Microphytoplankton community structure in the western Arctic Ocean: surface layer variability of geographic and temporal considerations in summer

Abstract

Arctic ocean environments are receiving increasing attention, due to the rapid thinning and recession of marine sea ice caused by climate change. The present study characterizes the structure and chlorophyll a (Chl a) of summer microphytoplankton communities in western Arctic Ocean surface layers, in terms of species composition, periodical succession, geographic distribution, community types, abundance, and Chl a variation during the Fourth Chinese National Arctic Research Expedition (CHINARE, July–September, 2010). Possible effects of environmental forces on microphytoplankton communities were analyzed, and associations with water masses and sea-ice retreat were assessed. Results show high species diversity in surface microphytoplankton communities, with significant geographic and temporal zonation relative to taxonomic composition, species abundance, and Chl a. A total of 153 taxa were identified, distributed among 68 genera of 9 phyla, and cluster analysis and multi-dimensional scaling showed a continual distribution of a distinct shelf assemblage and deep basin assemblage. Average abundance (892.7 × 102 cells/l), Chl a (1.63 mg/m3), species diversity (2.54), and species richness (19) were established for the shelf assemblage, with dominant species ranked as Navicula pelagica Cleve, Thalassiosira nordenskioeldii Cleve, Chaetoceros diadema (Ehrenberg) Gran, Leptocylindrus danicus Cleve, Pseudo-nitzschia seriata (Cleve) H. Peragallo, Cylindrotheca closterium (Ehrenberg) Reimann & Lewin, Nitzschia longissima (Brebisson) Ralfs, and Navicula vanhoeffenii Gran. It is of note that a succession from pennate to centric diatom was accompanied by a significantly decreased amplitude of abundance and Chl a, between the inbound and the return voyage across the Chukchi shelf. Comparatively, deep basin assemblage displayed lower values of abundance (27.7 × 102 cells/l), Chl a (0.12 mg/m3), species diversity (2.49), and species richness (11), and the community was dominated by Thalassionema nitzschioides Grunow and Navicula pelagica Cleve. Silicate and nitrate concentrations were major factors that affected abundance and Chl a variability in both Pearson correlation analysis and canonical correspondence analysis, while the dynamics of oceanic circulation and sea-ice retreat affected summer microphytoplankton community assembly and fluctuations in the surface layer of the western Arctic Ocean.