Production of Exopolymeric Substances by Arctic Sea Ice Algae

提案概要：光合微藻产生的外聚合物质（EPS）作为水生系统初级生产的重要但高度可变的组成部分，正逐渐得到认可。EPS的产生可能在藻类的运动、浮力、附着表面、养分清除、防御和光合碳溢出中起关键作用。EPS也是透明外聚合物颗粒（TEP）的来源，TEP与控制海洋碳转化和出口的许多关键机制有关。在硅藻培养和浮游植物繁殖中，EPS和TEP的产生被研究得最多。这些物质通过定植生物和物理聚集过程（如海洋雪）进行转化，并受到微生物降解和浮游动物的放牧。北极海冰和下层水域显示与硅藻华有关的高TEP积累。当海冰中的TEP被释放到水柱中时，它有可能增加聚集（增加地表水的碳输出）。因此，TEP的生产具有不同于颗粒碳或溶解碳的初级生产的属性，这意味着需要对北冰洋碳循环模型进行速率过程测量。要验证的主要假设是，北极海冰中EPS和TEP的高产量是硅藻华期间氮胁迫的结果。对培养硅藻和底栖硅藻群落（类似于海冰冰-海水界面中出现的薄而高生物量的藻类群落）的研究表明，低氮和磷的有效性可以导致高EPS的产生。营养压力已在北极海冰硅藻华中得到证实，最常见的原因是氮或硅的供应。该项目将测试所有3种常量营养元素（N， P和Si）的效果。它将测量EPS和溶解有机碳产量作为初级生产的一部分的速率，以及TEP积累的测量，使用实验操作和现场观察来验证这一假设。作为加拿大北极大陆架交换研究（CASES）的一部分，该实地项目将在波弗特海进行。CASES的主要目标是了解海冰变率和变化的生物地球化学和生态后果。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，这个新项目将增加EPS和TEP产量的划分。case的实地研究将集中在春季的近海浮冰上，其优势是遇到各种各样的海冰栖息地，这些栖息地可能会产生不同的TEP。海冰是一种极端的环境，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，这可能是由于人类引起的气候变化，这凸显了了解这一生态系统的必要性。外展活动将制作以海冰和极地海洋学为重点的教材，纳入为社区大学生开发的在线课程材料。教材的开发将与富勒顿学院的学生和教师合作完成。产品将作为社区大学海洋学课程的一部分进行评估，并将纳入在北极野外季节展示国际科学合作“行动”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.