BCM-C, UiB (BCCR)

The University of Bergen (UiB) run two model setups within EPOCA. the fully coupled Bergen Earth System Model (BCM-C), as included in the EPOCA model archive, is detailed below. The second set up is a trand-alone MICOM/HAMOCC run forced by NCAR reanalysis data. The evaluation of this system is described in detail in appendix 1.

The fully coupled Bergen Earth System Model (BCM-C) is an extension of the Bergen Climate Model with an addition of terrestrial (LPJ) and oceanic carbon cycle model (HAMOCC5.1). The physical climate model constists of ARPEGE from Meteo-France and the Miami Isopycnic Coordinate Ocean Model (MICOM). The model simulation is fully coupled and forced by historical emissions of CO₂. For more details on BCM-C see Tjiputra et al. (2010). MICOM is documented in Bleck and Smith (1990) and Bleck et al. (1992). Updates to the model code ar described in Bentsen et al. (2004) and Assmann et al. (2010). With the exception of the equatorial region, the grid configuration employed here is almost regular with a horizontal grid spacing of approximately 2.4° × 2.4°. In order to better resolve the dynamics near the equator, the horizontal spacing in the meridional direction is gradually decreased to 0.8 along the Equator. The model has a time step of 4800 seconds and a stack of 34 isopycnic layers in the vertical coordinate, with potential densities ranging from 1029.514 to 1037.800 kg m^-3. A non-isopycnic surface mixed layer on top provides the linkage between the atmospheric forcing and the oceanic interior.

The current version of HAMOCC (Maier-Reimer et al., 2005) includes an NPZD-type (nutrient, phytoplankton, zooplankton an detritus) ecosystem model following Six and Maier-Reimer (1996). The model contains over 30 biogeochemical tracers, which include dissolved inorganic carbon, total alkalinity, oxygen, nitrate, phosphate, silicate, iron, phytoplankton and zooplankton. Fixed Redfield ratios (i.e., P:N:C:ΔO₂) are used for production and remineralization of biogenic matter. In addition to temperature and light, the phytoplankton growth rate is also co-limited by nitrate, phosphate and iron concentrations. The modelled bulk phytoplankton concentration is divided into diatom and coccolithophore compartments, based on silicate concentration (i.e. higher diatom fraction when the prognotic silicate concentration is high). In the tropical oligothophic nitrate-depleted regions, the marine ecosystem module accounts for atmospheric nitrogen figation as for cyanobacteria growth. Particulate organic carbon, produced due to the ecosystem dynamics, is exported out of the euphotic zone with a constant sinking speed. Once exported, the organic matter is remineralized at depth, and the non-remineralized particles are collected by the sediment. The inorganic carbon chemistry in the model is based on Maier-Reimer and Hasselmann (1987). The surface pCO₂ is computed prognostically as a function of alkalinity, total DIC, temperature, pressure and salinity. The dissolution of calcium carbonate at depth is computed as a function of carbonate ion saturation state and a constant dissolution rate. The air-sea gas (i.e., CO₂ and O₂) exchange processis are formulated as a function of gas solubility, transfer velocity and the difference between partial pressure tracers in air and water.