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Millennial-Scale Cycling of the East Asian Monsoon
Reference
Ji, J., Chen, J., Balsam, W., Lu, H., Sun, Y. and Xu, H.  2004.  High resolution hematite/goethite records from Chinese loess sequences for the last glacial-interglacial cycle: Rapid climatic response of the East Asian Monsoon to the tropical Pacific.  Geophysical Research Letters 31: 10.1029/2003GL018975.

What was done
The authors analyzed high-resolution hematite (Hm) and goethite (Gt) data they obtained by means of diffuse reflectance spectroscopy - as well as grain size and magnetic susceptibility data - from two sections of the Loess Plateau of China (Huanxian and Yanchang) with an eye to learning something about the historical behavior of the East Asian Monsoon (EAM).

What was learned
Ji et al. report that their Hm/Gt ratio records "display a series of abrupt and pronounced humid and dry events which compare to the Dansgaard-Oeschger cycles and Heinrich events described in the North Atlantic Ocean and Greenland (Heinrich, 1988; Bond et al., 1993; Broecker, 1994)," with the highest ratios reflecting driest conditions, corresponding to stadials or Heinrich events at high latitudes, and the lowest ratios reflecting humid times, coinciding with interstadials or Dansgaard-Oeschger cycles.  They further note that "these pronounced humid and dry events reveal a pattern of significantly enhanced and reduced summer EAM moisture or precipitation on a millennial scale," which "are closely correlated to tropical hydrological cycles and support a potent role of tropical Pacific changes in the millennial-scale oscillations of EAM."

What it means
These results add to the growing body of evidence that demonstrates the worldwide nature of the millennial-scale cycling of earth's climate [see Climate Oscillations (Millennial Variability) in our Subject Index].  They also demonstrate the need to include precipitation as an integral part of this pervasive climate cycle, as attempted by Soon and Baliunas (2003) and Soon et al. (2003), but criticized by Mann et al. (2003).

References
Bond, G., Broecker, W., Johnsen, S., McManus, J., Labeyrie, L., Jouzel, J. and Bonani, G.  1993.  Correlations between climate records from North Atlantic sediments and Greenland ice.  Nature 365: 143-147.

Broecker, W.S.  1994.  Massive iceberg discharges as triggers for global climate change.  Nature 372: 421-424.

Heinrich, H.  1988.  Origin and consequences of cyclic ice rafting in the northeast North Atlantic Ocean during the past 130,000 years.  Quaternary Research 29: 143-152.

Mann, M., Amman, C., Bradley, R., Briffa, K., Jones, P., Osborn, T., Crowley, T., Hughes, M., Oppenheimer, M., Overpeck, J., Rutherford, S., Trenberth, K. and Wigley, T.  2003.  On past temperatures and anomalous late-20th century warmth.  EOS, Transactions, American Geophysical Union 84: 256-257.

Soon, W. and Baliunas, S.  2003.  Proxy climatic and environmental changes of the past 1000 years.  Climate Research 23: 89-110.

Soon, W, Baliunas, S., Idso, C., Idso, S. and Legates, D.R.  2003.  Reconstructing climatic and environmental changes of the past 1000 years: A reappraisal.  Energy & Environment 14: 233-296.


Reviewed 31 March 2004