Description of task
In this task we aim at observing and understanding the interaction of the ice cover with the underlying waters originating in the gateway flows to the circumarctic shelves and central Arctic.
In the central Arctic Ocean the inflows from Atlantic and Pacific Oceans and the products of the Arctic shelves merge and are redistributed. Most of the Arctic river runoff spreads in the central basin in a thin fresh surface layer which together with the cold halocline disconnects the sea-ice cover from the warm Atlantic water layer below. In order to assess the vertical heat fluxes from the Atlantic water to the sea-ice we will observe the freshwater flow and storage and the halocline circulation in the Arctic Ocean. At the same time, the circulation and mesoscale processes which transfer the oceanic heat of Atlantic water from the boundary current into the central basins will be quantified. We will monitor the atmospherically forced strengthening and weakening of the basin-wide gyres and of the trans-polar flow which modifies the position, the extent and the thickness of the fresh surface layer and the halocline. One -dimensional models will be used in combination with measurements of the shear between the ice-cover and the underlying water and the vertical stratification. The heat flux from the Atlantic layer and modification of the surface mixed layer and halocline have a strong seasonal signal and thus year-round monitoring of the water properties and circulation are both needed to identify their roles in the development of the Arctic ice-cover.
The central Arctic Ocean component of DAMOCLES will inevitably be very innovative since the presence of a perennial ice cover puts limits on the use of conventional instruments and moorings. The DAMOCLES central Arctic Ocean observing system will be based on an extensive integrated array of Ice-Tethered Platforms (ITPs), floats and gliders. All will provide subsurface profiles of temperature and salinity of the upper 1000m, and the floats and Ice-Tethered Acoustic current profilers (ITACs) will also provide current measurements. The gliders will move along transects from the Transpolar Drift to the boundary current north of the Barents, Kara and Laptev Seas, receiving measurement-control and navigation information via a net of ITPs which communicate data to satellites in near real time. The ITPs themselves will deploy CTDs to obtain temperature and salinity profiles down to about 1000m depth and will collect meteorological and sea-ice data at the ice surface (WP1 and WP2). ITACs installed on the same flows as ITPs will provide current profiles from surface down to about 600m depth. Lagrangian Floats drifting at constant pressure (50 to 100m depth) will carry Upward Looking Sonar (ULS) and will provide information about sea-ice thickness distribution to validate satellite estimates of ice-thickness (WP1).
Though some of these systems already exist, others have to be developed (WP8). But by their use, direct measurements or validated estimates of the circulation, stratification and ice-volume of the Arctic Ocean will be possible with monthly-to-seasonal resolution for the first time. The DAMOCLES central basin array will take advantage of (a) the perennial sea ice cover for maintaining ITPs and ITACs in operation all-year-round during two years of the program and (b) long range acoustic propagation in deep waters facilitating underwater navigation and communication for high rate data transfer. The transfer of water masses from Arctic shelves into the deep basins across the continental margin (Task 2 of WP3) will be addressed by extensions of SBE transects with a heavy reliance on information from tracers such as Iodine 129, O18 and Barium in order to evaluate the integrative time-scales and pathways. We will perform detailed one-dimensional model studies at different locations using the available forcing and stratification data to quantify the heat flux from the warm Atlantic layer to the ice and thus assess how it affects the ice cover.
