Hydrothermal and microbial controls on organic carbon mobilization from Guaymas Basin sediments

海洋沉积物和沉积岩中储存的有机碳是全球碳循环的重要组成部分。埋藏的有机碳在很长一段时间内平衡大气中的二氧化碳浓度，并与地球气候的调节有关。微生物活动是分解和释放沉积物中碳的过程的关键驱动因素。该项目调查海洋沉积物中的有机碳，并检查其对微生物的生物有效性。该项目的背景是加利福尼亚州海湾的瓜伊马斯盆地，该盆地在季节性降雨期间从陆地和海面的海洋浮游植物接收有机物输入。瓜伊马斯盆地也是海底活动扩张和热液加热(即从岩浆向沉积物和海水转移热量)的所在地，这将使人们能够调查加热对有机碳生物可利用部分的影响。该项目的结果将提高我们对微生物如何将埋藏的有机碳重新引入“活性”碳循环，以及这种微生物活动如何受到水热加热和有机碳组成的影响的理解。该项目还包括美国和加拿大之间的国际合作和教育跨境学生交换。研究结果将通过特拉华州海洋基金制作的视频和加拿大播客广域科学制作的内容广泛分享。我们将利用瓜伊马斯盆地沉积物中可用的梯度，调查热水加热、埋藏深度(物理因素)、沉积有机碳组成和氧气可获得性(地球化学因素)和微生物群落(生物因素)对沉积有机碳的生物有效性和动员/利用的影响。瓜伊马斯盆地具有几个独特的优势，使其特别适合我们提出的研究，包括150米的沉积物厚度在放射性碳测年的分析窗口内，这将使我们能够利用14C(放射性碳)作为海洋碳源的天然示踪剂。温度和地球化学的大梯度也是由于广泛侵位于沉积柱中不同深度的岩浆岩床造成的。这种水热加热在压缩的、14C友好的时间尺度上，将某些地方的沉积有机碳从新合成的光合作用生物质转化为石油碳氢化合物。分析将包括：(1)沉积物中代表海洋、陆地和热液有机碳库的生物标志物的碳同位素分析；(2)代表自然微生物种群的生物分子的碳同位素测量；(3)沉积物与其自然微生物种群的好氧生物反应器培养，以及对呼吸作用释放的二氧化碳的同位素组成的分析；(4)为促进有机碳转化而经过预热的沉积物的好氧生物反应器培养，以及细菌分离物呼吸的二氧化碳的同位素分析。我们的结果将提供一个非常详细的视角，说明有机碳的生物有效性与埋藏深度、加热历史、原位温度、氧气可获得性、有机碳组成和微生物功能能力的关系，据我们所知，这将是史无前例的。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

Organic carbon stored in marine sediments and sedimentary rocks are a critical component of the global carbon cycle. Buried organic carbon balances atmospheric CO2 concentrations over long timescales and is linked to the regulation of Earth’s climate. Microbial activity is a key driver of processes that break down and release carbon from sediments. This project investigates organic carbon in marine sediments and examines its bioavailability to microbes. The setting for the project is the Guaymas Basin of the Gulf of California which receives organic matter inputs from land during seasonal rains and from marine phytoplankton at the sea surface. Guaymas Basin is also a site of active seafloor spreading and hydrothermal heating (i.e., the transfer of heat from magma to sediments and ocean water), which will allow the effects of heating on the bioavailable portion of organic carbon to be investigated. Results from this project will improve our understanding of how microbes reintroduce this buried organic carbon back into the “active” carbon cycle, as well as how this microbial activity is influenced by hydrothermal heating and organic carbon composition. The project also incorporates an international collaboration and an educational cross-border exchange of students between the US and Canada. Results will be shared broadly through videos produced by the Delaware Sea Grant and a content created by the Canadian podcast, Broad Science.Using the gradients available in the context of Guaymas Basin sediments, we will investigate the effects of hydrothermal heating, burial depth (physical factors), sedimentary organic carbon composition and oxygen availability (geochemical factors) and microbial community (biological factors) on the bioavailability and mobilization/utilization of sedimentary organic carbon. Guaymas Basin features several advantages that make it uniquely suited for our proposed studies including the fact that 150 meters of sediment thickness are within the analytical window of radiocarbon dating which will allow us to take advantage of 14C (radiocarbon) as a natural tracer of marine carbon sources. Large gradients of temperature and geochemistry are also created by widespread emplacement of magmatic sills at varied depths in the sediment column. Such hydrothermal heating transforms sedimentary organic carbon in some locations from freshly synthesized photosynthetic biomass to petroleum hydrocarbons on a compressed, 14C-friendly timescale. Analyses will include: (1) carbon isotopic analysis of biomarkers representative of marine-derived, terrestrial and hydrothermal organic carbon reservoirs within sediments, (2) carbon isotopic measurements on biomolecules representative of natural microbial populations, (3) aerobic bioreactor incubations of sediments with their natural microbial population and analysis of the isotopic composition of CO2 released by respiration, and (4) aerobic bioreactor incubations of sediments that have been pre-heated to promote organic carbon transformations and isotopic analysis of CO2 respired by a bacterial isolate. Our results will provide an exceptionally detailed view of the dependence of organic carbon bioavailability on burial depth, heating history, in situ temperature, oxygen availability, organic carbon composition, and microbial functional capabilities that, to our knowledge, will be unprecedented.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.