Dynamics of the Orkney Passage Outflow


Alberto Naveira Garabato (PI), Eleanor Frajka-Williams, Mike Meredith (BAS), Povl Abrahamsen (BAS) with partners Sonya Legg (GFDL) and Kurt Polzin (WHOI).

In DynOPO, we set out to test and, if necessary, redefine this hypothesis by:

(1) carrying out the first systematic measurements of how AABW flows through the Orkney Passage, how its properties change along the way, and what processes are important in determining the AABW flow and transformation in the passage;

(2) determining how and why the flux and properties of AABW in the Orkney Passage respond to wind forcing on time scales of up to several years.

To address task (1) above, we will measure the velocity and properties of AABW and the intensity of turbulent mixing at several key locations in the passage. The observations will be obtained both with instruments lowered to the seabed from a ship and with a novel autonomous underwater vehicle, which is particularly effective at measuring a range of potentially crucial processes occurring near the ocean floor. To address task (2), we will enhance an array of moorings recently deployed in the Orkney Passage by the British Antarctic Survey to monitor the flux and properties of AABW. We will equip the moorings with sufficient oceanographic instrumentation to identify the processes determining the AABW’s response to wind forcing, which are not resolved by the present array.

We will use our findings from tasks (1) and (2) to define how and why the volume and properties of the AABW escaping the Weddell Sea through the Orkney Passage react to changes in winds. Armed with this new understanding, we will revisit the widespread AABW warming and contraction observed over recent decades, and inform the international strategy to monitor future changes in AABW circulation.

Cruise photos, DynOPO JR310 We’ve completed the first cruise for DynOPO on the RRS James Clark Ross (Mar-Apr 2015). During the cruise, we successfully deployed 7 enhanced moorings in the Orkney Passage. See cruise photos at here. The recovery cruise with process study is planned for the southern hemisphere summer season in 2017. Stay tuned!

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