Lagrangian Pathways and Transformation of the Denmark Strait Overflow Water

Inga Koszalka, Tom Haine*, Earth and Planetary Sciences


Overflows (dense gravity currents) result when dense water formed through cooling or salinification in regions behind confining topographic barriers, or on continental shelves, escapes into the deep ocean over a sloped sea floor. The overflows evolve on scales below the grid scale of ocean models used for climate predictions and need to be parameterized. The Denmark Strait Overflow (DSO) cascades through the Denmark Strait sill into the Irminger Basin where it subsequently flows toward the North Atlantic supplying source waters to the Atlantic Meridional Overturning Circulation (AMOC), thus influencing the earth’s climate on decadal and longer time scales.

Using the computational resources of the Johns Hopkins University: The Homewood High Performance Compute Cluster (HHPC2) and the DATA SCOPE we have run a regional ocean model at an unprecedented resolution and simulated a set of O(10,000) Lagrangian particles to study the DSO in the Irminger Basin. Using Lagrangian particles deployed across the Denmark Strait we estimate travel time distributions of the DSO in the Irminger Basin. We have mapped novel dense water pathways on the continental shelf where the waters can recirculate for several weeks before they spill off the shelf break and join the overflow from the sill that follows the continental slope. These shelf recirculations contribute significantly to the dense overflow downstream (~ 25%). We assess transformation of the DSO temperature, salinity, and density finding that the density on particle trajectories decreases rapidly due to mixing with warm, salty Atlantic Water along the continental slope and due to mixing with fresh Polar Water on the shelf. Our study extends the conceptual view of the DSO in the Irminger Basin, motivated a NSF proposal, inspired an international field campaign and initiated a collaboration with GFDL/Princeton University regarding the parameterization of the DSO in ocean climate models.