Distribution of phytoplankton and other protists in the North Water

Specific taxa and community structure of the phytoplankton and other protists in the North Water, a productive polynya ecosystem between Ellesmere Island (Canada) and Greenland, were determined from April to July 1998. Distinct temporal and spatial trends were observed within different geographic regions, influenced by water masses determined by temperature and salinity (TS) characteristics. In April, the northernmost communities were primarily flagellates and dinoflagellates, resembling those of the Arctic Basin, while large centric diatoms dominated in May and persisted through July. Throughout the rest of the polynya in April, centric diatoms and alveolates (ciliates and dinoflagellates) dominated. In the eastern part of the polynya in May and June, centric diatoms, especially Thalassiosira spp., reached very high levels, comprising 50–80% of biomass carbon there, while in July the eastern community was primarily Chaetoceros spp. and large alveolates. The community in the western region in April was more mixed, with Actinocyclus spp./Coscinodiscus spp. and alveolates as the dominant groups. In May and June, pennate-ribbon diatoms were mixed with Thalassiosira and Chaetoceros spp., while in July western biomass was primarily alveolates and Chaetoceros spp. Throughout the polynya and the 4-month sampling period, the community of phytoplankton and other protists was dominated by microplankton (20–200 μm). Records of this size class from the current study were comparable to historical records collected since 1876. The planktonic communities along the southern border of the North Water, which was ice-covered until mid-June and had TS characteristics of the West Greenland Current (WGC), differed from those in the rest of the polynya. They contained few planktonic diatoms and had a higher proportion of nanoplankton size (2–20 μm) flagellates and gymnodinoid dinoflagellates. The WGC microplankton were dominated by thecate dinoflagellates such as Ceratium arcticum. Overall, the diatom-dominated phytoplankton bloom in the North Water was 2–3 months earlier than blooms in the southern region. In addition to blooming sooner, large cells persisted, were a dominant biomass component from May to July, and thus were major contributors to the overall productivity of the North Water.