Characterization of sinking particles in the ocean by pyrolysis-gas chromatography/mass spectrometry

Abstract

Pyrolysis-gas chromatography/mass spectrometry was applied to the study of the composition, source and chemical changes of organic matter in sinking particles, as part of efforts towards the understanding of the transport processes of organic carbon from surface waters to the sea-floor. Sinking particle samples were collected using sediment traps from the Japan Trench (site JT; water depths of 4519 and 8798 m) located in the northern Pacific Ocean. Trap samples from a coastal region of Japan were also analyzed for comparison purposes. The analysis was conducted using a CDS Pyroprobe connected to a gas chromatograph/mass spectrometer. The trap samples produced phenols, aromatic hydrocarbons, nitrogenous compounds, furans, alkenes/alkanes and aliphatic cyanides/fatty acids. These products are largely categorized into three classes of precursor: proteins (nitrogenous compounds such as pyrroles, pyridines, phenylalkyl nitriles and indoles), carbohydrates (furan derivatives) and lipids (alkenes/alkanes, alkyl nitriles/fatty acids). The degree of freshness (FD), defined as the ratio of pyrolysis product x (where x is pyrrole, indole, pyridine, furfural normalized by the sum of the alkanes and alkenes) in a sample to that in a reference material; or the ratio of a pyrrole/pyridine or alkene/alkane in a sample to that in a reference material, was proposed to characterize the trapped organic matter. The results revealed that the FD of organic matter in sinking particles at site JT varies over time.