| I studied the biogeochemistry, microbial ecology and paleontology of three anoxic environments. In the Black Sea, three studies dealt with the role of particle fluxes in sulfur cycling and microbial ecology. In the water column, iron sulfides form at the oxic-anoxic interface from dissolved sulfide left after chemical oxidation, based on sulfur isotopes; formation in deep water is minimal and iron-limited. Sinking organic aggregates transport iron sulfides to the bottom. Sedimentary sulfides may originate from sulfide fluxes and record intensity of chemical vs. microbial oxidation at the oxic-anoxic interface. Sulfate reduction rates from modelled diagenesis of organic carbon fluxes agree with other measured rates. A box model summarizes sulfur cycling between water column and sediments.; An algal sulfur compound, dimethylsulfoniopropionate (DMSP), precursor to dimethylsulfide (DMS), was measured in deep-sea particle fluxes. DMSP levels in particle fluxes vary seasonally and between oceans. Though DMSP is only 0.005% of organic carbon fluxes, its removal to the deep sea by fluxes may lessen sea-air DMS fluxes. A DMSP-DMS cycle for ocean and sediments is proposed.; A third study compared bacteria biomass and morphology in particle fluxes and water column, using TEM and epifluorescence microscopy. Some bacteria had intracellular structures indicating autotrophy. Concentrations in particle fluxes were high compared to sediment bacteria populations elsewhere, but bacterial carbon is a tiny fraction of total organic carbon. In contrast, phototrophic bacteria dominated a microbial mat in a salt marsh where sulfate reduction is important. Cyanobacteria, purple and green sulfur bacteria species were strongly depth-zoned, and cell sizes decreased as depth increased.; In a fifth study, I investigated spatiotemporal change in a fossil lingulid brachiopod from a suboxic facies, using gradient analyses of benthic invertebrate and planktonic graptolite assemblages. Leptobolus insignis lived in the Taconic trench slope (late Middle Ordovician, Trenton Group, New York). Sizes of growth stages (larval, juvenile, adult) changed over 2-3 my as the oxygen minimum zone fluctuated, probably due to OMZ-related environmental changes and not depth. |
