Collaborative Research: Sea-level rise, coastal wetland expansion, and proglacial lake contributions to abrupt increases in northern atmospheric CH4 during the last deglaciation

这项多学科研究旨在了解在最后一次冰消期（18-8 ka），北半球新被淹没的陆地区域对大气甲烷浓度快速增加的时间、幅度和总体贡献。极地冰芯记录揭示了这一时期大气甲烷浓度的动态增加，但这些甲烷的来源仍有很多争论。本研究将测量来自野外样本的甲烷排放的同位素值，以提供沿海湿地、泥炭地、前冰期湖泊和其他湖泊类型（如热岩溶和后冰期湖泊）自最后一次冰川消退以来的甲烷排放的区域特定估计，并与冰芯记录进行比较。这项研究将重建过去被淹没的冰川消融陆地地区的甲烷排放（可能代表这些时期大气甲烷浓度增加的未知北方来源），并评估它们对极地冰芯记录中观测到的甲烷突然增加的贡献。由于海平面上升、湿地扩张、永久冻土融化和相关湖泊的形成，新被淹没的陆地地区过去的甲烷排放将有助于更好地了解可能在该地区加速的全球气候反馈。这些知识对于回答关于北方系统在全球环境变化中的作用的更大的社会问题以及我们理解海平面上升和沿海洪水的级联效应的能力至关重要。本研究利用(a)北部大陆架地区和沿海湿地被快速消冰海平面上升（SLR）淹没和(b)前冰期湖泊地区被冰川和冰盖融化淹没的综合古生态记录，记录了它们过去对大气甲烷浓度突然增加的贡献。研究目标是：(1)综合新的和现有的陆架、滨海湿地、区域SLR曲线和前冰湖起始数据，重建30？N;(2)通过将新的和现有的甲烷通量整合到一个经验模型中，估算北部沿海淹没区从消耗甲烷的森林和草地地区向高排放的泥滩、沼泽和淡水湿地演变过程中的甲烷通量；(3)分析不同规模、年龄和地理位置的原冰湖新增和现有甲烷通量，建立重建18 ka至今（重点是18-8 ka）原冰湖排放的经验模型；(4)利用甲烷的稳定同位素（∂13C, &#8706；D）和14C定年来限制这些新淹没的陆地地区甲烷通量的大小和时间；(5)利用大气盒模型，将我们基于格陵兰岛和南极冰芯的更高分辨率甲烷同位素（∂13C, &#8706；D, 14C）重建的淹没冰架、沿海湿地和前冰期湖泊过去的甲烷排放和同位素通量与全球大气甲烷约束进行比较。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This multidisciplinary research seeks to understand the timing, magnitude, and overall contribution of newly flooded land areas in the northern hemisphere to rapid increases in atmospheric methane concentrations during the last deglaciation (18-8 ka). Polar ice core records reveal dynamic increases in atmospheric methane concentrations during this period, but the source of this methane remains the subject of much debate. This study will measure the isotopic values of methane emissions from field samples to provide region-specific estimates of methane emissions from coastal wetlands, peatlands, proglacial lakes, and other lake types (e.g. thermokarst and post-glacial lakes) since the last deglaciation for comparisons with ice core records. This research will reconstruct the past methane emissions from flooded deglacial land areas (potentially representing unknown northern sources of increased atmospheric methane concentrations during these periods) and assess their role in contributing to the abrupt methane increases observed in in polar ice core records. Knowledge of past methane emissions from newly inundated land areas flooded by sea level rise, wetland expansion, permafrost thaw, and associated lake formation will provide an improved understanding of global climate feedbacks that will likely accelerate in the region. This knowledge is critical to answering larger societal questions about the role of northern systems in global environmental change and our ability to understand the cascade of effects from sea level rise and coastal flooding.This research uses comprehensive paleoecological records of (a) northern continental shelf areas and coastal wetlands inundated by rapid deglacial sea-level rise (SLR) and (b) proglacial lake areas inundated by glacier and ice-sheet melt to document their past contributions to abrupt increases in atmospheric methane concentrations. The research goals are to: (1) synthesize new and existing shelf, coastal wetland, regional SLR curves, and proglacial-lake initiation data to reconstruct newly inundated areas poleward of 30? N; (2) estimate past methane flux from inundated northern coastal regions as they evolved from methane-consuming forest and grassland areas to higher emitting mudflats, marshes, and freshwater wetlands by integrating new and existing methane fluxes into an empirical model; (3) analyze new and existing methane fluxes from proglacial lakes of different sizes, ages and geographies to build an empirical model for reconstructing proglacial lake emissions from 18 ka to present (with an emphasis on the deglacial period,18-8 ka); (4) use stable isotopes (∂13C, ∂D) of methane and 14C dating to constrain the magnitude and timing of methane flux from these newly flooded land areas; and (5) compare our reconstructions of past methane emissions and isotope fluxes from inundated shelves, coastal wetlands, and proglacial lakes with global atmospheric methane constraints based on recent, higher resolution data of methane isotopes (∂13C, ∂D, 14C) from Greenland and Antarctic ice cores using atmospheric box modeling.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.