Summary Genetic markers and geochemical assays of microbial nitrogen cycling processes, including autotrophic and heterotrophic denitrification, anammox, ammonia oxidation, and nitrite oxidation, were examined across the oxycline, suboxic, and anoxic zones of the Cariaco Basin, Venezuela. Ammonia and nitrite oxidation genes were expressed through the entire gradient. Transcripts associated with autotrophic and heterotrophic de...

Particles able to settle distances of approximately a meter in 1–2 h are undersampled in water traditionally collected in Niskin bottles. Gardner (Limnol Oceanogr, 22, 764–768, 1977) demonstrated that particles sink into the space below the spout of Niskin bottles on timescales relevant to sample processing. We examined this effect on measurements of microbial abundance, community composition, and transparent stainable particl...

Distributions of bacterial populations in the anoxic Cariaco Basin were studied over 2 yr (five cruises) at three stations using fluorescence in situ hybridization (FISH) and terminal restriction fragment length polymorphism (T‐RFLP) of 16S ribosomal ribonucleic acid (rRNA) genes. FISH results demonstrate that the contribution of ɛ‐proteobacterial abundances to total prokaryotic inventories was relatively constant among cruise...

We examined variations in organic carbon (OC) pools and microplanktonic carbon fluxes at three stations in the Hudson River estuary during 12 cruises between Octobers of 1996 and 1998. Phytoplankton biomass and net primary production varied from 5 to 40 µmol C L −1 and 0.3 to 318.3 mmol C m −2 d −1 , respectively. Biomass and production of bacterioplankton in the surface layer commonly exceeded those of phytoplankton, varying...

Acetate oxidation frequently has been used as proxy of organic carbon decomposition in marine anoxic sediments. However, the importance of acetate uptake in carbon cycling in marine anoxic water columns is less well studied. Acetate concentrations and uptake rate constants, together with total bacterial numbers, primary and chemoautotrophic production rates, and particulate organic carbon (POC) fluxes, were measured in the wat...

During the CARIACO time series program, microbial standing stocks, bacterial production, and acetate turnover were consistently elevated in the redox transition zone (RTZ) of the Cariaco Basin, the depth interval (~240–450 m) of steepest gradient in oxidation‐reduction potential. Anomalously high fluxes of particulate carbon were captured in sediment traps below this zone (455 m) in 16 of 71 observations. Here we present new e...

A number of workers have suggested that rates of acetate cycling in sediments may approximate the rates of anaerobic decomposition of organic matter. However, few studies have examined whether this relationship holds over very short time scales, such as those encountered during the deposition of the spring bloom into coastal sediments. In this study, we measured acetate concentrations and uptake rate constants in surface and b...