Acoustic tomography as a component of the Fram Strait observing system

Abstract

The Fram Strait, a deep constriction between Svalbard and Greenland, is the primary location for the exchange of heat, mass and freshwater between the Arctic and Atlantic Oceans. With existing data and ocean modeling, current estimates of these exchanges, critical for understanding the Arctic Ocean climate, are inaccurate. To try to improve these estimates, during 2008-9 the DAMOCLES project deployed a test tomography path spanning the deep, ice-free part of the northward-flowing West Spitzbergen Current (WSC). Small-scale scintillations of sound speed due to eddies, fronts, and internal waves, are an important aspect of acoustic propagation of the region. Variability within Fram Strait, and the WSC in particular, is characterized by ubiquitous mesoscale eddies with 20-km scale. These eddies extend to depths of several hundred meters. Understanding the forward problem is essential for the inversion of acoustic data. The sound speed environment of Fram Strait generally prevents individual ray arrivals from being resolved in O(100-km) acoustic paths. An accurate inversion of these data for path-averaged sound speed (temperature) can be still be obtained, however. An objective mapping study, combining acoustic and existing data types, demonstrates that tomography will be a valuable and effective addition to the Fram Strait observing system.