Seasonal transition in water masses and plankton from Rijpfjorden in Svalbard to the Arctic Ocean

Haakon Hop 1, Philipp Assmy1, Arild Sundfjord1, Malin Daase1, Anette Wold1, Svein Kristiansen2, Vladimir Pavlov1, Jørgen Berge2, Stig Falk-Petersen1 ,2
1Norwegian Polar Institute, Tromsø, Norway, 2Faculty of Biosciences, Fisheries and Economics, University of Tromsø, Tromsø, Norway

The northern coast of Svalbard is lined with high-arctic fjords, such as Rijpfjorden (80oN 22o30'E) that face the Arctic Ocean. The West Spitsbergen Current (WSC), which transports Atlantic water and heat along Spitsbergen, bypasses these fjords along the shelf edge on route to the Nansen Basin. Even though Rijpfjorden is a cold Arctic system during most of the year (January-July), transformed Atlantic water is recorded in the fjord during late autumn. Models suggest that this area north of Svalbard will become particularly affected by temperature increase because of increased advection of heat by the WSC. This will also influence the position of the southern extent of the polar pack ice and its seasonal retreat off the shelf. In this setting, it is of particular interest to study the transition of water masses and plankton from fjord, via the shelf and shelf break into the deep Arctic Ocean. As part of the ICE-project (NPI) and Polar Night Cruise (Univ. Tromsø), we extended the established transect in Rijpfjorden northwards to cross the Atlantic and Arctic water masses on the shelf and slope to 2500 m depth. We here present preliminary results of nutrients, phytoplankton and zooplankton recorded in relation to water masses on this transect. The seasonal variation in production due to changes in radiation, melting and nutrients is large in the Arctic and we have addressed this in seasonal cruises (2010-2012) to cover processes during spring (April-May 2011), summer (July-August 2012), autumn (August-September 2010) and winter (January 2012). The seasonal patterns in nutrients and primary producers involved a spring bloom dominated by diatoms in nutrient replete surface layer, and summer to autumn post bloom situations with low nutrient and chlorophyll-a concentrations at the surface and sub-surface chlorophyll maxima at 30-50 m depth. The seasonal composition of zooplankton followed the development of blooms, with reproduction and naupliar stages of Calanus other zooplankters during the spring-summer blooms. The boreal Calanus finmarchicus dominated Atlantic water masses and was also abundant on the shelf, whereas Calanus glacialis, Pseudocalanus spp. and other Arctic zooplankton species dominated the cold water masses in Rijpfjorden. Rapid climate warming is expected to influence the rate of change in the marine ecosystem also on a season basis as the ice covered part of the year shortens and open water with associated processes will become a more dominant feature in the Arctic, particularly during summer and autumn.