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 i s presented. This instrument allows in situ injections of radiolabeled sulf ate into six enclosed sediment cores to determine sulfate reduction rates t o 60 cm sediment depth. In order to correct for possible artifacts caused b y decompression and rise in ambient water temperature during ascent and rec overy of the instrument, one set of three cores was incubated in situ for 2 0 h, whereas another set was injected shortly before the ascent. The turnov er 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 sedim ent cores from a coastal marine sediment. The results of a deployment at 15 5 m in the Gotland Basin, Baltic Sea, are presented. Sulfate reduction rate s 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 incubation s match well, showing slightly higher rates in the laboratory cores, especi ally in the deeper sediment strata. (C) 1998 Elsevier science Ltd. All righ ts reserved.