Collaborative Research: What Happens to Terrestrial Organic Matter in the Ocean? Solving the Mystery Behind an Iconic Question

合作研究：海洋中的陆地有机物会发生什么？

• 批准号: 1851494
• 负责人: Brad Rosenheim
• 金额: $ 35.77万
• 依托单位: University of South Florida
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-08-01 至 2024-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1851494&HistoricalAwards=false
• 关键词: Collaborative; Research; What; Happens; Terrestrial

The Amazon River is one of the largest and most important rivers in the world. It not only carries water through the Amazon rain forests, it also carries mud - lots of mud. This mud settles when the river joins the ocean, forming the Amazon delta. Waves and wind re-suspend some of this mud, which forms mud banks that slowly move from the coast of Brazil, to French Guiana, Suriname, and Guyana. Not only do these mud banks shape the coastlines of these areas, but they also serve as a storage for carbon that had been removed from the atmosphere by the Amazon rainforest, dropped to the forest floor and washed into the river, ultimately transported on particles of mud into the Amazon delta. Normally, this represents a transfer of carbon from the atmosphere to the sediment and rock record, hiding it away for thousands to millions of years and participating in the natural regulation of atmospheric carbon dioxide concentration. However, the Amazon's special case of mud banks that travel hundreds of miles along the coast has long been believed to stir up this carbon and release most of it back to the atmosphere. This idea has held for decades, but if wrong, may have a large impact on our understanding of the ocean's carbon cycle. This research will use new science and technology to change the way we look at river carbon cycling in the ocean by sampling the mud banks, ocean waters, and Amazon River waters more thoroughly than has been previously done, with the aim to understand and quantify the storage of land-derived carbon in marine mudbank sediments offshore the Amazon River. This research will serve as the core of two Ph.D. dissertations and will interface with the Woods Hole Partnership Educational Program (PEP) to provide under-represented minority college students an opportunity to gain practical experience in marine and environmental sciences. The project will also be incorporated into the Saint Petersburg Science Fest, an event that brings several thousand school children to University of South Florida campus during one weekend every autumn to showcase different research projects and initiatives.Twenty years ago, John Hedges posed a seminal question pertaining to the role of the ocean in the carbon cycle: "what happens to terrestrial organic matter in the oceans?" That question was set upon a conundrum - because riverine organic matter is highly degraded, it should be expected to suffer minimal respiration in the ocean, yet by most accounts continental margins seem to be incinerators of terrestrial organic matter. However, much of this paradigm was originally built upon biogeochemical studies of the Amazon sub-aqueous delta and the mobile fluidized mudbanks along the Guianas coast. However, preliminary state of the art characterizations of organic carbon in Amazon River and mudbank sediments suggest that a fraction of terrestrial organic carbon is actually not refractory and as such is rapidly and efficiently oxidized in the ocean, whereas another fraction is refractory and is in fact quantitatively preserved in marine sediments. Overall, the data suggest an underestimation of burial efficiency in the realm of 50-100%. This proposal focuses on gaining a transformative mechanistic and quantitative understanding of the fate of terrestrial organic carbon in the coastal ocean offshore of the Amazon River. This will be done through i) sampling the marine province offshore of the Guianas coast (the Guianas mudbanks) as well as the Amazon River delta, using a shallow-draft research vessel and ii) using novel state of the art geochemical analysis of organic carbon - in particular ramped oxidation and compound specific radiocarbon analysis - and elemental composition to demonstrate the selective nature of terrestrial organic carbon oxidation and provide new estimates of burial efficiency of this system - with implications for the global inventory of terrestrial organic carbon in the ocean.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.

亚马逊河是世界上最大、最重要的河流之一。它不仅带着水穿过亚马逊雨林，还带着泥巴--大量的泥土。当河流汇入海洋时，这些泥浆就会沉淀下来，形成亚马逊三角洲。海浪和风使一些泥浆重新悬浮，形成泥滩，慢慢地从巴西海岸移动到法属圭亚那、苏里南和圭亚那。这些泥滩不仅塑造了这些地区的海岸线，还充当了碳的储存库，这些碳被亚马逊雨林从大气中带走，掉到森林地面，冲入河流，最终以泥沙颗粒的形式输送到亚马逊三角洲。正常情况下，这代表着碳从大气转移到沉积物和岩石记录中，将其隐藏数千年至数百万年，并参与大气二氧化碳浓度的自然调节。然而，长期以来，人们一直认为亚马逊的特殊情况是沿海岸绵延数百英里的泥滩搅动了这些碳，并将其中大部分释放回大气中。这种观点已经坚持了几十年，但如果错了，可能会对我们对海洋碳循环的理解产生很大影响。这项研究将使用新的科学和技术来改变我们看待海洋中河流碳循环的方式，比以前更彻底地对泥滩、海水和亚马逊河水域进行采样，目的是了解和量化亚马逊河近海海洋泥岸沉积物中陆源碳的储量。这项研究将作为两篇博士论文的核心，并将与伍兹霍尔伙伴关系教育计划(PEP)相结合，为未被充分代表的少数族裔大学生提供在海洋和环境科学方面获得实践经验的机会。该项目还将被纳入圣彼得堡科学节，该活动在每年秋天的一个周末将数千名学童带到南佛罗里达大学校园，展示不同的研究项目和倡议。20年前，约翰·赫奇斯提出了一个与海洋在碳循环中的作用有关的开创性问题：“海洋中的陆地有机物发生了什么？”这个问题是在一个难题上提出的--因为河流中的有机物质被高度降解，应该预计它在海洋中会遭受最小的呼吸，但从大多数说法来看，大陆边缘似乎是陆地有机物质的焚烧炉。然而，这种模式的很大一部分最初是建立在对亚马孙水下三角洲和圭亚那海岸流动的流态化泥滩的生物地球化学研究的基础上的。然而，对亚马逊河和泥滩沉积物中有机碳的初步研究表明，一小部分陆地有机碳实际上不是难熔的，因此在海洋中可以快速有效地被氧化，而另一小部分是难熔的，实际上在海洋沉积物中得到了定量的保存。总体而言，数据表明，人们对埋葬效率的低估在50%-100%之间。这项提议的重点是对亚马逊河沿岸海洋陆地有机碳的命运进行变革性的、机械性的和定量的理解。这将通过以下方式完成：i)使用浅吃水考察船对圭亚那海岸(圭亚那泥滩)和亚马逊河三角洲近海的海洋省份进行采样，以及ii)使用最新的有机碳地球化学分析--特别是斜坡氧化和化合物特定放射性碳分析--和元素组成，以证明陆地有机碳氧化的选择性，并对该系统的埋藏效率提供新的估计--对全球海洋陆地有机碳清单的影响。这项裁决反映了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。