Page 103 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

The establishment of a peatland ecosystem in Late Pleistocene North Sea basin began with a birch dominated woodland, impacted by carr vegetation due to paludification and followed by the presence of Chenopodiaceae due to marine inundation (Wolters, Zeiler and Bungenstock 2010). The period of succession spanned 1,300 years (Wolters, Zeiler and Bungenstock 2010).
A high degree of peatland plant community variability results from the highly heterogeneous, irregular, and micro-ecosystem nature of peatlands (Clymo, Turunen and Tolonen 1998). It is likely that concurrent sea level-independent paludification occurred in isolated topographic features (e.g. local pools, valleys, streams), impacting local vegetation succession. The vegetation description of Wolters et al. (2010) is primarily based on pollen analysis, representative of regional-scale changes. To establish an understanding on the degree of variability between sites, more research is needed to compare the results of the Wolters et al. (2010) site with other locations in the North Sea basin.
Despite extensive efforts to map basal-peats at the global scale in recent decades (Xu et al. 2018; Treat et al. 2019), the task of measuring CH4 stores remains challenging (Dean et al. 2018). Seismic surveys indicate stores of naturally occurring biogenic CH4 within the North Sea basal-peat deposits (Missiaen et al. 2002), but the presence of CH4 in the widespread basal- peat deposits has not been confirmed or quantified by in situ observations. Consequently, these deposits are omitted from the global accounting of C and CH4 budgets of marine sediments (Saunois et al. 2019).
In most North Sea surface waters, CH4 concentrations are typically <0.005 μM L−1 (Niemann et al. 2005; Borges et al. 2016). However, much higher CH4 concentrations (1.1 μM L−1), among the highest in the world, are observed in the southern North Sea water column off the coast of Belgium (Borges et al. 2016). The release of CH4 from blowout craters linked to gas exploration could contribute to the high CH4 concentrations in the water column in the North Sea (Schneider von Deimling et al. 2015a; Steinle et al. 2016), but the basin-scale impacts are uncertain (Rehder et al. 1998). The basal-peat deposits that are widespread beneath the seafloor may be an important source of basin water CH4.
Microbial activity plays a large role in the biological CH4 cycle and is estimated to be responsible for reducing annual seabed CH4 emissions to the atmosphere by 1–35 Tg CH4
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