Modeling Interactions between the Gulf Stream and Deep Western Boundary Current by the Tail of the Grand Banks

Magdalena Andres, Physical Oceanography
Mike McCartney, Physical Oceanography



In some defined geographic regions, local changes in ocean currents have consequences for basin-wide or global-scale climate.  The area southeast of the Tail of the Grand Banks of Newfoundland in the North Atlantic is likely one such “big impact” site.  Here the swift Gulf Stream, which leaves the western boundary 1200 km upstream at Cape Hatteras to become a powerful eastward-flowing jet, converges with the equatorward-flowing Labrador Current and Deep Western Boundary Current as each navigates the abrupt topography of a submarine ridge that juts into their paths (the Southeast Newfoundland Rise).  A strong, deep-reaching, northward current - the North Atlantic Current - emerges from these interactions and transports warm waters poleward.  In this way, much of the Atlantic’s Meridional Overturning Circulation is funneled through the narrowly-defined region by the Tail of the Grand Banks.

While the area off Cape Hatteras (the second place where the Gulf Stream and Deep Western Boundary Current must contend with one another) has been well-studied with observations, theory, and models, flow by the Tail of the Grand Banks is not well-characterized with observations, nor has it been the focus of process models.  Our goals are to understand (1) the dynamics responsible for the shift of the current from a narrow zonal jet (Gulf Stream) to a nearly meridional jet (North Atlantic Current) and (2) whether the position of the Gulf Stream’s zonal path between Cape Hatteras and the Tail of the Grand Banks is sensitive to variability at the Tail.  This position is commonly used as a benchmark to evaluate climate models.

The Southeast Newfoundland Rise adds a layer of complexity to the dynamics controlling the flows by the Tail.  The currents’ encounter with one another and with the Southeast Newfoundland Rise shapes their paths and vertical structures, which in turn, affects the distribution of heat in the ocean and the atmosphere (via air-sea interactions).  How the currents’ interactions vary at different timescales (whether short timescales due to ocean eddies or abrupt changes in climate, or longer timescales associated with interannual wind variability or gradual climate change) is not known.  Further, this region may have implications for paleo-climate studies with some suggestions that it played an important role as a “switch” leading to in rapid change due to an adjustment in the path of the North Atlantic Current from a zonal flow to its present meridional configuration.

We propose to carry out a set of numerical modeling experiments aimed at investigating the dynamics that control how the Gulf Stream and Deep Western Boundary Current interact with each other and with the Southeast Newfoundland Rise by the Tail of the Grand Banks.  In addition to adding to our understanding of the Atlantic circulation, the results of the process modeling and a well-designed future field program may establish a new benchmark for assessing performance of coupled climate simulations.