Production of Exopolymeric Substances by Arctic Sea Ice Algae

建议提要：由光合作用微藻产生的胞外多聚体物质(EPS)作为水生系统初级生产力的一个重要但高度可变的组成部分正得到越来越多的认可。EPS的产生可能在藻类的运动性、浮力、附着表面、营养物质清除、防御和光合作用碳溢出方面发挥关键作用。EPS也是透明胞外聚合物颗粒(TEP)的来源，TEP与许多控制海洋中碳转化和出口的关键机制有关。在硅藻培养和浮游植物水华中，EPS和TEP的产生被最频繁地研究。这些物质通过生物定居和物理聚集过程(如海洋雪)进行转化，并受到微生物降解和浮游动物放牧的影响。北极海冰和下伏水域显示出与硅藻水华相关的高TEP积累。当海冰中的TEP释放到水柱中时，它有可能增加聚集(增加表层水域的碳出口。因此，TEP生产具有不同于颗粒或溶解碳初级生产的属性，这意味着需要对北冰洋碳循环模型进行速率过程测量。有待检验的主要假设是，北极海冰中EPS和TEP的高产量是硅藻水华期间氮素胁迫的结果。对养殖和底栖硅藻群落(类似于出现在海冰-海水界面的薄、高生物量藻类群落)中的硅藻的研究表明，低N和P有效性可导致EPS产量高。营养胁迫已在北冰洋海冰硅藻水华中得到证实，最常见的原因是N或Si的供应。该项目将测试所有三种常量营养素(N、P和Si)的效果。它将测量EPS和溶解有机碳的产量作为初级产量的一部分，以及TEP累积的测量，使用实验操作和现场观察来验证这一假设。该实地计划将作为加拿大北冰洋大陆架交换研究(CASE)的一部分在波弗特海进行。案例的主要目标是了解海冰的可变性和变化对生物、地球化学和生态的影响。加拿大研究人员将对藻类生物量和产量(溶解和颗粒)进行核心测量，这一新项目将增加EPS和TEP生产的分配。这些案例的实地研究将集中在春季的近海浮冰上，优势是可以遇到各种各样的海冰栖息地，这些栖息地的TEP产量可能会有所不同。海冰是一种极端环境，覆盖了世界海洋的很大一部分。最近发现，北极海冰覆盖面积正在减少，这可能是由于人类造成的气候变化，这突显了理解这一生态系统的必要性。外展活动将编写侧重于海冰和极地海洋学的教材，纳入为社区大学学生编写的在线课程教材。教材的开发将与富勒顿学院的学生和教师合作进行。产品将作为社区大学海洋学课程的一部分进行评估，还将包括在北极实地考察季节期间展示国际科学合作的机会。

Synopsis of proposal:Exopolymeric substances (EPS) produced by photosynthetic microalgae are gaining recognition as a significant but highly variable component of primary production in aquatic systems. EPS production may play critical roles in algal motility, buoyancy, attachment to surfaces, nutrient scavenging, defense, and photosynthetic carbon overflow. EPS is also a source for transparent exopolymer particles (TEP) that have been implicated in many critical mechanisms controlling carbon transformations and export in the sea. EPS and TEP production have been most frequently studied in diatom cultures and phytoplankton blooms. These materials are transformed by colonizing organisms and physical aggregation processes (e.g. marine snow), and subjected to microbial degradation as well as zooplankton grazing. Arctic sea ice and underlying waters show high TEP accumulations associated with diatom blooms. When TEP from the sea ice is released to the water column, it has the potential to increase aggregation (increasing carbon export from surface waters. Thus, TEP production has attributes distinct from primary production of particulate or dissolved carbon, implying a need for rate process measurements for Arctic ocean carbon cycle models. The main hypothesis to be tested is that high EPS and TEP production in Arctic sea ice is a consequence of nitrogen stress during diatom blooms. Studies on diatoms in culture and from benthic diatom communities (an analog to the thin, high-biomass algal communities that occur in the ice-seawater interface of sea ice) have shown that low N and P availability can lead to high EPS production. Nutrient stress has been demonstrated in Arctic sea ice diatom blooms, and most commonly attributed to the supply of N or Si. The project will test the effect of all 3 macronutrient elements (N, P and Si). It will make rate measurements for EPS and dissolved organic carbon production as a fraction of primary production, along with measurements of TEP accumulation, using both experimental manipulations and field observations to test this hypothesis. The field program will be carried out in the Beaufort Sea as part of the Canadian Arctic Shelf Exchange Study (CASES). The main goal of CASES is to understand the biogeochemical and ecological consequences of sea ice variability and change. Canadian researchers will be making core measurements of algal biomass and production (dissolved and particulate) to which this new project will add partitioning of EPS and TEP production. The CASES field studies will focus on offshore pack ice during the spring, with the advantage of encountering a wide variety of sea ice habitats that may differ in TEP production. Sea ice is an extreme environment covering a large fraction of the World Ocean. The recent discovery that Arctic sea ice cover is diminishing, possibly due to human-induced climate change, underscores the need to understand this ecosystem. Outreach activities will produce teaching materials focused on sea ice and polar oceanography for inclusion in on-line course materials developed for community college students. Development of educational materials will be done in collaboration with students and teachers at Fullerton College. Products will be assessed as part of a community college oceanography courses and will also incorporate opportunities to showcase international scientific collaboration "in action" during field seasons in the Arctic.