The influence of the SML on trace gas biogeochemistry and air–sea gas exchange

我们的动机来自实验室和现场证据，即海面微层(SML)极大地影响气候活跃和对大气重要的痕量气体的生物地球化学循环，如二氧化碳(CO2)、一氧化碳(CO)、甲烷(CH4)、一氧化二氮(N2O)和二甲基硫化物(DMS)：(I)PASSME和SOPRAN项目最近的研究强调，表面活性物质(即表面活性剂)的积累对SML/大气界面上的CO2和N2O通量都有很强的(抑制)作用。以及(2)微量气体可通过(微型)生物或(光)化学过程产生和消耗。因此，与混合层更深的水域相比，上层海洋，包括SML，可以是这些气体的不同来源或汇，这与BASS研究单位有明显的相关性。SML(或海洋上部厘米)中的二氧化碳、N2O和其他气体的浓度已被证明与其低于SML的总体浓度不同。通常，使用在混合层中测量的浓度和不考虑SML的气体传输速度来计算进入大气的重要痕量气体的净源和汇。这些差异将最终导致错误计算的通量值，这可能随后导致计算的气候强迫和地球系统模型中的空气质量存在很大的不确定性。通过将我们的痕量气体测量与(I)有机物和碳的动力学和分子特征(SP1.1；SP1.5)、(Ii)生物多样性和代谢活性(SP1.2)、(Iii)有机物的光学性质(SP1.3)、(Iv)有机物的光化学转化(SP1.4)和(V)物理传输过程(SP2.3)的测量联系起来，我们将全面了解SML如何驱动痕量气体通量的变化。

Our motivation stems from laboratory and in situ evidence that the sea-surface microlayer (SML) greatly impacts the biogeochemical cycling of climate-active and atmospherically important trace gases, such as carbon dioxide (CO2), carbon monoxide (CO), methane (CH4), nitrous oxide (N2O), and dimethyl sulfide (DMS): (i) recent studies from the PASSME and SOPRAN projects have emphasized that accumulations of surface-active substances (i.e., surfactants) have a strong (dampening) effect on both CO2 and N2O fluxes across the SML/atmosphere interface, and (ii) trace gases can be produced and consumed by (micro)biological or by (photo)chemical processes. Therefore, the upper ocean, including the SML, can be a distinct source or sink for these gases, as compared to waters deeper in the mixed layer, with clear relevance to the BASS research unit. Concentrations of CO2, N2O, and other gases in the SML (or upper centimeters of the ocean) have been shown to be different from their bulk concentrations below the SML. Typically, the net sources and sinks of important trace gases to the atmosphere are computed using concentrations measured in the mixed layer and with gas transfer velocities that do not take the SML into account. These discrepancies will culminate in incorrectly calculated flux values, which can lead, subsequently, to large uncertainties in computed climate forcing and air quality in Earth system models. By linking our trace gas measurements with measurements of (i) the dynamics and molecular characteristics of organic matter and carbon specifically (SP1.1; SP1.5), (ii) biological diversity and metabolic activity (SP1.2), (iii) the optical properties of organic matter (SP1.3), (iv) the photochemical transformation of organic matter (SP1.4), and (v) physical transport processes (SP2.3), we will gain a comprehensive understanding of how the SML drives trace gas flux variability.