Marine Coupled Model Systems

Virtually all prognostic 3D marine biogeochemical models employ traditional ecosystem modeling approaches to simulate biogeochemical cycling. These models have been applied over a wide range of spatial scales, that is, from small coastal tributary systems, to ocean basin-scale simulations and on up to global ocean biogeochemical models. Many of the global modeling efforts that have been carried out to date have been aimed at simulating the impact of global warming and anthropogenic influences on marine biogeochemical cycles. The ecosystem models employed in these studies vary in complexity from simple NPZD-type models to complex multielement models that are designed to provide general simulations of the C, N, P, Si, and Fe cycles in the ocean (see, e.g., the Dynamic Green Ocean Project at http:// lgmacweb.env.uea.ac.uk/green_ocean/index.shtml). These models are being applied to address fundamental questions about ocean ecosystem dynamics and biogeo-chemical cycling, for example, determining the role of the oceanic ecosystem in the global carbon cycle, assessing the current state of the global marine nitrogen budget, and simulating the influence of Fe cycling and limitation on primary production and carbon cycling.

Basin-scale applications of coupled 3D marine ecosystem models have been used for similar purposes, though these efforts are often more focused on providing insights into the role and dynamics of specific physical, biogeo-chemical, and ecological processes. For example, basin-scale modeling efforts are often undertaken in an effort to understand the factors that drive ecosystem response and biogeochemical variability in specific ocean regions. Developing improved models for predicting biogeochem-ical functions, like N2-fixation, denitrification, and calcification, is also an active area of modeling research. There have been several coupled physical-biogeochemical modeling studies that have focused on elucidating the role of mesoscale eddies in driving vertical nutrient fluxes and, hence, primary production in the ocean. The latter have typically employed relatively simple ecosystem models (e.g., NPZD-type formulations) to minimize computational demand in order to maximize horizontal resolution.

A vast array of coupled modeling studies have been carried out in coastal systems. Recent examples include models based on the Regional Ocean Modeling System (see Hydrodynamic Models) that extend all the way from Florida to Nova Scotia along the east coast of North America, and from the tip of Baja California to Alaska along the west coast of North America, with the latter including nested subdomains with greater resolution for process studies in specific regions. Most of these efforts have employed relatively simple NPZD-type ecosystem models (e.g., Figure 3). In contrast, a coupled model system has also been recently developed for the North Sea, which employs the European Regional Seas Ecosystem Model (ERSEM). ERSEM is a complex marine biogeochemical model that has been developed by a consortium of European universities. It includes multiple plankton size classes, multiple limiting nutrients, and explicit simulation of both pelagic and benthic biogeo-chemical processes (see http://www.ifm.uni-hamburg.de/ ^wwwem/res/ersem.html). This model has been used in a wide range of applications, from zero-dimensional

Ersem Benthic

Figure 3 A schematic diagram of the Fennel et al. N-cycle model which has been applied over the east coast of North America. In addition to the pelagic components, this model also includes benthic N-cycle processes, that is, sediment denitrification. Reproduced from Fennel K, Wilkin J, Levin J, etal. (2006) Nitrogen cycling in the Middle Atlantic Bight: Results from a three-dimensional model and implications for the North Atlantic nitrogen budget. Global Biogeochemical Cycles 20(3): Art. No. GB3007.

Figure 3 A schematic diagram of the Fennel et al. N-cycle model which has been applied over the east coast of North America. In addition to the pelagic components, this model also includes benthic N-cycle processes, that is, sediment denitrification. Reproduced from Fennel K, Wilkin J, Levin J, etal. (2006) Nitrogen cycling in the Middle Atlantic Bight: Results from a three-dimensional model and implications for the North Atlantic nitrogen budget. Global Biogeochemical Cycles 20(3): Art. No. GB3007.

simulations to fully coupled 3D models of inland seas and coastal regions (Figure 4)

Numerous coupled models have also been applied in estuarine systems. In many cases, these models have been developed for the explicit purpose of guiding water quality management and nutrient reduction efforts and so have sought to simulate nutrient cycling and ecosystem response in the estuary with as much realism as possible. As a result, there has been a tendency toward including more and more complexity in these kinds of management-oriented models.

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