DMSP removal and DMSO production in sedimenting particulate matter in the northern North Sea

Work was conducted to establish if the downward flux of sedimenting material represents a sink for particulate dimethylsulphoniopropionate (DMSP) and to investigate the fate of this DMSP within the sedimenting material. Four sediment traps were successfully deployed for a maximum of 24 h in the northern North Sea between the 5th June and the 1st July 1999. After recovery, samples were taken immediately and analysed for levels of dimethylsulphide (DMS), dimethylsulphoxide (DMSO) and DMSP. Any remaining trap material was incubated in the dark at in situ seawater temperature for a maximum of 120 h. Results from the sediment traps showed that only 1% of the DMSP standing stock was lost daily due to sedimentation. However, results from the incubation experiment demonstrated not only that the downward flux of DMSP is underestimated due to its degradation within the trap material, with between 30% and 47% of the DMSP being lost over 48 h, but also that up to 21% of the DMSP lost may be converted to DMSO. These results clearly demonstrate that DMSO is generated within sedimenting material.