| A coupled, three-dimensional, time-dependent numerical model of water circulation, plankton dynamics, and nutrient/CDOM loadings from the estuarine and deep-sea boundaries of the West Florida shelf (WFS) provided an assessment of the utility of nutrient and color signals as biochemical and bio-optical tracers of wind-forced and buoyancy-forced perturbations of the of this continental margin's physical circulation. The coupled model consisted of state variable quantities for temperature, salinity, horizontal/vertical velocity components, turbulent diffusion, spectral light, terrestrial and marine colored dissolved organic matter (CDOM), dissolved organic nitrogen, nitrate, ammonium, phosphate, phytoplankton (POC, PON, POP, chlorophyll, accessory pigments, heterotrophic bacteria, large and small particulate detritus of biotic origin, and lithogenic suspended sediments. Over the shelf and slope of the eastern Gulf of Mexico, from the Mississippi River Delta to the Florida Keys, three cases of the model were run during March-May of (1) local riverine forcings; (2) far-field shelf-break forcings; and (3) both terrestrial and deep-sea supplies. HyCODE and NEGOM shipboard data sets during 1998--2000 provided initial and boundary conditions for the coupled model. Independent validation data were concurrent satellite surveys of the near-surface color constituents of chlorophyll, absorption by CDOM, and backscatter by biogenic and lithogenic particles.; The simulation analyses indicated that a combination of both estuarine and deep-sea nutrient supplies is required to replicate the observed particulate forms of carbon, nitrogen, and phosphorus as well as in situ surface stocks of phytoplankton pigments on the WFS during spring 1998. High simulated attenuation of visible irradiance within surface low-salinity plumes, largely due to CDOM, inhibited the ability of sub-surface phytoplankton stocks to assimilate inorganic nutrients, thereby changing the simulated spatial and temporal patterns of phytoplankton biomass and productivity resulting from upwelling in the northeastern Gulf of Mexico. This work suggests that it is the physical circulation of the WFS---set in motion by winds, buoyancy fluxes, and intermittently by the Loop Current---that drives seasonal patterns of primary productivity. Subsequent interaction between estuarine outwellings and deep-sea water masses may then modulate both the ecological cycling of elements as well as seasonal patterns of surface phytoplankton stocks inferred from ocean color imagery. |
