Interaction of a Glacial Meltwater Outflow with a Shelf Break Jet

Abstract:

The fate of glacial meltwater discharged into the ocean is a problem of significant scientific and societal interest. The problem has received considerable attention in the past decade as a result of the estimated mass loss of the Greenland Ice Sheet. It also arises in paleoceanography, as the recurrent release of glacial meltwater from the Laurentide Ice Sheet is generally thought to have altered the meridional overturning circulation and the attendant poleward heat flux in the North Atlantic, leading to the sequence of abrupt climate changes of the last glacial period. The processes leading to the transport of glacial meltwater to the open ocean, however, remain poorly understood. Notably, glacial meltwater released into the ocean is expected to lead to the formation of a buoyant gravity current flowing along the coast in the Kelvin wave sense, rather than to spread directly offshore. Nevertheless, observations in the modern ocean suggest that different mechanisms may lead to the offshore export of buoyant water released along the coast.

Here the interaction of glacial meltwater released along the coast with an eddying jet at the shelf break is explored using numerical experiments with a regional model of ocean circulation. The model domain is idealized, comprising a shelf, a continental slope, and a deep basin. Numerical experiments of the fate of glacial meltwater discharged along the coast are conducted with O(1 km) horizontal resolution in order to resolve the (sub)mesoscale phenomena that are thought to favour the cross-shelf exchange of material at the shelf break. Emphasis is placed on the role of different factors in the offshore export of glacial meltwater discharged on the shelf, such as the temperature and salinity of the discharged water relatively to those of ambient shelf water, the strength of the glacial water outflow relatively to the strength of the shelf break jet, the depth and width of the shelf, and the level of eddy kinetic energy of the shelf break jet. An effort will be made to develop scaling relationships for the seaward export of glacial meltwater in terms of these variables, and the implications of our results for our understanding of the fate of glacial meltwater introduced on continental shelves will be clarified.