Abstract
AbstractIn the Arctic Ocean, limited measurements indicate that the strongest mixing below the atmospherically forced surface mixed layer occurs where tidal currents are strong. However, mechanisms of energy conversion from tides to turbulence and the overall contribution of tidally driven mixing to Arctic Ocean state are poorly understood. We present measurements from the shelf north of Svalbard that show abrupt isopycnal vertical displacements of 10–50 m and intense dissipation associated with cross‐isobath diurnal tidal currents of ∼0.15 m s−1. Energy from the barotropic tide accumulated in a trapped baroclinic lee wave during maximum downslope flow and was released around slack water. During a 6‐hr turbulent event, high‐frequency internal waves were present, the full 300‐m depth water column became turbulent, dissipation rates increased by a factor of 100, and turbulent heat flux averaged 15 W m−2 compared with the background rate of 1 W m−2.
Highlights
Much of the interior of the Arctic Ocean is quiescent (Fer, 2009; Lincoln et al, 2016), insulating the surface from heat imported into the Arctic Ocean by Atlantic Water intruding at intermediate depths (Carmack et al, 2015)
We present measurements from the shelf north of Svalbard that show abrupt isopycnal vertical displacements of 10–50 m and intense dissipation associated with cross‐isobath diurnal tidal currents of ∼0.15 m s−1
As we found for the dayof the transect, synthetic aperture radar (SAR) images near the start and end of the process station show the presence of nonlinear internal waves (NLIWs) (Figure 3b)
Summary
Much of the interior of the Arctic Ocean is quiescent (Fer, 2009; Lincoln et al, 2016), insulating the surface from heat imported into the Arctic Ocean by Atlantic Water intruding at intermediate depths (Carmack et al, 2015). In the critical region around Svalbard where warm water enters the Arctic Ocean, tides appear to play a key role in transporting this heat toward the surface. Mixing hotspots have been identified over regions of steep topography (Fer et al, 2010; Meyer et al, 2017; Padman & Dillon, 1991; Rippeth et al, 2015), where enhanced levels of turbulence cause diapycnal heat fluxes as large as 50 W m−2. The regions of energetic turbulent dissipation correspond with areas of conversion of barotropic tidal energy to baroclinic waves and mixing (Fer et al, 2015; Padman & Dillon, 1991; Rippeth et al, 2015). The hypothesized energy pathway at high latitudes is, instead, that the tidal flow over sloping topography induces a lee FER ET AL
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