Climate relevant trace gases in the Arctic

Feedback effects on cycling pathways of the climatically relevant biogases methane and DMS are likely, with DMSP catabolism in high latitudes possibly contributing to a warming effect on the earth’s climate through increasing production of the greenhouse gas, methane.

In aerobic surface water methane production may occur as a rapid response to environmental perturbations during the shift from a phytoplankton bloom to an oligotrophic system and is directly linked to the N, P and C cycles. Nitrate exhaustion is a primary requirement for methane production in aerobic water. A second pre-condition in the high latitudes is the phosphate excess, which is utilized as a P source by bacteria. Where phosphate is available as a source of P, methylated compounds like DMSP and its degradation products may serve as the bacterial C source.

DMSP is an abundant methylated substrate in the surface ocean and large amounts are produced annually by phytoplankton. DMSP can be degraded by a cleavage and a demethylation pathway. The best known cleavage product of DMSP is DMS (dimethylsulfide). DMS escapes partly to the atmosphere where it is the most important natural climate-cooling gas, counterbalancing the effect of greenhouse gases. Most of the dissolved DMSP, however, is sequentially demethylated. Aerobic as well as anaerobic demethylation pathways are known to provide bacteria with energy and carbon sources for biosynthesis. An intermediate product of both pathways is methanethiol. Methanethiol may serve as precursor for methane formation.

During a regenerated production, when a combination of these specific nutrient limitations exists, methane may be a metabolic by-product and its production could yield energy even under aerobic conditions. The metabolic activity (respiration) of unicellular organisms explains the presence of anaerobic conditions in the cellular environment.