Wind‐Driven Cross‐Shelf Exchange—West Spitsbergen Current as a Source of Heat and Salt for the Adjacent Shelf in Arctic Winters

Abstract

Cross‐shelf exchange can drive substantial hydrographic changes on shelves and along slopes. In this study, time series from moorings, profiles collected by a tagged seal, atmospheric reanalysis data, and weather regimes classification were used to investigate cross‐shelf exchange at the slope‐shelf interface south‐west of Spitsbergen during the four winters 2011–2014. Assessment of Ekman transport (ET) as a driving force and linking cross‐shelf exchange to large‐scale weather patterns were in focus. Strong positive correlations were found between zonal ET and hydrographic observations on the shelf, indicating its strong impact on cross‐shelf exchange. Strong negative correlations were found between the meridional ET and temperature and salinity measured on the shelf in winter 2012, indicating a suppressing role of westerly winds on fresher and colder outflows from the Barents Sea. The ETs in a wider area near the Svalbard Archipelago show substantial variations on short‐term, interannual and long‐term time scales due to changes in large‐scale atmospheric patterns. The regional wind speed shows a significant negative trend in winters between 1992 and 2016. At the same time, cumulative winter zonal ET increased on the north‐western Spitsbergen shelf, indicating a higher overall cross‐shelf exchange along the western Spitsbergen shelf break, while meridional ET south‐west of Spitsbergen decreased, indicating a reduced outflow of fresher and colder water from the Barents Sea. For the time period between 1980 and 2016, the winter air and sea surface temperatures (sea‐ice fraction) exhibit significant positive (negative) trends which even multiplied by factor of 2–3 in winters 2004–2016.

Inflow of Warm Water to the Inner Hornsund Fjord, Svalbard: Exchange Mechanisms and Influence on Local Sea Ice Cover and Glacier Front Melting

“…CTD transects from the fjord head in Brepollen to the fjord mouth show that the surface and intermediate layers of Hornsund were about 2 °C warmer in late July 2013 than at the same time in 2010; a difference they relate to more water of Atlantic origin being present on the shelf in 2013. Winter time series (December–March) at 103‐m depth of temperature and salinity from the shelf outside Hornsund are presented by Goszczko et al (). Their results show that the shelf was occupied by cold coastal water at freezing point from late December 2010.…”

“…Large‐scale atmospheric forcing (Christoffersen et al, ; Cottier et al, ; Muckenhuber et al, ; Nilsen et al, ) as well as, or in addition to, generation and propagation of internal Kelvin waves into fjord systems (Inall et al, ; Jackson et al, ; Svendsen et al, ) have been regarded as important mechanisms for driving cross‐shelf and shelf‐fjord exchange both on the west coast of Spitsbergen and in Greenland fjords. Recent studies showed strong correlation between cross shelf Ekman‐Transport and temperature and salinities on the shelf outside Hornsund and in the Hornsund interior during the same periods (Goszczko et al, ). Local forcing inside the fjords from sea ice production and cooling of the water column affects the properties of the local water masses, which in turn can be a controlling factor for inflowing water (Nilsen et al, , ; Tverberg et al, ).…”

Hydrography, transport and mixing of the West Spitsbergen Current: the Svalbard Branch in summer 2015

“…where is the efficiency coefficient, is the turbulent dissipation rate and N is the buoyancy frequency. The efficiency coefficient is variable and uncertain but is commonly set to 0.2, which is the recommended value for typical oceanographic applications (Gregg et al, 2018). The heat flux is calculated from the shear measurements using K ρ with = 0.2 and a vertical scale of 10 m for the background temperature and density gradients.…”

Cooling and Freshening of the West Spitsbergen Current by Shelf‐Origin Cold Core Lenses

“…Patches of warm AW from the WSC are found on the shelf (Nilsen et al, ). The upwelling of AW on the shelf is substantially wind driven (Goszczko et al, ) with Ekman transport oriented toward the shelf in the presence of southerly winds. Warm AW is found on the shelf in winter when cyclones and storms are frequent (Cottier et al, ).…”