Impacts of Climate Change in the Gulf of St. Lawrence

To explore modifications in water temperature and salinity under warmer climate change conditions, we performed simulations from 1970 to 2069 with the CANadian Ocean PArallelise (CANOPA) model for the Gulf of St. Lawrence and the Scotian Shelf. The surface fields to drive CANOPA were provided by the Canadian Regional Climate Model (CRCM), driven by the outputs from the third-generation Canadian Global Climate Model (CGCM3) following the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES) A1B climate change scenario. The sea-ice concentration and volume simulated by CANOPA are shown to have patterns consistent with those seen in observations; CANOPA is also shown to simulate sea surface temperature (SST) well. Although CANOPA can simulate the observed vertical structure of water temperature and salinity, it tends to underestimate the cold intermediate layer and overestimate water salinity in the central Gulf of St. Lawrence (GSL). In terms of the possible future climate, CANOPA simulations suggest that the GSL will be largely ice free in January, with ice volume in March steadily decreasing from about 80 km(3) in the 1980s to near zero by the late 2060s. On average, the GSL water will become warmer and fresher over this time period. In January, maximum SST increases occur near eastern Cabot Strait, with amplitudes of about 1.5 degrees-2.5 degrees C, corresponding to reduced sea ice in that area, and there is no notable change along the western and northern coasts of the GSL. In July, maximum SST increases occur over the western GSL corresponding to the largest increases in surface air temperature in the region. The maximum decreases in surface salinity also occur near western coastal areas and the Scotian Shelf, whereas reductions in the eastern GSL are relatively weak. Finally, compared with the present climate, the cold intermediate layer is significantly weaker in 2040-2069 than in 1980-2009.