Collaborative Research: Coupled Ocean-Atmosphere Recycling of Refractory Dissolved Organic Carbon in Seawater

海洋含有大量的有机碳，比所有陆地有机碳生物量的总和还要多。几乎所有的海洋有机碳都被溶解，95%以上是难降解的，在完全去除之前，它们在海洋中循环了几次。难溶有机碳（RDOC）的浓度是均匀的，在水柱的深度和代表的“背景”碳存在于整个海洋。然而，关于RDOC的生产和去除过程知之甚少。一种潜在的去除途径是通过RDOC吸附到由破碎波产生的上升气泡的表面上，并通过气泡破裂喷射到大气中。在先前研究的基础上，研究人员将在大西洋西北部的一次研究巡航中评估海洋-大气处理在回收海洋RDOC中的重要性。研究结果将提供有关RDOC的耦合海洋-大气损失的重要见解，从而提高对RDOC在海洋和大气地球化学，全球碳循环和地球气候中的作用的理解和预测能力。这项研究将涉及三个早期的职业教师，并将提供本科生和研究生researchers.Recent结果的基础上有限的一组observations表明，有机物质（OM）与初级海洋气溶胶（PMA）产生的破裂气泡破碎波在海面上的组成部分到全部的RDOC，而不是OM最近的生物起源已被广泛认为。与PMA及其随后的光化学氧化相关联的RDOC注入大气中是一个潜在的重要的和迄今未被认识到的汇RDOC在海洋中的足够大的规模关闭海洋碳预算，并帮助解决一个长期存在的难题关于海洋RDOC的去除机制。该项目将包括一项船上调查和模拟研究，以（1）量化海洋难溶有机碳（RDOC）对生物生产区和贫营养区近地表海水以及北大西洋深水产生的初级海洋气溶胶有机物（PMA OM）的相对贡献，并（2）确定大气光化学处理作为RDOC再循环途径的重要性。为了验证这些假设，将在西北大西洋的四个水文站部署大容量气溶胶发生器，以表征（1）PMA以及表层和深层海水中14 C的天然丰度;（2）气泡羽流的表面张力和物理特性;（3）PMA的粒径分辨通量、化学组成、有机碳富集、光谱吸收和光化学演化;（4）海水的含碳量、光学性质和物理性质。将通过模型计算解释通过PMA产生和光化学演变进行RDOC回收的重要性。

The 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 and more than 95% is refractory, and cycled through the oceans several times before complete removal. Refractory dissolved organic carbon (RDOC) concentrations are uniform with depth in the water column and represent the "background" carbon present throughout the oceans. However, very little is known regarding RDOC production and removal processes. One potential removal pathway is through adsorption of RDOC onto surfaces of rising bubbles produced by breaking waves and ejection via bubble bursting into the atmosphere. Building on prior research, the investigators will evaluate the importance of ocean- atmosphere processing in recycling marine RDOC during a research cruise in the northwestern Atlantic Ocean. Results of the research will provide important insights regarding the coupled ocean-atmosphere loss of RDOC, thereby improving understanding of and ability to predict the role of RDOC in oceanic and atmospheric biogeochemistry, the global carbon cycle, and Earth's climate. The research will involve three early career faculty, and will provide training for undergraduate and graduate researchers.Recent results based on a limited set of observations indicate that the organic matter (OM) associated with primary marine aerosol (PMA) produced by bursting bubbles from breaking waves at the sea surface is comprised partly to wholly of RDOC rather than OM of recent biological origin as has been widely assumed. The injection of RDOC into the atmosphere in association with PMA and its subsequent photochemical oxidation is a potentially important and hitherto unrecognized sink for RDOC in the oceans of sufficient magnitude to close the marine carbon budget and help resolve a long-standing conundrum regarding removal mechanisms for marine RDOC. This project will involve a shipboard investigation and modeling study to (1) quantify the relative contributions of marine refractory dissolved organic carbon (RDOC) to primary marine aerosol organic matter (PMA OM) produced from near-surface seawater in biologically productive and oligotrophic regions and from North Atlantic Deep Water, and to (2) determine the importance of atmospheric photochemical processing as a recycling pathway for RDOC. To test these hypotheses, a high-capacity aerosol generator will be deployed at four hydrographic stations in the NW Atlantic Ocean to characterize (1) the natural abundance of 14C in PMA and in surface and deep seawater; (2) the surface tension and physical properties of bubble plumes; (3) size-resolved production fluxes, chemical composition, organic carbon enrichments, spectral absorbance, and photochemical evolution of PMA; and (4) the carbon content, optical properties, and physical properties of seawater. The importance of RDOC recycling via PMA production and photochemical evolution will be interpreted with model calculations.