Dispatch 11: On Ice!     Print

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Mengnan Zhao

September 28, 2015

After our on-ice buoy deployments were postponed for two days due to weather, we finally made it onto the ice today. It was such a fantastic day, and there’s so much to write about! Around noon, after the morning fog lifted, the helicopter began ferrying gear and passengers to the ice floe chosen for the deployment earlier in the day by Rick. I was scheduled to be aboard the third flight, and I couldn’t wait to step on the sea ice for the first time, so I layered myself up right after lunch and waited anxiously in the helicopter hanger.

The floe was very close to the Louis – a huge multi-year ice floe, perfect for all our work – three buoy deployments and ice measurements. The first two groups had started work when I arrived on the ice. Away from the noise of the ship, it was so quiet and peaceful, with a thick layer of snow over the ice; I could clearly hear the gentle wind and the sound of my boots in the snow.

The sound of winches and motors drilling holes in the ice immediately jolted me back to reality. On this site, we were deploying: an Ice-Tethered Profiler (ITP), an O-buoy and an Ice Mass Balance Buoy (IMB). The first to be deployed was the IMB. As its name suggests, it consists of sensors monitoring snow, sea-ice growth, sea-ice surface and bottom melt – thus ice balance. This year, a newer version would be deployed. In this model, all the sensors are housed in a PVC cylinder about 3.5 m long. Rick Krishfield, Jeff O’Brien and Mike Dempsey carried it together and set it in the hole that had been drilled in the ice. They worked precisely, to make sure that the buoy was in contact with water, ice and air for reliable measurements.   

The deployments of the O-buoy and the ITP (the same two types of buoys that we recovered last Thursday) commenced at the same time. The O-buoy, which tracks Ozone, Carbon Dioxide and Bromine to understand the annual ozone depletion events between March and June, was deployed by John (Wes) Halfacre (Purdue University). Wes has been working towards this from the first day on board the Louis, assembling the buoy into two main parts: a bottom part consisting of a large yellow surface buoy housing with an aluminum cylinder stretching 2 m below containing sensors; and a top tower about 2 m tall with meteorological sensors, a camera, GPS, and satellite communications. Wes assembled these two parts and tested them extensively. It was exciting to witness the helicopter slinging the O-buoy and planting it in the hole drilled in ice (this buoy is so large, it cannot be lifted into the hole by hand).

While the O-buoy was being deployed, the WHOI group was busy deploying the ITP. Unlike the other two buoys, the ITP extends much deeper into the ocean; a wire tether over 750 m long extends from the bottom of the buoy housing into the deep water, held down by a weight at the bottom, and supporting a profiler going up and down logging measurements of pressure, salinity and temperature. The team first had to assemble a tripod and winch system to deploy the long wire and the ITP’s profiler. The tether’s bottom weight was put first through the drilled hole and sent deep. After this, the ITP profiler is mounted on the wire and sent through the hole. To top it off, the WHOI team places a large yellow buoy housing (attached to the other end of the tether) into the ice. I have been analyzing ITP data for the past three years, and am very familiar with the ITP system. I have to say that observing its deployment gave me a completely new appreciation – although the deployment procedure seems straightforward, each step needs tacit cooperation, extreme care and dedication to the task in harsh conditions. Thanks to the excellent teams on the ice today, all of the buoys were deployed efficiently and successfully.

The first ice station measurements (thickness and sea-ice core samples) were wrapped up after the buoys had been deployed. While waiting for the helicopter to pick us up, we played tag and long jump to keep warm. Playing games on the sea-ice and rolling in the pristine snow was such a wonderful experience that I will never forget!