Fluxes and distributions of plant wax n-alkanesin the Ulleung Basin (East Sea)

Abstract

In this study, we analyzed settling particles collected from March 2011 to February 2012 for long-chain n-alkanes and their stable carbon isotope ratio (δ13C) to investigate sources of terrestrial organic carbon in the Ulleung basin (East Sea). The settling particles were collected with 10 to 17-day intervals at 1000 m and 2300 m water depths. In general, the n-alkanes showed strong odd carbon number predominance at both water depths with higher fluxes of long-chain n-alkanes (C25-C35, 0.4-12.0 μg/m2/day at 1000 m water depth and 0.7-13.6 μg/m2/day at 2300 m water depth) than those of short-chain n-alkanes (C15-C23, 0.04-1.1 μg/m2/day at 1000 m water depth and 0.1-0.9 μg/m2/day at 2300 m water depth). The δ13C signatures of n-C27, n-C29, and n-C31 at 1000 m and 2300 m water depths were -31.0±0.5‰, -32.1±0.4‰, -32.4±0.8‰ and -30.9±0.9‰, -31.7±0.5‰, -32.3±0.4‰, respectively, indicating a large contribution of C3 plant as the main source of n-alkanes. The carbon Preference Index (CPI25-33) and the Natural n-alkanes Ratio (NAR) of both water depths varied between 3 and 9 and between 0.5 and 0.8, respectively. This suggests that the contribution of thermally matured petroleum-derived organic carbon to the particulate organic carbon pool is negligible. Hence, our results suggest that terrestrial plant n-alkanes are being deposited in the Ulleung Basin. However, more works are needed to constrain their transport pathway (aeolian vs. fluvial/current) to the Ulleung Basin.