Replication Data for: High-resolution underwater laser spectrometer sensing provides new insights into methane distribution at an Arctic seepage site

Abstract: Methane (CH4) in marine sediments has the potential to contribute to changes in the ocean- and climate system. Physical and biochemical processes that are difficult to quantify with current standard methods such as acoustic surveys and discrete sampling govern the distribution of dissolved CH4 in oceans and lakes. Detailed observations of aquatic CH4 concentrations are required for a better understanding of CH4 dynamics in the water column, how it can affect lake- and ocean acidification, the chemosynthetic ecosystem, and mixing ratios of atmospheric climate gases. Here we present pioneering high-resolution in-situ measurements of dissolved CH4 throughout the water column over a 400 m deep CH4 seepage area at the continental slope west of Svalbard. A new fast-response under-water membrane-inlet laser spectrometer sensor demonstrates technological advances and breakthroughs for ocean measurements. We reveal decametre-scale variations of dissolved CH4 concentrations over the CH4 seepage zone. Previous studies could not resolve such heterogeneity in the area, assumed smoother distribution and therefore lacked both details and insights to ongoing processes. We show good repeatability of the instrument measurements, which are also in agreement with discrete sampling. New numerical models, based on acoustically evidenced free gas emissions from the seafloor, support the observed heterogeneity and CH4 inventory. We identified sources of CH4, undetectable with echosounder, and rapid diffusion of dissolved CH4 away from the sources. Results from the continuous ocean laser-spectrometer measurements, supported by modelling, improve our understanding of CH4 fluxes and related physical processes over Arctic CH4 degassing regions.摘要：海洋沉积物中的甲烷（Methane, CH₄）具备引发海洋与气候系统变化的潜力。当前主流标准方法（如声学探测与离散采样）难以量化的物理与生物化学过程，主导着海洋与湖泊中溶解态甲烷的空间分布。为更透彻理解水柱内甲烷的动力学行为、其对湖泊与海洋酸化的影响、化能合成生态系统，以及大气气候气体的混合比，亟需开展水生甲烷浓度的精细化实地观测。本研究针对斯瓦尔巴群岛西侧大陆坡一处水深400米的甲烷渗漏区域，完成了贯穿整个水柱的开创性高分辨率原位测量。一款新型快速响应水下膜进样激光光谱传感器，展现了海洋探测领域的技术革新与突破性进展。研究揭示了甲烷渗漏带内溶解态甲烷浓度存在十米级尺度的空间异质性。过往相关研究未能解析该区域的此类异质性，曾假设其分布更为均一平缓，因此对当前持续发生的地球化学过程，既缺乏细节认知也未获得深入理解。本研究证实该仪器的测量结果具备良好的重复性，且与离散采样的实测数据吻合度较高。基于海底声学证据证实的游离气体排放所构建的新型数值模型，印证了本次观测到的空间异质性与甲烷存量特征。研究识别出回声测深仪无法探测到的甲烷释放源，以及溶解态甲烷从源区快速向外扩散的过程。结合数值模型辅助的连续海洋激光光谱测量结果，本研究深化了对北极甲烷脱气区域甲烷通量及相关物理过程的科学认知。