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）是海洋食物网和碳循环的关键组成部分，海洋DOC与大气之间的碳交换在近几十年到地质过去的时间尺度上影响着大气CO2水平。海洋表层藻类的生产是DOC的最大来源，其对海洋碳循环的影响已被广泛认识。然而，河流、热液喷口和甲烷渗漏等其他来源对DOC的贡献及其对海洋生态和化学的影响尚不清楚。每种来源的生物利用和年龄不同，影响了DOC在海洋盆地中的储存和分布。位于大陆边缘的甲烷渗漏尤其重要，因为它们可能将全球大量以天然气和天然气水合物的形式储存在海底以下的碳转移到海洋中。该项目将调查位于俄勒冈近海的水合物岭DOC的生产、通量、组成和生物利用潜力。水合物脊是一个具有大量天然气水合物聚集的显著甲烷泄漏点，也是胡安德富卡构造板块上海洋观测倡议电信电缆阵列的一个节点，它提供了连续的实时区域海洋学数据流。我们将对甲烷、DOC和其他物质进行取样和化学表征，以提供有关这些物质起源（深海还是浅海）、它们如何发生化学变化、它们可能在多大程度上为深海生物提供食物，或有助于DOC在海洋中的长期储存的信息。实验和分析将在为期7天的海洋探险中使用远程操作车辆Jason或载人车辆Alvin收集的沉积物岩心和底水样本进行。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持续对流体进行采样，从而使我们能够监测甲烷和DOC从海底排入海洋的运动，并限制甲烷渗漏时调节碳向海洋释放的过程。该项目将资助马里兰州一所社区学院和马萨诸塞州东南部一个低收入城市中心的一所学院的一名研究生和几名本科生。我们会在公众电视台制作一系列短片，向公众传播项目的研究结果。本研究将研究俄勒冈近海水合物岭甲烷（CH4）渗漏中甲烷衍生的溶解有机碳（DOC）的产生、通量和反应性。该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)渗漏对海洋贡献了多少ch4衍生的化石DOC ？(2)在CH4厌氧氧化过程中，CH4衍生的C在多大程度上并入DOC ？(3)渗漏DOC释放到深海时是生物可利用性还是顽固性？(4) DOC到水柱的通量如何随时间变化？我们将采用跨学科的策略，包括原位取样、实验室孵化和综合分析地球化学计划。来自南部水合物脊海洋观测倡议区域电缆阵列的数据将用于提供现场和实验数据的背景。有机和无机化学物质的组成和丰度以及孔隙水、块状沉积物和水柱C池的稳定和放射性碳同位素组成将用于确定DOC来源和量化以平流速率范围为特征的冷渗漏的通量。调查的核心部分将是在水合物岭进行为期7天的研究巡航，收集沉积物、孔隙流体和水柱样本，并部署OsmoSamplers进行连续时间序列流体采样。这些结果将为估算ch4源DOC对海洋DOC库的贡献奠定基础。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。

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.