Spatial and vertical variability of primary production in the Kara Sea in July and August 2016: the infuence of the river plume and subsurface chlorophyll maxima
A.B.Demidov, V.I.Gagarin, O.V.Vorobieva, P.N.Makkaveev, V.A.Artemiev, A.N.Khrapko, A.V.Grigoriev, S.V.Sheberstov

Abstract

Seasonal variations in primary production (PP) in the Kara Sea are underresearched. Previous studies only collected data during autumn or in late summer. However, the middle of summer is close to the beginning of the growing season, when PP can contribute signifcantly to annual water column integrated primary production (IPP). In addition, diferences can be expected in the spatial and vertical distribution of phytoplankton communities in this period. This gap in midsummer data was addressed within the framework of a multidisciplinary research cruise by the R/V “Akademik Mstislav Keldysh” (from 15 July to 18 August 2016). High values of IPP (> 200 mgC m−2 day−1) and surface chlorophyll a (Chl a) concentration (Chl0 > 1 mg m−3) were associated with the Ob–Yenisey river plume, located in the central part of the Kara Sea. Beyond the infuence of the plume, in the western and southwestern regions of the Kara Sea, well-pronounced subsurface chlorophyll maxima (SCM) were observed. In some cases, the Chl a concentration in SCM exceeded Chl0 by two orders of magnitude. SCM were often accompanied by subsurface PP maxima (SPM). At stations where SCM was pronounced, IPP values reached 500–800 mgC m−2 day−1, and > 30 % of IPP was accounted for by SPM-integrated PP. Thus, in the middle of summer in the Kara Sea, IPP was linked with the chlorophyll-specifc phytoplankton biomass and depended on the strength of the SCM.