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

点击翻译按钮获取中文摘要

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.