Oceanographic Observations in Support of Defining Vulnerable Marine Ecosystems in the NAFO Regulatory Area

An investigation of the oceanographic and lower-trophic-level biology has take place in the region of Orphan Knoll. This study has utilized existing data sets as well as collecting new data using shipboard and moored instrumentation over the period 2008-2010. Physical properties indicate that Orphan Knoll is in a boundary region between outflow from the Labrador Sea (subpolar gyre) and northward flow of the North Atlantic Current (subtropical gyre), with waters of primarily subpolar origin. However, near-bottom current measurements provide evidence for anti-cyclonic (clockwise) circulation around the knoll, and an upper-ocean incursion of more subtropical water from the North Atlantic Current was observed in one of the three study years. Chlorophyll, small phytoplankton and bacteria in the Orphan Basin-Orphan Knoll region show strong spatial and inter-annual variability, reflecting the complex and variable physical dynamics and growth conditions in the region. Overall, there is little evidence for enhanced lower trophic level biology in the water column above the knoll; however, the near-bottom anti-cyclonic circulation could have important implications for the benthic community.