The Kongsfjorden Transect: Seasonal and Inter-annual Variability in Hydrography

The Kongsfjorden conductivity, temperature and depth (CTD) Transect has been monitored annually since 1994. It covers the full length of the fjord and the shelf, and the upper part of the shelf slope outside Kongsfjorden. In addition to CTD profiles, data from vessel-mounted Acoustic Doppler Current Profiler (ADCP) and moorings have been collected. Previous studies noted that Atlantic Water (AW) from the West Spitsbergen Current was observed in the fjord every summer, but to a varying extent. The prolonged monitoring provided by the Kongsfjorden Transect data set examined here reveals continuous variations in AW content and vertical distribution in the fjord, both on seasonal and inter-annual timescales. Our focus in this paper is on this variable content of AW in Kongsfjorden, the forcing mechanisms that may govern the inflow of this water mass, and its distribution in the fjord. We classify three winter types linked to three characteristic scenarios for winter formation of water masses. During the historically typical winters of type “Winter Deep”, deep convection, often combined with sea ice formation, produces dense winter water that prevents AW from entering Kongsfjorden. Summer inflow of AW starts when density differences between fjord and shelf water allows for it, and occurs at some intermediate depth. During winters of type “Winter Intermediate”, AW advects into the fjord along the bottom via Kongsfjordrenna. Winter convection in Kongsfjorden will then be limited to intermediate depth, usually producing very cold intermediate water. Deep AW inflow continues during the following summer. A winter of type “Winter Open” seems to develop when open water convection produces very dense shelf water, and AW winter advection into Kongsfjorden occurs at the surface. Summer AW inflow is rather shallow after such winters. We find that variations between Winter Deep and Winter Intermediate winters are due to inherent natural variability. However, the Winter Open winters seem to be a consequence of the general trend of atmospheric and oceanic warming, and, more specifically, of the decreasing sea ice cover in the Arctic region. The Winter Open winters have all occurred after an unusual flooding of AW onto the West Spitsbergen shelf in February 2006.