Methane Sources and Fate in Two Different Arctic Marginal Seas

甲烷是一种强有力的温室气体，来自北极边缘海的海洋空气通量在气候、地缘政治和社会方面发挥着重要作用，但仍然是海洋科学中最具争议性的话题之一。最近对北极地区的一项评估确定了数以千亿吨(1 GT=1015克)的储存碳，这些碳被锁在永久冻土、石油和天然气储量中，并可能存在于天然气水合物中。考虑到与全球平均气温相比，北极温度上升的速度更快，这些沉积物可能构成未来100年气候变化的重要温室气体排放。然而，排放的速度和增加大气甲烷负担的可能性仍然很难预测。因此，位于符拉迪沃斯托克伊利切夫太平洋海洋研究所的Renat Shakirov博士和位于不来梅大学地球科学系的Susan Mau博士计划开展一项合作研究工作。我们建议确定和比较两个不同的北极边缘海：巴芬湾和东西伯利亚海的甲烷来源和命运。巴芬湾是一个超过1000米深的盆地，位于格陵兰冰盖以西，冰川从那里流入大海。相比之下，东西伯利亚海是一个几十米深的宽阔陆架区域，位于近海陆地上，以永久冻土和冻土带为标志，河流从那里将负荷带入大海。这两个地区都季节性地被冰覆盖，并在过去30年中显示出类似的海冰覆盖和表面变暖的变化。我们假设，在不久的将来，浅海陆架环境中的甲烷循环比冰川覆盖陆地附近地区更容易受到全球气候变化的影响。为了验证这一假设，我们计划了两次探险，一次是德国合作伙伴组织的巴芬湾探险，另一次是俄罗斯同事组织的东西伯利亚海探险。在这两次航行中，我们打算1)调查沉积物上部米处的轻烃(C1-C4)和有机质，2)绘制气泡排放、溶解甲烷羽流和水柱中的微量元素图，3)测量甲烷海-空气通量，4)确定微生物甲烷周转率和与沉积物和水柱中甲烷循环有关的微生物群落。这些数据将使我们能够确定1)进入两个边缘海的甲烷的主要来源(生源和热源，与煤或地下水排放有关)，2)目前在沉积物中产生了多少甲烷，以及3)甲烷海-气通量是否由于海底波动的气泡排放或由于水柱中好氧微生物甲烷氧化速率的不同而变化。这项定量基线研究将增加有价值的数据，以克服北极甲烷循环中的重大不确定性，并可能表明在调查时哪种边缘海可能更受全球变暖的影响。

The sea air flux of methane, a potent greenhouse gas, from the Arctic marginal seas plays a significant climatic, geopolitical, and social role, but remains one of the most debated topics in ocean sciences. A recent assessment of the Arctic region identified thousands of gigatonnes (1 Gt = 1015 g) of stored carbon, locked in permafrost, oil-gas reserves, and likely in gas hydrates. Considering the faster increase of Arctic temperatures compared to the global average these deposits may constitute important greenhouse gas emissions due to the climate change in the next 100 years. However, the rate of the release and the likelihood to add to the atmospheric methane burden remains difficult to predict. Therefore, Dr. Renat Shakirov located at V.I. Il’ichev Pacific Oceanological Institute, Vladivostok and Dr. Susan Mau situated at the Department of Geosciences at the University of Bremen plan a collaborative research effort. We propose to identify and compare methane sources and fate in two different Arctic marginal seas: Baffin Bay and East Siberian Sea. Baffin Bay is a more than thousand meter deep basin located west of the Greenland ice sheet from where glaciers discharge into the sea. In contrast, the East Siberian Sea is a several tens of meter deep broad shelf region situated offshore land that is marked by permafrost and tundra from where rivers carry their load into the sea. Both areas are seasonally ice covered and show similar changes in sea ice cover and surface warming in the last thirty years. We hypothesize that the methane cycle in the shallow marine shelf setting is more susceptible to global climate change than the area near glacier-covered land in the near future. In order to test the hypothesis, we plan two expeditions, one to the Baffin Bay organized by the German partners and one to the East Siberian Sea organized by the Russian colleagues. During both cruises, we intend to 1) investigate light hydrocarbons (C1-C4) and organic matter in the upper meters of the sediment, 2) map bubble emissions, dissolved methane plumes, and trace elements in the water column, 3) measure the methane sea-air flux, and 4) identify microbial methane turnover rates and the microbial community associated with the methane cycle in the sediment and the water column. These data will allow us to identify 1) the predominant source of methane to the two marginal seas (biogenic versus thermogenic, associated with coal or groundwater discharge), 2) how much methane is currently generated in the sediment, and 3) if methane sea-air flux varies due to fluctuating bubble emissions from the seafloor or due to different rates of aerobic microbial methane oxidation in the water column. This quantitative baseline study will add valuable data to overcome the significant uncertainties in the Arctic methane cycle and might indicate what kind of marginal sea might be more affected by global warming at the time of investigation.