A box model study of the Greenland Sea, Norwegian Sea, and Arctic Ocean

Abstract

We develop a simple dynamical system model of the Arctic Ocean and marginal seas by applying the Martinson, Killworth and Gordon box model of a high-latitude two-layer ocean to four regions connected together: the Greenland Sea, the Norwegian Sea, the Arctic Ocean, and the Greenland Gyre. The latter is a small convective region embedded in the northwest corner of the Norwegian Sea. The model for each region consists of a thermodynamic ice layer that covers two layers of saline water which can, under specific conditions, become statically unstable and hence create a state of active overturning. The system is forced by monthly mean atmospheric temperatures in the four regions, by continental runoffs and by inflows from adjacent oceans. The model predicts the ice thickness, and the temperature and salinity of the water in the upper layer of the four regions. Also determined are the water temperature and salinity of the lower layer in the Arctic Ocean box. The convective state of any given region, i.e. whether it is in an active overturning mode or not, is also determined as a continuous function of time. The different output variables of the model, which are the response to climatological forcing conditions, compare favourably with observed data. In the control run, the Arctic Ocean region is characterized by continuous ice cover, the Greenland Sea and Greenland Gyre have ice cover only during winter, and the Norwegian Sea region never forms an ice cover. Another feature of the control run is the winter time occurrence of convective overturning in the upper 200 m in the Greenland Gyre region. The model is also used for different anomaly experiments: a positive air temperature anomaly which represents a global warming of the earth, a negative salt anomaly in the Norwegian Sea which simulates the great salinity anomaly of the 1960s and 1970s, and an increase in the ice flux through Fram Strait which parameterizes anomalous ice production in the Arctic.