Previous work, using of a single column ice-ocean model, showed that resolving the high spatial variability in ice-ocean brine exchange has important implications for ocean mixing and consequent sea ice mass budgets that influence critical climate feedbacks. In particular, multiple ocean columns in each grid with leads that are realistically embedded within the ice cover were needed to improve simulations against Surface Heat Budget for the Arctic Ocean (SHEBA) observations. Currently, this method has not been tested or implemented in any climate models. Since the single column ice-ocean model study was limited to the summer ice melting season and in a 1-D format only, funds are provided to allow further studies on the multi-column ocean grid (MCOG) and related processes. Questions to be explored include: How does MCOG work during the ice growth period? How can MCOG be implemented in 3-D climate models? How does MCOG influence physical and biogeochemical tracers that have fluxes between ice and ocean? How much can MCOG reduce uncertainties in climate models? What is the importance of explicitly representing the high ice/ocean flux spatial heterogeneity in climate processes and feedbacks? How will representing this sub-gridscale variability reduce uncertainties in climate models?
A more systematic study and implementation of MCOG in climate models to reduce uncertainties associated with the high spatial heterogeneity in sea ice is the focus of this study. A Climate Process and Modeling Team will address MCOG-related problems and implementation in climate models systematically. The following studies are planned: 1) Use sea ice and ocean field data and a small regional ice-ocean model with and without MCOG to quantify key parameters and investigate climate and biogeochemical processes influenced by the MCOG, 2) Implement the MCOG scheme in the Community Climate System Model (CCSM) and GFDL climate models, conduct long-term runs, and investigate the influence on climate and biogeochemical feedbacks, 3) Validate the new model with observations, and conduct model inter-comparison with other Intergovernmental Panel on Climate Change (IPCC) climate models, and 4) Solicit more climate model users to participate in using and assessing the new method through workshops, web-based communications, and distribution of the new model code.
Significant changes have occured in the climate conditions in polar regions over the last 30-40 years. Perhaps the most dramatic of these, as revealed by the satellite record since 1979, are large reductions in sea ice cover within the Arctic and significant regional changes in Antarctic sea ice that largely compensate, leading to a small overall increase. Climate model's project that large future changes in sea ice are to be expected with increasing emissions of greenhouse gases and that overall sea ice will decline over the 21st century. However, while the sign of change is consistent across models, considerable differences are simulated in the rates of ice loss. This is in part due to different representations of physical processes within the model and indicates that model improvements are needed to reduce uncertainty in predictions of polar climate conditions and their related impacts. This project seeks to improve a particular aspect of sea ice within climate models, specifically the role that high spatial heterogeneity in sea ice, which is an observed and ubiquitous aspect of the ice cover, has on ocean conditions. As part of this effort new developments have been incorporated into the Community Earth System Model (CESM), a publically released climate model that is used by many scientists to address a diverse set of research questions. The model improvements developed under this project lead to significant improvements in the simulation of the marine ecosystem within polar regions, because different sunlight regimes, which have an influence on photosynthesis, are more accurately represented. This in turn allows for a more reliable simulation of the role of changing sea ice conditions on ocean primary productivity, enabling future research in this area. This has implications for the understanding of possible societal impacts of a changing polar sea ice cover, through the potential iinfluence on high latitude fisheries. It also has implications for the overall carbon cycle and the role that polar oceans play in the uptake of carbon. Additionally, these model improvements will be available to the general research community through releases of the CESM. As such, this project has contributed to the available climate research infrastructure.
