Microbial activity, methane production, and carbon storage in Early Holocene North Sea peats

Abstract

Abstract. Northern latitude peatlands act as important carbon sources and sinks but little is known about the greenhouse gas (GHG) budget of peatlands submerged beneath the North Sea during the last glacial-interglacial transition. We found that whilst peat formation was diachronous, commencing between 13,680 and 8,360 calibrated years before the present, stratigraphic layering and local vegetation succession were consistent across a large study area. The CH4 concentrations of the sediment pore waters were low at most sites, with the exception of two locations, and the stored carbon was large. 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 be not be detected. Heterotrophic Bathyarchaeia dominated the archaeal communities and bacterial populations were dominated by candidate phylum JS1 bacteria. Although CH4 accumulation is low at most sites, the presence of in situ methanogenic micro-organisms, the absence of methanotrophy, and large widespread stores of carbon hold the potential for GHG production if catalysed by a change in environmental conditions. Despite being earmarked as a critical source of CH4 seepage, seepage from these basal-peat deposits is restricted, as evidenced by low in situ CH4 concentrations.

Biomarker insights into a methane-enriched Holocene peat-setting from “Doggerland” (central North Sea)

“…Recent peats host various microbial groups and this holds also for buried submarine peats like those in the North Sea, which also host microoorganisms executing methane formation and oxidation (Lippmann et al, 2021). However, bottom water directly overlying the peat-containing sites, which are located a few hundreds of meters NNE of the salt dome “Britta” that were investigated in this study, was relatively poor in dissolved methane.…”

“…However, methane concentrations are not elevated in comparison with marine sediments elsewhere and also with other sediments in the central North Sea. Lippmann et al (2021) reported average CH 4 concentrations of sediment pore waters of 2.1 µM at ~2 to 5 mbsf. Irrespective of the different sampling depths applied in the two studies, this difference in methane concentrations suggests that methane in the region NNE of salt dome "Britta" is not much enriched compared to the situation in the broader area.…”

“…Relatively minor studied is, however, the role of peats for methane generation and other microbial processes in the recent North Sea sediments. One recent publication determined the microbial methane turnover and suggested a relatively minor role of peat-associated hydrocarbons for methane seepage in the area (Lippmann et al, 2021).…”