Collaborative Research: Investigating the Source and Flux of Dissolved Organic Carbon Released from Methane Seeps to the Deep-ocean

溶解有机碳(DOC)是海洋食物链和碳循环的关键组成部分，海洋DOC和大气之间的交换碳在近几十年到过去地质历史的时间尺度上影响了大气中的二氧化碳水平。海藻在表层海洋中产生的DOC是DOC的最大来源，其对海洋碳循环的影响得到了广泛的重视。然而，来自河流、热液喷口和甲烷渗漏等其他来源的DOC的贡献及其对海洋生态和化学的影响尚不清楚。每个来源的生物利用和年龄都不同，这影响了DOC在海洋盆地中的储存和分配。位于大陆边缘的甲烷渗漏特别重要，因为它们可能在全球范围内将大量储存在海底以下作为天然气和天然气水合物的碳转移到海洋中。该项目将调查位于俄勒冈州近海的水合物岭的DOC的生产、通量、组成和生物利用潜力。水合物脊是一个突出的甲烷渗漏，有大量的天然气水合物聚集，是胡安德富卡构造板块上海洋天文台倡议电信电缆阵列的一个节点，提供了连续的实时区域海洋数据。我们将对甲烷、DOC和其他物质进行采样和化学表征，以提供有关这些物质的来源(深水和浅水)、它们如何被化学改变、它们可能在多大程度上喂养深海生物，或者对海洋中DOC的长期储存做出贡献的信息。实验和分析将使用在为期7天的海洋探险期间使用遥控飞行器Jason或载人飞船Alvin收集的沉积物岩心和底层水样本进行。此外，该项目将在海底放置渗透驱动泵，在大约一年的时间内连续采样流体，从而使我们能够监测从海底排出的甲烷和DOC向海洋的运动，并限制在甲烷渗漏处向海洋释放碳的过程。该项目将支持一名研究生和几名本科生，他们来自马里兰州的一所社区大学和位于马萨诸塞州东南部低收入城市中心的一所大学。我们会在公共电视播放一系列录影带，向公众发放研究结果。这项研究将调查俄勒冈州近海水合物岭甲烷(CH4)渗漏中甲烷衍生的溶解有机碳(DOC)的产生、通量和反应性。这项研究将解决四个基本问题，以确定CH4衍生的DOC在海洋碳循环中的重要性：(1)CH4衍生的化石DOC渗漏对海洋有多少贡献？(2)在CH4的厌氧氧化过程中，CH4衍生的DOC在多大程度上并入DOC？(3)SEEP DOC释放到深海时是生物可用的还是顽固的？(4)DOC进入水柱的通量随着时间的变化？我们将采用跨学科战略，包括现场采样、实验室孵化和全面的分析地球化学计划。将利用海洋观测站倡议在南部水合物山脊的区域电缆阵列提供实地和实验数据的背景。有机和无机化学物种的组成和丰度，以及孔隙水、散体沉积物和C柱水池的稳定和放射性碳同位素组成，将被用来识别DOC的来源，并量化具有一系列平流率特征的冷泉的通量。调查的中心将是一艘为期7天的研究邮轮，前往水合物岭收集沉积物、孔隙流体和水柱样本，并部署渗透采样器进行连续的时间序列流体采样。这一结果将为评估甲烷衍生DOC对海洋DOC池的贡献奠定基础。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 organic carbon (DOC) is a key component of the ocean’s food web and carbon cycle, and carbon exchanged between oceanic DOC and the atmosphere has influenced atmospheric CO2 levels on timescales ranging from recent decades to the geologic past. Production by marine algae in the surface ocean is the largest source of DOC and its effects on the ocean carbon cycle are widely appreciated. However, the contribution of DOC from additional sources such as rivers, hydrothermal vents, and methane seeps and their impact on ocean ecology and chemistry are not well understood. Each source differs in terms of its biological utilization and age, which affects the storage and distribution of DOC among the ocean basins. Methane seeps located along continental margins are particularly significant because they may transfer globally significant quantities of carbon stored below the seafloor as natural gas and gas hydrate to the oceans. This project will investigate the production, flux, composition and potential for biological utilization of DOC at Hydrate Ridge, located offshore Oregon. Hydrate Ridge is a prominent methane seep with massive accumulations of gas hydrate and a node of the Ocean Observatories Initiative telecommunications cabled array on the Juan De Fuca tectonic plate, which provides a continuous stream of real-time regional oceanographic data. We will sample and chemically characterize methane, DOC, and other materials to provide information about where the materials originated (deep vs shallow), how they have been chemically altered, to what extent they may feed deep ocean organisms, or contribute to the long term storage of DOC in the ocean. Experiments and analysis will be conducted using sediment cores and bottom water samples collected using either the remotely operated vehicle Jason or the human occupied vehicle Alvin during a 7-day ocean expedition. Additionally, this project will place osmotically-driven pumps on the seafloor to continuously sample fluids for approximately one year, thereby allowing us to monitor the movement of methane and DOC expelled from the seafloor to the ocean and constrain processes that regulate the release of carbon to the oceans at methane seeps. This project will support one graduate student and several undergraduates from a community college in Maryland and a college located in a lower-income urban center in southeastern Massachusetts. We will disseminate project findings to the public with a series of videos for public TV. This study will investigate the production, flux and reactivity of methane-derived dissolved organic carbon (DOC) from methane (CH4) seeps at Hydrate Ridge, Offshore Oregon. The study will address four fundamental questions to determine the significance of CH4-derived DOC within the ocean carbon cycle: (1) How much CH4-derived fossil DOC do seeps contribute to the oceans? (2) To what extent is CH4-derived C incorporated into DOC during anaerobic oxidation of CH4? (3) Is seep DOC bioavailable or recalcitrant when released into the deep ocean? (4) How does the flux of DOC to the water column vary over time? We will employ an interdisciplinary strategy that includes in situ sampling, laboratory incubations, and a comprehensive analytical geochemistry program. Data from the Ocean Observatories Initiative Regional Cabled Array at Southern Hydrate Ridge will be used to provide context for field and experimental data. The composition and abundance of organic and inorganic chemical species along with the stable and radiocarbon isotope composition of pore water, bulk sediment, and water column C pools will be used to identify DOC sources and quantify fluxes from cold seeps characterized by a range of advection rates. The centerpiece of the investigation will be a 7-day research cruise to Hydrate Ridge to collect sediments, pore fluids, and water column samples, and deploy OsmoSamplers for continuous time series fluid sampling. The results will form the foundation for estimating the contribution of CH4-derived DOC to the oceanic DOC pool.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.