Takuvik team carries out test deployments of gliders

Named after the Inuktitut word for the small surface wake left by a diving marine mammal,  Takuvik’s two gliders Qala1 and Qala2  will perform high resolution measurements of physical and biogeochemical variables in the Marginal Ice Zone of the Arctic.

 To prepare for the Arctic deployments, Takuvik’s glider team (Eric Rehm and Guislain Bécu) approached the Ocean Tracking Network (OTN) at Dalhousie University for hands-on training in the lab and in the field.  In October, we took Qala1 and Qala2 to Halifax for test deployments.  First, with the help of OTN’s glider engineer Adam Comeau, we assured that Qala2 would be neutrally buoyant in the waters of Bedford Basin in OTN’s ballasting tanks.  Then Qala2 was deployed for several hours, running a very short, but important mission to verify that all of is flight controls and scientific sensors were functional.  The first dive is always done on a 10 m leash, so the glider is easy to recover if something goes wrong. Subsequent dives were limited to about 30 m due to the shallow bottom in Bedford Basin.
All Bedford Basin photos and video is here.

On April 5-6, Takuvik returned to Halifax, sharing an offshore deployment mission on the Scotian Shelf with OTN.  Traveling  about 7 km from Halifax Harbour in a rented boat, OTN’s Adam Comeau and Sue L’Orsa deployed their glider for a month-long mission and Takuvik deployed our other glider, Qala1, for an overnight mission.

See more Scotian Shelf deployment photos and video here.
A three part mission, identical that which is planned for Baffin Bay, was run over the course of 24 hours. The first part of the mission represents the approach to the marginal ice zone, surfacing safely about 1 km away. The second part of the mission is the most critical and risky: travelling under the ice during this part of the mission, the glider does not surface and stays well below the ice and ice keels, which may be over 20 m deep! The glider is commanded to travel 1-2 km under ice, turn around and surface only when it comes back to open water. Depending on how far under the ice we go and the prevailing currents, this can take more than 10 hours. Finally, the last part of the mission is to go a bit farther away from the ice, back to the starting location.

On the Scotian Shelf, the glider completed this mission with one error : an internal alarm, reset only when there is surface communication, went off at 10 hours while the glider was still traveling in the “under ice” portion of mission. So, the glider came up a bit early, and then went on to its planned recovery location.

To prevent this from happening in the field, and possibly surfacing under ice,  we can lengthen the time for this alarm to 12 or more hours.  So, realizing this situation in the safety of Scotian Shelf waters (with no ice) helps us get all of our glider mission settings correct.

The  high-resolution physical and bio-optical data show a strong pycnocline (sharp change in sci_water_temp, salinity and density) at 30 – 40 m. High concentrations of chlorophyll (sci_bbfldcd_chlor_units) and oxygen saturation (sci_oxy4_saturation) above 100 % above the pycnocline show that that Scotian Shelf surface waters are highly productive for phytoplankton.  Consequently, nutrient levels (sci_suna_nitratue_um) show that nitrate is being consumed by the phytoplankton above the pycnocline with strong concentrations below.  High values of optical backscattering at the pycnocline (e.g., bb3slov2_bb660_scaled) shows a typical situation where a large concentration of plankton (phytoplankton and their grazers) hang out at sharp changes in density.  Another high scattering layer can be seen just above the bottom of the Scotian Shelf due to sediments suspended by ocean bottom currents.

All the mission plots can be found here.

By studying this kind of high resolution data taken repeatedly over the course of the phytoplankton spring bloom in Baffin Bay, we will see the evolution of the life cycle of nature’s primary producers, which provide the basis for the rest of the Arctic food web.

Leave a Reply