The Climate System Model CSM1.4-carbon, developed by the U.S. National Center for Atmospheric Research (NCAR), is a comprehensive three dimensional climate-carbon cycle model described in detail in Doney et al. (2006) and Fung et al. (2005) and follow-up studies (e.g., Bozbiyik et al., 2011; Frölicher and Joos, 2011; Frölicher et al., 2011, Frölicher et al., 2009; Joos et al., 2011, Steinacher et al., 2011; Steinacher et al., 2009). It consists of ocean, atmosphere, land and sea ice components integrated via a flux coupler without flux adjustments (Boville et al., 2001; Boville and Gent, 1998). The atmospheric model CCM3 is run with a horizontal resolution of 3.75 degrees and 18 levels in the vertical (Kiehl et al., 1998). The ocean model is the NCAR CSM Ocean Model (NCOM) with 2 levels in the vertical and a resolution of 3.6 degrees in longitude and 0.8 degrees to 1.8 degrees in latitude (Gent et al., 1998). The sea ice component model runs at the same resolution as the ocean model, and the land surface model runs at the same resolution as the atmospheric model.

The CSM1.4-carbon model includes a modified version of the terrestrial biogeochemistry model CASA (Carnegie-Ames-Stanford Approach; Randerson et al., 1997), and a derivate of the OCMIP-2 (Ocean Carbon-Cycle Model Intercomparison Project Phase 2) ocean biogeochemistry model (Najjar et al., 2007). In the ocean model, the biological source-sink term has been changed from a nutrient restoring formulation to a prognostic formulation inspired by Maier-Reimer (1993). Biological productivity is modulated by temperature, surface solar irradiance, mixed layer depth and macro- and micro-nutrients. The empirical parameterization is intended to model the large-scale nutrient utilization by marine ecosystems. Following the OCMIP-2 protocols, total biological productivity is partitioned 1/3 into sinking POC flux and 2/3 into the formation of dissolved or suspended organic matter, where much of the latter is remineralized within the model euphotic zone. the ocean biogeochemical model includes the main proccesses of the organic and inorganic carbon cycle within the ocean and air-sea CO2 flux. A parametrization of the marin iron cycle (Doney et al., 2006) includes atmospheric dust deposition/iron dissolution, biological uptake, vertical particle transport and scavenging.


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