RATIONALE :
The Southern Ocean (SO) is the only ocean in the world that has no surrounding boundaries so that
it can be connected to the other major ocean basins (Atlantic, Pacific and Indian).
The circumpolar winds blowing clockwise around the Antarctic continent
generate upwelling of deep waters that, first, reach the surface ocean, and then
, second, are transported towards mid-latitudes. Upwelled Deep water carry with them a
high content of macro-nutrients (silicate, phosphate and nitrate) that are, with light,
the major limiting factors for ocean primary production. The biogeochemical processes
occurring in waters of the Southern Ocean act as a tap for the amount
of macro-nutrients that feed the global ocean thermocline through SubAntarctic Mode
Waters (SAMWs) as shown by Sarmiento et al. (2004). The change in the biogeochemical
processes and ocean circulation in the Antarcic (AA) and SubAntarctic (SAA) zones
can then impact the productivity of the global ocean.
We are trying to build a simplified theoretical framework where we can incorporate
all the processes that control in the AA and SAA zones the abundance of macro nutruents that from the
Southern Ocean reach the rest of the globe. Those are :
1) Residual Mean circulation (mainly reduced to 2D) as wind-driven (Ekman) plus eddy-driven (bolus).
2) Aeolian Iron Supply via Dust Deposition.
3) Sea-Ice Cover Seasonality (with special reference to LGM/present comparison).
4) Change in Si/N ratio during nutrient uptake by SO diatoms depending on Iron availability.
Investigation has started with a simple two-box model(coded in MATLAB) where now we numerically solve differential equations for surface ocean [Silicate].
We are also working on a box model where we solve for Si* (Si* = [Si(OH)4] - [NO3]) coupling together two
sets of differential equations following the approach of Sarmiento et al. (2004).
We plan to add a few other boxes to represent the full connection between the Southern Ocean
and the rest of the world ocean. Afterwards, we are planning to test the same ideas
using global ocean MITgcm (with 2.8 degree of horizontal resolution) coupled to a biogeochemical model that has both diatoms (or silicifiers) and non-diatoms Plankton Functional Types (Dutkiewicz et al., 2005).
REFERENCES
J. L. Sarmiento, N. Gruber, M. A. Brzezinski, J. P. Dunne (2004)
High latitude control of thermocline nutrients and low latitude
biological productivity, Nature Vol. 427, pp.56-60.
S. Dutkiewicz, M. J. Follows, P. Parekh (2005) Interactions of the iron and phosphorus cycles:
A three dimensional model study, Global Biogeochemical Cycles, Vol. 19, doi:10.1029/2004GB002342.