Formation, Transformation, and Northward Spreading of Dense Saline Water Derived from Terra Nova Bay, Ross Sea, Antarctica

Non-Technical Abstract The deep world ocean is flooded with near 0°C water, drawn from the margins of Antarctica. Antarctic Bottom Water, as it is referred to, is mainly derived from cold water formed the over the continental shelves of the Weddell and Ross Seas, where the coastal water is exposed to frigid polar air masses spreading off the Antarctic ice sheet. Antarctic Bottom Water is a key component of the global ocean overturning system, which is fundamental to the global ocean heat, carbon and nutrient inventories, and hence the climate and marine ecosystem. The processes producing the dense shelf waters involve small scale factors associated with ocean/atmosphere/sea and glacial ice interaction. What is lacking from previous work is a coordinated, synchronous observational study of the seaward spreading, from formation, to export across the continental shelf edge, to its descent into the deep ocean. This work fills the gap, by investigating the characteristics of dense shelf water formed within Terra Nova Bay, Ross Sea, its transformation, modification and northward spreading within the Drygalski Trough in the western Ross Sea, feeding into the spill-over at the continental slope into the deep boundary current adjacent to Cape Adare. The sequence of events will be observed with a series of instrumented moorings along the pathway from Terra Nova Bay, along the Drygalski Trough and onto the boundary current adjacent to Cape Adare. The project is an international collaboration that involves the USA (this proposal), S. Korea, New Zealand and Italy. Technical Abstract The lower kilometer or two of the world ocean is flooded with near 0°C water derived from the Southern Ocean, the Antarctic Bottom Water (AABW). The cold end-member of AABW is formed over various sectors of the continental shelf of Antarctica, notable in the Weddell and Ross Seas. The governing processes producing the dense shelf waters involve small scale spatial and temporal factors associated with ocean/sea ice interaction, often related to coastal polynyas and katabatic winds, along with further modification by ocean-glacial ice interaction. There have been studies of the formation of dense shelf water, of export of shelf water over the shelf/slope, the descent of gravity currents into the AABW realm, and of flow paths of AABW spreading across the deep ocean well into the northern hemisphere. What is lacking is a coordinated, synchronous observational study of the seaward spreading, from formation of the dense shelf water to its spreading to the shelf/slope break and descent into the deep ocean. This program fills the gap, by investigating the characteristics of dense shelf water formed within Terra Nova Bay (TNB), Ross Sea, its transformation, modification and northward spreading within the Drygalski Trough in the western Ross Sea, feeding into the spill-over at the continental slope and the deep boundary current adjacent to Cape Adare. The team will deploy a series of moorings – two heavily instrumented full water column moorings within TNB to capture high-salinity shelf water (HSSW) production and a series of bottom-focused moorings to evaluate the transformation and northward spreading of the dense saline water. The broad science goals of the project will be addressed by this program through a coordinated analysis of these mooring measurements. The project is an international collaboration that involves the USA (this proposal), S. Korea, New Zealand and Italy. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.