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

气体交换，即气体在大气和海洋表面（双向）之间的运动，是理解全球地球化学的一个重要过程。一个特别令人感兴趣的领域是二氧化碳和二甲基硫等气体的交换率，这些气体在地球气候中起着重要作用。了解和模拟全球范围内的海气交换需要了解气体交换率如何随温度、风速和海洋表面化学膜（称为表面活性剂）的存在等因素而变化。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）附近会发生什么，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合作项目，旨在解决这些问题。波罗的海GasEx的参与者将在春季水华之前和之后用不同的技术测量波罗的海的空气-海洋气体交换率，此时表面活性剂的浓度和成分将不同。考察将在一艘德国船只（Alkor）上进行，最终目标是量化风速与内海气体交换之间的关系，并了解表面活性剂对海-气气体交换的影响。该项目将涉及重要的国际合作，通过参与的美国机构进行公共教育和推广，并与国际合作者合作进行大量的学生培训。NSF的资金将支持波罗的海GasEx期间的氦-3和六氟化硫测量，以确定气体交换率。德国同事独立资助，以量化表面活性剂与交流伏安法，表面张力，和和频率生成;确定微层的化学特性;并估计气体交换率使用涡动协方差通量测量CO2和DMS。拟议的实验旨在解决开放的海洋风速/气体交换参数化是否可以适用于内陆海，如波罗的海的问题。此外，表面活性剂对气体交换的影响已在实验室中进行了广泛的研究，但几乎没有直接的现场证据表明表面活性剂对气体交换的影响。拟议的实验，与探险在高和低的表面活性剂浓度的时候，应该揭示新的光天然表面活性剂对气体交换的影响。最后，波罗的海的一些风速/气体交换参数化建议似乎高于典型的公海参数化。这些通常基于CO2的涡度协方差通量测量。然而，在开放的海洋实验中，氦-3/六氟化硫的方法和涡度协方差的CO2已被部署，似乎有气体传输速度与这两种技术测量之间的差异。这个实验应该表明，通过这两种技术测量的气体传输速度是否也存在类似的差异在波罗的海。这个奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

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.