Abstract The Cariaco Basin is the world's largest truly marine anoxic basin. We have conducted a comprehensive multidisciplinary investigation of the water column (42–750 m) bracketing the redox boundary (a 250-m thick “chemocline”) of the Cariaco Basin to evaluate linkages between lipid biomarkers, distributions of major dissolved chemical species, and the microbial community and associated redox processes. Our multidimensional data set includes: hydrography, water column chemistry, microbial distributions and rates, and lipid biomarkers. Multivariant statistical analysis of this data set partitions the investigated water column into 5 distinct zones, each characterized by different chemistries, microbiologies and biomarker compositions. The core of this chemocline is a 25-m thick suboxic zone where both dissolved oxygen and sulfide were below detection limits, bacterial and archaeal cell numbers and the rate of chemoautotrophic (dark) carbon fixation are elevated, and dissolved chemical species and bacterial and archaeal lipid biomarkers are indicative of tightly coupled cycles of carbon, nitrogen, and sulfur through chemoautotrophy.