Patterns of the Kara Sea primary production in autumn: Biotic and abiotic forcing of subsurface layer

Abstract

Primary production and fundamental environmental factors were measured during September–October 1993, 2007 and 2011 in the Kara Sea. Relationships between the depth-integrated primary production (PPint), the surface chlorophyll a (Chl0) concentration and the maximum chlorophyll specific carbon rate within water column (Pbopt) had shown that only 12% of PPint variability were determined by Chl0 and there were strong correlations between PPint and Pbopt (R2=0.64). Thus, in the autumn PPint values were largely influenced by the phytoplankton assimilation activity. At the end of a vegetative season high (close or above 1mgm−3) values of Chl0 were not an index of phytoplankton productivity within photosynthetic layer where the organic matter synthesis rate was low which testifies the lack of correlation between Chl0 and PPint (R2=0.12) and between Chl0 and depth-integrated chlorophyll a (chl a) (R2=0.22). This conclusion is based on the low assimilation activity within water column and small thickness of the photosynthetic layer. The latter corresponds to low insolation and water transparency. The lack of correlation between surface and depth-integrated productivity parameters is the challenge for satellite PPint estimations. In turn PPint and Pbopt depended mainly on photosynthetically available radiation (PAR) and weakly related to the nitrogen and phosphorus concentrations. At the end of a vegetative season PAR level, apparently, should be considered as the main factor for primary production in the Kara Sea. Comparison between the integrated primary production from shipboard in September and the simulated evaluations of productivity (PP models) suggests that PP models overestimate the in situ PPint by a factor of 3–7 in the different Kara Sea regions. Improving of Kara Sea primary production estimations implies the development of regional satellite chl a algorithm and local primary production model considering specific features of PP in this Arctic Ocean region.