DMS/P/O cycling

• Page authors: PRIMO
• Responsible curator: Hagen Buck-Wiese

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DMS/DMSP/DMSO cycling rates
Approach: isotope dilution with deuterated DMS/DMSP/DMSO standards; GC-MS detection
Context: in situ
Spatial scale: point sample
Temporal scale: 4–12 h
Units: nM d-1; rate constants h-1 or d-1
Community captured: all
Co-measurements: (none specified in inventory)

Method Overview

Turnover rates among dimethylsulfoniopropionate (DMSP), dimethylsulfide (DMS), and dimethylsulfoxide (DMSO) are measured by isotope dilution. Deuterium-labelled standards (e.g., D₃-DMSO, D₆-DMSP) are added to seawater samples, and the rate of label appearance in product pools (e.g., D₃-DMS from DMSO reduction) is tracked by GC-MS over a time course. Because the biological transformations process both labelled and unlabelled substrate simultaneously, the rate of label dilution (or appearance in the product pool) provides a direct measure of gross transformation rates. Both production and consumption of each compound can be quantified by combining multiple tracer experiments.

Scale of measurement

Point samples from 4–12 h incubations in sealed serum vials to prevent DMS outgassing during the experiment.

Data generated

First-order turnover rate constants (h^-1 or d^-1) and gross production/consumption rates (nM d^-1) for DMS, DMSP, and DMSO. These constrain the sulfur mass balance and the contribution of biological processes to sea-to-air DMS flux.

Units & currency

Units are nM d^-1 (rates) or h^-1 / d^-1 (rate constants). The currency is sulfur metabolite (DMS, DMSP, or DMSO).

Sample size

Typical samples are < 200 mL in volume.

Limitations

The method assumes that intracellular and dissolved pools are at steady state during the incubation, and that the added deuterated standard equilibrates rapidly with the endogenous substrate pool. Bottle and incubation artifacts can alter the biological activity and DMS outgassing relative to in situ conditions. For field studies, it is currently uncertain whether measured rates are representative of the whole community or only specific taxa active under the incubation conditions.

Example Applications & Protocols

Classic examples

• Asher et al. (2016) Processes driving seasonal variability in DMS, DMSP, and DMSO concentrations and turnover in coastal Antarctic waters

Common calculations/conversions

• Gross production rate = (dP_labelled/dt) / f_labelled; where P_labelled is the concentration of labelled product and f_labelled is the labelled fraction of the precursor pool.