Benthic foraminiferal δ 13C minimum events in the southeastern Okhotsk Sea over the last 180 ka

A total of six δ 13C minimum events, i.e., VI, V, IV, III, II, and I, were observed via a stable carbon and oxygen isotope analysis of infaunal benthic foraminifera Uvigerina spp. in gravity core OS03-1 in the southeastern Okhotsk Sea over the last 180 ka. These events occurred at 112–109, 102–90, 85–76, 57–54, 44–40, and 17–10 ka BP. The largest negative excursions reached 2.5 ‰ in event V and were greater than 1 ‰ in the other events. We proposed that all δ 13C minimum events were caused by the increase in sea surface water productivity, the weakened formation of Okhotsk Sea intermediate water, and the enhancement of the oxygen minimum zone. The negative excursions were unaffected by methane hydrate destabilization and subsequent methane release based on the results obtained by using archaeal lipid markers.