Late Season Productivity, Carbon, and Nutrient Dynamics in a Changing Arctic

不断变化的北极的晚季生产力、碳和养分动态

• 批准号: 1504394
• 负责人: Laurie Juranek
• 金额: $ 115.91万
• 依托单位: Oregon State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-08-01 至 2019-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1504394&HistoricalAwards=false
• 关键词: Late; Season; Productivity; Carbon; Nutrient

Satellite measurements have documented significant reductions in sea ice cover, thickness, and duration throughout the Arctic Ocean in recent decades. Because of the complex interactions and feedbacks among physical, biogeochemical and ecological processes in the Arctic, there is significant uncertainty regarding how these changes in sea ice will impact the marine biological pump, which fuels the rich bottom communities on Arctic ocean shelves and is key to the regional carbon cycle. While responses of the biological pump to increased light availability in spring are currently being pursued, a considerable gap in knowledge exists regarding biological processes in the late summer and early fall. Recent studies indicate a several-decade trend of intensifying wind forcing over the Alaskan margin along the Chukchi and Beaufort Seas in the late, ice-free season (September-November). These events could lead to mixing of nutrients into surface waters, fueling increased biological production and sequestering additional carbon into shelf bottom waters prior to the winter ice advance. However, the lack of direct, concurrent observations of primary and net community productivity rates, and nutrient and carbon distributions during this poorly-sampled time of year hinders efforts to assess the ecosystem implications of such changes. This project proposes to address the question of increasing biological production in the late season through intensive field sampling in two successive years.The investigators will use an innovative approach to better characterize how primary productivity (PP), net community productivity (NCP), and particulate and dissolved organic and inorganic carbon stocks (POC, DOC, DIC) are influenced by episodic nutrient inputs to the surface ocean in late summer and early fall. Over two field campaigns, they will collect high resolution surface measurements of dissolved gases, particulate and dissolved organic matter stocks and dissolved inorganic nutrients and carbon using a ship of opportunity (year 1) and dedicated research cruises (year 2). The use of geochemical rate tracers (oxygen/argon-based NCP and oxygen isotope-based PP; inventory changes of POC, DOC, nutrients, and DIC) offers a distinct advantage over incubation-based approaches by integrating processes on longer timescales (weekly to monthly). This approach is well-suited to capture the effects of episodic upwelling and subsequent ecosystem processing. On the dedicated regional research cruises in year 2 the investigators will also use a towed pumping sled to capture high-resolution vertical and cross-shelf observations. This towed sled will be equipped with standard CTD and optical sensors and interfaced to fast shipboard analyzers for measurement of nutrients and inorganic carbon (pCO2, DIC), as well as to automated samplers to collect water for oxygen/argon ratios, oxygen isotope, POC and DOC measurements. High-resolution chemical and biological distributions will be combined with ship-based ADCP measurements of water column velocities and continuity-based mass-balance calculations to constrain rates of NCP as well as the extent of vertical and lateral material fluxes. Outreach and education elements include a pilot program to engage pre-service secondary STEM teachers in educational planning and field work portions of the work. The program will provide field experience and on the job science training to teachers and result in short media outreach pieces and targeted curriculum addressing the three dimensions of science from the next generation science standards. The proposal will support one graduate student and several undergraduate students, who will participate in all aspects of the field and analytical work. The project will contribute to the early career development of a junior investigator.

卫星测量记录了近几十年来整个北冰洋海冰覆盖、厚度和持续时间的显着减少。由于北极物理、生物地球化学和生态过程之间复杂的相互作用和反馈，海冰的这些变化将如何影响海洋生物泵存在很大的不确定性，而海洋生物泵为北冰洋陆架上丰富的底部群落提供了燃料，并且是区域碳循环的关键。虽然目前正在研究生物泵对春季光照增加的反应，但关于夏末和初秋的生物过程的知识存在相当大的差距。最近的研究表明，在无冰季节末期（九月至十一月），阿拉斯加边缘楚科奇海和波弗特海的风力强迫呈增强趋势。这些事件可能导致营养物质混合到地表水中，促进生物产量的增加，并在冬季冰推进之前将额外的碳封存到陆架底部水中。然而，在一年中这个采样质量较差的时期，缺乏对初级和净群落生产力以及养分和碳分布的直接、同时的观察，阻碍了评估此类变化对生态系统影响的努力。该项目提出通过连续两年的密集实地采样来解决晚季生物产量增加的问题。研究人员将使用创新方法来更好地描述夏末和初秋时，初级生产力（PP）、净群落生产力（NCP）以及颗粒和溶解的有机和无机碳储量（POC、DOC、DIC）如何受到表层海洋养分输入的影响。在两次实地活动中，他们将使用机遇之船（第一年）和专门的研究巡航（第二年）收集溶解气体、颗粒物和溶解有机物质库以及溶解无机营养物和碳的高分辨率表面测量结果。地球化学速率示踪剂（基于氧/氩的 NCP 和基于氧同位素的 PP；POC、DOC、营养物和 DIC 的库存变化）的使用通过在较长时间尺度（每周到每月）上集成流程，比基于孵化的方法具有明显的优势。这种方法非常适合捕获间歇性上升流和随后的生态系统处理的影响。在第二年的专门区域研究巡航中，研究人员还将使用牵引式泵雪橇来捕获高分辨率的垂直和跨大陆架观测。该拖曳雪橇将配备标准 CTD 和光学传感器，并与快速船载分析仪连接以测量营养物和无机碳（pCO2、DIC），并连接自动采样器以收集水以进行氧/氩比、氧同位素、POC 和 DOC 测量。高分辨率化学和生物分布将与船载 ADCP 水柱速度测量和基于连续性的质量平衡计算相结合，以限制 NCP 速率以及垂直和横向物质通量的范围。外展和教育内容包括一项试点计划，让职前中学 STEM 教师参与教育规划和实地工作部分。该计划将为教师提供现场经验和在职科学培训，并产生简短的媒体宣传文章和有针对性的课程，解决下一代科学标准中科学的三个维度。该提案将支持一名研究生和几名本科生，他们将参与该领域的各个方面和分析工作。该项目将有助于初级研究员的早期职业发展。