The role of topography in cross-shelf-break exchange

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Submarine canyons are underwater canyons that usually occur on the continental shelf and slope.  Canyons enhance water exchange between the coastal ocean and deep ocean.  They are important in bringing deep water onto the shelf (upwelling).  This water is rich in nutrients important to the plant life that supports productive coastal fisheries.  Juan de Fuca Canyon off the coast of British Columbia is a canyon that causes significant upwelling. However other canyons cause significant movement of shelf water into the ocean (downwelling).  An example would be The Gully off the coast of Nova Scotia which was recently made a Marine Protected Area.  Using numerical modelling, laboratory modelling and observations we will gain an understanding of the processes that allow a canyon like The Gully to be so productive. By building an understanding of both upwelling and downwelling canyons we will be able to predict how the water exchanged between the coastal and deep oceans due to submarine canyons will change due to changes in ocean currents or stratification.  It will allow us to predict the amount and depth of the water exchanged.  As the coastal ocean is in general more productive than the open ocean, more carbon is formed into plants in the coastal ocean.  Transport of this carbon to the deep ocean is part of the ocean carbon cycle.  Knowing the amount and depth of water exchanged between the coastal ocean and deep ocean is necessary to quantify this part of the cycle.