Surface environments in the Japan Sea around the last glacial maximum

Abstract

Surface environments in the Japan Sea during the last glacial maximum (LGM: 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 -°C higher than present-day values. Furthermore, there are several different estimates ( -) of sea surface salinity (SSS) at the LGM compared to present-day value (ca. ). 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 presentday northern Japan Sea ( -°N) were present in the southern Japan Sea ( -°N) during the LGM, and that SSTs in May in the southern Japan Sea at the LGM (ca. -°C) were less than presentday May SSTs ( -°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. -). 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.

Phylogeography of a canopy‐forming kelp, Eisenia bicyclis (Laminariales, Phaeophyceae), based on a genome‐wide sequencing analysis

“…2020). During the LGM, in addition to cold water temperatures similar to current temperatures in the northern Sea of Japan of 46–48° N, low salinity (26–29) has been reported in the southern region of the Sea of Japan (Oba and Tanimura 2012). Although studies of salinity tolerance are lacking in E. bicyclis according to a few studies in the other kelp species, in general, kelps can grow within a salinity range of 26–29 (Bartsch et al.…”

Low Sea Surface Salinity Event of the Japan Sea During the Last Glacial Maximum

“…Furthermore, the warm LGM SST was not supported by micropaleontological studies (Yokoyama et al., 2007). Records from diatom, benthic and planktonic foraminifera, and radiolarian species revealed that SST during the LGM was much lower than that of today (Hyun et al., 2013; Itaki et al., 2007; Koizumi & Yamamoto, 2011; Matsui et al., 1998; Nakagawa et al., 2003; Oba & Tanimura, 2012). Although the SST of the Japan Sea during the LGM remains controversial, we assumed that, supported by the above descriptions, the SST during the LGM was not higher than that in other periods.…”

“…Following this assumption, the abnormal reduction in δ 18 O there strongly suggests a low S JP event (S. Gorbarenko et al., 2021; E. Lee, Kim, & Nam, 2008; Matsui et al., 1998). However, partly because of the unclear relationship between δ 18 O and S JP , previous studies leave the exact value of minimum S JP during the LGM as disputable (28, Oba et al., 1991; 20, Tada, 1999; 29.8, S. A. Gorbarenko & Southon, 2000; 26–29, Oba & Tanimura, 2012).…”

Paleo‐ocean Destratification Triggered by the Subduction of the Oyashio Water Into the Sea of Japan After the Last Glacial Maximum

“…The paleo Sea of Japan during the glacial low stand was mostly isolated from the North Pacific and received a continuous supply of freshwater from rivers and precipitation (Keigwin & Gorbarenko, 1992). Therefore, the seawater was stratified into two layers that were separated by a robust halocline, with less saline upper layer and a more saline lower layer (e.g., Gorbarenko & Southon, 2000;Lee, 2007;Matsui et al, 1998;Oba et al, 1991;Oba & Tanimura, 2012). The bottom deep-sea sediments deposited during this period had fine laminations, high sulfur content, and no benthic foraminifera, indicating that the halocline prevented the oxygen dissolved at the sea surface from diffusing into the deep layers (Crusius et al, 1999;Ishiwatari et al, 1994;Masuzawa & Kitano, 1984;Oba et al, 1991;Tada et al, 1999).…”

“…According to the Stommel‐Arons model, the downward diffusion of heat should be compensated by the upward heat advection associated with upwelling from the lower layer, which occurred together with the deep convection at both polar seas. However, it is unlikely that the deep convection process reached the deepest layer of the paleo Sea of Japan during the LGM, because the less saline seawater occupying the upper stratum would prevent the surface water from becoming heavier than 23.2 σ t despite surface cooling (Oba & Tanimura, ). Moreover, the absence of microfossils below the depth of 500 m suggests the presence of a pycnocline (hence, oxycline), which would have prevented the surface water from diffusing downward (Ikehara et al, ; Itaki et al, ).…”