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

近几十年来，卫星测量记录了整个北冰洋的海冰覆盖面积、厚度和持续时间的显著减少。由于北极的物理、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大陆架上丰富的底层群落提供燃料，是区域碳循环的关键。虽然目前正在追求的生物泵的响应，以增加在春季的光可用性，在知识上存在相当大的差距，在夏末和初秋的生物过程。最近的研究表明，几十年的趋势，加强风强迫阿拉斯加边缘沿着楚科奇海和博福特海在后期，无冰季节（9月至11月）。这些事件可能会导致营养物质混合到表面沃茨，促进生物生产的增加，并在冬季冰前进之前将额外的碳隔离到陆架底部沃茨。然而，在一年中的这个采样率低的时间，缺乏对初级和净群落生产率以及养分和碳分布的直接、同步观测，阻碍了评估这种变化对生态系统影响的努力。本项目拟通过连续两年的密集实地采样来解决在季节后期增加生物产量的问题。调查人员将使用一种创新的方法来更好地表征初级生产力（PP）、净群落生产力（NCP）以及颗粒和溶解有机和无机碳储量（POC、DOC、DIC）受到夏末和初秋向表层海洋的间歇性营养输入的影响。在两次实地活动中，他们将利用一艘机会船（第1年）和专门的研究航行（第2年）收集溶解气体、颗粒和溶解有机物存量以及溶解无机养分和碳的高分辨率表面测量数据。地球化学速率示踪剂（氧/氩为基础的NCP和氧同位素为基础的PP; POC，DOC，营养物质和DIC的库存变化）的使用提供了一个明显的优势，孵化为基础的方法，通过整合过程的较长的时间尺度（每周到每月）。这种方法非常适合捕捉的影响，情节上升流和随后的生态系统处理。在第二年的专门区域研究航行中，调查人员还将使用拖曳式抽水橇，获取高分辨率的垂直和跨大陆架观测数据。该拖橇将配备标准CTD和光学传感器，并连接到船上快速分析仪，用于测量营养物和无机碳（pCO 2，DIC），以及自动采样器，用于收集水，用于氧/氩比，氧同位素，POC和DOC测量。高分辨率的化学和生物分布将与船载ADCP测量的水柱速度和基于连续性的质量平衡计算相结合，以限制NCP的速率以及垂直和横向物质通量的范围。推广和教育要素包括一个试点计划，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实地经验和在职科学培训，并产生简短的媒体宣传片和有针对性的课程，从下一代科学标准中解决科学的三个方面。该提案将支持一名研究生和几名本科生，他们将参与实地和分析工作的各个方面。该项目将有助于初级调查员的早期职业发展。

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.