Esterase and dehydrogenase activities were determined in depth profiles of sediments from the south-east Atlantic using fluorometrtc methods. The sensitivity of both methods was sufficient to record enzymatic activities in deep-sea clay and foraminiferous sand. Depending on water depth and location, significant differences between the depth profiles of enzyme activities could be determined. They appear to be dependent on the organic-matter input from sedimentation. Conclusions about the mode of microbial degradation of organic matter (oxic, anoxic, type of electron acceptors) are possible, using suitable chemical parameters. Under oxic conditions (Eh > 200 my) it was possible (using the method developed for dehydrogenase activities) to determine depth profiles similar to those of the esterase activities. Under suboxic or anoxic conditions, an appropriate separation between biological (dehydrogenase activity) and chemical resazurin reduction was not possible.

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