Surface environments in the Japan Sea around the last glacial maximum

Oba Tadamichi, Tanimura Yoshihiro

doi:10.5575/geosoc.2012.0011

Surface environments in the Japan Sea during the last glacial maximum (LGM: 21 ± 3 ka) are poorly constrained. Microfossil studies based on sediment core data (i.e., on changes in diatom, planktonic foraminifera, radiolaria, and calcareous nannofossil assemblages) indicate that sea surface temperatures (SSTs) during the LGM were much colder than those of today. Studies on the degree of unsaturation of alkenones in sediment cores suggest that SSTs during the LGM were 2–3 °C higher than present-day values. Furthermore, there are several different estimates (16–30) of sea surface salinity (SSS) at the LGM compared to present-day value (ca. 34). In this study, we compared the relative abundance of left-coiling specimens of a planktonic foraminiferal species (Neogloboquardrina pachyderma) in four sediment cores retrieved from the southern part of the Japan Sea with the horizontal distribution of left-coiling specimens in surface sediments of the northern part of the Japan Sea. Our results reveal that surface conditions similar to those in the present-day northern Japan Sea (46–48 °N) were present in the southern Japan Sea (36–37 °N) during the LGM, and that SSTs in May in the southern Japan Sea at the LGM (ca. 3–6 °C) were less than present-day May SSTs (15–16 °C). Moreover, our estimates of SSSs calculated from oxygen isotope values of planktonic foraminifera in several cores indicate that SSSs during the LGM were low (ca. 26–29). Such low-temperature and low-salinity environments during the LGM are supported by temporal changes in diatom assemblages, based on data obtained from a sediment core from the southern Japan Sea.

Surface environments in the Japan Sea around the last glacial maximum

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