Vertical distribution of primary production and chlorophyll a in the Kara Sea

Abstract

On the basis of data obtained during three ecosystem expeditions in the Kara Sea, the vertical variability of the primary production (PP) and chlorophyll a (Chl) in autumn was studied. The Chl maximum was detected mainly on the surface (Chl0). A homogenous Chl distribution in the euphotic layer (1% photo-synthetically available radiation) and a nearly linear decrease in the Chl concentration below this layer were observed in waters with Chl0 values of 0.1–0.5 mg/m3. In waters with Chl0 > 0.5 mg/m3, the Chl concentration in the studied layer decreased linearly or exponentially. The subsurface Chl maximum (SCM) was registered weekly and was detected mostly in waters with a Chl0 content of 0.1–0.5 mg/m3. The SCM formation in the Kara Sea was consistent with the general patterns for the World Ocean. Water-column stability, the content of biogenic elements, and the level of subsurface irradiance had an approximately equal effect on SCM formation. The contribution of the SCM to the depth-integrated PP varied from 1 to 27%. The parameterization of vertical profiles of Chl was performed in order to be used in depth-integrated PP models. The Chl maximum on the surface and the negligible SCM facilitate the estimation of depth-integrated PP on the basis of satellite data and the use of vertical-resolution models.