Harald Svendsen

The physical environment of Kongsfjorden–Krossfjorden, an Arctic fjord system in Svalbard

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.

Water mass modification in an Arctic fjord through cross-shelf exchange: The seasonal hydrography of Kongsfjorden, Svalbard

[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. Slow modification of the fjord water during spring reduces the effectiveness of geostrophic control, and by midsummer, Atlantic Water intrudes into the fjord, switching from being Arctic dominant to Atlantic dominant. Atlantic Water continues to intrude throughout the summer and by September reaches some quasi steady state condition. The fjord adopts a ‘‘cold’’ or ‘‘warm’’ mode according to the degree of Atlantic Water occupation. Horizontal exchange across the shelf may be an important process causing seasonal variability in the northward heat transport to the Arctic.

Across the Arctic front west of Spitsbergen: high-resolution CTD sections from 1998–2000

The structure of the oceanic Arctic front west of Spitsbergen is investigated using data from high-resolution CTD sections from September 1998-2000. Below the fresher surface layer, the front appears as a temperature-salinity front situated near the shelf break. No clear corresponding front in density is found. Our analysis suggests that barotropic front instability is a main factor in provoking subsurface cross-front exchange. The subsurface heat loss in the West Spitsbergen Current due to this exchange is estimated to be of the same order of magnitude as the heat loss to the atmosphere in the surface layer.

Selected aspects of the physical oceanography and particle fluxes in fjords of northern Norway

Results regarding the physical oceanography and the dynamics of particulate fluxes in fjords of northern Norway are presented. The phytoplankton spring bloom takes usually place in April in almost homogeneous water and comes to an end before the estuarine circulation starts in late May/early June when snow and ice melting gives rise to usually one pronounced pulse of freshwater run-off. During late summer and autumn river run-off is usually small and of limited significance for the particulate dynamics. Much of the spring bloom material is apt to sink to the bottom, but overwintering herbivores give rise to decreased vertical losses from the upper layers as well as a tendency towards a decreased seasonal variability compared to more enclosed coastal systems in boreal fjords of southern Norway. While destruction and mineralisation of sedimenting matter is of significance below the euphotic zone, giving rise to a decrease in vertical flux, resuspension is of importance in the lower water column and close to the rivers. Coastal currents strongly influence the north Norwegian fjords and particulate signals from rivers are small and do not penetrate extensively into the fjords. Advection of particulate matter, phytoplankton and zooplankton along with various water masses in and out of the fjords seems to play an important role for the ecology and particulate fluxes in this area. The rapid exchange of water masses between the coastal currents and even the innermost fjords as well as the comparatively small discharge of freshwater gives rise to scenarios where particulate fluxes inside the coastal zone are to a large extent determined by external, oceanic forcing. North Norwegian fjords are, therefore, not independent entities, but in various degrees part of the Norwegian Coastal Current.

Banded structure of drifting macroalgae.

A massive bloom of macroalgae occurred in the western Yellow Sea at the end of May, 2008, and lasted for nearly 2 months. The surface-drifting macroalgae was observed to accumulate in a pattern dominated by linear bands. The maximum length of individual algal bands exceeded 10 km and the distance between neighboring bands ranged from hundreds of meters to 6 km. Seven satellite images were analyzed to determine the distances between neighboring bands. Proportions of about 24%, 38%, and 22% are responsible for the separation distances smaller than 1 km, between 1 and 2 km, and between 2 and 3 km, respectively. The separation of about five percent of the bands exceeds 4 km. The probability distribution of the separation distance is quite close to log-normal which is that found in Langmuir circulation. However, the observed algal band separation greatly exceeds the distances between convergence lines reported in Langmuir circulation.

Upwelling in broad fjords

Abstraet--A broad fjord is defined here as a stratified fjord whose width exceeds the first baroclinic radius defined from the stratification. When a longitudinal wind blows along such a fjord, the response entails upwelling on one side and downwelling on the other. The physics are identical to those of the classical theory of coastal upwelling, except that here upwelling and downwelling are simultaneously present and interfere with each other. Our solution is based on the impulse method suggested by CSANADY (1977, Journal of Geophysical research, 82,397-419) and assumes a two-layer stratification. Limiting cases of infinite lower-layer depth (toward one layer) and/or infinitely wide fjord (toward one coast) are explored to appreciate the dependency of the solution on the parameters it involves. The general conclusion is that the shallower and the narrower the fjord, the weaker the upwelling~lownwelling responsc. However, when the wind impulse is large, this is true only for upwelling. Relevance to Porsangerfjord in northern Norway and comparison with a numerical model demonstrate the applicability of the model to observed events.

Impact of freshwater runoff on physical oceanography and plankton distribution in a Western Norwegian fjord: an experiment with a controlled discharge from a hydroelectric power plant

Abstract Investigations were carried out in a 20-km long fjord branch prior to, during, and partly after a 51-h controlled discharge from a hydroelectric power plant. The freshwater runoff (230 m 3 s −1 ) generated an estuarine circulation which was most prominent along the mid-axis of the fjord. High velocities were recorded both in the outgoing surface current, with a maximum of 1 m s −1 (10 km downstream of the power plant), and in a compensatory current (registration at 10-m depth) with a maximum of 0·6 m s −1 (3 km downstream). Velocities were low at 5-m depth. During discharge, salinity increased in the surface layer and decreased at a depth of several metres because of more extensive mixing. Phytoplankton was partly flushed out in the upper layers throughout the fjord branch, but abundance increased in deeper layers in an outer station, and the horizontal patchiness increased. The vertical centre of zooplankton biomass descended significantly during running of the plant. Biomass maxima in the ingoing compensation current indicate net zooplankton import during running of the power plant, but no change in total zooplankton biomass in the fjord branch was found during this experiment.

Atmospheric-driven state transfer of shore-fast ice in the northeastern Kara Sea

Received 9 September 2004; revised 19 April 2005; accepted 2 June 2005; published 21 September 2005. [1] Frequencies of observed occurrences of shore-fast ice in the northeastern Kara Sea for each month during 1953–1990 reveal a multimodality of shore-fast ice extent in late winter and spring. The fast ice extent exhibits mainly three different configurations (modes) associated with the regional topography of coasts and islands. These modes show fast ice areas equal to approximately 98 ± 6, 122 ± 6, and 136 ± 8 1000 km 2 . Analysis of the time series of fast ice extent shows that favorable conditions for expansion of fast ice seaward in winter and spring are met if the atmospheric circulation over the northeastern Kara Sea is controlled by the Arctic high, resulting in offshore winds and a significant (up to 6� C) decrease of the monthly mean surface air temperature. In contrast, the penetration of the Icelandic low into the Kara Sea, accompanied by Arctic cyclones coming from the west, is responsible for the partial breakup and decrease of fast ice extent in winter or spring.

Oceanography and fluorescence at the shelf break off the north Norwegian coast (69°′N-70°30′N) during the main productive period in 1994

Abstract Data on hydrography, fluorescence, wind and currents from shelf studies on the Norwegian shelf between 69°30′N and 70°30′N are presented. The sampling was performed along five transects, covering a narrow shelfbreak site, a trench, and a bank. The sampling programme was conducted during cruises of 4-5 days duration each month from March until October 1994. Three distinct water masses were identified: i) Coastal Water (S 12 oq above the shelf and the shelfbreak (0-300 m depth), 2) Atlantic Water (S > 35; 5 10 oq off shelf (0-400 m depth) and below the Coastal Water in the trenches (300-400 m depth), and 3) Norwegian Sea Deep Water (S < 35; T < 0 °C) off the shelf break, below 700 m depth. Wind direction between southeast and northwest prevailed during all cruises, except in May, when northeasterly wind was most frequent. Typical wind speeds were in the order of 7-l2 m s-1, but the wind exceeded l 5 m s-1 frequently during the whole investigation period. Current regime above the...

Exchange Processes Above Sill Level between Fjords and Coastal Water

During the period from September 1972 to November 1975 the Geophysical Institute of the University of Bergen carried out an investigation in six fjords, Hylsfjord, Sandsfjord, Saudafjord, Erfjord, Josenfjord and Jelsafjord, in Ryfylke in the southern part of Norway, Fig. 1. The investigation was based on measurements of temperature, salinity, oxygen, current, freshwater runoff, water level and wind.