Collaborative research: Sinking rates and nutritional quality of organic matter exported from sea ice; the importance of exopolymeric substances

Available data concerning the sinking rates of ice algae are highly divergent, while the characteristics of particles formed from other large organic pools in sea ice have received little study. As an initial step to remedy this situation, funds are provided to study the role of exopolymeric substances (EPS), produced by ice algae, in particle formation. The importance of EPS to particle coagulation and sinking rate is well established for temperate water columns. In sea ice, EPS comprise 20-70% of total particulate organic carbon, but their role in the sinking rate and composition of particles exported from sea ice is poorly understood. Based on previous studies, the PIs predict both positive and negative effects of EPS on particle sinking rate depending on EPS quantity. EPS also is predicted to increase the ratio of carbon to nitrogen (C:N) in the organic matter, which serves as a nutritional indicator. Based on documented trends in the EPS content of first-year Arctic sea ice, the PIs specifically predict slower sinking rates and higher C:N in particles produced after the export of ice algae, and from the upper levels of the ice column. They also predict slower sinking rates and higher C:N where snow cover is thicker. They will measure the sinking rates of particles released from melted sea-ice cores and test their hypotheses by relating the observed sinking rates to variables such as EPS concentration in the ice. Changes in the contribution of the sea-ice community to different flux periods will be investigated using microscopy and DNA-based molecular techniques. Finally, to help explain the spatial variability in the EPS content of sea ice, they will quantify EPS production rates of cultured ice algae as a function of light level. This work is designed to provide a conceptual framework for understanding and predicting spatial and temporal variability in the sinking rates and nutritional quality of particles released from Arctic sea ice in relation to variables measured in the ice such as: snow depth, chlorophyll, particulate organic carbon, and EPS. The knowledge resulting from this study will contribute to our understanding of the Arctic Ocean carbon cycle and how it may be modified in response to climate variability.现有关于冰藻沉降速率的研究数据存在显著分歧，而海冰中其他大型有机库所形成的颗粒特征却鲜有研究。为改善这一研究现状，本项目获得资助，旨在探究冰藻分泌的胞外聚合物（exopolymeric substances, EPS）在颗粒形成过程中的作用。温带水柱环境中，EPS对颗粒凝聚与沉降速率的重要性已得到充分证实。在海冰环境中，EPS占总颗粒有机碳的20%~70%，但其对海冰输出颗粒的沉降速率与组成的影响仍鲜为人知。基于此前的研究，项目负责人（Principal Investigators, PIs）预测，EPS对颗粒沉降速率的影响存在正负两面，具体取决于EPS的含量。此外，EPS还被预测可提升有机质的碳氮比（C:N），而该比值可作为营养状况的指示指标。基于北极一年冰海冰中EPS含量的已记录变化趋势，项目负责人进一步预测：在冰藻输出后形成的颗粒以及冰柱上层区域的颗粒中，沉降速率会更慢，碳氮比也更高。他们同时预测，积雪覆盖越厚的区域，颗粒的沉降速率越慢、碳氮比越高。研究团队将测量融化海冰岩芯释放出的颗粒的沉降速率，并通过将观测到的沉降速率与海冰中的EPS浓度等变量建立关联，以此验证其提出的假说。研究团队还将利用显微镜技术与基于DNA的分子生物学技术，探究海冰群落对不同物质通量时期的贡献变化。最后，为解释海冰EPS含量的空间异质性，研究团队将量化培养条件下冰藻的EPS生成速率与光照水平的函数关系。本研究旨在构建一套概念框架，用于理解和预测北极海冰释放颗粒的沉降速率与营养品质随空间和时间的变化规律，相关变化与海冰中可测量的变量（如积雪深度、叶绿素、颗粒有机碳及EPS）密切相关。本研究产生的相关成果，将有助于我们加深对北冰洋碳循环及其如何响应气候变异发生改变的理解。