Paleoceanographic insights on meridional ventilation variations in the Japan Sea since the Last Glacial Maximum: A radiolarian assemblage perspective

Abstract

The Japan Sea is ideal for investigating deep water formation due to its unique topography and hydrography. However, because of the scarcity of reliable indicator and high-resolution ventilation records, the driving mechanisms behind ventilation changes in the entire Japan Sea since the Last Glacial Maximum (LGM) remain elusive. In this study, we analyze the radiolarian assemblage in three sediment cores from the southwestern, central, and northwestern Japan Sea to reveal ventilation variations over the last 25 ka. Our results suggest that weak ventilation was a widespread phenomenon in the Japan Sea during the LGM. This is inferred by the low relative abundances of species belonging into the Japan Sea Proper Water (JSPW) Assemblage, which are indicative of deep water ventilation in the Japan Sea. The JSPW Assemblage have gradually become the predominant species in studied cores from the last deglaciation to the early Holocene, suggesting an abrupt transition from oxygen poorer to oxygen richer conditions. All investigated regions show re-ventilation during the deglaciation, albeit at different times. The JSPW ventilation in the central Japan Sea started during the 19 ka Melt-water Pulse (MWP) and remained in an interglacial mode after MWP-1A (~14.7 ka), presumably due to the opening of the Tsushima Strait and intrusion of the Tsushima Warm Current (TWC). An abrupt increase in productive shallow water export during the Bølling-Allerød (B/A) was likely the key factor causing poorly oxygenated deep-water conditions in the southwestern Japan Sea. In contrast, the weakening ventilation in the northwestern Japan Sea during the B/A and Younger Dryas was probably caused by the blocking effect of the sea ice.