Variations in the hydrostatic pressure may trigger estuarine full water column anoxia

The present study was motivated by a severe incident of oxygen depletion in Mariager Fiord, Denmark in August 1997 where all living organisms were eradicated from the inner fiord. Multiple regression techniques were used to study natural and human oxygen regulating factors and here we showed that strong oxygen depletion surprisingly was favoured by hydrostatic pressure variations (atmospheric plus water pressure), low biomass and chlorophyll concentrations and less surprisingly, long periods of high temperatures (r2 ¼ 0:93). We understand that radical changes in pressure act as a mechanism that provokes the release of oxygen consuming H2S from the bottom. Secondly we found that high biomass and chlorophyll concentrations contribute to increased oxygen content in the water column through photosynthesis.