Surface Drifter Observations From the Arctic Ocean's Beaufort Sea: Evidence for Submesoscale Dynamics

Position and velocity data are analyzed from a release of surface ocean drifters in the Arctic Ocean's Beaufort Sea in ice-free conditions. Position information is returned at sufficiently high frequency to allow for the investigation of surface-ocean flows ranging from around 0.5 km in lateral scale (submesoscale, SM, flows) to flows that are tens of kilometers in horizontal extent. Lagrangian statistics from the drifter release are analyzed in conjunction with Eulerian (ship-based) measurements of surface ocean temperature and salinity. Results show dynamics that are largely consistent with flows at similar scales in the midlatitude oceans. Horizontal wavenumber k spectra of density in the surface ocean scale as k-2, consistent with energetic SM flows. Lagrangian drifters indicate local dispersion in the surface ocean layer at horizontal scales smaller than 10 km, which confirms the presence of active submesoscale dynamics. Features at these scales give rise to lateral diffusivities (in the range 1-10(3) m(2) s(-1)) of similar range to values inferred in the midlatitudes. Velocity structure functions present an energy-cascade inertial range at submesoscales with indication of a transition to a forward energy cascade at scales smaller than 1 km confirming the transition to 3-D turbulence. The active SM flow-field drives enhanced lateral and vertical fluxes in the Arctic Ocean mixed layer, which has first-order implications to the transport of heat, sea-ice floes, nutrients, and contaminants. Plain Language Summary Transport and distribution of pollutants and biogechemical tracers is driven by currents in the upper ocean. Surface-ocean observations in the midlatitudes, as well as numerical modeling, have shown that small-scale flows (i.e., submesoscale flows) play a key role in this transport. Here we present results from a drifter release experiment in the Arctic Ocean's Beaufort Sea. Results provide in-situ observational evidence, for the first time, for the presence of submesoscale flows in the Beaufort Sea. These results extend observations of submesoscale flows in the midlatitude oceans, and improve understanding of the Arctic Ocean system where the transport and distribution by submesoscale flows of ocean heat and sea-ice floes are of climate significance.