Although methane is a widely studied greenhouse gas, uncertainties remain with respect to the factors controlling its distribution and diffusive flux into the atmosphere, especially in highly dynamic coastal waters. In the southern North Sea, the Elbe and Weser rivers are two major tributaries contributing to the overall methane budget of the southern German Bight. In June 2019, we continuously measured methane and basic hydrographic parameters at a high temporal and spatial resolution (one measurement per minute every 200–300 m) on a transect between Cuxhaven and Helgoland. These measurements revealed that the overall driver of the coastal methane distribution is the dilution of riverine methane-rich water with methane-poor marine water. For both the Elbe and Weser, we determined an input concentration of 40–50 nmol/L compared to only 5 nmol/L in the marine area. Accordingly, we observed a comparatively steady dilution pattern of methane concentration toward the marine realm. Moreover, small-scale anomalous patterns with unexpectedly higher dissolved methane concentrations were discovered at certain sites and times. These patterns were associated with the highly significant correlations of methane with oxygen or turbidity. However, these local anomalies were not consistent over time (days, months). The calculated diffusive methane flux from the water into the atmosphere revealed local values approximately 3.5 times higher than background values (median of 36 and 128 μmol m^–2 d^–1). We evaluate that this occurred because of a combination of increasing wind speed and increasing methane concentration at those times and locations. Hence, our results demonstrate that improved temporal and spatial resolution of methane measurements can provide a more accurate estimation and, consequently, a more functional understanding of the temporal and spatial dynamics of the coastal methane flux.

尽管甲烷是一种广泛研究的温室气体，但在控制其分布和扩散到大气中的因素方面仍然存在不确定性，尤其是在高度动态的沿海水域。在北海南部，易北河和威悉河是德国湾南部总体甲烷收支的两条主要支流。2019 年 6 月，我们在 Cuxhaven 和 Helgoland 之间的断面上以高时空分辨率（每 200-300 m 每分钟测量一次）连续测量了甲烷和基本水文参数。这些测量结果表明，沿海甲烷分布的总体驱动因素是富含甲烷的河流水被贫甲烷的海水稀释。对于易北河和威悉河，我们确定的输入浓度为 40–50 nmol/L，而海洋区域仅为 5 nmol/L。因此，我们观察到甲烷浓度向海洋领域呈相对稳定的稀释模式。此外，在某些地点和时间发现了具有意外更高溶解甲烷浓度的小规模异常模式。这些模式与甲烷与氧气或浊度的高度显着相关性有关。然而，这些局部异常随着时间的推移（天、月）并不一致。计算出的从水到大气的扩散甲烷通量显示局部值比背景值高约 3.5 倍（中位数为 36 和 128 μmol m 此外，在某些地点和时间发现了具有意外更高溶解甲烷浓度的小规模异常模式。这些模式与甲烷与氧气或浊度的高度显着相关性有关。然而，这些局部异常随着时间的推移（天、月）并不一致。计算出的从水到大气的扩散甲烷通量显示局部值比背景值高约 3.5 倍（中位数为 36 和 128 μmol m 此外，在某些地点和时间发现了具有意外更高溶解甲烷浓度的小规模异常模式。这些模式与甲烷与氧气或浊度的高度显着相关性有关。然而，这些局部异常随着时间的推移（天、月）并不一致。计算出的从水到大气的扩散甲烷通量显示局部值比背景值高约 3.5 倍（中位数为 36 和 128 μmol m^–2 d ^–1 )。我们评估这是由于风速增加和这些时间和地点的甲烷浓度增加的组合而发生的。因此，我们的结果表明，改进的甲烷测量的时间和空间分辨率可以提供更准确的估计，从而对沿海甲烷通量的时间和空间动态有更深入的了解。