Dispatch 4: Entering the Deep Waters     Print

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Fred Marin

September 15, 2019

Location: 73° 27’ N 135° 41’ W

Sea Conditions: 3248m water depth; open water with random patches of ice.

Sunday marked our 4^th day steaming north in the Beaufort Sea aboard the CCGS Louis S. St-Laurent where we sailed open waters throughout the day.  There was a 1-3’ sea, but that was too small to be felt by the powerful ship, and the lack of ice allowed steady progress to be made between stations.

Stations CB-40 and CB-50 located over deep waters in the southeast region of the Canadian Basin were both visited today.  At these two stations, full water column CTD-rosette casts were made.  Station CB-40, the deepest of the two stations had a water depth of 3248m where the CTD-rosette was sent to a depth of 3242m, or ~3.2 kilometers!  Lowering a several hundred-pound suite of instruments to such a great depth, and getting that close to the seafloor without touching is no accident.  A sea-cable with insulated electrical conductors at its core lowers the CTD unit over the side of the vessel through a block and a-frame.  Through those insulated conducting wires within the steel cable, power is sent to the instruments and real-time data is transmitted back aboard the ship.  The precise depth of the instrument package is carefully monitored using the CTDs sensitive, yet durable pressure sensor (it is able to withstand many atmospheres of pressure and still resolve minute changes in pressure!).  This allows the CTD operators to get as close to the bottom as possible without having to do any guess work.  It is important to collect water column data close to the bottom of the ocean, but equally important to not set the CTD-rosette unit into the silty, soft, substrate which could foul and potentially damage the delicate instrumentation.

It took 1 hour and 8 minutes to descend from the surface to the bottom (3.2km), and about the same amount of time to haul the CTD-rosette back to the surface.  On the descent CTD data is gathered, and on the ascent that data is used to determine which depths each of the 24 Niskin bottles on the rosette will be triggered to collect a discrete water sample.  Once aboard, the water from the Niskin bottles is rationed out to the various groups of scientists for immediate processing as time quickly degrades the quality of the samples once they are aboard the ship.

The CTD-rosette was not the only instrument to sample the two stations we covered today.  The “bongo” net was again towed from 100m to the surface.  Additionally, the NORPAC net was used to sample plankton from discrete sections of the water column at depth intervals of 200-100m, 100-50m, and 50-0m.

That concludes our window into life aboard the CCGS Louis S. St-Laurent for today.  Stay tuned for our upcoming posts as we move north into the ice floes!