Spatial variability of chlorophyll- a in the Marginal Ice Zone of the Barents Sea, with relations to sea ice and oceanographic conditions

Abstract

The distribution of chlorophyll- a in the Barents Sea was observed from the optical satellite instrument Sea-viewing Wide Field-of-view Sensor (SeaWiFS) during May 1999. In the same period water samples were collected in situ and analysed. Contrary to previous studies of phytoplankton distribution in the Barents Sea, we rigourously analysed the chlorophyll- a distribution characteristics with respect to sea ice and oceanographic conditions, spatially and temporally. The spatial distribution of surface chlorophyll- a was analysed and related, statistically, to the ice edge and sea ice concentrations from the Special Sensor Microwave Imager (SSM/I) satellite instrument. The highest chlorophyll- a concentrations were observed near the ice edge, and then decreased further into the ice. The spatial variability of the chlorophyll- a concentrations in this region was high, even in open water along the ice edge. The chlorophyll- a observations indicated a strong primary bloom about 2 weeks after the ice edge had retreated from a given measurement point. There were also indications of several minor blooms about 2 weeks after the initial bloom. The vertical distributions of chlorophyll- a are presented for nine different stations in the Marginal Ice Zone (MIZ) of the northern Barents Sea and discussed in terms of simultaneously measured temperature–salinity CTD profiles. Water mass properties and sea ice history have a significant impact on the vertical distribution of phytoplankton. The surface chlorophyll- a concentration was about 60% higher (±70% S.D.) than the total column average. The correlation coefficient was 0.87, indicating that surface values are good predictors for relative levels of total phytoplankton biomass during spring conditions. We propose a method to identify the stage of the phytoplankton bloom based on satellite observations of chlorophyll- a, temperature, salinity and sea ice history. Based on an extensive set of field measurements at different times from many locations in the Barents Sea, we have produced empirical formulae to estimate the integrated chlorophyll- a content for the water column from surface (satellite) measurements during early spring (homogeneous water masses) and bloom conditions.