Characteristics of hydrocarbons in sediment core samples from the northern Okinawa Trough

Sediment core samples from the northern Okinawa Trough (OT) were analyzed to determine abundances and distributions of hydrocarbons by gas chromatography-mass spectrometer (GC-MS). The results show that the n-alkanes in this sediment core conform to a bimodal distribution, and exhibit an odd-to-even predominance of high molecular weights compared to an even-to-odd predominance in low molecular weight n-alkanes with maxima at C16 and C18. The concentrations of bitumen, alkanes and polyaromatic hydrocarbons (PAHs) were higher in samples S10-07 than all others. Three maturity parameters as well as the ratios between parent phenanthrenes (Ps) and methylphenanthrenes (MPs) in samples S10-07 and S10-17 were higher. The distribution and composition of hydrocarbons in sample S10-07 suggest that one, or several, undetected hydrothermal fields may be present in the region of this sediment core. Results also suggest that volcanism may be the main reason for the observed distribution and composition of hydrocarbons in S10-17 sample. •The hydrocarbons in the sediment core may be the result of terrigenous input and submarine macromolecular degradation.•The volcanism might be the main factor influencing the distribution and composition of hydrocarbons in the S10-17 sample•Hydrothermal alteration likely led to enrichment of bitumen, alkanes and PAHs in the S10-07 sample.•It remains possible that one or more undetected hydrothermal fields are present near the sediment core from the northern OT.