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Two sediment cores, KCES1 and ODP797, which were recovered from the Sea of Japan (JS), were measured for alkenone-derived sea surface temperatures ( $$U^{{\text{K}}^{\prime}}_{37} {\text{-SSTs}}$$ ). Our results revealed that the SSTs closely follow the glacial-interglacial cycles during the last 170 ka, except in the last glacial maximum (LGM), during which the SST was higher than in the Holocene. The anomalous high temperature in the LGM is considered as an effect of the intrusion of a low salinity water mass into the JS when the sea level was almost below 130 m. On the glacial-interglacial to orbital timescale, the $$ U^{{\text{K}}^{\prime }}_{37} {\text{-SSTs}} $$ record in the JS correlated well with the benthic foraminiferal δO record and solar insolation, which suggests the dominant control of solar insolation and its related sea ice development on the SST in the JS. On the sub-orbital/millennial timescale, reduced SST corresponds to an enhanced east asian winter monsoon (EAWM) during the last glacial period (MIS3 and MIS4), indicating the dominant control of sea ice expansion due to the enhanced EAWM on the SST in the JS. In contrast, during the last interglacial period (MIS5), the SST in the JS was controlled by variations in the east Asian summer monsoon. These results highlight the key role of solar insolation and associated glacial-interglacial conditions in the variations of the SST in the JS since the last 170 ka. [ABSTRACT FROM AUTHOR]

Biomarkers have been widely used to reconstruct phytoplankton productivity and community structure changes, and this method has been applied for the first time in the middle Okinawa Trough during the transition from the last deglaciation to the Holocene. The total content of all marine phytoplankton biomarkers, used as a total productivity indicator, reveals higher productivity during the deglaciation. The ratios of the biomarkers are used as community structure indicators which show that, compared with the Holocene, the contribution from haptophytes decreased while the contributions from diatoms and dinoflagellates increased during the deglaciation. The increased productivity during the deglaciation was likely caused by the stronger winter monsoon. Also increased nutrient supply from terrestrial sources contributes to the higher productivity due to lower sea-level, which is consistent with higher terrestrial biomarker (long-chain n-alkanols) content. These changes in the nutrient supply also contributed to the community structure changes in the Okinawa Trough. [ABSTRACT FROM AUTHOR]

Abstract: Glacial-interglacial sea level changes have caused drastic variations in the surface hydrography, ventilation and ecosystem structure in the Japan Sea. Previous reconstructions using microfossils and geochemical proxies suggested decreased productivity and a more calcareous plankton community during glacial periods. However, the inferred community structure change is not consistent with significantly lower salinity in the Japan Sea during the glacials, which would have had a deleterious effect on calcareous plankton growth. Here, biomarker records of ODP Site 797 are generated to further evaluate phytoplankton productivity and community structure changes in the Japan Sea over the last 166 kyr. Although the contents of the phytoplankton biomarkers changed by two to three orders of magnitude, there were no clear glacial-interglacial patterns as sediment biomarker contents reflected the combined effect of production and water column degradation. The collective assessments of our biomarker records and published records support previous conclusions of decreased productivity in the Japan Sea during the glacials. However, a community structure proxy based on the alkenone/brassicasterol ratio reveals a shift from a diatom-dominated community during the glacials to a coccolithophorid-dominated community during the interglacials, mainly as a result of surface salinity variations in the Japan Sea controlled by sea-level changes. Previous community structure reconstruction using biogenic carbonate/silica ratio could have been complicated by the different environmental factors governing silica and CaCO3 dissolution in the Japan Sea. [Copyright &y& Elsevier]

Understanding past changes in oceanic circulation and the corresponding heat, salt delivery variations are essential for assessing the climatic roles of ocean dynamic processes since the last glacial period. Unravelling salinity budget variation in the North Pacific and its controls is important to better understand the North Pacific Intermediate/Deep Water formation and associated climate impacts. The Tsushima Warm Current (TWC), the northernmost Kuroshio branch entering the semi-closed Japan Sea through the shallow strait, is regarded as a fundamental component for oceanographic changes in the Japan Sea. To obtain a comprehensive history of the Japan Sea salinity budget, this study reconstructed the evolution history of the TWC inflow by compiling paleo-hydrographic records in the Japan Sea. Following a persistent but weakened TWC inflow during Marine Isotope Stage 3, radiolarian assemblage data revealed that the TWC taxa disappeared since ∼30 thousand years ago (ka). The synchronous onset of the low salinity anomaly event was in response to the cutoff of saline TWC inflow due to the rapid fall in global sea level at 30 ka. Extreme restriction of seawater exchange caused a persistent freshening of the glacial Japan Sea and formed a low-salinity water mass in the upper ocean. The compiled paleodata confirmed that the Japan Sea accumulated excess freshwater during the glacial sea-level lowstands and the low-salinity pool extended downward to ∼900 m depths. Coinciding with the peak of the low salinity anomaly event, re-emerging TWC inflow after 19 ka reflected the reconnection of the open ocean to the Japan Sea. The persistent TWC inflow mainly drove the reduction in magnitude of the deep low-salinity pool during the last deglaciation. As a large and isolated freshwater sink for the glacial North Pacific, the deep low-salinity pool evolution could potentially have strong impacts on the North Pacific salinity budget and subsequent large-scale circulation. • Radiolarian reconstruction indicates a persistent but weakened influence of the TWC inflow in the Japan Sea during MIS 3. • The low-salinity pool extended downward to ∼900 m depths in the Japan Sea during the LGM. • The link between global sea-level change and deep low-salinity pool evolution is sought. [ABSTRACT FROM AUTHOR]

High-resolution lithological and isotope-geochemical analyses were made on a well age constrained sediment from the northeastern Japan (East) Sea which recorded 10 dark layers (DL) over the last 40 ka BP. Pollen analysis of the core allows us to reconstruct the history of surrounding landmass vegetation and to determine pronounced vegetation/climate changes. We found that DL 10 which correlated with a DO/Chinese interstadial 8 was forced by increased East Asian humidity and influx of the nutrient-rich water into the sea. DL 5 formed during the cold Heinrich event 3 (HE), at 30–31 ka BP, was most likely to be initiated by the global sea level descent and reduction of seawater exchange with the North Pacific. High resolution of δ 18 O pf records reflects a unique sensitivity of the Japan (East) Sea to input of the North Pacific water through the shallow Tsushima and Tsugaru Straits. This led us to the important evidence of the eustatic-sea level changes during the last 40 ka BP. Since 29 ka BP, δ 18 O pf curve shows a continuous descending sea level interrupted by sharp drops of HE 2 with a following rise of DO interstadial 2. A sharp δ 18 O pf increase since 18.6 ka BP is consistent with coral results which indicate abrupt termination of LGM low stand by a rapid sea level rise initiated at 19.0 ka BP. [ABSTRACT FROM AUTHOR]