Description of task
This task provides better knowledge of the exchange processes between the boundary and the interior of the Arctic Ocean with the ultimate goal of understanding and quantifying how much this exchange affects the ice cover.
The work focuses on observations along the boundary but also includes process-modelling elements. The strongest subsurface currents of the Arctic Ocean are constrained to follow topographic features, and moored arrays measuring velocity, temperature and salinity will be used to quantify volume, heat and salinity fluxes along the main transport paths. Significant reductions in boundary current transport imply loss to the surroundings, either to the shelves or the Arctic interior.
DAMOCLES will not be able to equip the Arctic with the necessary number of transport arrays, but will work in collaboration with US, Russian and Canadian efforts (notably the NABOS and CABOS experiments) to ensure a good coverage at three sites along the Eurasian slope:
- A mooring array at roughly 32 E, north of Spitsbergen.
- A mooring array east of St. Anna Trough.
- A mooring array in the Laptev Sea.
Moored CTD/velocity profilers, both in the boundary current arrays, and mounted on ice-tethered platforms in the interior (task 3.3), will obtain high horizontal and vertical resolution of thermohaline intrusions and mesoscale activity. The boundary current transport array along the Arctic margin will be combined with Sea Gliders. Some slope moorings will therefore be equipped with acoustic sound sources for glider navigation. The sea gliders will resolve the frontal structure between the boundary current and the interior. Integrated with the observations from profilers this allows for assessment of the regional loss of mass, heat and salinity from the boundary current to the Arctic interior. Where appropriate, double diffusive fluxes will be derived.
The mooring data will also be used to study the causes and impacts of mixing and water mass transformations at the slope. The major cooling of the Atlantic layer in the Arctic Ocean occurs through the heating of cold plumes penetrating into the Atlantic layer and through the entrainment of warm Atlantic water into these plumes. A simple slope convection model using the observations will be combined with the transports through Fram Strait to put bounds on the Atlantic water cooling and slope convection. One of the major sources of shelf plumes is Storfjorden at Svalbard. The strength and properties of the Storfjorden plume will be observed through the DAMOCLES period by two ADCP moorings, one at the sill and one at the slope, equipped with Microcat salinity sensors at 2500 and 3500m depth. Storfjorden will also be used as a test site for Lagrangian floats equipped with ULS before their use in the central Arctic.
The mooring program within this task will be complimented with hydrographic sections over the shelf break and into the deep ocean. Section work is planned at the Svalbard shelf and in the Laptev, East Siberian and Chukchi Seas, partly through the planned (Swedish national) use of R/V Oden. The location of the shelf-basin exchange (SBE) sections will be coordinated with the mooring program and with observations in the interior (task 3). The section work will provide detailed information of the spatial distribution of water masses and of intrusive structures as well as dense brine enriched slope plumes in the boundary current and deep ocean by use of CTD and tracer measurements. The spreading of river water will be investigated using tracer data.
In addition, the Russian partner will contribute oceanographic data obtained from the ice camps within the St. Anna and Franz-Victoria Troughs and historic data, systemized to characterize interannual and decadal scale variability of water masses on the shelf.
