The chemical composition of Black Sea suspended particulate organic matter: pyrolysis-GC/MS as a complementary tool to traditional oceanographic analyses

A “traditional” description of the abundance and chemical composition of suspended particulate organic matter (POM) in open and coastal waters of the southern Black Sea in June 1996 has been confirmed and extended by pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS) analyses. Py-GC/MS provided depth profiles of the relative concentrations of twenty three marker compounds characteristic of chlorophylls (CHL), lipids, carbohydrates (CBH) and proteins produced by thermal degradation of the POM retained on the filters. No terrestrial markers, characteristic of lignin or of plant waxes, were observed. Evidence was found for considerable changes in the chemical composition of POM in the water column from the surface down to the sulphidic water layer. In surface-mixed layer, both POC:CHL-a ratios and relative abundances of CBH markers were notably high, suggesting that the suspended POM was mainly composed of detritus. The profiles of both CHL and protein markers exhibit coherent maxima at the base of the euphotic zone, coinciding with the nutricline depth in the central cyclonic eddy, where the bulk POM possessed relatively low C:N ratios. Beneath the 0.1% light depth the absence of intact phytoplankton cells and the presence of bacteria and faecal pellets was accompanied by a change in the protein composition of the POM as shown by the changes in the ratio of pyrrole:indole markers. Lipid markers increased markedly from the euphotic zone into the oxycline and remained almost constant in the suboxic waters; they then decreased in the sulphidic interface, presumably due to consumption of lipids by anaerobic bacteria.