Iron cycling in bioturbated sediments - Fluxes, diagenetic redistribution, and isotopic signatures

溶解铁(Fe)是表层海洋中光合作用微藻的重要营养物质，海水中的低浓度会限制它们的生长。由于微藻是海洋食物网的基础，科学家们努力提高我们对海洋中铁的有效性以及不同铁源的重要性的理解。铁通过河流、地下水和风吹来的粉尘进入海洋；然而，从海底释放出来的铁可以是另一个来源，但这种贡献并不为人所知。在这个项目中，来自纽约州立大学石溪分校(SUNY-SB)的科学家将研究海洋沉积物和海底生物(如穴居的文蛤和蠕虫)中的化学反应如何影响铁从海底进入上覆水的运输。动物通过它们的洞穴抽水以获取氧气，在这个过程中，将溶解的铁从沉积物中输送到上面的水中。我们将分析泥质和沙质沉积物以及进出动物洞穴的水中的铁浓度，并确定铁的同位素组成。不同来源的铁可以有不同的同位素组成，这可能有助于追踪在海洋不同部分发现的这种元素的来源。对海底铁循环的更好了解将有助于我们更好地预测环境条件的变化，例如由于人类的影响，将如何影响海洋中的重要过程，如微藻的初级生产。该项目将允许两名博士生和几名本科生参与实验室实验工作，在研究巡航期间采集沉积物样本，并接受沉积物和水的化学分析培训。本科生的参与将通过纽约州立大学SB分校的本科生研究和创意活动(URECA)计划来促进。此外，与科学和技术进入计划(STEP)合作，将为历史上代表性不足和经济困难的高中生提供一个暑期模块“被活埋”。它结合了现场采样、实验室实验、数据分析和科学交流。学生们将建立自己的“海底蚂蚁农场”，并使用摄影设备记录生活在沉积物中的动物的活动。学生将接受使用图像分析软件制作延时电影的培训，他们将在节目的最后一天放映这些电影。将通过在纽约海洋科学节“潜水”和纽约州立大学-SB地球庆典日“地球股票”上进行年度“海底切片”亲身演示，实时可视化活体或用注射器注水引起的沉积物中的压力动态，促进公众宣传。该项目支持两名早期职业科学家的进步和发展，此前没有NSF的研究支持。溶解铁是表层海洋中光合作用微藻的重要营养物质，会限制它们的生产力。向海洋提供铁的来源有多种，包括河流、地下水、热液喷口，以及从海底释放出来的铁。该项目将填补我们在海底来源知识方面的主要空白，并强调陆上生物的生物扰动、底水氧气浓度、沉积有机质含量和沉积物渗透率对大陆边缘沉积物中铁循环和同位素重新分配的相互关联影响。具体地说，我们将从机理上了解在内陆洞穴内(作为灌溉活动和沉积环境的函数)和在上覆水中(响应大范围环境变化)变化的O2浓度对溶解铁通量和再降水的影响，与这些过程相关的同位素分馏，以及对水柱中溶解Fe和沉积物中保存的颗粒态Fe同位素特征的影响。该项目将极大地促进对沉积铁循环和利用铁同位素限制海底铁源向海洋的数量和动力学的了解。提高对沉积铁旋回的认识，将加强对生物地球化学过程的未来响应的预测，例如初级生产对快速变化的环境条件的响应，并从沉积记录中保存的自生铁矿物中最佳地推断过去的条件。在大陆架环境方面，这方面的知识尤其有价值。在大陆架环境中，人为影响正在改变有机碳的沉积模式和扩大氧的最小范围。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Dissolved iron (Fe) is an important nutrient for photosynthetic microalgae in the surface ocean and low concentrations in seawater can limit their growth. Because microalgae are the basis of marine food webs, scientists strive to improve our understanding of Fe availability in the oceans and the importance of different iron sources. Iron enters the ocean via rivers, groundwater, and wind-blown dust; however, release from the seafloor can be an additional source but this contribution is not well known. In this project, scientists from the State University of New York, Stony Brook (SUNY-SB) will investigate how chemical reactions in ocean sediments and bottom-dwelling organisms, such as burrowing clams and worms, affect the transport of Fe from the seafloor into the overlying water. Animals pump water through their burrows to obtain oxygen and in the process, transport dissolved Fe out of the sediment and into the overlying water. We will analyze the Fe concentration in both muddy and sandy sediment and in the water that enters and exits animal burrows, as well as determine the isotope composition of the Fe. Different sources of Fe can have different isotope compositions which may help trace the origin of this element found in different parts of the ocean. An improved understanding of Fe cycling at the ocean seafloor will help us to better predict how changing environmental conditions, for example due to human influence, will affect important processes in the ocean, such as primary production by microalgae. The project will allow two PhD students and several undergraduate students to take part in laboratory experimental work, sediment sampling during research cruises and train in chemical analysis of sediment and water. Undergraduate student involvement will be facilitated through the Undergraduate Research and Creative Activities (URECA) program at SUNY-SB. Also, in collaboration with the Science and Technology Entry Program (STEP), a summer module "Buried Alive" will be offered to historically underrepresented and economically disadvantaged high school students. It combines field sampling, laboratory experimentation, data analyses, and scientific communication. Students will set-up their own "seafloor ant farms" and record the activities of animals living in the sediment using photographic equipment. Students will be trained in using image analysis software to produce time-lapse movies which they will present on the final day of the program. Public outreach will be fostered through annual hands-on demonstrations of "seafloor slices" at the New York Marine Science Festival "Submerge" and at SUNY-SB earth celebration day "Earthstock" with real-time visualizations of pressure dynamics in the sediment induced by living organisms or by injecting water with syringes. The project supports the advancement and development of two Early Career Scientists with no prior NSF research support.Dissolved Fe is an important nutrient for photosynthetic microalgae in the surface ocean and can limit their productivity. Iron is supplied to the ocean from multiple sources, including rivers, groundwater, hydrothermal vents, and by release from the seabed. This project will fill key gaps in our knowledge of seabed sources, and emphasizes the interconnected effects of bioturbation by infaunal organisms, bottom water oxygen (O2) concentrations, sedimentary organic matter content, and sediment permeability on iron cycling and isotopic redistribution in continental margin sediments. Specifically, we will gain a mechanistic understanding of the impact of variable O2 concentrations within infaunal burrows (as a function of irrigation activity and sedimentary setting) and in the overlying water (in response to large scale environmental change) on dissolved Fe fluxes and re-precipitation, the isotopic fractionation related to these processes, and the consequences for isotopic signatures of dissolved Fe in the water column and particulate Fe preserved in sediments. This project will significantly advance understanding of sedimentary Fe cycling and the use of Fe isotopes to constrain the magnitude and dynamics of the benthic Fe source to the ocean. Improved understanding of sedimentary Fe cycle will enhance prediction of future responses of biogeochemical processes such as primary production to rapidly changing environmental conditions and to optimally infer past conditions from authigenic Fe minerals preserved in the sedimentary record. This knowledge is particularly valuable with regard to continental shelf environments where anthropogenic effects are altering deposition patterns of organic carbon and expanding oxygen minimum zones.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.