Semidiurnal current dynamics in the Arctic Ocean's eastern Eurasian Basin

Abstract

<p>In the Arctic Ocean, semidiurnal-band processes including tides and wind-forced inertial oscillations are significant drivers of ice motion, ocean currents and shear contributing to mixing. Two years (2013-2015) of current measurements from seven moorings deployed along 125°E from the Laptev Sea shelf (~50 m) down the continental slope into the deep Eurasian Basin (~3900 m) are analyzed and compared with models of baroclinic tides and inertial motion to identify the primary components of semidiurnal-band current (SBC) energy in this region. The strongest SBCs, exceeding 30 cm/s, are observed during summer in the upper ~30 m throughout the mooring array. The largest upper-ocean SBC signal consists of wind-forced oscillations during the ice-free summer. Strong barotropic tidal currents are only observed on the shallow shelf.  Baroclinic tidal currents, generated along the upper continental slope, can be significant. Their radiation away from source regions is governed by critical latitude effects: the S<sub>2</sub> baroclinic tide (period = 12.000 h) can radiate northwards into deep water but the M<sub>2</sub> (~12.421 h) baroclinic tide is trapped to the continental slope. Baroclinic upper-ocean tidal currents are sensitive to varying stratification, mean flows and sea ice cover.  This time-dependence of baroclinic tides complicates our ability to separate wind-forced inertial oscillations from tidal currents. Since the shear from both sources contributes to upper-ocean mixing that affects the seasonal cycle of the surface mixed layer properties, a better understanding of both, inertial motion and baroclinic tides is needed for projections of mixing and ice-ocean interactions in future Arctic climate states.</p>