Collaborative Research: Influence of Surfactants on Air-Sea Gas Exchange: 3He/SF6 Experiments in the Baltic Sea

气体交换是大气和海洋表面（双向）之间气体的运动，是全球生物地球化学中一个重要的过程。一个特别令人感兴趣的领域是二氧化碳和二甲基硫化物等气体的交换速率，它们在地球气候中起着重要作用。在全球范围内理解和模拟海气交换需要了解气体交换率如何随温度、风速和海洋中表面化学膜（称为表面活性剂）的存在等一系列因素而变化。在过去25年中，在了解公海的海气交换方面取得了重大进展，这主要是由于方法的改进和一些成功的过程研究。然而，一些重要的问题仍然存在，例如沿海地区（包括内海）发生了什么，以及表面活性剂如何影响气体交换。波罗的海天然气交换实验（Baltic GasEx）是美国和德国科学家之间的一项合作，旨在解决这些问题。波罗的海GasEx项目的参与者将使用不同的技术测量波罗的海在春华前后的空气-海洋气体交换率，届时表面活性剂的浓度和组成将有所不同。这次考察将在一艘德国船（Alkor）上进行，其最终目标是量化内海风速和气体交换之间的关系，并了解表面活性剂对海气交换的影响。该项目将涉及重要的国际合作、通过参与的美国机构进行的公共教育和宣传，以及与国际合作者合作开展的大量学生培训。美国国家科学基金会的资金将支持波罗的海GasEx期间氦-3和六氟化硫的测量，以确定气体交换率。德国同事独立资助，用交流伏安法、表面张力法和和频率生成法定量表面活性剂；测定微层的化学特性；并利用涡旋相关通量测量CO2和DMS来估计气体交换速率。提出的实验旨在解决开放海洋风速/气体交换参数化是否可以应用于波罗的海等内陆海的问题。此外，表面活性剂对气体交换的影响已经在实验室进行了广泛的研究，但很少有直接的现场证据表明表面活性剂对气体交换的影响。在高和低表面活性剂浓度的情况下进行考察的拟议实验，应该会对天然表面活性剂对气体交换的影响有新的认识。最后，为波罗的海提出的一些风速/气体交换参数化似乎比典型的公海参数化要高。这些通常是基于CO2的涡流相关通量测量。然而，在开放海洋实验中，氦-3/六氟化硫方法和二氧化碳的涡流相关方差都已被部署，似乎在两种技术测量的气体传递速度之间存在差异。这个实验应该表明，通过这两种技术测量的气体传输速度的类似差异是否也存在于波罗的海。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。

Gas exchange, the movement of gases between the atmosphere and the surface ocean (in both directions), is an important process to understand in global biogeochemistry. A particular area of interest is the rate of exchange of gases such as carbon dioxide and dimethyl sulfide, which play important roles in Earth's climate. Understanding and modeling air-sea exchange on a global scale requires understanding of how gas exchange rates vary in response to a number of factors such as temperature, wind speed, and the presence of surface chemical films (known as surfactants) in the ocean. Over the past 25 years, major advances have been made in understanding air-sea gas exchange in the open ocean, mainly due to improvements in methodology and a number of successful process studies. However, some important questions remain, such as what happens near coastal areas (including inland seas), and how surfactants affect gas exchange. The Baltic Sea Gas Exchange Experiment (Baltic GasEx) is a collaboration between scientists from the US and Germany designed to address these questions. Participants in Baltic GasEx will measure the air-sea gas exchange rates with different techniques in the Baltic Sea before and after the spring bloom, when concentrations and compositions of surfactants will be different. The expeditions will be conducted on a German ship (Alkor), with the ultimate goal of quantifying the relationship between wind speed and gas exchange in an inland sea, and understanding the impact of surfactants on air-sea gas exchange. The project will involve significant international collaboration, public education and outreach through both participating U.S. institutions, and substantial student training in partnership with the international collaborators.NSF funding will support helium-3 and sulfur hexafluoride measurements during Baltic GasEx to determine the gas exchange rate. German colleagues are independently funded to quantify surfactants with AC voltammetry, surface tension, and sum frequency generation; to determine chemical characteristics of the micro layer; and to estimate the gas exchange rate using eddy covariance flux measurements of CO2 and DMS. The proposed experiment is designed to address the question of whether open ocean wind speed/gas exchange parameterizations can be applied to inland seas like the Baltic. Also, the effect of surfactants on gas exchange has been studied extensively in the laboratory, but there is little direct field evidence for the effect of surfactants on gas exchange. The proposed experiment, with expeditions at times with both high and low surfactant concentrations, should shed new light on the effect of natural surfactants on gas exchange. Finally, some wind speed/gas exchange parameterizations proposed for the Baltic Sea appear to be higher than typical open ocean parameterizations. These are typically based on eddy covariance flux measurements of CO2. However, in open ocean experiments where both the helium-3/sulfur hexafluoride approach and eddy covariance of CO2 have been deployed, there seems to be a discrepancy between gas transfer velocities measured with the two techniques. This experiment should show whether a similar difference in gas transfer velocities measured via these two techniques also exists in the Baltic Sea.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.