晚中新世柴达木盆地低偏心率时期倾角驱动的干湿变化

Obliquity-driven moisture changes in Qaidam Basin in Late Miocene during low eccentricity period

  • 摘要: 当前间冰期正处在地球轨道低偏心率时期,在全球变暖的大趋势下北半球冰盖正逐渐消融。因此,解析北半球无冰背景下低偏心率时期亚洲内陆干湿变化规律和驱动机制,对预测该地区未来环境变化具有重要意义。然而,以前的研究关注亚洲内陆低偏心率时期环境变化的高分辨率记录较少,限制了对该区干湿循环和驱动机制的理解。柴达木盆地位于东亚季风降水边缘,对干湿变化非常敏感。选取柴达木盆地东北部大红沟剖面河湖相沉积地层,利用频率磁化率指标重建晚中新世时期(9~12 Ma)高分辨率干湿变化历史,揭示了典型的低偏心率时期干湿变化主导周期和轨道斜率驱动机制。结果表明,在低偏心率时期(9.2~9.4 、 9.6~9.8 和11.2~11.4 Ma),该区域干湿变化以4万年周期为主,对应倾角变化,说明在岁差振幅较小时,倾角变化可能上升为轨道调控干旱区干湿变化的主导因素。这一发现对理解未来气候变化具有一定的借鉴意义。

     

    Abstract: The present interglacial period is at a period of low eccentricity, and the ice sheets in the northern hemisphere are gradually melting due to the global warming. Understanding the variation and the mechanism of dry-wet alternation in Asian inland during low eccentricity period under the ice-free background of the northern hemisphere is very important to predict the future environmental changes in the area. At present, little attention is paid to high-resolution records of environment variations during low eccentricity periods in inland Asia, which limits the understanding of moisture changes and the mechanism in the region. The Qaidam Basin, located at the edge of East Asian monsoon rain zone, is very sensitive to dry-wet climate alternation. In this study, we selected the fluvial-lacustrine strata of the Dahonggou section in the northeastern Qaidam Basin, along which the frequency magnetic susceptibility was measured, to reconstruct the high-resolution moisture history of the Late Miocene (12~9 Ma). Results revealed typical dry-wet changes and show that the local climate change has a clear 40-ka cycle, corresponding to the obliquity in typical low eccentricity condition when the precession amplitude is small during 9.4~9.2 Ma, 9.8~9.6 Ma, and 11.4~11.2 Ma. It suggests that obliquity factor may rise and become a dominant factor on orbital regulation of environment in arid area. This finding has important implications for understanding future climate change.

     

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