REDUCING MICROZONES AND SULFIDE PRODUCTION IN MARINE SNOW

Using tetrazolium salts we tested the hypothesis that reducing microzones can form within detrital aggregates (i.e. marine snow). Even when the ambient waters were well oxygenated, patches of reduced tetrazolium salts were found in marine snow indicating that strongly reducing microzones were present in these aggregates. Further, in both laboratory-made and field-collected marine snow we found measurable amounts of sulfide. Sulfide was present in marine snow on 9 out of 10 sample dates and the sulfide concentration within marine snow ranged from 1.3 to 25 mumol S l-1. On only 1 out of 10 dates was sulfide detected in the oxygenated waters surrounding the aggregates. The sulfide in the marine snow was probably produced by anaerobic microbes in the reducing microzones in the marine snow. Our data suggest that the paradoxical production of sulfide in aerobic water columns is probably due to production within anoxic microzones within marine snow.