Collaborative Research: Constraining the source of oceanic dissolved black carbon using compound-specific stable carbon isotopes

合作研究：使用特定化合物的稳定碳同位素限制海洋溶解黑碳的来源

• 批准号: 1756733
• 负责人: Jay Brandes
• 金额: $ 12.08万
• 依托单位: University of Georgia Research Foundation Inc
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-04-01 至 2022-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1756733&HistoricalAwards=false
• 关键词: Collaborative; Research; Constraining; source; oceanic

The char and soot remaining after fire is broadly referred to as black carbon. When char interacts with water, some of it dissolves and is carried away by rivers to the ocean. This soluble component of char is termed "dissolved black carbon" (DBC). Recent research has revealed DBC to be a major component of the carbon cycle. Most notably, DBC is now known to make up 10% of all dissolved organic carbon that rivers carry to the sea. Once in the ocean, DBC remains there for thousands of years, storing carbon that would otherwise be in the atmosphere as carbon dioxide. As carbon dioxide contributes to the greenhouse effect, with higher carbon dioxide in the atmosphere leading to warmer global temperatures, it is important to understand where DBC in the ocean came from and how long it will stay locked away in the deep ocean. In this funded work, we set out to determine the source of the DBC in the ocean. Based upon our previous work that shows rivers export massive amounts of DBC to the coast, it has been suggested that rivers are the main source of DBC to the open ocean. However, in looking more closely at the DBC in rivers and the oceans, we found them to differ in one critical way: they have different isotopic signatures. This precludes them from having the same source, indicating that the DBC in the oceans is not from rivers. Our preliminary work only looked at a small river in Georgia, USA, and in the coastal waters offshore. In this funded project, we will take a global look at the isotopic signatures of DBC collected from large rivers such as the Amazon, Mississippi, and Yukon, and from the middle of the Atlantic and Pacific Oceans. If we find there is no overlap in the isotopes of the DBC from these major global rivers and ocean waters, we can conclude that rivers are not the main source of oceanic DBC and will need to search for new explanations of how molecules produced by fire end up in the deep ocean. The project will enhance the career and continue the training of a first-time investigator and train undergraduate students in real world research through the Northeastern University Cooperative Program. In addition, our findings be adapted to produce learning materials for high school students in collaboration with the Science Journal for Kids.Previous efforts to track DBC sources in natural waters have come with major limitations, preventing definitive connections to be made between oceanic DBC and its pyrogenic source. Photodegradation, a significant removal process for DBC in surface waters, drastically alters the molecular composition of DBC and erases any potential link between DBC chemical composition and its source. Bulk stable carbon isotopic measurements cannot unambiguously identify sources of DOC subcomponents, such as DBC. As such, this project aims to constrain the oceanic source of DBC by measuring compound-specific stable carbon isotopes of molecular markers (benzenepolycarboxylic acids, or BPCAs), derived exclusively from DBC. Our preliminary data show BPCA-specific isotopic values to have a sufficiently wide dynamic range between riverine and oceanic samples to test our hypotheses. In the current proposal, we aim to 1) isotopically characterize the largest quantified flux of DBC to the ocean (global rivers), 2) assess in situ oceanic variation in DBC stable carbon isotopic signatures, and 3) investigate the potential BPCA-specific fractionation effects of DBC photodegradation. In establishing a robust tracer for DBC source, we will be able to accurately constrain sources of oceanic DBC and further investigate the biogeochemical cycling of DBC across the terrestrial-marine continuum. The results of our research will also assist in answering larger research questions, specifically those regarding the fate of terrigenous DOM in the ocean, which have plagued biogeochemists for decades.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.

火灾后残留的炭和烟灰被广泛地称为黑碳。 当炭与水相互作用时，其中一些溶解并被河流带到海洋中。 这种炭的可溶性组分被称为“溶解黑碳”（DBC）。 最近的研究表明，DBC是碳循环的主要组成部分。 最值得注意的是，目前已知DBC占河流带入海洋的所有溶解有机碳的10%。 一旦进入海洋，DBC会在那里停留数千年，储存原本会以二氧化碳形式存在于大气中的碳。 由于二氧化碳会导致温室效应，大气中二氧化碳含量增加会导致全球气温升高，因此了解海洋中的DBC来自何处以及它将在深海中锁定多久非常重要。 在这项受资助的工作中，我们着手确定海洋中DBC的来源。 根据我们以前的工作，表明河流输出大量的DBC到海岸，它已经提出，河流是DBC的主要来源到公海。 然而，在更仔细地观察河流和海洋中的DBC时，我们发现它们在一个关键方面有所不同：它们具有不同的同位素特征。 这排除了它们具有相同来源的可能性，表明海洋中的DBC不是来自河流。 我们的初步工作只着眼于美国格鲁吉亚的一条小河，以及近海的沿海沃茨。 在这个资助的项目中，我们将从全球范围内观察从亚马逊河、密西西比河和育空地区等大河以及大西洋和太平洋中部收集的DBC的同位素特征。 如果我们发现这些全球主要河流和海洋沃茨中的DBC同位素没有重叠，我们可以得出结论，河流不是海洋DBC的主要来源，并且需要寻找新的解释，以解释火产生的分子如何最终进入深海。 该项目将通过东北大学合作项目加强职业生涯，继续培训首次调查员，并培训本科生从事真实的世界研究。 此外，我们的研究结果可以与《儿童科学杂志》合作，为高中生制作学习材料。以前追踪自然沃茨中DBC来源的努力有很大的局限性，阻止了海洋DBC和其热原来源之间的明确联系。 光降解是沃茨中DBC的一个重要去除过程，它会彻底改变DBC的分子组成，并消除DBC化学组成与其来源之间的任何潜在联系。 大量的稳定碳同位素测量不能明确地确定DOC亚组分的来源，如DBC。 因此，该项目旨在通过测量仅来自DBC的分子标记物（苯多羧酸或BPCA）的化合物特异性稳定碳同位素来限制DBC的海洋来源。 我们的初步数据显示，BPCA特定的同位素值有一个足够宽的动态范围之间的河流和海洋样品来测试我们的假设。 在目前的建议中，我们的目标是1）同位素表征的最大量化流量的DBC的海洋（全球河流），2）评估原位海洋变化的DBC稳定的碳同位素签名，和3）调查潜在的BPCA特定分馏效应的DBC光降解。 在建立一个强大的示踪剂的DBC源，我们将能够准确地限制海洋DBC的来源，并进一步研究的DBC在陆地-海洋连续体的地球化学循环。 我们的研究成果也将有助于回答更大的研究问题，特别是那些关于陆源DOM在海洋中的命运，这已经困扰了地球化学家几十年。这个奖项反映了NSF的法定使命，并已被认为是值得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的支持。