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

海洋中含有大量的有机碳，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了，超过95%的有机碳是难熔的，在完全清除之前会在海洋中循环几次。难熔溶解有机碳(RDoC)浓度随水柱深度的变化是一致的，代表着海洋中存在的“背景”碳。然而，人们对RDOC的生产和去除过程知之甚少。一种可能的去除途径是通过将RDOC吸附到破碎波产生的上升气泡的表面上，并通过气泡向大气中喷发。在先前研究的基础上，调查人员将在大西洋西北部的一次研究巡航期间评估海洋-大气处理在回收海洋RDOC方面的重要性。研究结果将提供有关RDoC海洋-大气耦合损失的重要见解，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理解和预测能力。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。最近的研究结果表明，与海面破裂海浪破裂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，而不是人们普遍认为的最近生物来源的OM。与PMA一起向大气中注入RDOC及其随后的光化学氧化是RDOC在海洋中的一个潜在的重要且迄今未被认识到的汇，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。该项目将涉及一项船上调查和模拟研究，以(1)量化海洋难溶有机碳(RDoC)对生物生产和低营养区域近地表海水和北大西洋深水产生的初级海洋气溶胶有机质(PMA OM)的相对贡献，并(2)确定大气光化学处理作为RDoC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一台大容量气溶胶发生器，以表征(1)PMA以及表层和深层海水中14C的自然丰度；(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、有机碳的富集度、光谱吸光度和光化学演变；(4)海水的碳含量、光学性质和物理性质。通过PMA生产和光化学演化的RDOC循环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.