Simulation of Sea Ice-Ocean Variability in the Arctic During 1955-2002 with an Intermediate Complexity Model

A number of recent sea ice and ocean changes in the Arctic and subarctic regions are investigated using the global UVic Earth System Climate Model version 2.6. This is an intermediate complexity model which includes a 3-D ocean model (MOM 2.2), an energy-moisture balance model for the atmosphere with heat and moisture advection, and a thermodynamic-dynamic sea ice model with elastic-viscous-plastic rheology. After spin-up, the model is run with interannually varying winds for the period 1948-2002 with an average wind-forcing interval of 2.5 days and an exponentially increasing atmospheric {CO_2} concentration varying from 315 to 365 ppm. However, the analysis of the model output is done only for the years 1955-2002. The simulated maximum and minimum sea ice extents for the Arctic are within 10% of the observed climatologies over the years 1978-2001. The model output also shows a small downward trend in sea ice extent that is, however, less than what has been observed during the past few decades. In addition, the model simulates a decrease of sea ice thickness in the SCICEX (Scientific Ice Expeditions) measurement area in the central Arctic that is consistent with but smaller than that recently summarized by Laxon et al. The observed variability and magnitude of the export of sea ice through Fram Strait is quite well captured in the simulation. The change in correlation between the NAO index and the sea ice export at around 1977 as found in a data study by Hilmer and Jung is also reproduced. Within the Arctic basin the model simulates well the patterns and the timing of the two major regimes of wind-forced sea ice drift circulation (cyclonic and anticyclonic) as found earlier by Proshutinsky and Johnson. The impacts of these two circulation regimes and the Fram Strait export variation on the strength of the thermohaline circulation in the northern North Atlantic are also determined. The temperature and salinity increase at depths of 200-300 m as observed in the eastern Arctic by Morison et al. between the USS Pargo cruise in 1993 and the EWG climatology of the years 1948-1987, are just visible in the model simulation. The increases are more noticeable, however, when the ocean model data are averaged over the pentade 1995-2000 and compared with that averaged over the pentade 1955-1960. The fact that these and some of the other modelled changes are smaller than the observed changes can likely be attributed to the relatively coarse resolution of the UVic Earth System Climate Model (3.6^o E-W and 1.8^o N-S). Nevertheless, the fact that the model captures qualitatively many of the recent sea ice and ocean changes in the Arctic suggests that it can be successfully used to investigate other Arctic-North Atlantic ocean climate interactions during past and future eras.