The outflow from Hudson Strait and its contribution to the Labrador Current

Abstract

Hudson Strait delivers a large amount of fresh water to the subpolar North Atlantic due to a large riverine input into the upstream Hudson Bay System and to the rerouting of Arctic Ocean waters. The fresh waters flowing out of Hudson Strait feed the Labrador Current, a current that has a significant impact on the climate and ecosystem of the entire northeastern seaboard. The lack of measurements from the strait have, until recently, made it difficult to determine the relative contribution of Hudson Strait to the properties and variability of the Labrador Current compared to other sources. This study describes the first year round observations of the outflow as obtained from a moored array deployed midstrait from August 2004 to 2005, and from a highresolution hydrographic section conducted in September of 2005. The outflow from Hudson Strait has the structure of a buoyant boundary current spread across the sloping topography of its southern edge. The variability in the flow is dominated by the extreme semidiurnal tides and by vigorous, mostly barotropic, fluctuations over several days. The fresh water export is seasonally concentrated between June and March with a peak in NovemberDecember, consistent with the seasonal riverine input and seaice melt. It is highly variable on weekly timescales due to synchronous salinity and velocity variations. The estimated volume and liquid fresh water transports during 20042005 are respectively of 11.2 Sv and 7888 (2829) mSv relative to a salinity of 34.8 (33). This implies that the Hudson Strait outflow accounts for approximately 15% of the volume and 50% of the fresh water transports of the Labrador Current. This larger than previously estimated contribution is partially due to the recycling, within the Hudson Bay System, of relatively fresh waters that flow into Hudson Strait, along its northern edge. It is speculated that the source of this inflow is the outflow from Davis Strait.