Carbon isotope composition of bishomohopanoic acid in Miocene to recent marine sediments from the Nankai Trough (ODP Leg 190, Site 1178)

Abstract

The distribution and carbon isotope composition of 17β(H), 21β(H)-bishomohopanoic acid (ββC₃₂-HA) were investigated in Miocene to recent marine sediments from Site 1178 of ODP Leg 190, Nankai Trough, offshore Shikoku, Japan. The concentration of ββC₃₂-HA tends to be higher in accreted sediments, which are characterized by a large contribution of terrestrial organic matter. The δ¹³C values of ββC₃₂-HA are lighter in accreted sediments than in slope sediments, indicating different sources to some degree. The constant δ¹³C values within the slope sediments and within the accreted sediments indicate that the sources of ββC₃₂-HA were unchanged during the deposition of each unit. In accreted sediments, the δ¹³C value of ββC₃₂-HA is similar to that in soil components, suggesting that the hopanoic acids in accreted sediments may be mainly terrestrial organic compounds derived from the oxidation products of bacteriohopanepolyols on land.