Timing and Mechanisms of the Formation of the Dark Layers in the Sea of Japan During the Last 40 kyr

The marginal location of the Sea of Japan and its constrained water exchange with the western Pacific make this sea a subtle subject for the investigation of orbital and suborbital climate changes. However, the response of this unique basin to the climate and sea level changes at the end of the last glaciation and deglaciation and during the Holocene is not fully understood. We provided detailed reconstructions of the dark layers including the timing and mechanisms responsible for their formation, during the last 40 degrees kyr, based on the multiproxy correlation of three cores from the northern and central parts of the sea with well-dated delta O-18 records of the Greenland ice and China cave stalagmites. High resolution color photo lightness, the conventional color parameters L* and b*, AMS C-14 data, chlorin and carbonate calcium content and pollen climate parameters allowed the correlation of the DLs of these cores with Greenland interstadials (GI), Heinrich stadials (HS) and summer East Asian monsoon intensity. DLs 9, 8, 7, and 6, formed after Heinrich stadials 4 (38.5-39.5 degrees ka), were triggered by GIs 8, 7, 6 and 5, coeval with the intensification of the East Asian summer monsoon and the increase of surface water stratification and productivity. The long-lasting GI 8, accompanied by significant climate warming, led to the formation of the more intense DL 9. The accumulation of DL five was forced by a rapid global sea level fall, coeval with cold HS 3, due to the decrease of saline Tsushima Current water input into the sea, increased surface water stratification and a drop in deep water ventilation. DL four was probably launched by GI 3 and summer East Asian monsoon intensification. Further falls in global sea level during the last glacial maximum led to the formation of DLs 3 and 2 during the periods 27.0-24.2 degrees ka and 23.5-17.0 degrees ka, respectively. DL 1 was associated with significant summer East Asian monsoon intensification and environmental warming at the onset of the Holocene.

Automated summary

By correlating data from three cores in the Sea of Japan with records from Greenland ice and Chinese cave stalagmites, researchers were able to reconstruct the formation timing and mechanisms of dark layers over the past 40,000 years. This allowed for a deeper understanding of how the sea basin responded to climate and sea level changes during different periods.