Influence of continental margin iron on phytoplankton species composition and production in the northern Gulf of Alaska

阿拉斯加湾北部（GOA）是海洋中最具生产力的生态系统之一，并支持丰富的沿海渔业。虽然浮游植物的强跨陆架梯度（近海叶绿素下降）已经确定，但调节和控制初级生产的具体因素仅是假设的。初级生产/物种组成的跨架模式与铁可用性梯度一致（Strom等人，出版中），但这还有待严格测试。该项目与美国国家科学基金会资助的“富铁沿海水域与营养丰富的HNLC水域混合导致浮游植物生物量增加：以阿拉斯加西北湾为重点”项目（K. Bruland）合作，将利用互补的高分辨率铁数据并以以往研究结果为基础，研究跨大陆架交换和物理化学梯度对果阿北部浮游植物分布、生理和组合结构的影响。拟议的工作直接补充了美国GLOBEC阿拉斯加沿海海湾（CGOA）计划所完成的研究，并且将Bruland对微量金属动力学和物种形成的研究与关键生物过程联系起来至关重要。Bruland的项目旨在量化来自AK铜河的铁输入，并表征和评估河流输入与大陆架/近海系统之间的相互作用。准天气抽样方案可以在中尺度上进行表征，中尺度是该地区变率的主要尺度。台站网格允许准天气采样，同时保持灵活，以利用有趣的中尺度特征。如果存在中尺度涡旋，则研究将侧重于涡旋环流在促进生物活性微量金属的离岸运输中所起的作用（Stabeno etal ., 2004）。该项目旨在提供浮游植物速率、组合结构和对铁和光梯度跨大陆架运输/混合的响应的详细检查，以更好地参数化卫星观测和未来的建模工作。具体问题包括：1)铁的跨大陆架梯度是否与果阿北部浮游植物的碳同化、营养吸收、新生产和物种组成模式相对应？2)铁和光是否相互作用于物种组合结构和碳同化模式？3)额叶区如何影响浮游植物的分布和生理？4)不同水体（近海/近海）的生物光学特性是什么？卫星观测对浮游植物存量和速率的描述有多好？5) Lam等人（2006）确定的深层铁源的化学特征是什么？当与近地表水混合时，这种物质的生物利用度是什么？本研究将首次同时测量果阿北部水域的铁浓度和浮游植物生理参数。更广泛的影响。拟议的工作对于检验GLOBEC CGOA多年努力所产生的假设将非常有价值。这项研究的数据将进一步加深我们对经济和生态重要地区海洋-气候相互作用的理解。这一结果对我们对陆架生态系统耦合生物地球化学循环的基本认识具有深远的意义。这将对我们对碳循环的理解以及其他研究人员如何参数化区域和全球生物地球化学模型产生直接和间接的影响。本科、研究生和博士后教育将通过积极参与实验室、实地和数据综合活动来进一步发展。两名全日制研究生和一名博士后（本提案和NSERC奖学金）将获得多学科海洋学的独特教育背景，涵盖物理，化学和生物过程。

The northern Gulf of Alaska (GOA) is among the ocean's most productive ecosystems and supports a rich coastal fisheries. Although strong cross-shelf gradients in phytoplankton (chlorophyll decreasing offshore) have been identified, yet the specific factors that regulate and control primary production have only been hypothesized. Cross-shelf patterns in primary production/species composition are consistent with a gradient of iron availability (Strom et al., in press), but this has yet to be rigorously tested. In collaboration with the NSF-funded project Mixing of iron-rich coastal waters with nutrient-rich HNLC waters leading to enhanced phytoplankton biomass: a focus on the northwest Gulf ofAlaska (K. Bruland), this project will examine the influence of cross-shelf exchange and physico-chemical gradients on phytoplankton distributions, physiology, and assemblage structure in the northern GOA, making use of complementary high-resolution iron data and building on the results from previous studies. The proposed work directly complements studies accomplished by the US GLOBEC Coastal Gulf of Alaska (CGOA) program, and is essential to link Bruland's study of trace metal dynamics and speciation to key biological processes. Bruland's project seeks to quantify the inputs of iron from the Copper River, AK, and to characterize and assess the interactions among river inputs and shelf/offshore systems. The quasi-synoptic sampling scheme enables characterization at the mesoscale, the dominant scale of variability in the region. The station grid allows quasi-synoptic sampling while remaining flexible to take advantage of interesting mesoscale features. Should a mesoscale eddy be present, the study will focus on the role that eddy circulation plays in facilitating the offshore transport (suggested by Stabeno et al., 2004) of bio-active trace metals. This project aims to provide a detailed examination of the phytoplankton rates, assemblage structure, and response to cross-shelf transport/ mixing across gradients in iron and light to better parameterize satellite observations and future modeling efforts. Specific questions include: 1) Do cross-shelf gradients in iron correspond to patterns of carbon assimilation, nutrient uptake, new production, and species composition of phytoplankton in the northern GOA? 2) Do iron and light interact to structure species assemblages and patterns of carbon assimilation? 3) How do frontal regions influence phytoplankton distributions and physiology? 4) What bio-optical properties characterize the different water masses (inshore/offshore), and how well do satellite observations describe phytoplankton standing stocks and rates? 5) What chemical characteristics define the deep Fe-source identified by Lam et al. (2006), and what is the bioavailability of this material when mixed with near-surface waters? This study will provide the first concurrent measurements of iron concentration and phytoplankton physiological parameters in the waters of the northern GOA. Broader Impacts. The proposed work will be extremely valuable in testing hypotheses arising from many years of effort by GLOBEC CGOA. Data from this study will further our understanding of ocean-climate interactions in an economically and ecologically important region. The results could have far-reaching implications for our basic understanding of coupled biogeochemical cycles in shelf ecosystems. This will have both direct and indirect impacts on our understanding of carbon cycling, as well as how other researchers parameterize regional and global biogeochemical models. Undergraduate, graduate and post-doctoral education will be furthered through active participation in lab, field, and data synthesis activities. Two full time graduate students and a post-doc (this proposal and an NSERC Fellowship) will receive a unique educational background in multidisciplinary oceanography, spanning physical, chemical, and biological processes.