Deepak Cherian


Research Summary

I study the interaction of large deep ocean eddies with the continental shelf and slope. These eddies represent a particularly interesting example of the interaction between deep oceanic waters (generally warm and salty) with the cooler and fresher waters on the continental shelf. The patch of ocean that most motivates my work is the Mid-Atlantic Bight - a section of the continental shelf just south of Cape Cod.

A short explanation of what happens is as follows. The Gulf Stream, found much farther offshore, is unstable and sheds eddies that are approximately 100km wide and 1000-2000m deep. Because the earth rotates, these eddies move westwards towards the shelf and slam into the extremely steep slope. The major consequence of this interaction are an enhanced exchange of waters between the deep ocean (warm and salty) and the coastal ocean (cold and fresh). But how much water is transported in these interactions? Is the exchange permanent; in the sense that any water that moves off the shelf doesn't go back onto it? More fundamental questions concern the behaviour of eddies over steeply sloping topography (here, the continental slope). Does the eddy lose some of it's vertical structure over the slope? What stops the eddy from crossing the slope onto the shelf?

These are questions that I seek to answer during my stay in the Joint Program working with my advisor, Ken Brink. The problem has been studied for at least three decades now and it is still unclear what the answers are. Such interactions are hard to study observationally because you need to be exactly in the right place at the right time. Satellite observations show us tantalizing images of such interactions but reveal no information about the vertical extents of the physics. So, I use very idealized numerical models to study the problem. Essentially, I run numerical experiments where eddies of different sizes slam into shelves and slopes of different geometries. The idea is to understand the system in all it's different configurations and explore how the relevant physical parameters modulate the interaction. This is important because similar interactions take place all over the world; for example, off northeastern Brazil, the west coast of South Africa, in the Gulf of Mexico and in the Mediterranean. Changing the eddy and topography parameters lets me approximate interactions in vastly different areas of the ocean.

In studying this problem, I have gradually become more interested in the dynamics of the "Slope Sea" which is the patch of ocean between the coastal ocean (which ends at the shelfbreak) and the deep ocean, with an very steep sloping bottom. The role of more gently sloping topography is better understood and so, this region presents some interesting challenges in understanding it. I think that is what I will be studying in the near future; where the deep ocean transitions to the shallow ocean.