Increase in the Asian SW Monsoon During the Past Four Centuries

Indian Monsoon scematic, June 1988, NASA GSFC, http// Increase in the Asian SW Monsoon During the Past Four Centuries
Science Volume 297, Number 5581, 26 July 2002.

1 Anderson, D. M., 2Overpeck, J. T., and 3Gupta, A. K.
1NOAA Paleoclimatology Program
2Institute for the Study of Planet Earth, University of Arizona
3Indian Institute of Technology

Climate reconstructions reveal unprecedented warming in the last century, however little is known about trends in aspects such as the monsoon. We reconstructed the monsoon winds for the last 1,000 years using fossil Globigerina bulloides abundance in box cores from the Arabian Sea, and found that monsoon wind strength increased during the past 4 centuries, as the northern hemisphere warmed. We infer that the observed link between Eurasian warmth/ snow cover and the SW monsoon persists on the centennial scale. Alternately, the forcing implicated in the warming trend (volcanic aerosols, solar output, greenhouse gases) may directly affect the monsoon. Either interpretation is consistent with the hypothesis that the SW monsoon strength will increase during the coming century as greenhouse gas concentrations continue to rise and northern latitudes continue to warm.


Download the data from this study from the WDC Paleo Archive.
fig.1 Stratigraphy fig.2 G. bulloides abundance and N. Hemisphere Temperature
Fig. 1. Calcium carbonate (squares) and G. bulloides (circles) stratigraphy for RC2730 (A) and RC2735 (B). Also shown in (A) are the corrected AMS 14C ages for RC2730. The correlation between RC2730 and RC2735 (shown by two lines between the panels) was made by correlating a combination of carbonate, G. bulloides, and coarse fraction events seen in both cores, also constrained by the 0- to 40-cm carbonate stratigraphy (fig. S2). Fig. 2. (A) Time series of G. bulloides abundance from box cores RC2730 (solid circles) and RC2735 (open circles), and the composite record produced by averaging samples within 50-year intervals during the past 1000 years (thick line). Duplicate counts are indicated by open circles with a center point. (B) Time series of Northern Hemisphere temperature variations (thin line) superimposed on the index linearly related to monsoon wind speed, the square root of the difference in composite G. bulloides abundance with respect to the 1975 average (thick line).

To read or view the full study, please visit the Science website.
It was published in Science, Volume 297, Number 5581, 26 July 2002.
Note also the Perspective on the SW Asian Monsoon by D.E. Black in this issue,
and Media Reports on this research.

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25 July 2002