Physicochemical characteristics and protist occurrence at stations sampled in 2007/2008 in the eastern Beaufort Sea

This study documents, for the first time, the abundance and species composition of protist assemblages in Arctic sea ice during the dark winter period. Lack of knowledge of sea-ice assemblages during the dark period has left questions about the retention and survival of protist species that initiate the ice algal bloom. Sea-ice and surface water samples were collected between December 27, 2007 and January 31, 2008 within the Cape Bathurst flaw lead, Canadian Beaufort Sea. Samples were analyzed for protist identification and counts, chlorophyll (chl) a, and total particulate carbon and nitrogen concentrations. Sea-ice chl a concentrations (max. 0.27 µg/l) and total protist abundances (max. 4 x 10**3 cells/l) were very low, indicating minimal retention of protists in the ice during winter. The diversity of winter ice protists (134 taxa) was comparable to spring ice assemblages. Pennate diatoms dominated the winter protist assemblage numerically (averaging 77% of total protist abundances), with Nitzschia frigida being the most abundant species. Only 56 taxa were identified in surface waters, where dinoflagellates were the dominant group. Our results indicate that differences in the timing of ice formation may have a greater impact on the abundance than structure of protist assemblages present in winter sea ice and at the onset of the spring ice algal bloom.本研究首次记录了北极海冰黑暗冬季期间的原生生物（protist）群落丰度与物种组成。此前学界对黑暗期海冰群落的认知空白，使得引发冰藻华（ice algal bloom）的原生生物物种的留存与存活机制长期悬而未决。2007年12月27日至2008年1月31日期间，研究团队于加拿大波弗特海的巴瑟斯特角冰间水道（flaw lead）内采集海冰与地表水样本，并对样本开展了原生生物鉴定与计数、叶绿素a（chl a）以及总颗粒态碳、氮浓度检测。检测结果显示，海冰叶绿素a浓度最高仅0.27 μg/L，总原生生物丰度最高达4×10³个/升，两项指标均处于极低水平，表明冬季海冰中原生生物的留存量极少。冬季海冰原生生物的多样性（共134个分类单元）与春季海冰群落相当。羽纹硅藻（pennate diatoms）在冬季原生生物群落的数量占比上占据主导地位，平均占总原生生物丰度的77%，其中冷菱形藻（Nitzschia frigida）为最优势物种。地表水样本中仅鉴定出56个分类单元，优势类群为甲藻（dinoflagellates）。本研究结果表明，海冰形成时间的差异，对冬季海冰及春季冰藻华爆发初期原生生物群落丰度的影响，显著大于对群落结构的影响。