COLLABORATIVE RESEARCH: IS NITROGEN FIXATION WIDESPREAD IN THE CHUKCHI AND BEAUFORT SEAS?

夏季北极海冰损失的范围正在增加，现在发生在一年中的早些时候。因此，据预测，在北极海域内，浮游植物的生长速度将会加快。浮游植物是海洋食物网的基础，维持着当地人口赖以生存的海洋收成。可利用氮是浮游植物所必需的营养物质，其数量有限，最终将限制其生长水平。溶解在海洋中的氮气可以转化为浮游植物易于利用的形式，但这主要被认为是一个温水过程。该项目的主要研究人员最近在北冰洋观察到了这一过程，但由于数据太少，其程度仍然是高度推测的。如果它广泛传播，它将改变我们对北极海洋生态系统变化、自给渔业以及潜在的北极商业渔业未来情景的看法。该项目还将有助于劳动力发展。首席研究员是一位刚出道不久的女科学家。她将利用这个项目作为一种机制，来培养一名本科生从事研究。她还将利用这个项目来维持弗吉尼亚海洋科学研究所和汉普顿大学之间现有的教育合作。汉普顿大学是一所历史悠久的黑人大学。据推测，楚科奇海和波弗特海存在能够固定N2的微生物（重氮营养体），它们在北极近岸和近海海水中产生可测量的N2固定率，重氮营养体群落组成在受陆地输入影响的沿海地点与开放水域地点之间存在差异。楚科奇海和波弗特海将在2016年夏末的一次巡航中取样，当时的水文和营养条件可能有利于重氮营养化种群。氮固定对北极生态系统的影响取决于其速率、空间范围和有利条件。因此，在每次巡航中，pi建议确定重氮营养群落组成，根据氮酶基因（nifH）的存在检查它们的分布，使用15N和13C示踪技术测量初级生产力和无机和有机N和C基质的吸收率，并将其与沿着巡航样带制作的水文、营养和整体微生物群落组成剖面进行比较。拟议的工作将在其他关键生物地球化学和微生物群落参数的背景下确定该地区活性氮固定的程度。

The extent of summer Arctic sea ice loss is increasing and now occurs earlier in the year. As a result, it is predicted that the rate of growth of phytoplankton, the base of the marine food web that sustains subsistence marine harvests by native populations, will increase within the Arctic seas. The limited amount of available nitrogen, a required nutrient for phytoplankton, eventually will restrict the level of growth. Nitrogen gas dissolved in the ocean can be converted to a form readily utilizable by phytoplankton, but this has been considered primarily a warm-water process. The principal investigators of this project recently have observed this process in the Arctic Ocean, but there is so little data that its extent remains highly speculative. If it is widespread, it will change the way we think about future scenarios for the changing Arctic marine ecosystem, subsistence fishing, and, potentially, commercial fishing in the Arctic. The project will also contribute to workforce development. The principal investigator is an early-career, female scientist. She will use the project as a mechanism to entrain an undergraduate student into research. She will also use the project to sustain an existing educational collaboration between the Virginia Institute of Marine Sciences and Hampton University, a historically black university.It is hypothesized that microorganisms capable of fixing N2 (diazotrophs) are present in the Chukchi and Beaufort Seas, that they produce measurable rates of N2 fixation in near shore and offshore Arctic marine waters and that diazotroph community composition will differ between coastal sites, which are influenced by terrestrial inputs, versus open water sites. The Chukchi and Beaufort Seas will be sampled during a cruise in late summer 2016, when hydrographic and nutrient conditions are likely to favor diazotrophic populations. The impact that N2 fixation will have on Arctic ecosystems is dependent on its rate, spatial extent and the conditions that favor it. As a consequence, on each cruise the PIs propose to determine diazotroph community composition, examine their distributions based on the presence of the nitrogenase gene (nifH), measure rates of primary productivity and uptake of inorganic and organic N and C substrates using 15N and 13C tracer techniques, and to compare these to hydrographic, nutrient, and overall microbial community composition profiles made along cruise transects. The proposed work will determine the extent of active N2 fixation within the region in the context of other key biogeochemical and microbial community parameters.