Hydrothermal vent fluids were sampled with a pumped flow-through system with PFA sampling bottles (Kiel Pumping System KIPS) by the ROV QUEST. Fuid chemical parameters were determined immediately after sample recovery. Ph was measured at 20°C in unfiltered sample aliquots. Sulfide concentrations were measured colorimetrcally following the methylene blue method. Fe(II) and Fe(III) was measured colorimetrically with the phenantroline assay. Total Fe was measured by reducing all Fe(III) to Fe(II) with ascorbic acid. Fe(III) was calculated from the diffrence between Fe(II) and total Fe. Light dissolved hydrocharbons were analysed on board applying a purge and trap technique. Dissolved hydrogen was mesured onboard by a GC equipped with a PDD. Stable carbon isotope signatures of methane were analysed using coupled gas chromatography-combustion-isotope ration mass spectrometry. The abundance of bacterial and archaeal taxa was investigated by sequencing of the 16S rRNA gene. The diversity of the cbbL, cbbM and aclb was investigated by sequencing of the genes.

Sequence data have been submitted to DDBJ/EMBL/GenBank databases under accession numbers, see data table.