Geoscience

The East Asian Winter Monsoon over Last 15,000 Years

The East Asian winter monsoon (EAWM) not only plays an important role within the Asian climate system, but also acts as a link between the polar and tropical regions and even inter-hemispheric climate systems. However, past changes of the EAWM have not been clearly established so far due to the lack of suitable proxy records. Moreover, the traditional view is that of a weakening of the EAWM from early to late Holocene although it contradicts the observed changes in the size of ice sheets and in winter insolation. Dr. Wangluo et al. from Institute of Geology and Geophysics, CAS at first establish an index of the EAWM by comparing the results of a sediment trap experiment and a 100- year sedimentary record from Huguang Maar Lake (HML, South China) with modern records of the EAWM, Siberian High (SH) and Arctic Oscillation (AO). Secondly, they present a continuous record of the strength of the EAWM for the past 15,000 years based on sedimentary diatom assemblages in HML. The diatom record of the past 15,000 years shows that the EAWM shifted from strong to weak instead of strengthening from the early to late Holocene. The record shows that the EAWM and East Asian summer monsoon (EASM) were in-phase instead of anti-correlated on orbital time scales during the Holocene. On a millennial time scales, the relationship between the EAWM and EASM show spatial and temporal variability, and is dependent on the strength of the EAWM. Anti-phase of the Australian Summer Monsoon (ASM) with summer insolation in the Southern Hemisphere is an enigmatic exception that cannot be explained by the classic theory of insolation. During the early Holocene the EAWM was in-phase with the ASM, which provides the first direct evidence to support the hypothesis that the intensity of the EAWM affected, at least in part, the strength of the ASM. The result has been published inQuaternary Science Reviews (Wangluo. et al., The East Asian Winter Monsoon over the last 15,000 years: its links to high-latitudes and tropical climate systems and complex correlation to the summer monsoon. Quaternary Science Reviews. 2012, 32: 131-142, doi:10.1016/j.quascirev. 2011.11.003).