Projecting the Effects of Climate Change on Northwest North Atlantic Shelf Hydrography and Biological Productivity

Wenxia Zhang, Dalhousie University, Oceanography, Halifax, NS, Canada, Katja Fennel, Dalhousie University, Department of Oceanography, Halifax, NS, Canada, David Brickman, Bedford Institute of Oceanography, Fisheries and Oceans Canada, Dartmouth, NS, Canada and Arnaud Laurent, Dalhousie University, Halifax, NS, Canada
Abstract:
The northwest North Atlantic shelf, at the confluence of the North Atlantic subpolar and subtropical gyres, hosts highly productive and historically rich fishing grounds. As one of the hydrographically most variable regions in the North Atlantic Ocean, hydrography and biogeochemistry are likely to change over the coming century with unknown implications for biological productivity. Global climate models lack the necessary resolution to accurately project changes in the region; hence, regional downscaling approaches are needed. In this study we investigate climate change scenarios for this region using a downscaled physical-biological Regional Ocean Modeling System (ROMS) covering the Gulf of Maine, the Gulf of St. Lawrence, the Grand Banks and the adjacent deep ocean. Surface atmospheric forcing for the future scenario is derived from an ensemble of climate models using the delta method (i.e. the mean climatic change between the climate simulations for future and reference time period are added to the forcing of our baseline run). Future hydrographical initial and boundary conditions are also prescribed using the delta method and based on a future scenario simulated by a 1/12-degree NEMO model for the North Atlantic. Biological initial/boundary conditions are derived using property-property relationships from a CMIP5 model ensemble. By comparing the future scenarios to present-day runs, we identify climate change influences on the regional hydrography including the location of the Gulf Stream path and the strength of vertical stratification, and how these influence biological dynamics. The sensitivity of the regional shelf dynamics to changes in different factors (i.e. atmospheric forcing versus boundary conditions) is examined individually and in combination. Preliminary results indicate an earlier spring bloom and generally lower surface nutrient levels resulting from warmer temperatures and stronger vertical stratification in the future.
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