Pulses of labile carbon cause transient decoupling of fermentation and respiration in permeable sediments.

Dihydrogen (H) is an important intermediate in anaerobic microbial processes, and concentrations are tightly controlled by thermodynamic limits of consumption and production. However, recent studies reported unusual H accumulation in permeable marine sediments under anoxic conditions, suggesting decoupling of fermentation and sulfate reduction, the dominant respiratory process in anoxic permeable marine sediments. Yet, the extent, prevalence and potential triggers for such H accumulation and decoupling remain unknown.

A GC-IRMS method for measuring sulfur isotope ratios of carbonyl sulfide from small air samples.

A new system was developed for measuring sulfur isotopes δ S and δ S from atmospheric carbonyl sulfide (COS) on small air samples of several liters, using pre-concentration and gas chromatography - isotope ratio mass spectrometry (GC-IRMS). Measurements of COS isotopes provide a tool for quantifying the COS budget, which will help towards better understanding climate feedback mechanisms. For a 4 liter sample at ambient COS mixing ratio, ~500 parts per trillion (ppt), we obtain a reproducibility error of 2.

H clumped isotope measurements at natural isotopic abundances.

Rationale: Molecular hydrogen (H ) is an important gas for atmospheric chemistry, and an indirect greenhouse gas due to its reaction with OH. The isotopic composition of H (δD) has been used to investigate its atmospheric budget; here we add a new observable, the clumped isotopic signature ΔDD, to the tools that can be used to study the global cycle of H .

Methods: A method for determining ΔDD in H was developed using the high-resolution MAT 253-Ultra isotope ratio mass spectrometer (Thermo Fisher).