Effects of Freshwater Forcing on the Atlantic Deep Circulation: A Study with an OGCM Forced by Two Different Surface Freshwater Flux Datasets

Abstract

Numerical experiments are conducted using a sea ice?coupled ocean general circulation model (OGCM) forced by two different freshwater flux datasets. These two datasets are the National Centers for Environmental Prediction? National Center for Atmospheric Research (NCEP?NCAR) reanalysis and the European Centre for Medium-Range Weather Forecasts (ECMWF)-based climatological datasets, which are widely used to force OGCMs. It is found that the strength of the simulated Atlantic deep circulation considerably differs between the two experiments. To explain the resulting difference, these two freshwater fluxes are compared and additional experiments are carried out, focusing on the difference at northern high and midlatitudes, at low latitudes, and in the Southern Ocean, separately. An examination of these experiments shows that the difference in the simulated Atlantic deep circulation comes mainly from the difference in the river runoff data, especially at the northern high latitudes. Although the amount of the difference in the river runoff data at northern high latitudes is small, compared with that of the evaporation and the precipitation in other regions, it has a considerable influence on the strength of the Atlantic deep circulation. It indicates that the strength of the Atlantic deep circulation is affected more significantly by the accuracy of the river runoff data than that of the evaporation and the precipitation data.