Deciphering the physical controls on the fate of terrestrially-derived organic carbon in a high-yield tectonically-active margin

大型河流携带的沉积物聚集在邻近的大陆架上，形成了矿物和相关有机物的主要沉积物。在全球范围内，这些沉积物是海洋中有机物的主要埋藏地，有助于调节大气中的二氧化碳。保存在特殊陆架沉积物中的碳的数量取决于沉积物被埋藏的速度。当沉积物埋藏得更快时，更多的有机碳被去除。然而，在能量非常旺盛的陆架环境中，海浪和潮汐会导致沉积物重新悬浮。这种再悬浮会导致有机物的氧化和分解，从而向大气中释放二氧化碳。安达曼海北部的艾洛瓦迪-桑尔温河水系是全球第三大水系，但以前从未就其碳封存潜力进行过评估。它是亚洲仅存的没有受到人类活动严重影响的大型水系。人类在许多系统中改变了河流沉积物向海洋的输送，对全球碳收支造成了未知的后果。这项研究使用了2017年一次研究巡航期间收集的一组现有核心样本和其他数据。其目标是研究有机物从河流到海洋的转化。这项研究还探索了决定有机碳埋藏效率的物理过程。这将通过对洋流、海浪、潮汐和风暴的模拟来确定。这项研究的结果将为未来的变化提供基线，包括在这些河流上计划的主要大坝建设。随着人类对这一系统的修改越来越多，以及气候变化导致的风暴频率增加，这项研究将有助于更好地了解这个人口稠密、环境敏感的系统的未来。该项目将支持一名博士生和一名博士后科学家。此外，为该项目开发的模型将用于社区模拟工作。大陆边缘是河流输送泥浆的主要沉积中心，记录了丰富的陆地和海洋条件历史，并占海洋有机碳(OC)埋藏的大部分。艾洛瓦迪河和坦尔温河进入安达曼海北部和孟加拉湾东部的活跃边缘。研究相对较少，就泥沙和有机碳供应而言，它们的综合输入在世界水系中排名前三。PIS 2017年进行的一次研究巡航发现了一组独特且史无前例的观测和沉积物样本，这项研究利用这些现有样本并修改了一个数值模型，以解决关于沉积物和有机碳在这个全球重要系统中的扩散和命运的令人兴奋的新问题。具体地说：1)沉积物在海湾停留的时间和这种物质向盆地沉积中心转移的机制(S)？2)相关的物理过程如何影响有机碳从浅海陆架向盆地转移的转化和封存？3)季节性(季风)海洋条件和周期性事件(气旋)在影响沉积物向沉积中心和西北陆架扩散的相对作用是什么。在2017年邮轮航行时，艾耶罗瓦迪和坦尔温是热带和亚热带亚洲最后两条自由流动的巨型河流。因此，这项研究为未来的某些变化提供了一个基线。为该项目开发的数值模型将通过社区建模工作应用于其他受河流影响的边缘地区。这项研究支持培养一名有前途的博士生，他将专注于本文提出的有机地球化学，以及一名博士后科学家，他将专注于流体泥浆运输在该系统中的潜在关键作用。在前一个项目期间，私人投资机构与缅甸研究界建立了牢固的关系，并提议通过共同参加一次国际会议来继续这种接触。随着人类对A-T系统的修改迅速增加，以及对气候变化导致未来飓风频率增加的预测，这项研究将有助于理解这个人口稠密且对环境敏感的系统的未来轨迹。该奖项反映了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。

Sediment carried by large rivers accumulates on the adjacent continental shelves forming major deposits of mineral and associated organic matter. Globally, these deposits represent the major burial sites for organic matter in the ocean and help to regulate atmospheric CO2. The amount of carbon preserved in a paticular shelf deposit depends on how fast the sediment is buried. When sediment is buried faster, more organic carbon is removed. In very energetic shelf settings, however, waves and tides can cause sediment resuspension. This resuspension leads to oxidation and breakdown of organic matter that releases CO2 to the atmosphere. The Ayeyarwady-Thanlwin river system in the northern Andaman Sea is the third largest globally but has not previously been assessed for its carbon sequestration potential. It is the only remaining large river system in Asia that has not been severely affected by human activity. Humans have altered the delivery of river sediment to the ocean in many systems with unknown consequence on the global carbon budget. This study uses an existing set of core samples and other data collectd during a 2017 research cruise. The goal is to examine the transformation of organic matter from the rivers to the ocean. The study also explores the physical processes that determine the burial efficiency for orgainc carbon. This will be determined through modeling of ocean currents, waves, tides and storms. The results of this study will provide a baseline for future changes, including planned major dam construction on these rivers. With increasing human modifications to this system and increased storm frequency driven by climate change, this research will help better understand the future of this heavily populated and environmentally sensitive system. This project will support a Ph.D. student and a post-doctoral scientist. In addition, the models developed for this project will be available for community modeling efforts.Continental margins are the primary depocenters of mud delivered by rivers, record a rich history of terrestrial and oceanographic conditions, and account for most of the organic carbon (OC) burial in the ocean. The Ayeyarwady and Thanlwin rivers enter an active margin in the northern Andaman Sea and eastern Bay of Bengal. Relatively understudied, their combined inputs rank in the top three of the world’s river systems in terms of sediment and OC supply. A 2017 research cruise conducted by the PIs recovered a unique and unprecedented set of observations and sediment samples, and this study leverages these existing samples and modifies a numerical model to address exciting new questions regarding the dispersal and fate of sediment and OC in this globally important system. Specifically: 1) what is the residence time of sediment in the Gulf and mechanism(s) for transfer of this material to the basin depocenter?, 2) how do the associated physical processes affect the transformation and sequestration of organic carbon as it transits the shallow shelf to the basin?, and 3) what are the relative roles of seasonal (monsoonal) oceanographic conditions and episodic events (cyclones) in affecting sediment dispersal to the depocenter and northwestern shelf. At the time of the 2017 cruise, the Ayeyarwady and Thanlwin were the last free-flowing mega-rivers in tropical and subtropical Asia. Therefore, this study provides a baseline for certain future change. Numerical models developed for this project will be available for application to other river-influenced margins via community modeling efforts. This research supports the education of a promising Ph.D. candidate who will focus on the organic geochemistry proposed herein, and a post-doctoral scientist who will focus on the potentially critical role of fluid mud transport in this system. The PIs forged strong relationships with the Myanmar research community during the previous project, and propose to continue this engagement through joint participation at an international meeting. With rapidly increasing human modifications to the A-T system and predictions of future increased cyclone frequency driven by climate change, this research will be instrumental in understanding the future trajectory of this heavily populated and environmentally sensitive system.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.