# gfdl's home page > people > anand gnanadesikan's home page > research foci
Southern Ocean Control of Global Density Structure
One of the fundamental issues in physical oceanography is what sets the global density structure. In a series of papers, I have argued that three processes are dominant- namely Southern Ocean winds, Southern Ocean eddies and low-latitude diffusion within the pycnocline. Recent work by Giulio Boccaletti suggests that tropical wind stress is also very important.
The basic idea is that the vast majority of the conversion of light water to dense water associated with the meridional overturning circulation occurs in the North Atlantic. The corresponding conversion of dense water to light water can occur either in the Southern Ocean, or in the pycnocline as the result of vertical diffusion. Mesoscale eddy processes determine the partition of upwelled water in the Southern Ocean which comes from the dense water sphere vs. that which comes from the light water sphere. Strong eddies result in a balance where most of the dense-to-light water conversion must occur in the pycnocline. Similarly, strongly pycnocline diffusivity results in a situation where most of the dense-to-light water conversion must occur within the pycnocline.
In a paper published in Science in 1999 I developed a simple theory which shows how this balance plays out. The basic theory described here was recently verified by Barry Klinger and colleagues in both isopycnal and level-coordinate general circulation models.
This work implies that there is a relationship between wind stress in the Southern Ocean and the depth of the pycnocline to the north of the Southern Ocean. Bob Hallberg and I have explored this in two papers. More recently, we have run eddy-resolving simulations of the Southern Ocean to look at how eddies affect the response to winds. Joellen Russell, Robbie Toggweiler and I have also begun looking at the impact of the position of the Southern Hemisphere westerlies on the circulation.
References
Gnanadesikan, A., 1999: A simple theory for the structure of the oceanic pycnocline, Science , 283 , 2077-2079.
Gnanadesikan, A. and R.W. Hallberg, 2000: On the relationship of the Circumpolar Current to Southern Hemisphere winds in coarse-resolution ocean models, Journal of Physical Oceanography , 30, 2013-2034.
Hallberg, R.W., and A. Gnanadesikan, 2001: An exploration of the role of transient eddies in determining the transport of a zonally re-entrant current, Journal of Physical Oceanography, 30 , 3312-3330.
Gnanadesikan, A., R.D. Slater, N. Gruber and J.L. Sarmiento, 2002: Oceanic vertical exchange and new production: a comparison between models and observations, Deep Sea Research, Part II , 49, 363-401.
Gnanadesikan, A., R.D. Slater and B.L. Samuels, 2003: Sensitivity of water mass transformation to subgridscale mixing in coarse-resolution ocean models, Geophysical Research Letters , 30, 1967, doi:10.1029/2003GL018036.
Gnanadesikan, A., R.D. Slater, P.S. Swathi and G.K. Vallis, 2005: The energetics of ocean heat transport, Journal of Climate, 18, 2604-2616.
Gnanadesikan, A. and 27 others,2006: GFDL's CM2 global coupled climate models- Part 2: The baseline ocean simulation, Journal of Climate , 19,675-697.
Hallberg, R.W. and A. Gnanadesikan, 2006: The role of eddies in determining the structure and response of the wind-driven Southern Hemisphere overturning: Initial results from the Modeling Eddies in the Southern Ocean Project, Journal of Physical Oceanography , 36, 2232-2252.
Russell, J., K.W. Dixon, A. Gnanadesikan, R.J. Stouffer, and J.R. Toggweiler, 2006: The Southern Hemisphere Westerlies in a warming world: Propping open the door to the deep ocean, Journal of Climate 19 , 6381-5390.