Description: The foraminifera and geochemical element records from the Core CS2 in the center of the Okinawa Trough (OT) revealed a history of current circulation and bottom redox conditions over the last 19 Ka. During the last glaciation, the few Kuroshio Current (KC) and tropical/subtropical species components, the shoaled depth of thermocline (DOT) and high infaunal foraminifera, together suggest the hypoxia in the isolated and semiclosed OT might be related to an absence/shift of the KC. Furthermore, the hypoxia variations in three episodes coincided with changes in the North Pacific Intermediate Water (NPIW), as stronger hypoxia and enhanced NPIW occurred in the Heinrich Stadia 1 and Younger Dryas periods, and rapidly decreasing hypoxia corresponded with weaker NPIW ventilation in the Bølling/Allerød period. Previously recorded hypoxia in the OT occurred broadly at a water depth of between ~1,300 and 1,800 m. Meanwhile, the lowest productivity precluded the possibility of hypoxia caused by organic matter consumption. We thereby infer the enhanced glacial NPIW might be another reason for the hypoxia. After the postglaciation, the OT transitioned into a fully oceanic environment and was reoccupied by main pathway of the KC. This reoccupation greatly alleviated the hypoxia via weakening stratification and increasing vertical mixing. Evolution research of current circulation and bottom redox conditions can help in understanding the changes in the storage/release of carbon as the paleoclimate changed. Moreover, the variations in bottom redox conditions in the OT offer a possible informative window for understanding the influence of glacial NPIW in the mid-latitude zone.

Description: The Kuroshio Current (KC) is the northward branch of the North Pacific subtropical gyre (NPG) and exerts influence on the exchange of physical, chemical, and biological properties of downstream regions in the Pacific Ocean. Resolving long-term changes in the flow of the KC water masses is, therefore, crucial for advancing our understanding of the Pacific's role in global ocean and climate variability. Here, we reconstruct changes in KC dynamics over the past 20 ka based on grain-size spectra, clay mineral, and Sr–Nd isotope constraints of sediments from the northern Okinawa Trough. Combined with published sediment records surrounding the NPG, we suggest that the KC remained in the Okinawa Trough throughout the Last Glacial Maximum. Together with Earth-System-Model simulations, our results additionally indicate that KC intensified considerably during the early Holocene (EH). The synchronous establishment of the KC “water barrier” and the modern circulation pattern during the EH highstand shaped the sediment transport patterns. This is ascribed to the precession-induced increase in the occurrence of La Niña-like state and the strength of the East Asian summer monsoon. The synchronicity of the shifts in the intensity of the KC, Kuroshio extension, and El Niño/La Niña-Southern Oscillation (ENSO) variability may further indicate that the western branch of the NPG has been subject to basin-scale changes in wind stress curl over the North Pacific in response to low-latitude insolation. Superimposed on this long-term trend are high-amplitude, large century, and millennial-scale variations during last 5 ka, which are ascribed to the advent of modern ENSO when the equatorial oceans experienced stronger insolation during the boreal winter.

Description: Highlights • Kuroshio Current proxy was established by statistical analyses on grain size spectrum. • Sr–Nd isotope analyses on Kuroshio grain size spectrum reveals source of Taiwan. • Synchronous shift in ENSO and the North Pacific Gyre is subject to the insolation. • Earth System Modeling results confirm our proxies-indicated Kuroshio Current strength. Abstract The Kuroshio Current (KC) is the northward branch of the North Pacific subtropical gyre (NPG) and exerts influence on the exchange of physical, chemical, and biological properties of downstream regions in the Pacific Ocean. Resolving long-term changes in the flow of the KC water masses is, therefore, crucial for advancing our understanding of the Pacific's role in global ocean and climate variability. Here, we reconstruct changes in KC dynamics over the past 20 ka based on grain-size spectra, clay mineral, and Sr–Nd isotope constraints of sediments from the northern Okinawa Trough. Combined with published sediment records surrounding the NPG, we suggest that the KC remained in the Okinawa Trough throughout the Last Glacial Maximum. Together with Earth-System-Model simulations, our results additionally indicate that KC intensified considerably during the early Holocene (EH). The synchronous establishment of the KC “water barrier” and the modern circulation pattern during the EH highstand shaped the sediment transport patterns. This is ascribed to the precession-induced increase in the occurrence of La Niña-like state and the strength of the East Asian summer monsoon. The synchronicity of the shifts in the intensity of the KC, Kuroshio extension, and El Niño/La Niña-Southern Oscillation (ENSO) variability may further indicate that the western branch of the NPG has been subject to basin-scale changes in wind stress curl over the North Pacific in response to low-latitude insolation. Superimposed on this long-term trend are high-amplitude, large century, and millennial-scale variations during last 5 ka, which are ascribed to the advent of modern ENSO when the equatorial oceans experienced stronger insolation during the boreal winter.