Monitoring the Export of Fresh Arctic-Origin Water from the Boundary to the Interior of the Subpolar North Atlautic: The Role of the Labrador Current Retroflection

Paula Fratantoni, Physical Oceanography
Mike McCartney, Physical Oceanography


Arctic Research Initiative
2010 Funded Project


There is a lot of activity in the climate research community aimed at understanding how high latitude freshening in the North Atlantic may alter the ocean circulation and its participation in the climate system.  However, to understand its impact, it is of utmost importance that we understand where, and by what mechanisms, this freshwater enters the interior Atlantic.  The majority of the fresh water that enters the North Atlantic does so within the confines of a long, interconnected coastal boundary current, extending from the east coast of Greenland, around the Labrador Sea and southward along the east coast of North America.  This boundary current provides the main advective pathway for the equator ward transport of arctic water exported through Denmark, Davis, and Hudson Straits, accumulated continental discharge, and melt-water from the Greenland Ice Sheet – all dominant sources of freshwater to this region and all showing signs of significant variations in recent years.  The portion of the boundary current that follows the continental shelf between Hudson Strait and the Grand Banks of Newfoundland is called the Labrador Current.  Freshwater transported by the Labrador Current is largely constrained to follow the boundary along its extended advection pathway.  However there are a few specific locations where portions of the flow are diverted offshore, resulting in the export of mass and freshwater from the boundary.  The most prominent of these export pathways is along the Grand Banks of Newfoundland in the southwest corner of the subpolar gyre.  Here, a significant portion of the Labrador Current turns offshore and back toward the north (retroflects), carrying most of the cold, fresh arctic water mass into the interior.     Immediately after it leaves the boundary the retroflected water encounters the North Atlantic Current, carrying a large volume of very salty water northward toward the interior of the subpolar gyre.  On average, the freshening that is imparted to the North Atlantic Current east of the Grand Banks contributes to the cooling and freshening of the northward flowing subtropical waters and their subsequent transformation in the Arctic basin – the northern limb of the Atlantic Meridional Overturning Circulation (AMOC).  However, the potential impact of this freshwater and its variations on the larger climate system depends on which processes are dominant in its interaction with the North Atlantic Current.  In this study, we will fly a single ocean glider across the retroflecting Labrador Current for a period of three months.  The glider has already been deployed using discretionary funds from ARI in response to a time-sensitive opportunity for collaboration with Canadian colleagues.  The high-resolution data collected as part of this study will be used to assess the feasibility and intellectual merit of using ocean gliders as the centerpiece of a future NSF program designed to monitor the flux of arctic-origin water out of the boundary current and to identify the processes involved in its absorption by the North Atlantic Current.