Negative δ13C Excursions in Foraminiferal Records: The Holocene History of Methane Events in the Central Sea of Okhotsk

Abstract

Abstract—Several negative δ13C excursions in benthic foraminifera from gas-bearing core LV50-05 sampled offshore on the eastern slope of Sakhalin Island, Sea of Okhotsk, in an area of active methane seepage record the local history of methane events (ME). The core chronostratigraphy has been contrained from AMS 14C ages and biostratigraphic data. Benthic foraminifera (Nonionellina labradorica and Uvigerina parvocostata) from some core intervals show normal marine δ13C values about –1‰ but some intervals are marked by extremely depleted compositions as low as –34.5‰ δ13C (relative to VPDB). The negative δ13C excursions are interpreted as a record of seabed methane emanation during primary and secondary biomineralization of carbonate foraminifera. The results reveal four Holocene methane events (ME) in the area: two brief (ME-1 at 700–900 yr BP and ME-2 at 1200–1400 yr BP) and two long (ME-3 at 2500–4700 yr BP and ME-4 at 7400–10000 yr BP) events.