Abstract Geological gas seepage in petroleum-bearing sedimentary basins is an important natural source of atmospheric methane. In methane budget models geological emissions are generally considered constant over time, not affecting decadal atmospheric methane changes. Here, we report the case of a considerable sub-decadal variation of methane seepage from one of the largest thermogenic gas seep sites in Europe, Katakolo Harbour (Western Peloponnese, Greece). Based on gas flux measurements by accumulation chamber performed in 2010 and 2018, methane emission from cracks and fissures throughout the asphalt and concrete pavement of the harbour increased about four times (from 57 to 225 kg d−1) with emission factor changing from ~4,000 to 15,000 t km−2 y−1. Multiple lines of evidence, including mechanical deformation and fissuring of concrete and asphalt pavement, increased exhalation with constant fissure conditions, and no significant cracking with operating corrosion from 2004 to 2010, suggest that the methane emission increase is mainly due to intensification of subsurface gas flow (seepage) after 2010. Deep gas pressure and fault permeability variations, likely induced by the numerous earthquakes of the region, might have played a role. We estimate that if similar short-term variations of emission factor occur in large seepage areas worldwide, the global geological methane emission can significantly change, contributing to decadal changes of atmospheric methane budget.

中文翻译：

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卡塔科洛港（希腊西部）天然气渗漏造成的甲烷排放增加

摘要 含油气沉积盆地地质气体渗流是大气甲烷的重要天然来源。在甲烷收支模型中，地质排放通常被认为是随时间恒定的，不会影响年代际大气甲烷变化。在这里，我们报告了欧洲最大的热成因气体渗漏点之一 Katakolo 港（希腊西伯罗奔尼撒半岛）的甲烷渗流在次年代发生了相当大的变化。根据 2010 年和 2018 年蓄积室的气体通量测量，港口沥青和混凝土路面的裂缝和裂缝的甲烷排放量增加了约四倍（从 57 到 225 kg d-1），排放因子从~4,000 变化到 15,000 t km−2 y−1。多条证据，包括混凝土和沥青路面的机械变形和裂缝，裂缝条件恒定的呼气量增加，以及 2004 年至 2010 年运行腐蚀未出现明显裂缝，表明 2010 年以后甲烷排放量增加主要是由于地下气流（渗流）加剧. 深部气压和断层渗透率的变化可能是由该地区的多次地震引起的，可能起到了一定的作用。我们估计，如果类似的排放因子短期变化发生在全球大渗流区，全球地质甲烷排放量可能会发生显着变化，从而导致大气甲烷收支的十年变化。表明甲烷排放的增加主要是由于 2010 年后地下气体流动（渗流）的加剧。深部气压和断层渗透率变化可能是由该地区的多次地震引起的。我们估计，如果类似的排放因子短期变化发生在全球大渗流区，全球地质甲烷排放量可能会发生显着变化，从而导致大气甲烷收支的十年变化。表明甲烷排放的增加主要是由于 2010 年之后地下气体流动（渗流）的加剧。深部气体压力和断层渗透率变化可能是由该地区的多次地震引起的。我们估计，如果类似的排放因子短期变化发生在全球大渗流区，全球地质甲烷排放量可能会发生显着变化，从而导致大气甲烷收支的十年变化。