Analytical pyrolysis of suspended particulate organic matter from the Black Sea water column

Abstract

Abstract The chemical composition of suspended particulate organic matter (SPOM) in the Black Sea water column has been characterized by pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS). The results are discussed in terms of the hydro-chemical properties of the water column. Phytoplankton cultures grown in the lab also were analyzed to provide reference information for the euphotic zone SPOM. The composition of SPOM in the Black Sea displays important vertical variations dependent on specific distinct biochemical processes in the water column. Identical pyrolysis markers indicative for proteins, lipids, carbohydrates and chlorophylls were obtained from SPOM in the euphotic zone of the Black Sea and the phytoplankton cultures. Nevertheless, the relative contribution of lipids and carbohydrates to Black Sea SPOM was higher than in phytoplankton cultures. The lipid to protein ratio throughout the water column seems to determine the C/N ratio of SPOM. Below the oxycline, the relative contribution of proteins to the SPOM pool increased while the lipid content of the SPOM decreased. The protein composition changed substantially in the suboxic/anoxic transition zone, as expressed by the increase in pyrrole/indole ratio. Elemental sulfur was observed in particulates suspended at the upper anoxic zone, and the relative intensity of the S8 peak varied regionally with more intense multi-peaks in SW shelf-break station, in agreement with the lateral flux of O2. Sulfur-containing organic compounds (e.g. thiophenes), including organic polysulphides (e.g. 1,2-dithiole-3-thiones) were detected in some deep anoxic samples, indicating that sulphurization of organic matter may be active in the water column.