To clarify interannual variability in sea ice, ocean heat transport, marine ecosystem, and acidification in the Arctic Ocean, seasonal to decadal hindcast experiments are performed using a pan-Arctic sea ice-ocean model. Horizontal resolution is approximately 5 km so that mesoscale eddies and narrow boundary currents can be resolved.

The physical part of the coupled sea ice-ocean model is the “Center for Climate System Research Ocean Component Model (COCO)” version 4.9 (Hasumi, 2006). The sea ice component includes a multi-thickness-category configuration based on that of Bitz et al. (2001) with a one-layer thermodynamic formulation (Bitz and Lipscomb, 1999), the linear-remapping method for category transfer (Lipscomb, 2001), and the elastic-viscous-plastic rheology (Hunke and Dukowicz, 1997). In addition to the open water category, the lower limit of sea ice thickness in each category is set to 10, 30, 60, 100, 250, and 500 cm, respectively (i.e., 7 categories). The ocean component is a free-surface general circulation model formulated using the advection scheme of Leonard et al. (1994) and the turbulence closure mixed-layer scheme of Noh and Kim (1999). The COCO model can be coupled with a lower-trophic marine ecosystem model, “North Pacific Ecosystem Model for Understanding Regional Oceanography (NEMURO)”. The detailed configuration of the original NEMURO model, which represents pelagic plankton species (i.e., diatom, flagellate, and copepod), is described in Kishi et al. (2007). Sea ice ecosystem was also incorporated in the GRENE project. In the developed model (called “Arctic NEMURO”, hereafter), the habitat of ice algae is confined to a thin skeletal layer. The biogeochemical variables in the sea ice component comprise ice algae (IA), ice-related fauna (IF), nitrate (NO3), ammonium (NH4), silicate (SIL), dissolved organic nitrogen (DON), particulate organic nitrogen (PON), and opal (OPL). The model domain contains the entire Arctic Ocean, the Greenland-Iceland-Norwegian Seas, and the northern part of the North Atlantic. The horizontal resolution is 5 km, and there are 1,280 × 1,024 grid points. There are 42 hybrid σ-z vertical levels. Vertical resolution varies from 2 m at the top to 500 m at the bottom. The σ-coordinate composed of three levels is applied to the uppermost 10 m. The atmospheric forcing components were constructed from the National Centers for Environmental Prediction/Climate Forecast System Reanalysis (NCEP/CFSR) 6-hourly dataset (Saha et al., 2010). Pacific water inflow is provided at the Bering Strait, based on Woodgate et al. (2005). The integration period covers seasonal to interannual timescales depending on computational resources.

JAMSTEC Earth Simulator

03:21 on Thu October 17, 2019