Arctic Ice–Ocean Modeling with and without Climate Restoring

Abstract

A coupled ice?mixed layer?ocean model is constructed for the Arctic Ocean, the Barents Sea, and the Greenland?Iceland?Norwegian Sea. The model is used to address Arctic numerical modeling with and without climate restoring. The model without climate restoring reproduces basic observed features of the Arctic ice?ocean circulation. The simulated oceanic processes adjust to the surface and lateral fluxes and transport heat and mass in a way that achieves a rough salt and heat balance in the Arctic in the integration period of seven decades. The main deficiency of the model is its prediction of unrealistically high salinity in the central Arctic, which tends to weaken the ocean currents. The introduction of corrective salinity and temperature restoring terms has a significant impact on prediction of the ice?ocean circulation in the Arctic. The impact results from a chain reaction. First, the restoring terms change the salinity and thermal states in the oceanic mixed layer and below. The altered density structure, in turn, influences the ocean circulation by altering the ocean?s dynamic and thermodynamic processes. The ocean circulation then affects ice motion and ice thickness by altering the dynamics and thermodynamics of the ice. Restoring only ocean salinity induces a heat surplus or deficit, which causes the oceanic thermal state to drift away from the climatology. This is also the case with restoring both salinity and temperature in the upper ocean. Only restoring salinity and temperature in the deeper ocean is likely to avoid climate drift in the Arctic. This paper points out the problems of using models without climate restoring and the consequences of using models with climate restoring for Arctic ice?ocean modeling. It stresses the need to use a realistic representation of surface fluxes in order to improve prognostic simulations. It also stresses the importance of oceanic processes such as convective overturning and vertical advection both in the Arctic and in the adjacent oceans. If these processes are not reasonably represented, the models can predict overwarm intermediate layers in the Arctic and an excessive heat influx at Fram Strait, causing the Arctic ice pack to possibly shrink gradually, a scenario global climate models should avoid.