Variations in hydrography, nutrients and chlorophyll a in the marginal ice-zone and the central Barents Sea

Abstract

The project “Climatic variability and vertical carbon flux in the marginal ice zone in the central Barents Sea” was initiated to fill some of the gaps in our knowledge on the biological processes related to the dynamic hydrography in the Barents Sea. A previously modelled transect from the Atlantic waters, crossing the Polar Front into the Arctic waters and the MIZ in the central Barents Sea, was investigated to cover the zonal structure and different water masses. The present paper describes the hydrography, nutrients and Chl a distribution in March, May 1998 and July 1999 along this transect. Based on the nutrient consumption, the new production is estimated and discussed as related to topography, water masses and climate change. Atlantic water dominated in south with a Polar Front shaped by the bank topography, and water with more Arctic characteristics in north. A high, uniform nutrient regime in March was depleted giving a spring bloom in May with Chl a accumulation <100 m in the Atlantic dominated region. The phytoplankton biomass was concentrated in the upper 30 m in the strongly stratified MIZ. The new production estimates for the period ranged 30–80 g C m −2 (0.5–1.4 g C m −2 day −1). New production rates were closely related to the mixing depth with highest rates in the deeper mixed Atlantic region and trenches where the Polar Front was located. Non-Si demanding species were more important for new production in the deeper mixed regions. Seasonal changes from May to July was most likely masked by interannual variations as the July cruise took place the following year, characterised as a warmer year than 1998 in the Barents Sea due to increased Atlantic inflow in 1999 A locally produced cold but saline water mass observed on Sentralbanken in March and May resulting from the freezing process in the waters above the bank was replaced by warmer waters in July and the strongly stratified MIZ was pushed further north. Interannually variable hydrographic regimes in different regions influence the new production and the biological community in the Barents Sea.