Laboratory Experiments Investigating the Influence of Sea Ice Extent on the Distribution of Pacific-origin Water in the Arctic Ocean
AbstractPacific water enters the Arctic Ocean via the Bering Strait and, after being modified on the Chukchi Shelf, flows along the shelf break around the boundary of the Beaufort Sea. The mechanisms by which Pacific-origin water ‘escapes’ the topographic constraint and brings the Pacific signature nutrients, temperature and salinity into the interior of the Arctic Ocean are still partly unknown. Eddies were recently found to be an efficient and important mechanism to bring Pacific-origin water into the interior and ventilate the Arctic halocline. Mechanisms for ventilation of the halocline are of fundamental importance to the global climate since the halocline ‘insulates’ the sea ice cover from the warmer Atlantic waters found at depth.
The Canada Basin is filled with anticyclonic eddies formed by different mechanisms. Neither locally generated eddies in regions of buoyancy loss in the interior, nor those produced by frontal subduction, can bring Pacific-origin waters off the shelf break. However, the Pacific-origin water flowing in the current along the boundary of the Beaufort Sea can generate dipoles (i.e. an anticyclonic-cyclonic pair) by either baroclinic instability of the current itself, or by the presence of canyons which induce dipole formation at their mouth. Preliminary experiments suggest that Barrow Canyon, in the north-east corner of the Chukchi Sea, could be a prime spot for the latter mechanism to occur.
The self-propagating characteristic of dipoles is necessary to bring the Pacific-origin water into the Canada Basin. However, numerical experiments have shown that the upper-layer cyclonic part of these dipoles is dissipated by sea ice cover. Once the cyclonic vortex disappears, the remnant anticyclonic vortex is no longer able to self-propagate into the basin and is passively advected by the Beaufort Gyre around the basin. This scenario highlights the possibility that sea ice extent plays a significant role in dipole propagation, and consequently Pacific-origin water distribution, in the Arctic Ocean. Hence, there is the need to better understand the propagation of dipoles in the presence of sea ice cover. Several questions then arise: How is the dipoles’ propagation affected by different sea ice extent? Can the forecasted sea ice retreat cause a change in distribution of Pacific-origin nutrients, temperature and salinity in the Arctic Ocean? Can a positive feedback exist between dipole propagation and sea ice extent?
In order to answer these questions I propose to use a set of idealized laboratory experiments to investigate the influence of sea ice extent and roughness on the propagation of dipoles away from the coastline. The ventilation of the halocline and the distribution of Pacific-origin water in the Arctic Ocean impact the circulation and the ecosystem of the Arctic Ocean and the global climate. If funded, this study will give me the unique opportunity to apply my expertise in eddy formation and propagation to identify a possible positive feedback between dipole propagation and sea ice extent. This feedback could have a great societal impact since changes in the sea ice extent can have significant consequences on the global climate system. This study will foster collaboration since it is complementary to the observational and numerical work that Drs. Plueddemann, Pickart and Spall are conducting in the Beaufort Sea. Finally, this study will allow me to obtain some important preliminary results to submit a larger study to OPP-NSF, possibly in collaboration with Drs. Spall and Plueddemann, investigating the entire Pacific water cycle in the Arctic, from dipole formation to its dissipation, and its influence on the sea ice extent and the global climate.