Late Quaternary environmental changes on the southeastern slope of the Sea of Okhotsk inferred from benthic foraminifera

Abstract

Benthic foraminifera were studied in 117 sediment samples from a 1112-cm-long core obtained from the Kamchatka continental slope (52°02.514′ N, 153°05.949′ E) at a sea depth of 684 m. The section covers the last 180 ky, from marine isotopic stage (MIS) 6 to the present time. The substantial quantitative and taxonomic changes in the assemblages of benthic foraminifera reflect the climatic and paleoceanographic variations. The insignificant contents of foraminiferal tests in the sediments that accumulated during glaciations (MIS 6, MIS 5(d-a)-MIS 2) suggest a minimal organic flux to the sea bottom. During deglaciation and in the Holocene (MIS 1) and, particularly, in the interglacial optimum (MIS 5e), the organic flux to the bottom significantly increased. Sestonophagous species prevailed in the foraminiferal assemblages of glacial periods, when the production of the young Sea of Okhotsk Intermediate Water (SOIW) increased. The assemblages of warm periods (MIS 1 and 5e) are mainly composed of detritophagous species. Now, conditions favorable for these species exist in the bottom areas influenced by the old Pacific waters. During the warm interglacial optimum (MIS 5e), when the SOIW production decreased, its thickness became reduced and the boundary with the Pacific water mass substantially rose (probably by 200-400 m). During MIS 1, the decrease in the SOIW production and the rise of its lower boundary were less significant