1465 / 2024-09-27 14:05:14

The evolution of oxygen concentration of North Pacific deep water and its climatic effects during Mid-Pleistocene Transition

ODP Site 882, Mid-Pleistocene Transition, Pacific Meridional Overturning Circulation, North Pacific, redox-sensitive trace metals, carbon storage

The benthic δ¹⁸O record is mainly controlled by deep-water temperature and salinity as well as global ice volume. Based on this proxy, paleoceanography has revealed that Earth’s climate change has been paced by glacial-interglacial cycles over the past few million years. Particularly around the Middle Pleistocene, period of the dominant glacial cycles changed from about 40,000 years to about 100,000 years, namely the so-called the Mid-Pleistocene Transition (MPT).



Milankovitch theory proposed that the Earth's glacial cycles are the result of small periodic changes in Earth's orbital parameters that regulate the insolation. However, there is no significant change in orbital parameters along with solar radiation during the MPT, which makes it difficult to explain the mechanism of MPT from the perspective of Earth’s orbital geometry. Therefore, the Earth's internal feedback could be the main reason of the MPT.



As an important part of global thermohaline circulation, ocean meridional overturning circulation plays a crucial role in air-sea CO₂ exchange and meridional heat transfer, directly affecting global climate. In modern times, the Atlantic Meridional Overturning Circulation (AMOC) is strong, while the Pacific Meridional Overturning Circulation (PMOC) does not exist. But that may not have been the case in the geological past. In recent years, a number of studies focusing on the Last Glacial Maximum (LGM) 20,000 years ago found the probably existing PMOC in the North Pacific, which significantly affected deep CO₂ storage and heat transport in the North Pacific, suggesting that PMOC may have played a key role in the internal feedback of climate system.



MPT marks the dramatic changes in global climate, and the ocean circulation patterns in the North Atlantic and Southern Ocean have also changed. However, studies on PMOC during the MPT are still weak, and relevant records in the deep ocean are still lacking.



The authigenic Uranium (aU) concentration is sensitive to sedimentary redox conditions, which can be used to reconstruct the oxygen concentrations of overlaying bottom waters and indicate the strength of the meridional overturning circulation.



In this study, by using the deep-sea sediment core samples obtained from Ocean Drilling Program Site 882 (50.36°N, 167.60°E, water depth 3244 m) in the North Pacific, we analyzed the concentrations of aU and other elements to reveal the evolution of the PMOC and its climatic effects during the MPT. Moreover, combining with relevant records and modeling results from prior research, we try to interpret the role of the North Pacific in the MPT.