Turbulent heat and momentum fluxes in the upper ocean under Arctic sea ice

Abstract

We report observations of heat and momentum fluxes measured in the ice‐ocean boundary layer from four drift stations between January and June 2015, covering from the typical Arctic basin conditions in the Nansen Basin to energetic spots of interaction with the warm Atlantic Water branches near the Yermak Plateau and over the North Spitsbergen slope. A wide range of oceanic turbulent heat flux values are observed, reflecting the variations in space and time over the five month duration of the experiment. Oceanic heat flux is weakly positive in winter over the Nansen Basin during quiescent conditions, increasing by an order of magnitude during storm events. An event of local upwelling and mixing in the winter‐time Nansen basin highlights the importance of individual events. Spring‐time drift is confined to the Yermak Plateau and its slopes, where vertical mixing is enhanced. Wind events cause an approximate doubling of oceanic heat fluxes compared to calm periods. In June, melting conditions near the ice edge lead to heat fluxes of O(100 W m−2). The combination of wind forcing with shallow Atlantic Water layer and proximity to open waters leads to maximum heat fluxes reaching 367 W m−2, concurrent with rapid melting. Observed ocean‐to‐ice heat fluxes agree well with those estimated from a bulk parameterization except when accumulated freshwater from sea ice melt in spring probably causes the bulk formula to overestimate the oceanic heat flux.

Winter to summer oceanographic observations in the Arctic Ocean north of Svalbard

“…The vertical temperature gradient at the base of the mixed layer also showed a shift on the 25 May with a mean value prior to this date of 0.25°C m −1 that dropped to 0.01°C m −1 afterward. Large basal sea ice melt events took place after 25 May driven by large ocean heat flux from Atlantic Water [ Peterson et al , ; Meyer et al , ], leading to a freshening of the upper surface waters, an increase in buoyancy, and was likely responsible for the new shallow mixed layer.…”

“…The sea ice drift is determined by a combination of wind forcing, sea ice stresses and ocean forcing (tides and currents). During the N‐ICE2015 expedition, the wind component was largest when the ice camps were closest to the ice edge (Floes 3 and 4) [ Peterson et al , ]. When drifting deeper inside the pack ice (Floes 1 and 2), internal sea ice stress and oceanic forcing dominated.…”

On the Increasing Importance of Air-Sea Exchanges in a Thawing Arctic: A Review

“…Norwegian Young Sea-Ice Campaign (N-ICE2015) [112] January-June 2015 Arctic Ocean north of Svalbard Surface energy budget measurements over young, thin ice were taken during the transition from freezing to melting ice conditions, highlighting the complex relationship between clouds, winds, heat/moisture advection, and the surface ocean on surface energy components over this ice type [113,121,122]. Confirmed existence of bimodal longwave surface radiative flux distribution in January and February that also existed in SHEBA [103,123].…”

Turbulent Upper-Ocean Mixing Affected by Meltwater Layers during Arctic Summer

“…Surface buoyancy fluxes were in the range 4 3 10 Peterson et al 2017). Larger Ds u was associated with larger hw 0 b 0 i 0 or sampling later in the melt season (Fig.…”