Dispatch 12: Recovery of Mooring B     Print

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Mengnan Zhao

September 29, 2015

One of the major goals of our expedition is to understand long-term changes in the Beaufort Gyre. In this region, the Arctic Ocean is relatively fresh due to the clockwise atmospheric winds. The strength of this wind forcing controls the accumulation of relatively fresh surface water, as well as its release (when the atmospheric forcing becomes weaker). The large-scale wind forcing not only impacts the salinity and stratification of the Arctic Ocean, but has implications to the entire Arctic ecosystem and global climate. For this reason, the response of the ocean to evolving atmospheric forcing as the sea-ice cover changes requires thorough study. Three to four mooring systems (instruments anchored to the sea-floor, measuring the water column above) have been installed each year since 2003; these measurements of water properties, including salinity (to measure the fresh water) and temperature, have provided us with more than a decade of information.

Today we arrived at one of the mooring sites for the recovery of Mooring B, on the northwest side of the Canada Basin. Three moorings in total will be recovered and redeployed during this year’s cruise. The entire mooring has three main parts: a bottom 3800 lb anchor; a top floating sphere that is buoyant enough to keep the mooring in a vertical line most of the time; and a long wire between them supporting the sensors. Four devices are attached: an Upward Looking Sonar (ULS) mounted in the top of the flotation sphere that pings on the bottom of the sea-ice to infer sea-ice thickness; a unit called a McLane Moored Profiler (MMP) that moves up and down on the wire measuring water properties including current speeds; a sediment trap installed at around 3000 m on the wire to measure particles sinking through the water column; and a bottom pressure recorder (BPR) attached to the anchor. Also attached to the anchor is a set of two acoustic releases and floatation. The releases can be sent an acoustic signal from the ship that triggers the release to detach from the anchor for the recovery.

In addition to these instruments, a Remote Access Sampler (RAS) was attached at about 40 m designed to take water samples of dissolved inorganic carbon, nutrients, oxygen, and alkalinity every week for the entire year. Scientist Michiyo Yamamoto-Kawai (Tokyo University of Marine Science and Technology) is most excited about the samples made in winter – samples during the winter are rare in the Arctic when an icebreaker expedition is not possible. Michiyo and her student (Mika Hasegawa) will analyze these measurements to understand the seasonality of Arctic Ocean acidification.

Today’s recovery of Mooring B by the WHOI team and ship’s crew went smoothly. My extremely busy day ended with two rosette casts finishing around midnight. Enjoying the beautiful moon after a heavy snow in the Arctic with a cup of warm tea and my dear colleagues’ company felt wonderful.