Search

Carbon release from the North Pacific in glacial‐interglacial cycles has been mainly linked to the North Pacific Intermediate Water (NPIW) formation and associated carbon/nutrient water upwelling and biological productivity changes. However, relationship between NPIW and atmospheric CO2 change in the early interglacial remains unclear. Here we report a high‐resolution sediment record of NPIW evolution based on paleo‐redox changes in the Western North Pacific during the last 400 ka. Our proxy and model results reveal a delayed collapse of NPIW after the glacial termination was coeval with decreased salinity of intermediate water and increased net rainfall in the North Pacific. Such weakened NPIW formation in the North Pacific probably make a contribution to maintain high atmospheric CO2 concentrations through weakened intermediate‐to‐deep ocean stratification and reduced subsurface biological pump net efficiency, countering the return to more stratified conditions in the Southern Ocean, which should drive down atmospheric CO2 during the early interglacial. Plain Language Summary: The high‐latitude North Pacific is an important region where ocean interacts with the atmospheric carbon cycle. CO2 outgassing from the interior ocean of North Pacific to the surface is mainly controlled by the upwelling as well as the biological productivity determined by the NPIW formation. Relationship between changes in the NPIW and atmospheric CO2 in the early interglacial remains unclear. Here we reconstructed the NPIW evolution during the last 400 ka, and combined with climate model results, we found a delayed collapse of NPIW compared with the Southern Ocean deglacial warming, which was synchronous with the decreased seawater salinity in response to increased net rainfall in the North Pacific. This NPIW collapse after glacial termination should weaken the intermediate‐to‐deep ocean stratification, and thus favored the upwelling of nutrient/carbon‐rich deep water to the surface. Besides, combined with the decreased nutrient‐poor subtropical waters supply from the weakened Pacific meridional overturning circulation, the biological pump net efficiency was reduced and thus consumed less CO2. These would counter the return to more stratified conditions in the Southern Ocean, which should drive down atmospheric CO2 during the early interglacial, and thus probably make a contribution to maintain high atmospheric CO2 concentration during the early interglacial. Key Points: NPIW evolution during the last 400 ka was reconstructed based on the paleo‐redox changes in the northern Okinawa TroughPrecessional changes of NPIW formation were mainly forced by the net rainfall in the North PacificDelayed collapse of NPIW probably contributed to maintain high atmospheric CO2 concentrations during the early interglacial [ABSTRACT FROM AUTHOR]

Abstract During the Quaternary, global sea level was characterized by large fluctuations in amplitude and increased frequency. However, the eastern marginal seas of China, especially the northern East China Sea and Yellow Sea did not experience large-scale transgression until the middle Pleistocene. The Zhe-Min (Zhejiang-Fujian) Uplift was an important barrier in the East China Sea preventing transgression of sea water into the northern marginal seas of China, but its Quaternary evolution is still poorly constrained. Here we present a thick sand layer record (the top age is ~416 ka) of the Integrated Ocean Drilling Program (IODP) Site U1428 from the northern Okinawa Trough to reconstruct the history of the Zhe-Min Uplift since the middle Pleistocene. Provenance analysis indicates that sediments from both sand and imbedded fine-grained calcareous-rich clay layers at the study site were mainly derived from the Yellow River, which for the first time indicates that the Yellow River sediments could influence the northern Okinawa Trough since at least the middle Pleistocene. Significant change of lithology at IODP Site U1428 at ~416 ka was attributed to the large-scale subsidence of the Zhe-Min Uplift, which is probably due to the rapid uplifting of Tibet during 0.52–0.38 Ma. Before ~416 ka, obstacle of the emersed Zhe-Min Uplift induced extremely severe reworking and promoted sand ridge formation in the shelf edge of southeastern Yellow Sea, and supplied sand sediments to the northern Okinawa Trough during transgression and high sea-level stages. After the subsidence of the Zhe-Min Uplift at ~416 ka, westward of tidal sand ridge and Yellow River mouth with the process of shelf transgressions favored fine-grained sediments input to the northern Okinawa Trough. Even during low sea-level stages, the flat terrain of the East Asian marginal sea shelf and low rainfall amount resulted in low discharge of Yellow River, and supplied fine-grained particles to the northern Okinawa Trough. Highlights • The Yellow River sediments influenced northern Okinawa Trough before ~416 ka. • Thick sand layer was mainly supplied by sand ridges in Yellow Sea shelf edge. • Large scale subsidence of the Zhe-Min Uplift occurred at ~416 ka. [ABSTRACT FROM AUTHOR]

Thermocline conditions in the tropical western Pacific are closely linked to regional- and basin-scale hydrological variation and may have played a critical role in global climate evolution on various timescales. However, long-term changes in thermocline hydrology in the subtropical northwestern Pacific and their connection to the tropical Pacific remain unclear. Based on planktonic foraminiferal Mg/Ca and δ18O, we reconstructed the temperature and salinity of thermocline water since the last deglaciation, using core OKI02 from the Okinawa Trough (OKT) in the subtropical northwestern Pacific. The results indicated a discrepancy in evolution of both temperature and δ18O between the thermocline and surface water over the past 19 ka. Unlike for surface water, changes in thermocline hydrology correlated with changing conditions in the tropical western Pacific, indicating a close relationship between these regions since the last deglaciation. Thermocline temperature and salinity gradients between the OKT and the tropical western Pacific increased from ∼16.5 to 10 ka BP, reached their maximum values at approximately 10 ka BP, and then decreased from the Early Holocene to present. Variations in temperature and salinity gradients correlated with changes in the El Niño–Southern Oscillation (ENSO) over the past 19 ka, which were coupled with equatorial summer insolation variations. We suggest that the ENSO-like process, forced by equatorial summer insolation, regulated thermocline dynamics in the subtropical northwestern Pacific Ocean since the last deglaciation, by influencing the strength of the Kuroshio Current. • TWT changes were different from those of SST in OKT for the past 19 ka • Thermocline conditions in OKT linked to hydrological climate variations in the tropical western Pacific through the KC • ENSO state could have controlled the thermohaline variations in the OKT • Reduced TWT and salinity gradients between the tropical western Pacific and OKT since the Early Holocene [ABSTRACT FROM AUTHOR]