Continental margin systems are important contributors to global nutrient and carbon budgets. Effort is needed to quantify this contribution and how it will be modified under changing patterns of climate and land use. Coupled models will be used to provide projections of future states of continental margin systems. Thus, it is appropriate to consider the limitations that impede the development of realistic models. Here, we provide an overview of the current state of modeling carbon cycling on continental margins as well as the processes and issues that provide the next challenges to such models. Our overview is done within the context of a coupled circulation-biogeochemical model developed for the northeastern North American continental shelf region. Particular choices of forcing and initial fields and process parameterizations are used to illustrate the consequences for simulated distributions, as revealed by comparisons to observations using quantitative statistical metrics.

[1] The near-shore waters of the New York/New Jersey Bight in April 2005 exhibited distinct regions of turbid water with clearly differing optical properties associated with the Hudson River plume. We examined the effect of variable light attenuation on the hydrodynamics and ecological response of the Hudson River plume and its environs using field observations and a 3-dimensional biophysical model. Important feedback mechanisms between the attenuation of light and the resulting impact on the mixed layer depth were revealed from the modeling results. High concentrations of chlorophyll, detritus and colored dissolved organic matter in the upper water column as a result of enhanced stratification increase the attenuation of light and modify the buoyancy driven circulation. This further impacts the growth of phytoplankton in the model and subsequently modifies the vertical profile of the attenuation coefficient, which in turn feeds back into the overall heat budget. Citation: Cahill, B., O. Schofield, R. Chant, J. Wilkin, E. Hunter, S. Glenn, and P. Bissett (2008), Dynamics of turbid buoyant plumes and the feedbacks on nearshore biogeochemistry and physics, Geophys. Res. Lett., 35, L10605,

Uncertainty in continental shelf air‐sea CO2 fluxes motivated us to investigate the impact of interannual and seasonal variabilities in atmospheric forcing on the capacity of three shelf regions along the U.S. eastern continental shelf to act as a sink or source of atmospheric CO2. Our study uses a coupled biogeochemical‐circulation model to simulate scenarios of “present‐day” and “future‐perturbed” mesoscale forcing variability. Overall, the U.S. eastern continental shelf acts as a sink for atmospheric CO2. There is a clear gradient in air‐sea CO2 flux along the shelf region, with estimates ranging from −0.6 Mt C yr−1 in the South Atlantic Bight (SAB) to −1.0 Mt C yr−1 in the Mid‐Atlantic Bight (MAB) and −2.5 Mt C yr−1 in the Gulf of Maine (GOM). These fluxes are associated with considerable interannual variability, with the largest interannual signal exhibited in the Gulf of Maine. Seasonal variability in the fluxes is also evident, with autumn and winter being the strongest CO2 sink periods and summer months exhibiting some outgassing. In our future‐perturbed scenario spatial differences tend to cancel each other out when the fluxes are integrated over the MAB and GOM, resulting in only minor differences between future‐perturbed and present‐day air‐sea CO2 fluxes. This is not the case in the SAB where the position of the along‐shelf gradient shifts northward and the SAB becomes a source of CO2 to the atmosphere (0.7 Mt C yr−1) primarily in response to surface warming. Our results highlight the importance of temperature in regulating air‐sea CO2 flux variability.

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