Compound-specific radiocarbon ages of fatty acids in marine sediments from the western North Pacific.

Abstract

Compound-specific radiocarbon analysis of five fatty-acid biomarkers was conducted for marine sediments collected from the western North Pacific. The fatty acids (C (sub 12) to C (sub 34) ) showed a typical bimodal distribution pattern with two maxima at C (sub 16) and C (sub 26) . Their carbon isotopic compositions ranged from -25.1 per mil (C (sub 16) ) to -31.8 per mil (C (sub 28) ), suggesting that they derived from terrestrial higher plants and marine organisms. A large variations of (super 14) C ages were found among the fatty acids detected in the same sedimentary horizon of the core, ranging from 530 BP (C (sub 18) ) to 3250 BP (C (sub 28) ). The results of (super 14) C analysis of fatty acids could be divided into two groups, i.e., lower molecular weight (LMW) fatty acids (C (sub 16) , C (sub 18) ) derived from marine organisms and higher molecular weight (HMW) fatty acids (C (sub 24) , C (sub 26) , C (sub 28) ) derived from terrestrial higher plants. The HMW fatty acids showed older ages, ranging from 2550 BP (C (sub 24) ) to 3250 BP (C (sub 28) ), than LMW fatty acids (530 BP [C (sub 18) ] to 1,820 years BP [C (sub 16) ]). On the other hand, bulk-phase total organic matter (TOM) showed the age of 2260 BP that is between those two groups, suggesting that it was likely a mixture of organic matter derived from marine and terrestrial sources. The compound specific (super 14) C ages and delta (super 13) C data of sedimentary fatty acids presented here could provide useful information to decipher the fate and transport process of terrestrial organic matter to marine sediments.