CARBON-ISOTOPE COMPOSITION OF INDIVIDUAL N-ALKANES IN RECENT SEDIMENTS

Carbon isotope composition of individual long-chain n-alkanes from Tokyo Bay sediments (a 3 m-core sample and surficial sediment samples) was determined by using gas chromatography/isotope ratio mass spectrometry (GC-IRMS). DeltaC-13 values for C27-C33 n-alkanes in shallow (0-40 cm in depth, present-1965 AD) sections range from -31.5 to -28.2 parts per thousand, showing even carbon number n-alkanes being isotopically heavier than the co-occurring odd n-alkanes. C27-C33 n-alkanes in the deep sections (70-220 cm in depth) have the deltaC-13 values ranging from -29.6 to -32.9 parts per thousand (average value: 31.2 +/- 0.7 parts per thousand), with no isotopic differences between odd and even numbered n-alkanes. The results for n-alkanes in shallow sediments are satisfactorily explained by a two end-member mixing model of indigenous higher plant wax n-alkanes with n-alkanes from oil pollution. The onset of significant levels of pollution in Tokyo Bay was between 1960 and 1965.