A simple coupled atmosphere-ocean-sea ice-land surface-ice sheet model for climate and paleoclimate studies.

摘要

We develop a new coupled atmosphere-ocean-sea ice-land surface-ice sheet model for long-term climate change studies. This five-component model incorporates the seasonal cycle, and the three major ocean basins, the Antarctic Circumpolar Current region and the major continents are resolved. The model variables are sectorially averaged across the different ocean basins and continents.; The above coupled model (less the ice sheet component) is first used to simulate the major features of the present day climate. In a global warming (cooling) experiment, the thermohaline circulation (THC) in the North Atlantic Ocean is weakened (intensified) due to the increased (reduced) moisture transport to, and warmer (cooler) sea surface temperatures at northern high latitudes.; Secondly, the above four-component model is employed to investigate the initiation of glaciation, which is accomplished by reducing the solar radiation and increasing the planetary emissivity only in high northern latitudes. When land ice is growing, the THC in the North Atlantic Ocean is intensified, resulting in a warm subpolar North Atlantic Ocean. The intensified THC maintains a large land-ocean thermal contrast at high latitudes, which leads to enhanced land ice accumulation. We conclude that increased fresh water or massive iceberg discharge from land is responsible for a weak or collapsed THC.; Lastly, a dynamic ice sheet model is coupled to the above four-component model. Sensitivity experiments show that a smaller lateral (east-west) ice discharge rate maintains a larger ice volume and extent in our model. Also, a reduced atmospheric CO₂ concentration, which is parameterized as an increased planetary emissivity, may lead to the expansion of the ice sheets and hence a larger ice volume and extent. A simple iceberg calving scheme is next introduced to investigate ice sheet-THC interactions on the millennial timescale. We find that the longer the duration of iceberg calving, the longer the time that must elapse before the next calving event can occur. Also, it is shown that the strength of the THC in the North Atlantic Ocean is very sensitive to the discharge rate of the ice sheets. This makes the simulation of the interactions between ice sheets and the THC extremely challenging.