Molecular characterization of suspended and sedimentary organic matter in an Arctic delta

Abstract

Curie‐point pyrolysis‐gas chromatography (CuPy‐GC) and Curie‐point pyrolysis‐gas chromatography‐mass spectrometry (CuPy‐GC‐MS) were used to characterize the macromolecular organic content of suspended particles in surface waters, at intermediate water depths, and in the surface sediments of the Lena delta and the adjacent Laptev Sea, eastern Siberia. The chromatograms of the pyrolysates of the Lena River particles revealed several compound classes of biogenic significance: polysaccharides, phenolic substances, and lipid constituents of higher plants. The pyrolysates of the surface‐suspended particles of the Laptev Sea suggested mixed inputs. Some fatty acids, phytadienes, and n‐alkylnitriles were assigned to planktonic organisms. Pyrolysis products from terrigenous material encountered in the river were also present. At intermediate water depths, major differences with respect to the surface particles were evident. In all cases we observed a substantial decrease of the precursors of phytadienes and the fatty acids that undergo biotransformation processes. A peculiar pattern of three series of C14, C16, and C18 alkanes and alkenes [normal alkane, the alk‐1‐ene, the (E)‐alk‐2‐ene, and the (Z)‐alk‐2‐ene] was the prominent feature of these pyrolysates. Further investigations of the particle solvent extract and the corresponding residue suggested that these alkenes, as well as the fatty acids, derived from wax esters. The composition of the sedimentary material in the Laptev Sea indicated preservation of the refractory terrigenous constituents. However, the presence of some algal constituents suggested that a fraction of marine‐derived macromolecules is resistant to degradation.