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Precession-band variance missing from East Asian monsoon runoff.
S C Clemens1, A Holbourn2, Y Kubota3
1Earth, Environmental, and Planetary Sciences, Brown University, Providence, 02912, RI, USA. Steven_Clemens@Brown.edu.
Nature Communications
|August 24, 2018
Summary
Speleothem oxygen isotopes (δ¹⁸O) complicate paleomonsoon reconstructions. New offshore records reveal East Asian monsoon rainfall is sensitive to greenhouse gases and ice sheets, not just solar insolation.
Area of Science:
- Paleoclimatology
- Geochemistry
- Oceanography
Background:
- Speleothem CaCO₃ δ¹⁸O is a common paleomonsoon proxy.
- Inferring rainfall amount from speleothem δ¹⁸O is complex due to factors like source water variations and temperature effects.
- Planktonic foraminiferal CaCO₃ δ¹⁸O offers a more direct proxy for local precipitation and runoff.
Purpose of the Study:
- To develop a more reliable proxy for East Asian monsoon rainfall.
- To disentangle the influences of various factors on paleomonsoon reconstructions.
- To investigate the primary drivers of East Asian monsoon variability.
Main Methods:
- Analysis of planktonic foraminiferal CaCO₃ δ¹⁸O offshore from the Yangtze River Valley (YRV).
- Quantitative removal of global seawater δ¹⁸O and local temperature effects.
- Comparison of YRV speleothem δ¹⁸O records with offshore seawater δ¹⁸O records.
Main Results:
- Offshore seawater δ¹⁸O records show dominance of eccentricity (100 ky) and obliquity (41 ky) cycles.
- YRV speleothem δ¹⁸O records are dominated by precession-band (23 ky) cyclicity.
- East Asian monsoon rainfall exhibits minimal precession-scale variance in seawater δ¹⁸O records.
Conclusions:
- East Asian monsoon rainfall is more responsive to greenhouse gas and high-latitude ice sheet forcing.
- Monsoon rainfall shows less sensitivity to direct insolation forcing.
- Offshore planktonic foraminifera provide a robust proxy for reconstructing monsoon precipitation history.
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