Role of exopolymers in the cycling of carbon in arctic seas

海冰具有各种生态作用，从它对地球气候和北冰洋淡水平衡的影响，到它对海洋食物链的重要意义。季节性海冰约占北冰洋总冰面的50%。在过去的二十年里，观察到北极迅速变暖和相应的冰盖减少。目前的模型表明，这一趋势将继续下去。海冰支持着各种各样的生物群落，从病毒和细菌、鞭毛虫、纤毛虫、甲壳类动物和其他小型动物。海冰的初级生产力通常由硅藻主导，在春季，硅藻的生物量可以达到非常高的水平。硅藻也是夏季开放水域浮游植物大量繁殖的原因。硅藻是胞外聚合物(EPS)的主要生产者，EPS是一种凝胶状物质，可以贡献春季海冰中有机碳的很大一部分。因为EPS是粘性凝胶，它们可以促进藻类生物量在水华结束时的聚集和快速下沉。人们对EPS在北极的作用以及调节其生产的因素知之甚少。这项研究将调查季节性海冰和季节性冰盖覆盖的北冰洋硅藻水华结束时水柱中EPS的动态。这项研究的总体目标是：1)评估生物和非生物因素对季节性冰盖北冰洋海冰和开阔水域EPS浓度和产量的影响；2)评估EPS在北极不同生化环境下藻类水华的循环和沉没中的作用。这项研究将有助于我们了解北极的碳循环，并将为考虑到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.