Table 1. The geochemical fingerprint of electrogenic sulphur oxidation was observed at three sites in the coastal North Sea under field conditions.

Site name	Coordinates	Dates of sampling	OPD (mm)	DOU (mmol m−2 d−1)	Current density (mA m−2)	O2 consumed by cathodic reaction (%)
RSM, Oosterschelde, The Netherlands	N 51° 26′ 21′′ E 04° 10′ 11′′	22 June 2011 25 February 2013	0.7±0.1 1.3±0.4	30.3±3.6 19.9±2.2	29.9±10.7 7.3±4.0	22.7±10.1 8.2±4.3
Station 130, BCZ	N 51° 16′ 13′′ E 02° 54′ 19′′	10 October 2011 1 March 2013	0.7±0.1 1.2±0.8	32.3±15.0 24.8±20.9	25.2±2.6 4.6±1.8	19.1±7.1 5.3±2.9
MLG, Holpervoet and Den Osse basins, The Netherlands	N 51° 46′ 24′′ E 03° 56′ 16′′	3 November 2011 22 January 2012 24 February 2012	0.9±0.2 1.4±0.4 1.8±0.4	44.1±16.1 13.9±4.1 22.2±9.5	24.8±5.5 16.1±10.4 27.0±16.2	14.0±7.9 29.5±25.3 33.7±30.6
OSF, The Netherlands	N 51° 26′ 52′′ E 04° 05′ 47′′	17 May 2011 15 August 2011	1.6±0.3 1.5±0.3	4.8±1.6 3.5±0.5	NA	NA

Abbreviations: BCZ, Belgian Coastal Zone; DOU, diffusive oxygen uptake across the sediment–water interface; MLG, Marine Lake Grevelingen; OPD, Oxygen Penetration Depth; OSF, Oosterschelde sand flats; RSM, Rattekaai Salt Marsh.

Values indicate means of between 2 and 4 replicate cores. Reported error is standard deviation between replicate cores.