Magnetic evidence of redox transition event in the Okinawa Trough during the early-middle Holocene and its links to the Kuroshio Current evolution

Abstract

The Kuroshio Current significantly influences the physical, chemical, and biological properties in the western Pacific Ocean, while its strength and path in the Okinawa Trough during the Holocene remains unclear. Previous studies have not established consistent conclusions due to the multiple explanations for sediment provenance proxies, but these inconsistencies can potentially be addressed by identifying redox variability through diagenetic effects on magnetic minerals. Magnetic data (χ, SIRM, χARM, and S-ratios) obtained from cores SHDZ10 and A4 in the middle Okinawa Trough indicate an intensified reductive diagenesis effect prior to the early-middle Holocene period, whereas a contrasting trend is observed since the early-middle Holocene. Geochemical analyses (Mo, Mn, Mo/Mn, Mn/Al, TOC and TS) and Pulleniatina obliquiloculata content variations suggest that the decrease in early diagenesis since early-middle Holocene was a consequence of increased oxygenation, which is related to a strengthened Kuroshio Current and enhanced deep-water ventilation. By synthesizing the observed redox transition phenomena in nearby sediment cores (MD012403, MD012404, KX12–3, MD063–05, CSH1), we discover a coherent redox transition event during the early-middle Holocene. The occurrence ages show millennial-scale variability from south to north, which may suggest a periodic northward movement trajectory of a strengthened Kuroshio Current. This study not only provides novel insights into the reconstruction of the Kuroshio Current evolution, but also highlights the applicability of environmental magnetism methods in investigating deep-water ventilation.