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

海洋拥有大量的有机碳，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是溶解的，95%以上是难降解的，在完全去除之前，它们在海洋中循环几次。难溶性有机碳（RDOC）浓度随水柱深度而均匀，代表了整个海洋中存在的“背景”碳。然而，关于RDOC的生产和去除过程所知甚少。一种潜在的去除途径是通过将RDOC吸附到破碎波产生的上升气泡表面，并通过气泡破裂喷射到大气中。在先前研究的基础上，研究人员将在西北大西洋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。研究结果将为RDOC的海洋-大气耦合损失提供重要见解，从而提高对RDOC在海洋和大气生物地球化学、全球碳循环和地球气候中的作用的认识和预测能力。这项研究将涉及三名早期职业教师，并将为本科生和研究生研究人员提供培训。基于有限的一组观测结果的最近结果表明，与海面破碎波浪产生的气泡产生的初级海洋气溶胶（PMA）相关的有机物（OM）部分或全部由RDOC组成，而不是像人们普遍认为的那样由近期生物来源的OM组成。与PMA相关的RDOC注入大气及其随后的光化学氧化是海洋中RDOC潜在的重要且迄今未被认识的汇，其规模足以关闭海洋碳收支，并有助于解决关于海洋RDOC去除机制的长期难题。该项目将包括一项船载调查和建模研究，以(1)量化海洋难溶性溶解有机碳（RDOC）对主要海洋气溶胶有机质（PMA OM）的相对贡献，这些有机物来自生物生产力和低营养区以及北大西洋深水的近地表海水，以及(2)确定大气光化学处理作为RDOC回收途径的重要性。为了验证这些假设，将在西北大西洋的四个水文测量站部署一个高容量气溶胶发生器，以表征(1)PMA、表层和深层海水中14C的天然丰度；(2)气泡羽流的表面张力和物理性质；(3) PMA的尺寸分辨生产通量、化学成分、有机碳富集、光谱吸光度和光化学演化；(4)海水的含碳量、光学性质和物理性质。通过PMA生产和光化学演变的RDOC回收的重要性将通过模型计算来解释。

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.