HR: 17:30h
AN: U52C-07    [PDF]
TI: Biogeochemical Regime Shifts in a Model of the Subtropical Oceans
AU: * Follows, M J
EM: mick@mit.edu
AF: Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 United States
AU: Monteiro, F
EM: fmonteir@mit.edu
AF: Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 United States
AB: Recent observations show that the inorganic nitrogen to phosphorus ratio in the ocean's subtropical gyres changes on interannual to decadal timescales in association with biogeochemical regime shifts. Here in a highly idealized model of the subtropical oceans we illustrate how competition between diazotrophs and other phytoplankton might lead to such changes and regime shifts on decadal timescales. The simple two layer (mixed layer and thermocline) model exhibits a sustained oscillation in which the surface subtropical ocean switches between phosphorus and nitrogen limited regimes, and the role of nitrogen fixing organisms waxes and wanes on timescales of decades. While the physical communication between surface and thermocline waters sets the timescale of the oscillation there is no interannual or decadal variability in the models circulation. The decadal oscillation in this idealized model is due to biogeochemical interactions and not a response to climate change. We will describe the model and its behaviour in detail and discuss the implications for observed changes in the subtropical oceans of the North Atlantic and North Pacific.
DE: 4805 Biogeochemical cycles (1615)
DE: 4845 Nutrients and nutrient cycling
DE: 4855 Plankton
SC: U
MN: 2003 Fall Meeting