Understanding the dynamics and fate of methane (CH4) release from oceanic seepages from margins and shelves into the water column, and quantifying the budget of its total discharge at different spatial and temporal scales, currently represents a major scientific undertaking. The assessment of methane’s sensitivity to global warming, its injection into the atmosphere and its role in the oceanic carbon cycle are only a few of the potential research fields. Previous works on the fate of methane escaping from the seafloor underlined the challenge in both, estimating its concentration distribution and identifying gradients. Here, accuracy and precision are prerequisites to a reliable analysis. During the Envri+ Methane Cruise onboard the R/V Mare Nigrum in April 2019, acoustic surveys, continuous in-situ measurements from a membrane inlet laser spectrometer (MILS) and a commercial methane sensor (METS) from Franatech GmbH, as well as discrete water sampling followed by onshore laboratory analysis were conducted and will be discussed here. The results highlight the challenge to obtain reliable and precise measurements of dissolved gases due to instrumental limitations, as well as the complexity of mapping the seepage area due to large spatial and temporal variability of the water mass composition. In-situ techniques and acoustic data revealed a good qualitative matching of the spatial distribution of methane emissions. The accuracy of the in situ sensors to measure dissolved methane concentration was then assessed by a quantitative comparison with standard onshore methods. From vertical profiles (from both continuous and discrete measurements), a dissolved methane profile following an expected exponential dissolution function was observed at both sites. At the deeper site (~120 m water depth), dissolved methane transported by the bubbles may reach up to ~45 m from the seafloor, while at the shallower site (~55 m water depth) CH4 concentrations at the sea surface were four times higher than the expected equilibrium concentrations. High spatial resolution surface data also support this hypothesis, suggesting a transfer of CH4 from the sea to the atmosphere at shallower depths. Well localized methane enriched waters were found near the surface but they appear decoupled with the location of the seafloor seepages,

中文翻译：

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使用多技术方法比较西黑海两个地点海底排放水体中甲烷的空间分布

了解从边缘和陆架进入水体的海洋渗流中甲烷 (CH4) 释放的动态和归宿，并量化其在不同空间和时间尺度上的总排放量预算，目前是一项重大的科学事业。评估甲烷对全球变暖的敏感性、其注入大气及其在海洋碳循环中的作用只是潜在研究领域中的一小部分。先前关于从海底逸出的甲烷的命运的研究强调了两者的挑战，估计其浓度分布和识别梯度。在这里，准确度和精密度是可靠分析的先决条件。在 2019 年 4 月 R/V Mare Nigrum 上的 Envri+ 甲烷巡航期间，声学调查、进行了来自 Franatech GmbH 的膜入口激光光谱仪 (MILS) 和商用甲烷传感器 (METS) 的连续原位测量，以及离散水采样和陆上实验室分析，并将在此处进行讨论。由于仪器的限制，以及由于水团成分的空间和时间变化很大，绘制渗流区域的复杂性，结果突出了获得溶解气体的可靠和精确测量的挑战。现场技术和声学数据揭示了甲烷排放空间分布的良好定性匹配。然后通过与标准陆上方法的定量比较来评估原位传感器测量溶解甲烷浓度的准确性。从垂直剖面（来自连续和离散测量），在两个地点都观察到遵循预期指数溶解函数的溶解甲烷剖面。在较深的地点（~120 m 水深），气泡输送的溶解甲烷可能达到海底~45 m，而在较浅的地点（~55 m 水深），海面的 CH4 浓度是四倍高于预期的平衡浓度。高空间分辨率表面数据也支持这一假设，表明 CH4 从海洋转移到较浅深度的大气中。在地表附近发现了定位良好的富含甲烷的水，但它们似乎与海底渗漏的位置脱钩，在两个地点都观察到了遵循预期指数溶解函数的溶解甲烷分布。在较深的地点（~120 m 水深），气泡输送的溶解甲烷可能达到海底~45 m，而在较浅的地点（~55 m 水深），海面的 CH4 浓度是四倍高于预期的平衡浓度。高空间分辨率表面数据也支持这一假设，表明 CH4 从海洋转移到较浅深度的大气中。在地表附近发现了定位良好的富含甲烷的水，但它们似乎与海底渗漏的位置脱钩，在两个地点都观察到了遵循预期指数溶解函数的溶解甲烷分布。在较深的地点（~120 m 水深），气泡输送的溶解甲烷可能达到海底~45 m，而在较浅的地点（~55 m 水深），海面的 CH4 浓度是四倍高于预期的平衡浓度。高空间分辨率表面数据也支持这一假设，表明 CH4 从海洋转移到较浅深度的大气中。在地表附近发现了定位良好的富含甲烷的水，但它们似乎与海底渗漏的位置脱钩，而在较浅的地点（约 55 m 水深），海面的 CH4 浓度比预期的平衡浓度高四倍。高空间分辨率表面数据也支持这一假设，表明 CH4 从海洋转移到较浅深度的大气中。在地表附近发现了定位良好的富含甲烷的水，但它们似乎与海底渗漏的位置脱钩，而在较浅的地点（约 55 m 水深），海面的 CH4 浓度比预期的平衡浓度高四倍。高空间分辨率表面数据也支持这一假设，表明 CH4 从海洋转移到较浅深度的大气中。在地表附近发现了定位良好的富含甲烷的水，但它们似乎与海底渗漏的位置脱钩，