Carbon isotopes of benthic foraminifera associated with methane seeps in the Four-Way Closure Ridge, offshore southwestern Taiwan
Date Issued
2016
Date
2016
Author(s)
Wang, Wei-Ru
Abstract
Release of large amounts of methane from marine gas hydrate reservoirs has been considered as a possible trigger of climate change. The degassing of methane could be recorded by stable carbon isotopes (d13C) of benthic foraminifera in the sediments. Many previous studies have shown that foraminiferal d13C become more negative when influenced by methane seeps. However, values of d13C of benthic foraminifera might vary with different species and sedimentary settings in different regions. Seismic profiles in offshore southwestern Taiwan have shown a wide distribution of the Bottom Simulating Reflector (BSR), indicative of gas hydrate reservoirs. Various methane seepages have been found, and they are suspected to be related to the gas hydrates buried underneath. A better understanding of the d13C signals of benthic foraminifera near the methane seepages can further clarify the origin of the methane and to evaluate it as a proxy of methane release for the geologic past. We analyzed d13C of benthic foraminifera Uvigerina proboscidea (150-250 μm) in the topmost 15 cm sediments in five marine cores (OR1-1092-WFWC-1, OR1-1092-WFWC-4, OR1-1092-WFWC-6, OR3-1806-C5-2 and OR3-1806-C10) collected from the Four-Way Closure Ridge in offshore southwestern Taiwan (water depth from 1330 to 1580 m). Our results show that d13C values of U. proboscidea range from -0.98‰ to -6.21‰ (VPDB) for core OR3-1806-C5-2, which is considered as a seeps-influenced site. On the other hand, d13C values of U. proboscidea from the background sites range from -0.40‰ to -0.86‰. The difference between the methane seep-affected and the background sites is in the range of 0.12‰ to 5.81‰, comparable to those documented in previous studies in other areas. The significant negative excursion in carbon isotopes in the seep site foraminifera. Suggests an incorporation of light biogenic carbon generated by methanogenesis in the system.
Subjects
gas hydrate
methane
benthic foraminifera
carbon isotopes
Type
thesis
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