Page 106 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

Chapter 5. Early Holocene carbon storage and microbial activity in North Sea peats
Methane sampling
The analysis of submerged peats followed standard protocols for headspace sampling and analysis in marine sediments based on (Reeburgh 2007) Reeburgh and described further elsewhere (Egger et al. 2015, 2017). Peat was recovered at all sites, except Easting Down, Stormvogel, and Darci’s site. The seismic signal at the Easting Down and Stormvogel sites indicated a peat layer. However, the layers were beyond the range of the vibrocorer, and contained a peat-like gyttja (compact organic matter accumulated on the floor of an inland water body), at the Easting Down and Stormvogel sites, respectively.
Prior to coring, the core liner was pre-drilled with 2-cm diameter holes at 10-cm resolution and taped to be gastight. Upon retrieval, the top and bottom of the core were stoppered immediately. Working with speed, custom-made metal syringes were inserted into each taped hole. Ten millilitres of wet sediment was extracted and deposited into a 65-ml glass bottle filled with saturated NaCl solution. Each bottle was sealed with a black rubber stopper and a screw cap and stored upside down.
In the laboratory, the CH4 bottles were prepared for CH4 analysis. Ten millilitres of N2 was injected into each CH4 bottle (with a needle inserted through the septum, allowing excess water to escape) to create a headspace. From this headspace, a subsample was collected with a gas- tight syringe. Methane concentrations were determined after injection into a Thermo Finnigan TRACETM gas chromatograph (Flame Ionization Detector) at Utrecht University. The concentrations reported here were calculated using the measured sediment porosity (cm3 per cm3).
Sediment analysis
Sub-samples for loss on ignition (LOI) analysis were taken at the eight sites corresponding to the sites of the molecular analyses. Sub-sampling was performed at 2-cm resolution within peat layers and 10-cm resolution in non-peat layers. Organic matter (OM) content (in %) was measured using a Leco® TGA701 Thermogravimetric Analyzer at Vrije Universiteit Amsterdam. Dried samples were weighed, burned at 330°C and 550°C, and weighed again to calculate the mass loss (%). Fixed-volume sub-samples (42.39 cm3) were taken to measure volumetric water content, bulk density, and porosity. These samples were saturated with deionized water, weighed, dried at 60°C for five days, and then re-weighed. The volume of the
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