Photosynthetically active radiation and microalgae and protist occurrence at ice stations of POLARSTERN cruise ARK-XIX/1

Pack ice around Svalbard was sampled during the expedition ARK XIX/1 of RV "Polarstern" (March-April 2003) in order to determine environmental conditions, species composition and abundances of sea-ice algae and heterotrophic protists during late winter. As compared to other seasons, species diversity of algae (total 40 taxa) was not low, but abundances (5,000-448,000 cells/l) were lower by one to two orders of magnitude. Layers of high algal abundances were observed both at the bottom and in the ice interior. Inorganic nutrient concentrations (NO2, NO3, PO4, Si(OH)4) within the ice were mostly higher than during other seasons, and enriched compared to seawater by enrichment indices of 1.6-24.6 (corrected for losses through the desalination process). Thus, the survival of algae in Arctic pack ice was not limited by nutrients at the beginning of the productive season. Based on less-detailed physical data, light was considered as the most probable factor controlling the onset of the spring ice-algal bloom in the lower part of the ice, while low temperatures and salinities inhibit algal growth in the upper part of the ice at the end of the winter. Incorporation of ice algae probably took place during the entire freezing period. Possible overwintering strategies during the dark period, such as facultative heterotrophy, energy reserves, and resting spores are discussed.

本研究依托“极地号”（RV Polarstern）科考船的ARK XIX/1航次（2003年3—4月），对斯瓦尔巴群岛周边的浮冰开展采样，旨在解析晚冬季节的环境条件、海冰藻类与异养原生生物的物种组成及细胞丰度。与其他季节相比，该区域藻类的物种多样性（共计40个分类单元）并未偏低，但其细胞丰度（5000~448000个/升）则低1~2个数量级。研究观测到，海冰底部与冰体内部均存在藻类丰度较高的层位。海冰内部的无机营养盐浓度（NO₂、NO₃、PO₄、Si(OH)₄）整体高于其他季节，相较于海水的富集系数为1.6~24.6（该系数已校正脱盐过程中的营养盐损失）。因此，在春季生产季初期，北极浮冰内藻类的存活并未受到营养盐的限制。基于精度有限的物理观测数据，光照被认为是调控海冰下层春季冰藻水华爆发的最关键因素；而冬末时节海冰上层的低温与低盐度会抑制藻类生长。海冰藻类的物质累积过程大概率发生于整个结冰周期内。研究还探讨了黑暗期内藻类可能存在的越冬策略，包括兼性异养、能量储备以及休眠孢子等。