Climate forcing: Observations from Chinese Loess Plateau and a perspective of the influence of ocean-ridge processes.

摘要

This study involves improving knowledge of the climatic and environmental changes during the past 3 million years in the region of the Chinese Loess Plateau and the forcing mechanisms of global glacial-interglacial climate oscillations during the Quaternary. Loess sections consisting of loess-paleosol sequence, fluviolacustrine sequence, and the red clay formation were selected for detailed study. Laboratory methods used included analyses of paleomagnetism, {dollar}sp{lcub}14{rcub}{dollar}C dating, bulk sample mineralogy, grain-size distribution, clay mineralogy, major and trace element geochemistry, iron geochemistry, stable carbon-isotopes, carbonate content, organic matter content, pollen and pedo-micromorphology by photomicroscopy and SEM.; The fluviolacustrine sequence in the Shijiawan section was deposited between 3.05 and 1.9 Ma B.P. with a dominant alluvial facies. The red clay formation was developed under a constant warm-dry climate 2.7 Ma ago. The paleovegetation in the southern Guanzhong basin was of typical sage steppe type during the period of 3.0-2.7 Ma B.P. Evidence suggests that the red clay was derived from the northwest deserts by aeolian transport, indicating dust deposition stated long before the major loess accumulation. The dustfall rate in the late Pliocene is much lower than in the Quaternary, implying that the Siberian cold high was abruptly intensified 2.6 Ma B.P. Pollen evidence, pedological studies and dustfall rate indicate that a profound climatic change and regional climate regime replacement were coincident with the advent of the first Quaternary glaciation. As demonstrated, the Quaternary climate in the loess plateau responded strongly to the world glacial-interglacial signals which are related to the sea level-coastal position-precipitation linkage.; As has been suggested by many workers, the last and rapid deglaciation must be linked to major changes in ocean circulation. It is difficult to explain this change by changes in solar insolation alone. In fact, the albedo changes might have worked to maintain the ice age. A first attempt has been made to examine if ice loading could have contributed to asthenosphere flow and intensified ocean ridge volcanism which in turn could perturb ocean circulation patterns and increase atmospheric CO{dollar}sb2.{dollar} The first modeling results suggest that the process could be of quantitative significance.