Collaborative Research: Seasonal variability in refractory dissolved organic carbon fluxes associated with primary marine aerosol emitted from the oceans

合作研究：与海洋排放的初级海洋气溶胶有关的难溶解有机碳通量的季节变化。海洋含有大量的有机碳，其数量大于所有陆地有机碳生物量的总和。几乎所有的海洋有机碳都被溶解了。平均而言，它有几千年的历史，化学性质稳定，在完全被带走之前，它被带到整个海洋好几次。然而，人们对这种被称为难熔溶解有机碳（RDOC）的旧碳的产生和去除过程知之甚少。一种潜在的去除途径是RDOC附着在破碎波产生的上升气泡表面。这些气泡最终在海面上破裂，喷出微小颗粒（初级海洋气溶胶，“PMA”），将RDOC带入大气。大多数PMA有机碳与在大气中漂浮数天至数周的最小颗粒（直径小于1 μm）有关。在此期间，这些颗粒中的RDOC可以光化学降解（通过阳光），部分向陆地输送，和/或返回海洋。当这种RDOC转化为无机碳（如二氧化碳）或在大气中降解为更活泼的成分时，它就能有效地从海洋RDOC储存库中去除。根据初步结果，通过这一过程从海洋中去除RDOC的年速率与所有其他已知的RDOC损失（与颗粒相互作用、生物降解和热液循环）相似，但海水中的光化学降解除外。在先前研究的基础上，本项目将通过对西北大西洋的三次研究巡航，确定从海洋中去除RDOC的季节性变化。该项目的研究结果将为RDOC在海洋-大气耦合损失方面提供重要的研究成果，并提高对RDOC在全球碳循环和地球气候中的作用的认识。这项研究将涉及两名早期职业教师，并将为本科生、研究生和博士后研究人员提供培训。放射性碳（C-14）测量表明，RDOC包含19%至40%与海面气泡破裂产生的PMA相关的有机碳。将RDOC与PMA一起注入大气是一个潜在的重要过程，每年可从海洋中去除多达2至20 Tg的RDOC。该项目将通过量化：(1)PMA OC中RDOC的比例，以及(2)其与近地表海水中生物产生的不稳定和半不稳定溶解有机质丰度的关系，来测量PMA介导的海洋RDOC向大气排放的季节变化。这些关系将在百慕大大西洋时序站进行三次研究巡航（一次在7月，两次在1月）期间进行评估。在巡航期间，调查人员将测量：(1)海水中PMA及其有机源物质的天然丰度C-14值；(2)海水的动态和平衡表面张力和物理性质，包括气泡大小分布；(3) PMA中主要离子、有机碳、碳水化合物、多肽和蛋白质、表面活性剂的浓度；(4)近地表海水和表层微层中溶解性有机物质（CDOM）和溶解性有机碳、叶绿素a、主要离子、碳水化合物、多肽和蛋白质、表面活性剂的浓度。基于这些化学测量和物理性质，本研究将揭示RDOC作为PMA组成部分输入大气的幅度和潜在控制。该奖项反映了美国国家科学基金会的法定使命，并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，被认为值得支持。

Collaborative Research: Seasonal variability in refractory dissolved organic carbon fluxes associated with primary marine aerosol emitted from the oceansThe oceans hold a massive quantity of organic carbon that is greater than all terrestrial organic carbon biomass combined. Nearly all marine organic carbon is dissolved. On average, it is thousands of years old, chemically stable, and carried throughout the entire ocean several times before complete removal. However, little is known about the processes that produce and remove this old carbon, referred to as refractory dissolved organic carbon (RDOC). One potential removal pathway involves RDOC adhering onto the surfaces of rising bubbles produced by breaking waves. The bubbles ultimately burst at the sea surface, ejecting tiny particles (primary marine aerosol, “PMA”) that carry the RDOC into the atmosphere. Most of this PMA organic carbon is associated with the smallest particles (less than 1 μm diameter) that drift in the atmosphere for several days to weeks. During this time, RDOC in these particles can be degraded photochemically (by sunlight), partially transported landward, and/or returned to the sea. When this RDOC is converted to inorganic carbon (e.g., carbon dioxide) or degraded to more reactive constituents in the atmosphere, it is effectively removed from the marine RDOC reservoir. Based on preliminary results, the annual rate at which RDOC is removed from the ocean by this process is similar to all other known RDOC losses (interactions with particles, biological degradation, and hydrothermal circulation), except for photochemical degradation in seawater. Building on this prior research, this project will identify seasonal changes in the removal of RDOC from the oceans through this process during three research cruises to the northwestern Atlantic Ocean. Results from this project will provide important findings about the coupled ocean-atmosphere loss of RDOC and improve understanding of the role of RDOC in the global carbon cycle and Earth's climate. The research will involve two early career faculty, and will provide training for undergraduate, graduate, and postdoctoral researchers.Radiocarbon (C-14) measurements indicate that RDOC comprises 19 to 40 % of the organic carbon associated with PMA produced by bursting bubbles at the sea surface. Injection of RDOC into the atmosphere in association with PMA is a potentially important process that removes as much as 2 to 20 Tg RDOC yr-1 from the oceans. This project will measure seasonal variations in the PMA-mediated emission of marine RDOC to the atmosphere by quantifying: (1) the fraction of RDOC in PMA OC and (2) its relationship to the abundance of biologically produced labile and semi-labile dissolved organic matter in near surface seawater. These relationships will be evaluated at the Bermuda Atlantic Time-series Station during three research cruises (one in July, two in January). During the cruises, the investigators will measure: (1) the natural abundance C-14 values for PMA and its organic source materials in seawater; (2) the dynamic and equilibrium surface tension and physical properties of seawater, including bubble size distributions; (3) concentrations of major ions, organic carbon, carbohydrates, peptides and proteins, and surfactants in PMA; and (4) chromophoric dissolved organic matter (CDOM) and the concentrations of dissolved organic carbon, chlorophyll a, major ions, carbohydrates, peptides and proteins, and surfactants in near-surface seawater and in the sea-surface microlayer. Based on these chemical measurements and physical properties, this study will reveal the magnitude and potential controls on RDOC inputs into the atmosphere as a component of PMA.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.