Comparison of Milankovitch periods between continental loess and deep sea records over the last 2.5 Ma |
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| Institution: | 1. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;2. University of Chinese Academy of Sciences, Beijing 100039, China;3. Radiogenic Isotope Facility, School of Earth and Environmental Sciences, The University of Queensland, Brisbane, Queensland 4072, Australia;1. Institute of Earth Environment, Chinese Academy of Sciences, 710061 Xi''an, China;2. Institute of Surface-Earth System Science, Tianjin University, 300072 Tianjin, China;3. University of Chinese Academy of Sciences, 100049 Beijing, China;4. Paleoecology & Landscape Ecology, Institute for Biodiversity & Ecosystem Dynamics (IBED), University of Amsterdam, 1090 GE Amsterdam, the Netherlands;1. Institute for Paleoenvironment of Northern Regions, Koyocho 3-7-5, Kitahiroshima 061-1134, Japan;2. Faculty of Environmental Earth Science, Hokkaido University, N10W5, Kita-ku, Sapporo 060-0810, Japan;3. Department of Earth and Planetary Sciences, Faculty of Science, Hokkaido University, N10W8, Kita-ku, Sapporo 060-0810, Japan;4. Graduate School of Environmental Science, Hokkaido University, N10W5, Kita-ku, Sapporo 060-0810, Japan |
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| Abstract: | A high-resolution East Asian winter monsoon proxy record reconstructed from the Baoji loess section in China shows two major shifts in climate modes over the past 2.5 Ma, one occurring at about 1.7–1.6 Ma BP and the other at about 0.8–0.5 Ma BP. The 1.7–1.6 Ma shift is characterized by a rather abrupt transition of winter monsoon variability from various periodicities to dominant 41-ka cycles, and accompanied by a substantial increase in intensity of winter monsoon winds as manifested by an increase in average loess grain size. The 0.8–0.5 Ma event shows a relatively gradual transition from constant 41-ka cycles to predominant 100-ka climatic oscillations with a significant increase in amplitude. The 0.8–0.5 Ma shift matches that registered in deep-sea δ18O records, whereas the 1.7–1.6 Ma shift is absent in global ice volume changes. This comparison suggests that at about 1.6 Ma BP, the ice sheets in the Northern Hemisphere may have reached a critical size, sufficient to modulate changes in the global climate system. The discrepancy of climate cyclicity between loess and deep-sea records over the 2.5–1.6 Ma interval suggests that the older Matuyama climate evolution cannot be understood simply by a regular 41 ka cycle model on a global scale. More long proxy records derived from continental deposits are needed. |
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