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.

大火后剩下的炭和烟灰被广泛称为黑碳。 当炭与水相互作用时，其中一些溶解并被河流带到海洋。 CHAR的这种可溶成分称为“溶解的黑碳”（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，众所周知，DBC占河流携带的所有溶解有机碳的10％。 一旦进入海洋，DBC就在那里呆了数千年，将碳储存在大气中作为二氧化碳。 随着二氧化碳有助于温室效应，大气中二氧化碳较高，导致全球温度升高，重要的是要了解海洋中的DBC的来源以及将其锁定在深海中的时间。 在这项资助的工作中，我们着手确定海洋中DBC的来源。 根据我们以前显示河流出口DBC大量DBC的工作，有人建议河流是开阔海洋DBC的主要来源。 但是，在更仔细地查看河流和海洋中的DBC时，我们发现它们以一种关键方式有所不同：它们具有不同的同位素特征。 这使他们无法拥有相同的来源，表明海洋中的DBC不是来自河流。 我们的初步工作只看着乔治亚州佐治亚州的一条小河和海上沿海水域。 在这个资助的项目中，我们将全球介绍从亚马逊，密西西比州和育空地区等大河流中收集的DBC的同位素特征，以及大西洋和太平洋中部。 如果我们发现DBC的同位素在这些主要的全球河流和海洋水域中没有重叠，我们可以得出结论，河流不是海洋DBC的主要来源，并且需要寻找有关火灾产生的分子如何在深海中产生的新解释。 该项目将改善职业生涯，并继续通过东北大学合作计划对现实世界研究的初次研究员进行培训。 此外，我们的发现适应了与儿童科学杂志合作生产学习材料。追踪自然水域中DBC来源的努力已受到重大限制，从而阻止了海洋DBC及其生殖器来源之间的确定联系。 光降解是地表水中DBC的显着去除过程，极大地改变了DBC的分子组成，并消除了DBC化学组成与其来源之间的任何潜在联系。 体积稳定的同位素测量值无法明确识别DOC子组件的来源，例如DBC。 因此，该项目旨在通过测量分子标记物（苯甲甲酸羧酸或BPCAS）的化合物特异性稳定碳同位素来限制DBC的海洋来源，该碳同位素专用于DBC。 我们的初步数据表明，BPCA特异性同位素值在河流和海洋样品之间具有足够宽的动态范围，以检验我们的假设。 在当前的提案中，我们的目的是1）同位素对DBC的最大量化通量（全球河流），2）评估DBC稳定碳同位素特征的原位海洋变化，3）研究DBC PhodeDodradation的潜在BPCA特异性分数效应。 在为DBC源建立强大的示踪剂时，我们将能够准确限制海洋DBC的来源，并进一步研究DBC跨陆地式野生型连续体的生物地球化学循环。 我们的研究结果还将有助于回答更大的研究问题，尤其是关于海洋中陆原DOM的命运的问题，这些问题已经困扰了生物地球化学家数十年了。这项奖项反映了NSF的法定任务，并被认为是值得通过基金会的知识分子优点和更广泛影响的审查标准来通过评估来通过评估来支持的。