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

亚马逊河是世界上最大和最重要的河流之一。它不仅带着水穿过亚马逊雨林，还带着泥--很多泥。当河流汇入海洋时，这些泥浆沉淀下来，形成了亚马逊三角洲。海浪和风使一些泥浆重新悬浮起来，形成了从巴西海岸缓慢移动到法属圭亚那，苏里南和圭亚那的泥滩。这些泥滩不仅塑造了这些地区的海岸线，而且它们还作为亚马逊雨林从大气中移除的碳的储存库，这些碳被降落到森林地面并被冲入河流，最终被泥土颗粒运送到亚马逊三角洲。通常情况下，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，亚马逊河沿岸沿着数百英里的泥滩是一种特殊情况，它搅动了这些碳，并将大部分碳释放回大气。这个想法已经存在了几十年，但如果错误的话，可能会对我们对海洋碳循环的理解产生重大影响。这项研究将使用新的科学和技术来改变我们对海洋中河流碳循环的看法，方法是对泥滩、海洋沃茨和亚马逊河沃茨进行比以前更彻底的采样，目的是了解和量化亚马逊河近海海洋泥滩沉积物中陆地来源的碳的储存。 本研究将作为两个博士学位的核心。此外，该学院还将提供学位论文，并将与伍兹霍尔合作教育计划（PEP）对接，为代表性不足的少数民族大学生提供获得海洋和环境科学实践经验的机会。该项目还将被纳入圣彼得堡科学节，该活动每年秋季的一个周末将数千名学生聚集在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·赫奇斯提出了一个关于海洋在碳循环中的作用的开创性问题：“海洋中的陆地有机物会发生什么？“这个问题是一个难题-因为河流中的有机物高度降解，预计它在海洋中的呼吸作用最小，但大多数人认为，大陆边缘似乎是陆地有机物的焚化炉。然而，这种模式最初是建立在亚马逊水下三角洲和移动的流化泥滩沿着圭亚那海岸的地球化学研究。 然而，亚马逊河和泥滩沉积物中的有机碳的最新特征表明，陆地有机碳的一部分实际上并不难降解，因此在海洋中被迅速有效地氧化，而另一部分是难降解的，实际上定量地保存在海洋沉积物中。总的来说，数据表明埋葬效率被低估了50- 100%。该提案的重点是获得亚马逊河沿岸海洋陆地有机碳命运的变革机制和定量理解。这将通过i）对圭亚那海岸近海的海洋省进行采样来完成（圭亚那泥滩）以及亚马逊河三角洲，使用浅吃水研究船和ii）使用有机碳的最新技术水平的地球化学分析-特别是斜坡氧化和化合物特异性放射性碳分析-和元素组成，以证明陆地有机碳氧化的选择性，并提供该系统埋藏效率的新估计-该奖项反映了NSF的法定使命，并被认为值得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来支持。

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.