Abstract
Abstract. The East Asian Monsoon (EAM) exhibits a significant variability on timescales ranging from tectonic to centennial as inferred from loess, speleothem and marine records. However, the relative contributions and plausible driving forces of the monsoon variability at different timescales remain controversial. Here, we spectrally explore time series of loess grain size and speleothem δ18O records and decompose the two proxies into intrinsic components using the empirical mode decomposition method. Spectral results of these two proxies display clear glacial and orbital periodicities corresponding to ice volume and solar cycles, and evident millennial signals which are in pace with Heinrich rhythm and Dansgaard–Oeschger (DO) cycles. Five intrinsic components are parsed out from loess grain size and six intrinsic components from speleothem δ18O records. Combined signals are correlated further with possible driving factors including the ice volume, insolation and North Atlantic cooling from a linear point of view. The relative contributions of components differ significantly between loess grain size and speleothem δ18O records. Coexistence of glacial and orbital components in the loess grain size implies that both ice volume and insolation have distinctive impacts on the winter monsoon variability, in contrast to the predominant precessional impact on the speleothem δ18O variability. Moreover, the millennial components are evident in loess grain size and speleothem δ18O records with variances of 13 and 17 %, respectively. A comparison of the millennial-scale signals of these two proxies reveals that abrupt changes in the winter and summer monsoons over the last 260 kyr share common features and similar driving forces linked to high-latitude Northern Hemisphere climate.
Highlights
The East Asian Monsoon (EAM), as a significant part of Asian monsoon circulation, plays an important role in driving the palaeoenvironmental changes in East Asia (An, 2000)
Multiscale monsoon variability has been inferred from numerous proxies generated from deep-sea sediments (e.g. Wang et al, 1999, 2005), eolian deposits (e.g. An, 2000; Sun et al, 2012), and speleothem records (e.g. Wang et al, 2001, 2008), which provide valuable insights into the changing processes and potential driving forces of the EAM variability
Chinese loess has been investigated intensively as a direct and complete preserver of the EAM changes, with great effort spent on deciphering the EAM variability at both orbital and millennial scales (e.g. An et al, 1990; Ding et al, 1994, 2002; Porter and An, 1995; Guo et al, 1996; Chen et al, 1997; Liu and Ding, 1998; Liu et al, 1999; An, 2000; Chen et al, 2006)
Summary
The East Asian Monsoon (EAM), as a significant part of Asian monsoon circulation, plays an important role in driving the palaeoenvironmental changes in East Asia (An, 2000). The millennial-scale monsoon variability during the last glacial period was strongly coupled to climate changes recorded in the Greenland ice core and North Atlantic sediments, indicating a dynamic connection between the EAM variability and the high-latitude Northern Hemisphere climate (Porter and An, 1995; Guo et al, 1996; Chen et al, 1997; Fang et al, 1999). A combination of proxies from Chinese loess, speleothem, and Greenland ice core with modelling results indicated that the Atlantic meridional overturning circulation might have played an important role in driving the rapid monsoon changes in East Asia during the last glaciation (Sun et al, 2012). In these two widely used monsoon proxies, and to emphasise the glacial–interglacial discrepancy and millennial similarity between loess and speleothem records during the last two glacial cycles
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