“Flashes” of Chlorophyll-a Concentration Derived from in Situ and Remote Sensing Data at the Polar Front in the Barents Sea

ABSTRACT

The Polar Front Zone (PFZ) in the Barents Sea is an area where warm, salty water of the North Atlantic (AtW) interacts with cold, less dense, Arctic water (ArW) and the fresher water produced by melting ice (MW). In the spring a large-scale transformation of the structure of the PFZ is accompanied by the development of mesoscale eddies with characteristic sizes of 25 to 40 km. The vertical velocity in the centre of such cyclonic eddies can be up to 20 m/day, transporting deep water with high nutrient concentration up to the surface. Photosynthesis at the surface leads to intense phytoplankton development, which is registered by the color scanners of SeaWiFS and MODIS as a sharp increase, or “flash,” in chlorophyll-a concentration. A statistical analysis of such flashes for the last 11 years has shown that the most probable time for their occurrence is the last week of May. Maxima of the chlorophyll-a concentration have a Rayleigh distribution with a mean of 3.82 mg /m³ and a standard deviation of 1.98 3 mg /m³ . The characteristic sizes of the areas where a flash occurs correspond to the size of mesoscale eddies determined from estimations of the internal Rossby deformation radius. The positions of these eddies, observed by the R/V “Lance” survey coincide with the zones of high chlorophyll-a concentration seen in the data from the optical scanner of SeaWiFS.