Pyrolysis–GC–MS to trace terrigenous organic matter in marine sediments: a comparison between pyrolytic and lipid markers in the Adriatic Sea

Abstract

The effectiveness of semiquantitative pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS) as a rapid analytical technique for sourcing continental organic matter (OM) in marine sediments was examined by comparison with classical GC–MS analyses of solvent extractable lipid markers. Py–GC–MS was directly applied to HCl/HF de-ashed surface sediment samples collected in five stations located in north western Adriatic Sea. The resulting pyrolysates were characterised by compounds indicative of different biological precursors (e.g. proteins, carbohydrates, chlorophylls), including lignin methoxyphenols diagnostic for continental inputs. The relative abundance of pyrolytic markers was compared to the distribution of n-alkanes, n-alkanols and sterols extracted from the same sediments and determined by GC–MS analyses. For each class of molecular indicators, the terrigenous to aquatic ratio (TAR) was determined as follows: relative abundance of methoxyphenol/protein markers (TAR PY), concentration ratios of (C27 + C29 + C31)/(C15 + C17 + C19) n-alkanes (TAR HC), (C26 + C28+ C30)/(C14 + C16) n-alkanols (TAR AL) and sitosterol/cholesterol (TAR ST). A positive correlation was found between TAR PY and both TAR HC and TAR AL indicating a decreasing contribution of land-plant-derived materials seaward in two investigated transects. TAR ST values displayed a different trend suggesting a mixed origin for sitosterol. The distribution of TAR PY values was also in good agreement with that of atomic C/N ratios. Considering the complexity of environmental systems (diagenetic alteration, different fractions of OM analysed) the obtained results indicate that the pyrolytic marker approach by Py–GC–MS is valuable for sourcing marine OM on a semiquantitative base, providing data consistent with GC–MS determinations of lipid markers and elemental bulk analyses.