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Mooring work, CTD casts, and surface seawater analysis

Mooring work, CTD casts, and surface seawater analysis

Lonny Lundsten and Michelle Côté

The principal activities conducted during this expedition on Sir Wilfrid Laurier are led by Chief Scientist Humphrey Melling of Fisheries and Oceans Canada. These activities include the servicing of subsea oceanographic instruments and moorings for ocean and sea‐ice monitoring, CTD rosette casts at selected locations, and continuous underway measurement of surface seawater accessed via a pumped thermo‐salinograph. Observations made by instruments mounted on these oceanographic moorings provide continuous year‐round ocean data that complement the detailed, but short‐lived, surveys conducted from ships. The moorings enable affordable long‐term monitoring of the seas surrounding Arctic Canada.

Some of the instruments in the mooring packages have a compass that needs to be calibrated.  We went ashore on a rocky island in the bay near Kugluktuk on a beautiful afternoon to calibrate the compass.

Chief Scientist Humfrey Melling and Jo Poole, a research technician of Fisheries and Oceans Canada, calibrate a compass.

The instruments used on these moorings acquire intriguing and ecosystem‐relevant views of the polar ocean at times of the year when humans are not there to see them. Upward‐looking sonar at the moorings’ tops measures ice thickness and topography, revealing the presence of ridges, level ice, and ecologically important leads; the sonar activates an interleaved second mode in summer to measure storm waves and surges (important to ocean mixing and to safety on shore and at sea).

Doppler sonar positioned deeper in the water column measures ice drift and ocean current at all depths, revealing opening and closing of the opening between the pack ice and fast ice in winter and the upwelling of nutrient rich water towards the photic zone. The strength of the echoes received by Doppler sonar reveals the ever-changing distribution of zooplankton in the water column. Sediment traps collect falling detritus, delivered by currents from river mouths and eroding coastlines, or originating from the bodies of living and dead marine organisms. Ambient sound recorders provide continuous recordings of sounds from marine mammals (e.g., bowheads, belugas, bearded seals, walruses), human activity (e.g., aircraft, shipping, distant seismic survey), and natural processes (e.g., ice fracture, ridge building, wind waves, blowing snow, seabed gas venting). Conventional sensors for seawater temperature and salinity reveal the seasonal cycles in shelf‐water properties driven by heating, cooling, freezing, and weather events.