Degradation and Preservation of Organic Matter in Marine Macroaggregates

Solid-state 13 C NMR and FTIR spectroscopy were applied to establish the chemical features of bulk mucous macroaggregates of phytoplanktonic origin at two different depths, surface and bottom, in the Gulf of Trieste (northern Adriatic Sea) in June 2000. The bottom sample was poor in organic matter (5% C org , 0.5% N tot ) compared to the surface sample (17.2% C org , 1.2% N tot ) and contained mostly senescent and degraded cells. An increase in mineral particles (quartz and calcite) was also evident. This was due to the degradation of the organic fraction and the contribution of bottom sediment resuspension. The 13 C-NMR–based estimate showed the approximate composition of sampled macroaggregates: 26% aliphatic C, 14% O/N alkyl structures, 39% carbohydrates, 15% aromatic and olefinic C and 6% ester and/or amide C. The solid-state 13 C NMR spectrum of the sedimented macroaggregate revealed the preservation of aliphatic (lipidic) material and a portion of the labile nitrogencontaining compounds.