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Dispatch 10: A Day of Recovery

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Joey Wenig

September 30, 2014


Lots to write about after a busy day of pulling instruments out of the ice. I’ll get right to it.

The second mooring recovery of the cruise, at station BGOS-A, got underway this morning around noon. We will be redeploying this one tomorrow with some new instruments—including a strange looking device from the folks at the Tokyo University of Marine Science and Technology (incidentally, TUMSAT is my favorite institutional acronym)—but I’ll talk about them in a later dispatch. Apart from a weird power outage to the winch when one of the ship’s breakers flipped, the recovery went smoothly. John Kemp and Meghan Donohue (who continue to impress me with their skill and bionic hands that are, as far as I can tell, impervious to cold) had the whole thing on board in no time at all, giving us time to veer south-east, off the course we had set for station CB-7, in pursuit of ITP 79, which was rumored to be hanging out in the area.

An ITP (Ice Tethered Profiler) consists of a large yellow buoy shaped like a cone with the pointy end sliced off about halfway along, and with a ‘profiler’ dangling beneath it on an 800-meter length of plastic-encased steel cable. The profiler climbs up and down the cable on a preprogrammed schedule. It has a CTD unit (instrument for measuring seawater conductivity, temperature, and depth—the conductivity translates directly into salinity), and, on this particular version, a device measures water velocity. The profiler sends data up to a surface control unit installed in the buoy. The surface control unit records GPS fixes every hour and sends that information, along with all data received from the profiler, directly to the offices of researchers via satellite. (Because it’s cool: The profiler communicates with the surface control unit using an inductive modem. A toroid—Google this if necessary—induces a pattern of current pulses in the steel cable. These pulses travel up the cable and pass through another inductive modem in the surface control unit, which translates the pattern back into a form that can be stored and relayed. In order to close the current loop, both the profiler and the surface control unit have components that are exposed to the conducting seawater. This is important because it means that if an Arctic cod could understand modulation language, it would learn a lot about its environment just by hanging out under the ITP.)

The ITPs were designed by a group at WHOI lead by John Toole and Rick Krishfield as a way of collecting oceanographic data from the ice-covered waters year-round. Deploying one involves drilling into the ice floe, lowering the profiler and cable through, and setting the buoy in the hole like a plug in a drain. Then the ITP is left to follow the ice wherever it goes. If the buoy happens to melt out, it continues to operate normally in open water. Some ITPs have journeyed massive distances over multiple years from the point where they were originally deployed, in many cases even leaving the Arctic Ocean by way of Fram Strait east of Greenland. ITP 79 hadn’t gotten very far since it was deployed last April, however, and a bug in the software that was preventing it from operating properly meant that it was worth our time to go grab it.

Having already bagged a mooring and an ITP, you’d think we might call it a day. But with an hour or so left before supper, the decision was made to also pick up an Acoustic Navigation Source (ANS) belonging to another WHOI engineer named Lee Freitag (not onboard ship). Briefly, the ANS has a buoy shaped like that of an ITP (but a quarter of the size) on top, and an acoustic source (think loudspeaker) hanging in the water about 150 meters below. A GPS in the buoy sends position information down to the acoustic source, which broadcasts that information as sound waves into the water. While probably as useless to eavesdropping Arctic cod as the electrocution they suffered at the hands of the ITP, this information is more significant to Autonomous Underwater Vehicles (AUVs) that use the acoustic signals to pinpoint their position. Despite the thick fog hanging over the icepack, we spotted the ANS without trouble. However, in the process of bringing it up, the cable connecting the buoy to the acoustic source got sandwiched between ice chunks and required some tricky maneuvering to dislodge. Fortunately for everyone involved, we had the thing safely onboard in time to feast on the ribs cooked up for dinner. 

Ending the day, for me at least, was a late CTD/rosette cast at station CB-7. While keeping an eye out for rogue ice, I got some valuable lessons on cribbage strategy from winch operator Leo Rose, who had watched an earlier match I had played against Yusuke Ogiwara and felt that my game needed a little refining. Moderate temperatures and large snowflakes illuminated by floodlights made it nice to be out on deck in the darkness. With the heavy silence pressing in from all around and the clean coolness of the breeze, I was reminded of snowy ski days back home in the Rockies and also, somewhat sentimentally, of Christmas Eve.



Last updated: September 18, 2017
 


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