Toward Resolution of Imbalance between Microbiological Energy Demand and Supply to Cariaco's Redoxcline: Horizontal Productivity Gradients

The Cariaco Basin's redoxcline or transition zone between oxic and anoxic waters typically resides between 250 and 450 m and hosts anomalously high microbiological production. At Station CARIACO, chemoautotrophic bacterial production in the redoxcline on average represents 70% (median) of local primary production in surface waters (upper 100 m). Presumably chemoautotrophs are fueled by inorganic end products (reduced S species, NH₄^{ +}, CH₄, H₂) supplied by remineralization of residual surface production in the Basin's interior. However, less than 10% of local surface production (in C units) sinks to the redoxcline. Simple 1-D mass balance calculations based on measurements from our time-series station demonstrate that <10% of chemoautotrophs' demands for reductant (energy) can be met by local vertical flux of biogenic debris. Both temporal and spatial variability in chemical and biological processes are likely to be important in creating this perceived imbalance. We hypothesize that enriched, non-local sources of reductant are advected in bottom waters to support higher-than-expected chemoautotrophic production at Station CARIACO. Four years of SeaWiFS ocean color satellite imagery clearly demonstrate that mean annual primary production is significantly higher east of Station Cariaco and that seasonal blooms propagate westward. Using SeaWiFS images and published algorithms, we will estimate local and basin-wide production and organic sedimentation based on bathymetry and flux models. From accepted diagenetic models and biological stoichiometries, we will estimate potential reductant production and requisite transit velocities required to balance observed biological demand.