A benthic lander for tracer studies in the sea bed: in situ measurements of sulfate reduction

A new benhic lander for in situ tracer studies to a water depth of 6000 m is presented. This instrument allows in situ injections of radiolabeled sulfate into six enclosed sediment cores to determine sulfate reduction rates to 60 cm sediment depth. In order to correct for possible artifacts caused by decompression and rise in ambient water temperature during ascent and recovery of the instrument, one set of three cores was incubated in situ for 20 h, whereas another set was injected shortly before the ascent. The turnover of sulfate in the latter was subtracted from the first set to calculate the true in situ rates. This approach was tested in the laboratory on sediment cores from a coastal marine sediment. The results of a deployment at 155 m in the Gotland Basin, Baltic Sea, are presented. Sulfate reduction rates were measured to a sediment depth of 40 cm both in situ by the lander and in parallel onboard the ship. Results of in situ and laboratory incubations match well, showing slightly higher rates in the laboratory cores, especially in the deeper sediment strata.