Abstract
Abstract. The Arctic Ocean is a major sink for heat and salt for the global ocean. Ocean mixing contributes to this sink by mixing the Atlantic- and Pacific-origin waters with surrounding waters. We investigate the drivers of ocean mixing north of Svalbard, in the Atlantic sector of the Arctic, based on observations collected during two research cruises in summer and fall 2018. Estimates of vertical turbulent heat flux from the Atlantic Water layer up to the mixed layer reach 30 W m−2 in the core of the boundary current, and average to 8 W m−2, accounting for ∼1 % of the total heat loss of the Atlantic layer in the region. In the mixed layer, there is a nonlinear relation between the layer-integrated dissipation and wind energy input; convection was active at a few stations and was responsible for enhanced turbulence compared to what was expected from the wind stress alone. Summer melting of sea ice reduces the temperature, salinity and depth of the mixed layer and increases salt and buoyancy fluxes at the base of the mixed layer. Deeper in the water column and near the seabed, tidal forcing is a major source of turbulence: diapycnal diffusivity in the bottom 250 m of the water column is enhanced during strong tidal currents, reaching on average 10−3 m2 s−1. The average profile of diffusivity decays with distance from the seabed with an e-folding scale of 22 m compared to 18 m in conditions with weaker tidal currents. A nonlinear relation is inferred between the depth-integrated dissipation in the bottom 250 m of the water column and the tidally driven bottom drag and is used to estimate the bottom dissipation along the continental slope of the Eurasian Basin. Computation of an inverse Froude number suggests that nonlinear internal waves forced by the diurnal tidal currents (K1 constituent) can develop north of Svalbard and in the Laptev and Kara seas, with the potential to mix the entire water column vertically. Understanding the drivers of turbulence and the nonlinear pathways for the energy to turbulence in the Arctic Ocean will help improve the description and representation of the rapidly changing Arctic climate system.
Highlights
The Arctic Ocean is a sink for salt and heat
In both summer and fall, dissipation rates, buoyancy fluxes and turbulent heat fluxes increased at the base and just below the mixed layer compared to the rest of the water column (Fig. 5 and Table 2)
We present two estimates for the dissipation: the vertically integrated dissipation rate in the bottom 250 m, D250, averaged laterally between the 400 and 1200 m isobaths, and D250 integrated meridionally between the 400 and 1200 m isobaths. This volume-integrated dissipation rate, per unit meter along the shelf break, shows variations similar to the averaged D250, except at 70◦ E. This is the location of the Santa Anna Trough, where the Atlantic Water from the Barents Sea flows into the Arctic Ocean and where the distance between the 400 and 1200 m isobaths triples compared to the rest of the Eurasian continental slope
Summary
The Arctic Ocean is a sink for salt and heat. Relatively warm and salty Atlantic waters enter the Arctic Ocean via Fram Strait and the Barents Sea through-flow, and colder and fresher Arctic waters exit flowing east of Greenland through the East Greenland Current. North of Svalbard is a location with enhanced mixing It is a key region for the Arctic Ocean heat and salt budget, as it is the gateway for Fram Strait inflow of Atlantic Water. Ice-free regions have been observed along the path of the Atlantic Water, in the Barents Sea first and in the Eurasian Arctic Ocean, with warm and saline water extending up to the surface (Årthun et al, 2012; Ivanov et al, 2016). Detailed observations of the ocean dynamics north of Svalbard are needed to evaluate the active processes modifying the Atlantic Water layer in a changing Arctic, and their potential influence on the sea ice. Turbulence production by background shear will not be addressed in this study as the vertical resolution (8 m) of the current data collected during the cruises is not sufficient to resolve shear instabilities
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
