Abstract
Abstract. Northern latitude peatlands act as important carbon sources and sinks, but little is known about the greenhouse gas (GHG) budgets of peatlands that were submerged beneath the North Sea during the last glacial–interglacial transition. We found that whilst peat formation was diachronous, commencing between 13 680 and 8360 calibrated years before the present, stratigraphic layering and local vegetation succession were consistent across a large study area. Large carbon stores were measured. In situ methane (CH4) concentrations of sediment pore waters were widespread but low at most sites, with the exception of two locations. Incubation experiments in the laboratory revealed molecular signatures of methanogenic archaea, with strong increases in rates of activity upon methylated substrate amendment. Remarkably, methanotrophic activity and the respective diagnostic molecular signatures could not be detected. Heterotrophic Bathyarchaeota dominated the archaeal communities, and bacterial populations were dominated by candidate phylum JS1 bacteria. In the absence of active methanogenic microorganisms, we conclude that these sediment harbour low concentrations of widespread millennia-old CH4. The presence of large widespread stores of carbon and in situ methanogenic microorganisms, in the absence of methanotrophic microorganisms, holds the potential for microbial CH4 production if catalysed by a change in environmental conditions.
Highlights
The expansion and submersion of northern latitude peatlands play a key role in global methane (CH4) and carbon (C) cycles (e.g. Charman et al, 2013; Morris et al, 2018)
High CH4 concentrations in surface waters of continental shelves are due to CH4 inputs from estuaries and seafloor sediments, where methanogenesis is fuelled by high organic matter (OM) sedimentation (Carr et al, 2018; Zhuang et al, 2018)
To provide a better understanding of submerged basal peats and their role in the global C, CO2, and CH4 cycles, we present in situ CH4 concentrations and OM content of North Sea basal peat deposits
Summary
The expansion and submersion of northern latitude peatlands play a key role in global methane (CH4) and carbon (C) cycles (e.g. Charman et al, 2013; Morris et al, 2018). At the time of the Last Glacial Maximum (LGM), peatlands stored 600 000 Tg C worldwide (Yu et al, 2010). This estimate is calculated using ocean-basin-scale peat layer thickness and depth. Continental shelves and deltas are important sinks within the global carbon cycle (Oppo et al, 2020; Saunois et al, 2020) and are responsible for 80 %–85 % of oceanic carbon sequestration (Muller-Karger et al, 2005). Reducing the uncertainties in these estimates requires further work at both regional and global scales (Oppo et al, 2020; Saunois et al, 2020). Methane entering the water column from the seafloor arrives by ebullition and pore water diffusion and is of either biogenic or thermogenic origin
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