Role of exopolymers in the cycling of carbon in arctic seas

海冰具有多种生态作用，从对地球气候和北冰洋淡水平衡的影响，到对海洋食物链的重要性。季节性海冰约占北冰洋总冰面面积的50%。在过去的二十年中，已经观察到北极的快速变暖以及与之相关的冰盖减少。目前的模型表明，这一趋势将继续下去。海冰支持着多种多样的生物群落，包括病毒和细菌、鞭毛虫、纤毛虫、甲壳类动物和其他小型动物。海冰的初级生产通常以硅藻为主，在春季可以达到很高的生物量。硅藻也是夏季开阔水域浮游植物大量繁殖的原因。硅藻是外聚合物物质（EPS）的主要生产者，这种凝胶状物质在春季的海冰中可以贡献很大一部分有机碳。由于EPS是粘性凝胶，它们有利于藻华结束时藻类生物量的聚集和快速下沉。在北极，人们对EPS的作用以及调节其产生的因素知之甚少。本研究将研究季节性海冰中EPS的动态变化，以及在季节性冰覆盖的北极海域硅藻繁殖结束时水柱中的EPS变化。本研究的总体目标是：1)评估生物和非生物因素对季节性冰覆盖北极海域海冰和开放水域中EPS浓度和产生的影响；2)评估不同生化环境下EPS在北极藻华循环和下沉中的作用。这项研究将有助于我们对北极碳循环的理解，并将为北极正在发生的变化的预测模型提供关键知识。

Sea-ice harbors various ecological roles, which range from its influence on the Earth's climate and the freshwater balance of the Arctic Ocean, to its significance for the marine food chain. Seasonal sea-ice constitute about 50% of the total ice surface in the Arctic Ocean. During the past two decades, rapid warming of the Arctic and an associated decrease in ice cover have been observed. Current models suggest that this trend will continue. Sea-ice supports a diverse community of organisms, from viruses and bacteria, flagellates, ciliates, crustaceans, and other meiofauna. Primary production in the sea-ice is usually dominated by diatoms, which can reach very high biomasses in the spring. Diatoms are also responsible for intense phytoplankton blooms taking place in open waters during the summer. Diatoms are main producers of exopolymeric substances (EPS), gel-like substances that can contribute a large fraction of the organic carbon in the sea-ice in the spring. Because EPS are sticky gels, they can favor aggregation and rapid sinking of algal biomass at the termination of blooms. Very little is known on the role of EPS, and the factors that regulate their production, in the Arctic. This research will investigate the dynamics of EPS in seasonal sea-ice and in the water column at the end of diatom blooms in seasonally ice-covered Arctic seas. The general objectives of this study are: 1) to evaluate the influence of biotic and abiotic factors on EPS concentrations and production in the sea-ice and open water in seasonally ice-covered Arctic seas, and 2) to assess the role of EPS in the cycling and sinking of algal blooms under contrasting biochemical environments in the Arctic. This research will contribute to our understanding of the carbon cycle in the Arctic and will provide key knowledge for predictive models in view of on-going changes taking place in the Arctic.