity And Temperature, which is what the instruments measure, and what we what we need in order to calculate the speed of sound in the ocean.  The way sound travels in the Arctic Ocean is largely dependent on the temperature and salinity changes that result from interactions with the ice, which happens near the surface of the ocean (we’ll talk more about that later).  The hydrophones and other oceanographic instruments were concentrated towards the top of the mooring to capture all this excitement in the upper ocean.

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