Abstract The biological sources and distribution of the aliphatic amines, monomethylamine (MMA), dimethylamine (DMA) and trimethylamine (TMA), were studied in the anoxic marine sediments of Flax Pond salt marsh, Long Island, New York. Laboratory experiments demonstrated that Spartina alterniflora releases amines, especially TMA, to salt marsh sediment during decomposition. Benthic animals and phytoplankton also contained high amine concentrations and could be sources of amines to salt marsh sediments either by direct release or during decomposition. MMA, DMA and TMA were present in FP sediment porewaters and solid phases throughout the year. Concentrations generally ranged from 10 nM to 1 μM in porewaters and 1–100 nmol/g dry wt in the solid phase. DMA dominated the porewater profiles, TMA the exchangeable pool, and MMA the fixed pool of amines. Concentrations varied seasonally with highest concentrations found in the fall when S. alterniflora began to senesce. The C/N ratio of organic matter undergoing decomposition in the sediment was calculated to be 11–12 from the annual sulfate reduction and ammonium and ΣCO 2 production rates. This C/N ratio is higher than the Redfield ratio, again suggesting that S. alterniflora is a major organic matter source to the sediment.