Anaerobic metabolism and oxygen distribution in the carbonate sediments of a submarine canyon

Abstract

Microelectrodes were used in situ to measure the distnbution of oxygen in the organic- poor, carbonate sediments of a tropical submanne canyon and in selments from a shallow organic- ennched bay Analyses of sulfate reduction nitrogen fixation (acetylene reduction) and several porewatei and bulk sediment parameters were conducted in parallel Oxygen penetration was gener- ally hmited to depths of 5 to 10mm wlth occasional penetration to greater depths related to turbulence in the water column Oxygen supersaturation at the sediment-water interface or at depths of a few millimeters Indicated that benthic photosynthesis contributed in part to the controls of oxygen distnbu- tion Highest rates of sulfate reduchon were usually observed between 1 and 3cm depths Rates of sulfate reduction Integrated over a lOcm interval were hlgher in the bay than canyon sediments which was consistent with differences in organic content There was also a correlation between Integrated rates of reduction and the presence of surface algal films as indicated by chlorophyll concentrations Trends s~mllar to those for sulfate reduction were observed for the distribution of solld-phase reduced sulfur species and for acetylene reduchon