SOURCES AND TRANSPORT OF LIPIDS ON AMAZON CONTINENTAL-SHELF

Dissolved material and recent sediment from the Amazon continental she lf have been analyzed for hydrocarbons to study the sources and potent ial fate of the transported organic matter. Dissolved n-alkanes are pr esent at low concentrations (ppb level) and are dominated by lipids fr om marine phytoplankton with carbon number maxima (C-max) at C-18/C-22 and an even-to-odd carbon predominance < C-30 (CPI17-27 from 0.18 to 0.54). In the sediments, bimodal distributions of n-alkane chain lengt h suggest a mixed input of terrestrial (C-max at C-27/C-29/C-31 and CP I25-33 from 0.75 to 1.82) and phytoplanktonic/microbial (C-max at C-20 and CPI15-33 from 0.38 to 0.62) organic matter. Sesquiterpenes were t he most significant cyclic compounds in all the dissolved samples anal yzed reflecting a contribution from resinous trees to the terrestrial organic pool. On the other hand, enhanced concentrations of these comp ounds in the dissolved phase on the northwest portion of the Amazon sh elf, contrasting with decreased concentrations in the sediment samples , suggest that dissolved lipids are released from solid phase in the i ntensely stirred seabed. Structured organic matter in the sediment has been characterized as being composed of, on average: 19% plant cuticl es, 25% woody tissue, 13% pollens and spores, 24% amorphous material, 7% bituminite and 12% altered organic material.