The Tale of Three Systems: Fate of Primary Production in the Chukchi Sea

单细胞光合作用初级生产者产生大部分固定碳，支持北冰洋食物网并驱动大量生物地球化学循环。已经确定了北冰洋净初级产量（NPP）的三个主要来源，其主要差异在于它们在水柱内的时间和位置。这些包括(1)生长在海冰内的单细胞微藻，(2)在海冰下水（UIB）中繁殖的浮游植物，以及(3)在开放水域(包括边缘冰带（MIZ）和水下叶绿素最大值深度（SCM）中繁殖的浮游植物。如果我们要了解持续的海冰损失，以及冰藻和浮游植物繁殖动态的相关变化，将如何不同地影响整个北冰洋浅海的底底生物和中上层食物网，包括土著人口依赖的许多生物，那么增加我们对这三个系统的NPP相对速率和颗粒输出效率的了解是至关重要的。这一提议的粒子通量方面可能真正具有变革性。我们对海冰、ubs和开放水域浮游植物的相对碳通量知之甚少，对控制这些通量的过程几乎一无所知。我们首次对这三种关键微藻群落中每个个体的浮力调节进行表征的能力，将揭示这些有机物质通量如何随着藻类细胞大小、分类、生理状态以及环境条件的变化而变化。这些信息将极大地有助于了解现在和将来可能发生的重大生态系统变化所需的知识基础。此外，该项目通过参与斯坦福大学地球科学与工程（SURGE）暑期本科生研究项目，扩大了代表性不足群体的参与。Arrigo实验室还参加了斯坦福大学地球科学学院的高中实习项目。这项工作的结果将被整合到斯坦福大学的讲座和实验课中，以探索ubs对北冰洋生物学和生物地球化学的影响。最后，本项目将为2名博士研究生（1名女性非裔美国人）和1名博士后提供教育和培训。本科生的培训将是这个项目的一个组成部分，我们预计有4-6人参加这次巡航。对楚科奇海微藻华的详细观察主要是在一年中大部分楚科奇陆架已经处于开放水域的时候进行的。因此，海冰微藻、冰下浮游植物华（uib）和开阔水域浮游植物华的日净初级产量（NPP）的相对比率尚不清楚。此外，与这三个核电厂来源有关的有机物的命运尚不清楚。因此，迫切需要从晚春开始进行全面的测量，以捕获所有三种华花，特别强调粒子出口事件。本研究的主要目标是利用从楚科奇海的船舶实地项目中获得的数据，1)测量与MIZ和SCM中海冰、ubs和开放水域浮游植物相关的NPP率，2)使用沉积物捕集器来表征和量化来自海冰、ubs和开放水域浮游植物华的大块颗粒物质的垂直下沉通量。3)使用我们新开发的水动力跑步机来确定所有三个核电站来源的微藻的下沉速度如何随群落组成，生理状态和环境条件而变化。我们提议的项目的核心是将于2023年6月进行的为期45天的过程研究巡航。这次航行将包括一系列的水文调查/部分，这些调查/部分将在深冰堆和边缘冰带之间反复转换。150个水文测量站将包括温度、盐度、水流、光线、营养物质和Chl - a浓度的垂直剖面。在其中90个生物采样站（称为生物采样站），我们还将收集样本以测量藻类和浮游动物的丰度/种类/大小（后者使用水下视觉剖面仪，UVP），藻类生理学，NPP， POC，颗粒沉降速度（水动力跑步机），部署Haps覆盖物测量沉积物Chl a，并部署沉积物捕集器测量冰藻，浮游植物，碎屑和粪便颗粒的垂直通量（在1/3的生物采样站）。在过境期间，我们将持续测量大气条件以及海面温度，盐度和各种船舶系统的Chl a荧光，以提供冰上冰下这些参数的详细地图。大约每隔一天，我们将在太阳正午附近进行一个6小时的海冰（SI）站，在那里我们将测量浮冰和下面的地表水的物理、化学和生物特性（见上文），并部署沉积物捕集器来测量海冰和UIB中藻类、碎屑和粪便颗粒的下沉通量。该船还将用作表征浮力调节的平台，并使用水动力跑步机测量微藻细胞和聚集体在各种操纵环境条件下的下沉速度。该仪器为粒子的主动垂直跟踪提供了无限的范围（无标度），同时提供微米和毫秒尺度的时空分辨率。水动力跑步机还可以直接测量硅藻周围的流场，以测量与单个细胞相关的任何结合的基质材料（不可见的光学），并可以提供颗粒孔隙度和密度的估计。在每个BS和SI站点，对下沉速度的测量将与对藻类分类组成、生理和大小结构以及环境特征（如光、温度、营养）的详细分析相结合，以确定功能关系并评估三种主要藻华群落对下沉颗粒通量的相对重要性。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Part 1Single-celled photosynthetic primary producers generate most of the fixed carbon that supports Arctic Ocean food webs and drives numerous biogeochemical cycles. Three main sources of net primary production (NPP) have been identified in the Arctic Ocean that differ primarily in their timing and location within the water column. These include (1) single-celled microalgae growing within the sea ice, (2) phytoplankton that bloom in water under the sea ice (UIB), and (3) phytoplankton that bloom in open water, including in the marginal ice zone (MIZ) and at the depth of the subsurface chlorophyll maximum (SCM). Increasing our knowledge of the relative rates of NPP and particle export efficiency from these three systems is critical if we are to understand how continued sea ice loss, and the associated shifts in ice algal and phytoplankton bloom dynamics, will differentially impact benthic and pelagic food webs in shallow seas throughout the Arctic Ocean, including many organisms on which Indigenous human populations rely. The particle flux aspects of this proposal could be truly transformative. We know very little about the relative carbon fluxes from sea ice, UIBs, and open water phytoplankton blooms and virtually nothing about the processes that control those fluxes. Our ability to characterize, for the first time, buoyancy regulation by individual members of each of these three critical microalgal communities will shed new light on how these organic matter fluxes vary as a function of algal cell size, taxonomy, and physiological state, as well as environmental conditions. This information will contribute greatly to the foundation of knowledge needed to understand potentially significant ecosystem changes, both now and in the future. Furthermore, the project broadens the participation of underrepresented groups through participation in Stanford University’s Summer Undergraduate Research in Geoscience and Engineering (SURGE) program. The Arrigo lab also takes part in Stanford’s School of Earth Sciences high school internship program. Results of this work will be integrated into lecture and laboratory classes at Stanford exploring the effect of UIBs on the biology and biogeochemistry of the Arctic Ocean. Finally, this project will contribute to the education and training of two Ph.D. students (one female African American) and one post-doc. Training of undergraduates will be an integral part of this project, and we expect 4-6 to participate in this cruise.Part 2Detailed observations of microalgal blooms in the Chukchi Sea have been largely made at a time of year when most of the Chukchi shelf is already in open water. As such, the relative rates of daily net primary production (NPP) by sea ice microalgae, under-ice phytoplankton blooms (UIBs), and open water phytoplankton blooms are not well known. Additionally, the fate of the organic matter associated with these three NPP sources is poorly known. Hence, there is a strong need for comprehensive measurements beginning in late spring that capture all three blooms, with particular emphasis on particle export events. The primary objectives of this proposed study are to utilize data obtained from a ship-based field program to the Chukchi Sea to 1) measure rates of NPP associated with the sea ice, UIBs, and open water phytoplankton in both the MIZ and SCM, 2) use sediment traps to characterize and quantify the vertical sinking fluxes of bulk particulate matter from the sea ice, UIBs, and open water phytoplankton blooms, and 3) use our newly developed Hydrodynamic treadmill to determine how sinking speeds of microalgae from all three NPP sources vary by community composition, physiological state, and environmental condition. The centerpiece of our proposed program is a 45-day process study cruise that will take place in June 2023. The cruise will consist of a series of hydrographic surveys/sections that will repeatedly transition between the deep ice pack and the marginal ice zone. 150 hydrographic survey (HS) stations will include vertical profiles of temperature, salinity, currents, light, nutrients, and Chl a concentration. At 90 of these (referred to as biological sampling (BS) stations), we will also collect samples to measure algal and zooplankton abundance/species/size (the latter using the underwater vision profiler, UVP), algal physiology, NPP, POC, particle sinking speeds (Hydrodynamic treadmill), deploy a Haps corer to measure sediment Chl a, and deploy sediment traps to measure vertical fluxes of ice algae, phytoplankton, detritus, and fecal pellets (at 1/3 of the BS stations). During transits, we will continuously measure atmospheric conditions as well as sea surface temperature, salinity, and Chl a fluorescence from the various ship’s systems to provide detailed maps of these parameters above and below the ice. About every second day, we will conduct a 6-hour sea ice (SI) station near solar noon where we will measure the physical, chemical, and biological properties (see above) of the ice pack and underlying surface water, as well as deploy sediment traps to measure sinking fluxes of algae, detritus, and fecal pellets from the sea ice and from the UIB. The ship will also be used as a platform for characterizing buoyancy regulation and measuring sinking speeds of microalgal cells and aggregates under various manipulated environmental conditions using the Hydrodynamic treadmill. This instrument provides unlimited scope for active vertical tracking of particles (scale-free), while concurrently providing micron and millisecond-scale spatiotemporal resolution. The Hydrodynamic treadmill also directly measures the flow field around the diatom to measure any bound matrix materials (not visible optically) associated with a single cell and can provide estimates of particle porosity and density. At each BS and SI station, measurements of sinking speed will be combined with detailed analyses of algal taxonomic composition, physiology, and size structure, as well as environmental characteristics (e.g., light, temperature, nutrients) to determine functional relationships and assess the relative importance of each of the three primary bloom communities to sinking particle fluxes.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.