Methane Changes in the Wetlands of Beringia

The mouth of the Noatak River where it joins Kotzebue Sounds and the Chukchi Sea. USGS/Mike Records

Greenhouse gases like carbon dioxide and methane are important components of Earth’s climate. Over the past 20,000 years, the concentration of methane in the atmosphere has undergone dramatic changes, but their causes are not entirely clear. One change that has occurred is deglaciation, or the loss of glacial cover, since the Last Glacial Maximum. As glaciers and ice sheets receded, lakes and peatlands formed, both of which are important sources of methane to the atmosphere. In this study, researchers at the National Park Service, U.S. Geological Survey, and several universities studied a different cause of atmospheric methane changes: sea-level rise, inundation of soils, and the formation of coastal wetlands in Beringia. To study this process, the authors modeled sea-level rise and changing wetland area over the past 20,000 years. Using present-day measurements of methane release to the atmosphere, they estimated past contributions of methane as coastal wetland area expanded with sea-level rise. Findings from this study indicate that Beringian coastal wetland formation was an major source of methane to the atmosphere. These findings have important implications, indicating that future sea-level rise may also impact the methane concentrations in Earth’s atmosphere.

Abstract

Atmospheric methane (CH4) concentrations have gone through rapid changes since the last deglaciation; however, the reasons for abrupt increases around 14,700 and 11,600 years before present (yrs BP) are not fully understood. Concurrent with deglaciation, sea-level rise gradually inundated vast areas of the low-lying Beringian shelf. This transformation of what was once a terrestrial-permafrost tundra-steppe landscape, into coastal, and subsequently, marine environments led to new sources of CH4 from the region to the atmosphere. Here, we estimate, based on an extended geospatial analysis, the area of Beringian coastal wetlands in 1000-year intervals and their potential contribution to northern CH4 flux (based on present day CH4 fluxes from coastal wetland) during the past 20,000 years. At its maximum (∼14,000 yrs BP) we estimated CH4 fluxes from Beringia coastal wetlands to be 3.5 (+4.0/-1.9) Tg CH4 yr−1. This shifts the onset of CH4 fluxes from northern regions earlier, towards the Bølling-Allerød, preceding peak emissions from the formation of northern high latitude thermokarst lakes and wetlands. Emissions associated with the inundation of Beringian coastal wetlands better align with polar ice core reconstructions of northern hemisphere sources of atmospheric CH4 during the last deglaciation, suggesting a connection between rising sea level, coastal wetland expansion, and enhanced CH4 emissions.

Fuchs, M., M. Jones, E. Gowan, S. Frolking, K. W. Walter Anthony, G. Grosse, B. Jones, L. Brosius, J. A. O’Donnell, and C. Treat. 2024.

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