Bioturbation and the early diagenesis of carbon and sulfur

Abstract

The expected amounts of organic matter decomposition and reduced sulfur (mainly pyrite) formation over selected sediment depth ranges have been calculated, from /sup 35/S measurements of in situ rates of sulfate reduction, for four anoxic sediment sites in Long Island Sound. Measured changes over the same depth ranges are found to be less than those calculated, and deviations correlate well with the degree of bioturbational and other enhanced transport activity in the sediment. This means that extra organic matter is added to sediment layers at depth by bioturbation. It also means that the amount of pyrite formed during burial records only a fraction of the total H/sub 2/S produced by bacterial sulfate reduction. The remaining H/sub 2/S is lost via the oxidation of reduced sulfur compounds by O/sub 2/ mixed into the sediment by the benthos and, to a lesser extent, via enhanced H/sub 2/S transport resulting from benthic irrigation. For one unusually organic-rich site (BH), H/sub 2/S loss is also probably due to stripping by upward-moving methane bubbles.