No abstract

[1] Kongsfjorden and the West Spitsbergen Shelf is a region whose seasonal hydrography is dominated by the balance of Atlantic Water, Arctic waters, and glacial melt. Regional seasonality and the cross-shelf exchange processes have been investigated using conductivity-temperature-depth (CTD) observations from 2000-2003 and a 5-month mooring deployment through the spring and summer of 2002. Modeling of shelf-fjord dynamics was performed with the Bergen Ocean Model. Observations show a rapid and overwhelming intrusion of Atlantic Water across the shelf and into the fjord during midsummer giving rise to intense seasonality. Pockets of Atlantic Water, from the West Spitsbergen Current, form through barotropic instabilities at the shelf front. These leak onto the shelf and propagate as topographically steered features toward the fjord. Model results indicate that such cross-front exchange is enhanced by north winds. Normally, Atlantic Water penetration into the fjord is inhibited by a density front at the fjord mouth. This geostrophic control mechanism is found to be more important than the hydraulic control common to many fjords.

Kongsfjorden‐Krossfjorden and the adjacent West Spitsbergen Shelf meet at the common mouth of the two fjord arms. This paper presents our most up‐to‐date information about the physical environment of this fjord system and identifies important gaps in knowledge. Particular attention is given to the steep physical gradients along the main fjord axis, as well as to seasonal environmental changes. Physical processes on different scales control the large‐scale circulation and small‐scale (irreversible) mixing of water and its constituents. It is shown that, in addition to the tide, run‐off (glacier ablation, snowmelt, summer rainfall and ice calving) and local winds are the main driving forces acting on the upper water masses in the fjord system. The tide is dominated by the semi‐diurnal component and the freshwater supply shows a marked seasonal variation pattern and also varies interannually. The wind conditions are characterized by prevailing katabatic winds, which at times are strengthened by the geostrophic wind field over Svalbard. Rotational dynamics have a considerable influence on the circulation patterns within the fjord system and give rise to a strong interaction between the fjord arms. Such dynamics are also the main reason why variations in the shelf water density field, caused by remote forces (tide and coastal winds), propagate as a Kelvin wave into the fjord system. This exchange affects mainly the intermediate and deep water, which is also affected by vertical convection processes driven by cooling of the surface and brine release during ice formation in the inner reaches of the fjord arms. Further aspects covered by this paper include the geological and geomorphological characteristics of the Kongsfjorden area, climate and meteorology, the influence of glaciers, freshwater supply, sea ice conditions, sedimentation processes as well as underwater radiation conditions. The fjord system is assumed to be vulnerable to possible climate changes, and thus is very suitable as a site for the demonstration and investigation of phenomena related to climate change.

Observations on the West Spitsbergen Shelf have shown that the dynamic response of the shelf to wind forcing has a profound effect on the heat content of the water. Hydrographic and atmospheric data have been analysed with respect to the relative importance of surface heat fluxes and advective processes on ocean temperature. During the Arctic winter of 2005/06 periods of sustained along‐shelf winds generated upwelling and cross‐shelf exchange causing extensive flooding of the coastal waters with warm Atlantic Water from the West Spitsbergen Current. The winter temperature of the West Spitsbergen Shelf reverted to that typical of fall, interrupting the normal cycle of sea ice formation in the region.

[1] The Eastern Weddell Sea is characterized by narrow continental shelves and Warm Deep Water (WDW) is located in close proximity to the ice shelves in this region. The exchange of WDW across the Antarctic Slope Front (ASF) determines the rate of basal ice shelf melting. Here, we present a unique data set consisting of 2351 vertical profiles of temperature and salinity collected by southern elephant seals (Mirounga leonina) and a profile beneath the Fimbul Ice Shelf (FIS), obtained via drilling through 395 m of ice. This data set reveals variations in salinity and temperature through winter, and using a conceptual model of the coastal salt budget we quantify the main exchange processes. Our data show that modified WDW, with temperatures below −1.5°C, is advected onto the shelf and into the ice shelf cavities by an eddy overturning of the ASF. The onshore Ekman flux of surface waters during summer is the main source of freshwater that leads to the formation of low salinity shelf waters in the region. The modified WDW that reaches beneath the ice shelves is too cold for basal ice shelf melting to create such low salinity water. A high-resolution model of an idealized ASF-continental shelf-ice shelf system supports the conclusions from the data analysis. The inflow of WDW onto the continental shelf and into the ice shelf cavity occurs within a bottom boundary layer where the eddy advection in the model is particularly strong, in close agreement with the observed vertical profile of temperature beneath the FIS.

Fjords have long been recognized for their value as sites of sediment deposition, recording past climatic conditions. Recently, Arctic fjords have been recognized as the critical gateway through which oceanic waters can impact on the stability of glaciers. Arctic fjords are also used as idealized locations to study ice-influenced physical, biological and geochemical processes. In all cases a clear understanding of the physical oceanographic environment is required to interpret and predict related impacts and linkages. In this review we consider the characteristic elements of Arctic fjords and the important dynamical processes. We show how the intense seasonality of these regions is reflected in the varying stratification of the fjords. In particular, we show that sea ice has a central role in terms of the fjord salinity which ultimately influences the exchange with oceanic waters. When the fjord is ice free, wind forcing from the intense down-fjord katabatic winds gives rise to rapidly changing cross-fjord gradients, upwelling and strong surface circulations. The stratification and dimensions of Arctic fjords mean that they are often classed as 'broad' fjords where rotational effects are important in their circulation. We refer to the link between the physical oceanographic conditions and the related depositional records throughout.

Heat and freshwater transports through Fram Strait are understood to have a significant influence on the hydrographic conditions in the Arctic Ocean and on water mass modifications in the Nordic seas. To determine these transports and their variability reliable estimates of the volume transport through the strait are required. Current meter moorings were deployed in Fram Strait from September 1997 to September 1999 in the framework of the EU MAST III Variability of Exchanges in the Northern Seas programme. The monthly mean velocity fields reveal marked velocity variations over seasonal and annual time scales, and the spatial structure of the northward flowing West Spitsbergen Current and the southward East Greenland Current with a maximum in spring and a minimum in summer. The volume transport obtained by averaging the monthly means over two years amounts to 9.5 ± 1.4 Sv to the north and 11.1 ± 1.7 Sv to the south (1 Sv = 10 6 m 3 s -1 ). The West Spitsbergen Current has a strong barotropic and a weaker baroclinic component; in the East Greenland Current barotropic and baroclinic components are of similar magnitude. The net transport through the strait is 4.2 ± 2.3 Sv to the south. The obtained northward and southward transports are significantly larger than earlier estimates in the literature; however, within its range of uncertainty the balance obtained from a two year average is consistent with earlier estimates.

No abstract