Coupled physical-biogeochemical models provide a useful framework for testing our ideas about the underlying physical, biological and chemical controls on elemental cycling in the ocean. Up to now, efforts to do so on basin scales have produced mixed results.  The seminal work of Sarmiento et al (1993) and Fasham et al (1993) demonstrated that the large scale distributions of chlorophyll in the surface waters of the North Atlantic could be simulated with a reasonable degree of accuracy using a simple planktonic ecosystem embedded in a coarse resolution general circulation model.  While the general characteristics of these large scale patterns were consistent with observations, detailed comparisons with time series data at specific sites revealed that the underlying flux balances maintaining these distributions were not as satisfactory. In particular, the nutrient budget in the Sargasso Sea was dominated by horizontal advection.  This result is quite different from recent regional modeling studies (McGillicuddy 1995; McGillicuddy and Robinson, 1997) which have suggested that upwelling in the interiors of cyclonic mesoscale eddies is the dominant mode of nutrient supply to the euphotic zone in the open ocean.

During the last several years, the World Ocean Circulation Experiment Community Modeling Effort (CME) has made significant progress in the development of more realistic general circulation models. Areas of improvement particularly relevant to biogeochemical processes include (1) aspects of the time-mean flow, (2) treatment of the surface boundary layer, and (3) the resolution of mesoscale eddies. This next generation of GCMs represents a substantial step forward in the physical bases on which coupled biogeochemical simulations can be built. It is proposed herein to construct the first basin scale eddy-resolving biogeochemical simulations of the North Atlantic to examine the impact of mesoscale processes on large scale elemental budgets.  A suite of experiments is planned which are based on 1 degree (coarse), 1/3 degree (eddy-permitting) and 1/6 degree (eddy-resolving) CME simulations.  The coarse resolution runs will be used to benchmark the Sarmiento and Fasham results, and serve as a control run for the higher resolution calculations.  Although the eddy-permitting case will most likely not be entirely sufficient for a comprehensive study of mesoscale processes, it does represent a meaningful intermediate step that will provide useful information without incurring the substantial computational cost of the 1/6 degree runs.  This will set the stage for a relatively small number of fully eddy-resolving runs which have only recently become feasible from a computational point of view.  Understanding gained from these experiments will be used to guide the development of parameterizations for mesoscale biogeochemical processes to permit their inclusion in larger scale (global) models.

Basin-scale model results for the North Atlantic

Additional results may still be available via the project website: http://science.whoi.edu/users/mcgillic/pop-bgc/pop-bgc.html
Anyone who wishes access to the model solution (located on the mass store at NCAR) should contact Dr. McGillicuddy directly.

McGillicuddy, D.J., Robinson, A.R., Siegel, D.A., Jannasch, H.W., Johnson, R., Dickey, T.D., McNeil, J., Michaels, A.F. and A.H. Knap. 1998. Influence of mesoscale eddies on new production in the Sargasso Sea. Nature, 394, p 263-266.

McGillicuddy, D.J., Johnson, R.J. Siegel, D.A., Michaels, A.F., Bates, N.R., and A.H. Knap. 1999. Mesoscale variations of biogeochemical properties in the Sargasso Sea, J. Geophys. Res., 104, p 13,381-13,394.

Siegel, D.A., McGillicuddy, D.J. and E.A. Fields. 1999. Mesoscale eddies, satellite altimetry and new production in the Sargasso Sea, J. Geophys. Res., 104, p 13,359-13,379.

McNeil, J.D., Jannasch, H.W., Dickey, T.D., McGillicuddy, D.J., Brzezinski, M. and C.M. Sakamoto. 1999. New chemical, bio-optical and physical observations of upper ocean response to the passage of a mesoscale eddy off Bermuda, J. Geophys. Res., 104, p 15,537-15,548.

McGillicuddy, D.J., Kosnyrev, V.K., Ryan, J.P. and J.A. Yoder. 2001. Covariation of mesoscale ocean color and sea surface temperature patterns in the Sargasso Sea, Deep-Sea Res. II, 48, p 1823-1836.

Garcon, V.C., Oschlies, A., Doney, S.C., McGillicuddy, D.J. and J. Waniek. 2001. The role of mesoscale variability on plankton dynamics in the North Atlantic, Deep-Sea Res. II, 48, p 2199-2226.

McGillicuddy, D.J. 2001. The internal weather of the sea and its influences on ocean biogeochemistry, Oceanography, vol. 4(4), p 78-92.

McGillicuddy, D.J. 2001. Models of small-scale patchiness, In: Encyclopedia of Ocean Sciences - Vol. 5 (S), Steele, J.H., Turekian, K.K. and S.A. Thorpe (eds.), Academic Press, London, pp. 2820-2833.

Flierl, G.R. and D.J. McGillicuddy. 2002. Mesoscale and submesoscale physical-biological interactions, In: Biological-Physical Interactions in the Sea, The Sea, vol. 12, A.R. Robinson, J.J. McCarthy and B. Rothschild (eds.), John Wiley & Sons, New York, p 113-185.

McGillicuddy, D.J., Anderson, L.A., Doney, S.C., and M.E. Maltrud. 2003. Eddy-driven sources and sinks of nutrients in the upper ocean: Results from a 0.1 degree resolution model of the North Atlantic, Global Biogeochem. Cycles, 17(2), 1035, doi:10.1029/2002GB001987.

McGillicuddy and Kosnyrev  "Modeling mesoscale biogeochemical processes in a TOPEX/POSEIDON diamond surrounding the US.JGOFS Bermuda Atlantic Time Series"
(also published on Final Data report CD-ROM volume 2)

McGillicuddy  "Impacts of mesoscale processes on biogeochemical fluxes in the North Atlantic:  Basins-scale eddy-resolving simulations"

Larry Anderson
Department of Applied Ocean Physics and Engineering
Woods Hole Oceanographic Institution
98 Water Street, MS#9
Woods Hole, MA 02543
tel: (508) 289-3742
fax: (508) 457-2194
landerson@whoi.edu
http://www.whoi.edu/science/AOPE/people/landerson/index.html