Recent sedimentary hopanoids in the northwestern Pacific alongside the Japanese Islands - their concentrations and carbon isotopic compositions

Two hopanoids, 17 beta>(*) over bar * (H),21 beta>(*) over bar * (29)-hop-2 2(29)-ene (diploptene) and 17 beta>(*) over bar * (H),21 beta>(*) over bar * (H)-bishomohopanoic acid (beta betaC(32)-HA), are the most abundant among the pentacyclic triterpenoids found in Recent sediments of the Pacific Oce an alongside the Japanese Islands. The concentration of diploptene normaliz ed to organic carbon content is higher in sediments where C-37 polyunsatura ted alkene (a biomarker of Haptophytes) is in high concentration, suggestin g that the diploptene may be associated with the accumulation of marine org anic matter. In open marine settings, delta C-13 values of beta betaC(32)-H A range from -23.8 to -19.4 parts per thousand (relative to PDB), being enr iched in C-13 relative to diploptene (-31.6 to -26.3 parts per thousand) by 5-9 parts per thousand. Thr isotopic difference indicates the presence of at least partially different sources for the two hopanoids. While diplopten e is derived from cyanobacteria and chemotrophic bacteria in the water colu mn or sediment, bishomohopanoic acid may be produced mainly by heterotrophs in the sediment using marine organic matter. In contrast, the delta C-13 v alues of the two hopanoids From river and bay sediments are similar (simila r to -31 to -29 parts per thousand), indicating a common source derived fro m soil components (terrestrial plants or bacteria in soils). (C) 2000 Elsev ier Science Ltd. All rights reserved.