Abstract
AbstractHigh‐resolution ocean temperature, salinity, current, and turbulence data were collected at an Arctic thermohaline front in the Nansen Basin. The front was close to the sea ice edge and separated the cold and fresh surface melt water from the warm and saline mixed layer. Measurements were made on 18 September 2018, in the upper 100 m, from a research vessel and an autonomous underwater vehicle. Destabilizing surface buoyancy fluxes from a combination of heat loss to the atmosphere and cross‐front Ekman transport by down‐front winds reduced the potential vorticity in the upper ocean. Turbulence structure in the mixed layer was generally consistent with turbulence production through convection by heat loss to atmosphere and mechanical forcing by moderate winds. Conditions at the front were favorable for forced symmetric instability, a mechanism drawing energy from the frontal geostrophic current. A clear signature of increased dissipation from symmetric instability could not be identified; however, this instability could potentially account for the increased dissipation rates at the front location down to 40 m depth that could not be explained by the atmospheric forcing. This turbulence was associated with turbulent heat fluxes of up to 10 W m−2, eroding the warm and cold intrusions observed between 30 and 60 m depth. A Seaglider sampled across a similar frontal structure in the same region 10 days after our survey. The submesoscale‐to‐turbulence‐scale transitions and resulting mixing can be widespread and important in the Atlantic sector of the Arctic Ocean.
Highlights
Warm Atlantic Water is the main source of oceanic heat to the Arctic Ocean (Carmack et al, 2015; Rudels et al, 2015)
In the Arctic Ocean, vertical mixing is typically dominated by turbulence generated by processes over topography and along margins, mainly forced by tides (Fer et al, 2015; Lenn et al, 2011; Padman & Dillon, 1991; Rippeth et al, 2015)
In this study we present detailed observations characterizing the structure of hydrography, currents, and turbulence at a near-surface front in the Arctic Ocean in the Nansen Basin away from topography, 4–5 km away from the sea ice edge (Figure 1a)
Summary
Warm Atlantic Water is the main source of oceanic heat to the Arctic Ocean (Carmack et al, 2015; Rudels et al, 2015). As the Atlantic Water boundary current flows cyclonically along the upper continental slope, it mixes vertically and laterally, spreading its heat to the interior Arctic basins; the processes of vertical and lateral mixing, are not well understood (Carmack et al, 2015). In the central Arctic, sea ice limits the energy input from wind, and the vertical mixing is weak (Fer, 2009; Rainville & Winsor, 2008). Episodic energetic vertical mixing in the interior ocean has been observed in response to strong winds and ice divergence. North of Svalbard, winter storms increased the pycnocline fluxes by a factor of 2 (Meyer, Fer, et al, 2017) and the ocean-to-ice fluxes by a factor of 3 (Graham et al, 2019)
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