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Strong Evidence for the Asian Monsoon's Solar Connection
Reference
Wang, Y., Cheng, H., Edwards, R.L., He, Y., Kong, X., An, Z., Wu, J., Kelly, M.J., Dykoski, C.A. and Li, X.  2005.  The Holocene Asian monsoon: Links to solar changes and North Atlantic climate.  Science 308: 854-857.

What was done
The authors, who have previously reported on a Chinese Holocene record of the Asian Monsoon (AM), build on that work - which shows that shifts in stalagmite δ18O largely reflect changes in precipitation that relate to changes in AM strength (Yuan et al., 2004; Dykoski et al., 2005) - with a 9000-year-long higher resolution (4.5-year) absolute-dated δ18O record of a stalagmite recovered from Dongge Cave (2517'N, 1085'E) in southern China, which they compare with the atmospheric 14C record (a proxy for solar activity) and climate records from lands surrounding the North Atlantic Ocean.

What was learned
Wang et al. report that their record broadly follows summer insolation but is punctuated by eight significantly weaker monsoon periods lasting from one to five centuries, most of which correlate with North Atlantic ice-rafting events.  In addition, they find that "cross-correlation of the decadal- to centennial-scale monsoon record with the atmospheric carbon-14 record shows that some, but not all, of the monsoon variability at these frequencies results from changes in solar output," similar to "the relation observed in the record from a southern Oman stalagmite (Fleitmann et al., 2003)."

What it means
In a News item (Kerr, 2005) that accompanies the report of Wang et al., one of the report's authors (Hai Cheng of the University of Minnesota) says their study clearly suggests that "the intensity of the summer [East Asian] monsoon is affected by solar activity."  Dominik Fleitman, who worked with the Oman stalagmite, also says "the correlation is very strong," stating that it is probably the best monsoon record he has seen, calling it "even better than ours."  Last of all, Gerald North of Texas A & M University, who Kerr calls a "longtime doubter," says he finds the monsoon's solar connection "very hard to refute," although he says that "the big mystery is that the solar signal should be too small to trigger anything."  Clearly, it is time to put more effort into solving that "big mystery," for as is readily apparent from the wealth of material archived in the Solar Effects section of our Subject Index, there are a host of climatic phenomena that owe their existence to some type of solar-climate connection.

References
Dykoski, C.A., Edwards, R.L., Cheng, H., Yuan, D., Cai, Y., Zhang, M., Lin, Y., Qing, J., An, Z. and Revenaugh, J.  2005.  A high-resolution, absolute-dated Holocene and deglacial Asian monsoon record from Dongge Cave, China.  Earth and Planetary Science Letters 233: 71-86.

Fleitmann, D., Burns, S.J., Mudelsee, M., Neff, U., Kramers, J., Mangini, A. and Matter, A.  2003.  Holocene forcing of the Indian monsoon recorded in a stalagmite from southern Oman.  Science 300: 1737-1739.

Kerr, R.A.  2005.  Changes in the sun may sway the tropical monsoon.  Science 308: 787.

Yuan, D., Cheng, H., Edwards, R.L., Dykoski, C.A., Kelly, M.J., Zhang, M., Qing, J., Lin, Y., Wang, Y., Wu, J., Dorale, J.A., An, Z. and Cai , Y.  2004.  Timing, duration, and transitions of the last interglacial Asian monsoon.  Science 304: 575-578.

Reviewed 17 August 2005