A simple box model expressing conservation of salt, heat, and mass for the top 50 m of four regions of the Gulf of St. Lawrence was developed. All available temperature and salinity data were combined with monthly estimates of freshwater input and surface heat flux to obtain an idea of the average annual variation in vertical and horizontal exchanges for the period March through December. Calculated horizontal transports agreed very well with available geostrophic calculations, and nutrient fluxes implied by the calculated upwelling of water from below 50 rn are capable of supporting the estimated primary production in the Estuary and Northwestern Gulf. The main effect of the increasing freshwater discharge and surface heat flux in the spring seems to be a decrease in eddy exchange between the surface and deeper layers due to increased stratification. On a mis au point un mod& simple en fome de boitier exprimant la conservation du sel, de la chaleur et de la masse dans les 50 m sugrieurs de quatre rkgions du golfe du Saint-Laurent. Toutes les donnCes de tempkrature et de salinitk ont etk combindes avec les estimations mensuelles d9apport d'eau douce et de flux calorique superficiel afin d'avoir une idCe de la variation annuelle moyenne des Cchanges verticaux et horizontaux entre mars et d6cembre inclusivement. Les transports horizontaux calcules s'accordent trks bien avec les calculs gCostrophiques disponibles, et les flux d'kldments nutritifs que suggkrent les calculs des remontdes d'eau des profondeurs sugrieures A 50 m sont capables de supporter la production primaire estim6e de 19estuaire et du nord-ouest du Golfe. L'augmentation du debit d'eau douce et du flux calorique superficiel au printemps semble avoir pour effet principal de diminuer 1'6change tourbillionnaire entre la surface et les couches profondes par suite d'une stratification accrue.

No abstract

Marine bivalves have been designated ecosystem engineers owing to their capacity to control estuarine water quality, particle dynamics, and primary production. Globally, bivalves have higher production than any other cultured animal. Large populations of natural, invasive, and cultured bivalves are suggested to cause changes in coastal ecosystem function through suspension-feeding of particles and biodeposition of waste materials. Association of bivalves with particle depletion is a trophic tenet of coastal ecosystems, but there are no previous observations of this process except at small scales. Using airborne hyperspectral remote sensing, we show direct evidence of aquaculture impacts at the ecosystem scale (kilometres), documenting significant depletion of phytoplankton through a blue mussel (Mytilus edulis) farm in eastern Canada, compared with dispersion in circulation model results without mussels. Understanding of factors controlling primary production and ecosystem processes in the coastal zone is critical in light of growing reliance on this region for development and resource extraction worldwide.

Physical Oceanography of the Bras D'Or Lakes

No abstract