Description: Atmospheric CO2 and global climate are closely coupled. Since 800 ka CO2 concentrations have been up to 50% higher during interglacial compared to glacial periods. Because of its dependence on temperature, humidity, and erosion rates, chemical weathering of exposed silicate minerals was suggested to have dampened these cyclic variations of atmospheric composition. Cooler and drier conditions and lower non-glacial erosion rates suppressed in situ chemical weathering rates during glacial periods. However, using systematic variations in major element geochemistry, Sr–Nd isotopes and clay mineral records from Ocean Drilling Program Sites 1143 and 1144 in the South China Sea spanning the last 1.1 Ma, we show that sediment deposited during glacial periods was more weathered than sediment delivered during interglacials. We attribute this to subaerial exposure and weathering of unconsolidated shelf sediments during glacial sealevel lowstands. Our estimates suggest that enhanced silicate weathering of tropical shelf sediments exposed during glacial lowstands can account for ~9% of the carbon dioxide removed from the atmosphere during the glacial and thus represent a significant part of the observed glacial–interglacial variation of ~80 ppmv. As a result, if similar magnitudes can be identified in other tropical shelf-slope systems, the effects of increased sediment exposure and subsequent silicate weathering during lowstands could have potentially enhanced the drawdown of atmospheric CO2 during cold stages of the Quaternary. This in turn would have caused an intensification of glacial cycles.

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.

Description: Highlights • Yangtze and Yellow River sediments can be distinguished with SrNd isotope. • Okinawa Trough (OT) sediments derived from the Yangtze River from 18.0 to 10.5 ka. • Yangtze and Yellow River contributed sediment to the OT from 10.5 to 7.0 ka. • Kuroshio Current control Taiwan sediment to the OT after 7.0 ka. • Yellow River sediment was transported to the OT by the coastal current in the last 10.5 ka. Abstract The Okinawa Trough (OT) is a large sink of sediments supplied by the East Asian continent. Identifying the provenance of the OT sediments is key to reconstructing the temporal and spatial variations of the terrigenous supply to this area and is important for understanding the impact of paleoclimatic and paleoceanographic variability on the sediment supply to this marginal sea over the late Quaternary. In this contribution, we show that radiogenic strontium (Sr) and neodymium (Nd) isotopes allow to efficiently distinguish Yellow and Yangtze/Taiwan River detrital sediments, and can be used to reconstruct distinct changes in the provenance of the detrital fraction of marine sediments from the middle and northern OT since the last deglaciation. The Sr and Nd isotope signatures are compared to those of the potential sediment sources, namely the Yellow and Yangtze Rivers, the Taiwan orogen, and volcanic material from the OT and nearby islands, and the relative contributions of these sources are reconstructed. The Sr and Nd isotope compositions of the detrital fraction in the two sediment cores recovered from the middle and northern OT show that the sediments mainly originated from the Yangtze River between 18 and 10.5 ka, which was caused by low sea level and a widely developed channel system on the continental shelf. During the period between 10.5 and 7.0 ka, the rising sea level resulted in elevated Yangtze and Yellow Rivers sediment input into the OT. Simultaneously, large-scale volcanic activity also contributed significant amounts of material to the OT. During the last 7.0 ka, besides important contributions from the Yellow River, the intensification of the Kuroshio Current resulted in increased delivery of sediment from Taiwan to the OT.