Alternative modes of Quaternary pelagic biosiliceous and carbonate sedimentation: A perspective from the East Sea (Japan Sea)

Six piston cores (95PC-1, MB97PC-19, TY99-PC18, 95PC-3, 95PC-4 and 96EBP-4) from the East Sea (Japan Sea) were examined to assess the fluctuations in carbonate and biogenic silica sedimentation. Data from four of these cores (95PC-1, MB97PC-19, TY99-PC18 and 96EBP-4), collected from depths above the present carbonate compensation depth (CCD), clearly show that carbonate content increased during glacial periods and decreased during interglacial periods, whereas biogenic silica content shows the opposite pattern. The two cores collected below the CCD also show glacial/interglacial variations in carbonate and biogenic opal contents with patterns similar to the cores collected above the CCD.This study provides strong evidence for cyclic variations of biogenic components corresponding to interglacial–glacial cycles, even though variations in carbonate and opal contents seem to be affected by dissolution and dilution. The inverse correlation between carbonate and biogenic silica contents suggests that two mutually exclusive oceanic modes affected the biogenic sedimentation. These modes may have resulted from sea level changes that led to water column stratification during glacial low stands and breakdown of water column stratification, and consequent active vertical mixing during interglacial high stands.