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Planktonic Ecosystem Response to Changing Sea Ice and Upper Ocean Physics in the Chukchi and Beaufort Seas: Modeling, Satellite and In Situ Observations


Funded by NASA Ocean Biology & Biogeochemistry and Cryosphere Programs

Jinlun Zhang and Mike Steele (University of Washington)
Carin J. Ashjian (Woods Hole Oceanographic Institution)
Robert G. Campbell (University of Rhode Island)
Victoria Hill (Old Dominion University)
Yvette H. Spitz (Oregon State University)




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Description of the Biology/Ice/Ocean Modeling and Assimilation System (BIOMAS) for the Chukchi and Beaufort seas (CBS)

BIOMAS (Zhang et al. 2010) consists of a Parallel Ocean and sea Ice Model (POIM, Zhang and Rothrock 2003) and a biological model. The POIM couples the Parallel Ocean Program (POP) with a thickness and enthalpy distribution (TED) sea ice model (Hibler 1980; Zhang and Rothrock 2003). Sea ice dynamics is calculated using the line successive relaxation (LSR, Zhang and Hibler 1997) method which is computationally efficient for high-resolution modeling.  BIOMAS grid configuration is based on a generalized orthogonal curvilinear coordinate system with the 'north pole' of the model grid displaced into Alaska. It has a high horizontal resolution for the Chukchi and Beaufort seas (CBS), ranging from an average of 4 km in the Alaskan coastal areas to an average of about 10 km for the whole CBS (Figure 1). This model grid configuration can resolve the Beaufort shelfbreak jet and the slope eddies and should improve the simulation of upwelling/downwelling in that region, which is essential to capture the shelf and basin processes and interactions in the CBS. There are 20 ocean grid cells across Bering Strait to resolve the fresh, nutrient-poor Alaskan Coastal Current as well as the saltier, nutrient-rich Gulf of Anadyr water entering the CBS. To create the right water masses and transports, critical to biological processes in the CBS, the regional ice/ocean model is one-way nested to a global ice/ocean model of Zhang (2005). Open ocean boundary conditions provided by the global ice/ocean model have been imposed along the southern boundary of the model along 39N latitude to properly simulate the Pacific and Atlantic water masses and transports. Observations of sea ice concentration and sea surface temperature are to be assimilated in BIOMAS. The biological model will consist of a sea ice ecosystem model and a water column ecosystem model. The schematic of the 11-component water column ecosystem model (Zhang et al. 2010) is shown in Figure 2.

The configuration of the finite-difference grid of BIOMAS is shown below.

model Grid
Figure 1. Model grid configuration showing (a) the entire model domain, consisting of the Arctic, North Pacific, and North Atlantic oceans and (b) the subdomain of the Chukchi and Beaufort seas. The model domain covers all the ocean north of 39N. The color contours in (a) indicate the model’s varying horizontal resolution in km. In (b), the thin red, green, and blue lines represent isobaths of 200, 1000, and 2000 m, respectively. The model has open boundaries along 39N (both in the Pacific and the Atlantic) and is nested to a global ice–ocean model (Zhang 2005).

bio model
Figure 2. Schematic of the BIOMAS pelagic ecosystem model which consists of 11 components including 2 phytoplankton groups (diatoms; flagellates), 3 zooplankton groups (microzooplankton; copepods; predator zooplankton), dissolved organic nitrogen, detrital particulate organic nitrogen, particulate organic silica, nitrate, ammonium, and silicate (Zhang et al. 2010).

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