Physical Qualification and Quantification of the Water Masses in the Kongsfjorden-Krossfjorden System Cross Section

Abstract

The Kongsfjorden-Krossfjorden system, situated on the northwest coast of Spitsbergen, is connected to the continental shelf slope by a trough, Kongsfjordrenna, that crosses the 50 km wide shelf. Kongsfjorden is the southern arm of this fjord system, and has a maximum depth of 400 m. The fjord system has no typical fjord sill, but Kongsfjordrenna seems to function as a sill of around 270 meters. This means that most of the water column in Kongsfjorden is susceptible to exchange with warm and salty Atlantic Water (AW) from the West Spitsbergen Current (WSC) flowing along the shelf slope and with colder and fresher water from the shelf. The water masses found in Kongsfjorden can be viewed on as a mixture between the AW, Winter Cooled Water (WCW) and fresh water either as melt water or river runoff. Winds at the west Spitsbergen coast cause Eknian drift to either pile up or remove surface water from the coast. The result is an altering of the stratification of the water outside the fjord system in the form of downwelling or upwelling. This builds up a horizontal pressure gradient between the coast and the fjord system, forcing water in or out of the fjord area. Conservation of volume demands that exchange takes place in both directions. The exchange with the adjacent shelf is shown to be related to irreversible exchange across the front between the AW along the shelf slope and the ArW on the shelf. Most of the exchanged water crosses the shelf and numerous intrusions to the fjord system take place every year. The marine ecosystem is dependent on such variations, especially on the lower trophic level, such as microbial and zooplankton production. The relative composition of zooplankton depends on water masses and sea ice concentration. Changes in the zooplankton composition will result in altered energy transfer within the pelagic food web with potential consequences for growth and survival of seabirds. This work is based on CTD data from four cruises to Kongsfjorden: last week of April, first week of June, first week of July and third week of September. The volume of AW and freshwater in Kongsfjorden during each of these periods was estimated mainly to investigate the variability in the content of these water types. Estimation of fresh water content due to ice melting and river runoff and the estimation of the amount of fresh water was carried out by subtracting all measured salinities from the maximum salinity measured in the standard shelf slope station The areal network was used to estimate the volume of the mentioned water masses. Variations in the amount of AW and fresh water have been observed between these periods. The comparison of TS profiles at one position in the fjord from all the four cruises, and two profiles from a station in the AW on the shelf slope show some of these characteristics. Evidence that these variations are caused by AW entering the fjord by eddies escaping from the WSC due to instabilities along the front between the WSC and the shelf water has been encounter.