末次间冰期以来黄土高原西北缘风成沉积序列的磁-气候响应过程与机理

在腾格里沙漠-毛乌素沙地与黄土高原交接带南侧的稳定塬面上堆积的厚层黄土是记录高分辨率古气候和古地磁信息的良好载体。然而由于多种因素的限制，目前在该地区的磁学工作相当匮乏。本项目拟在该地区选取3-4个典型黄土-古土壤序列，对末次间冰期以来的黄土地层开展精细的古地磁、岩石磁学和环境磁学对比分析，综合评估地磁极性事件在高堆积速率、弱成壤条件下记录的可靠性及期间地磁场行为和空间变化特征；查明各类人工磁参数及其组合的时空变化特征和控制磁信号的主要因素，结合粒度和地球化学指标分析结果，深入分析区域降水梯度和沙漠进退对磁信号的影响，进而提取出指示区域季风变迁和古气候演化历史的磁性气候替代性指标；通过轨道-亚轨道-千年尺度上与该区域已报道的古气候记录、东亚石笋、太阳辐射变化和全球重要古环境记录的详细对比，来揭示黄土-沙漠边界带降雨量存在显著差异的黄土-古土壤序列的磁-气候响应过程、敏感度和驱动机制。

The well-preserved loess-paleosol sequences in the transitional zone between the Tengger Desert-Mu Us Desert and the northwestern the Chinese Loess Plateau (CLP) contain valuable regional paleoclimatic and geomagnetic information. However, the present magnetically-related studies are rather scarce due to uncertain reasons. Based on detailed magnetostratigraphic, rock magnetic and environmental magnetic analyses, together with redness, grain size, and geochemical determinations for 3-4 typical loess-paleosol sequences since the last interglacial along a precipitation gradient transect, this proposal aims to (1) carefully assess the recording fidelity of several geomagnetic excursions, e.g., Blake, Laschamp, and Mono Lake; (2) examine spatiotemporal variations of various magnetic parameters and possible influence of regional paleoprecipitation variations and expansion of desert environment to magnetoclimatological records; and (3) ascertain mechanism(s) of magnetic enhancement in the high-sedimentation-rate but weakly-weathered loess. Relying on detailed comparison with presently available paleoclimatic records from the western CLP, δ18O records from Chinese speleothem and Greenland ice core, and summer insolation, we finally evaluate the robustness of magnetoclimatological proxies for faithfully resolving high-resolution monsoon fluctuations on orbital-to-millennial scale in the northwestern summit of the East Asian summer monsoon.