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Climate of the Past An interactive open-access journal of the European Geosciences Union
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Volume 14, issue 5
Clim. Past, 14, 653-664, 2018
https://doi.org/10.5194/cp-14-653-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: Climate of the past 2000 years: regional and trans-regional...

Clim. Past, 14, 653-664, 2018
https://doi.org/10.5194/cp-14-653-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 24 May 2018

Research article | 24 May 2018

Decreasing Indian summer monsoon on the northern Indian sub-continent during the last 180 years: evidence from five tree-ring cellulose oxygen isotope chronologies

Chenxi Xu1,2, Masaki Sano3,4, Ashok Priyadarshan Dimri5, Rengaswamy Ramesh6,7,†, Takeshi Nakatsuka3, Feng Shi1,2, and Zhengtang Guo1,2,8 Chenxi Xu et al.
  • 1Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
  • 2CAS Center for Excellence in Life and Paleoenvironment, Beijing, 100044, China
  • 3Research Institute for Humanity and Nature, 457-4 Motoyama, Kamigamo, Kita, Kyoto, Japan
  • 4Faculty of Human Sciences, Waseda University, 2-579-15 Mikajima, Tokorozawa 359-1192, Japan
  • 5School of Environmental Sciences, Jawaharlal Nehru University, New Delhi, India
  • 6Geoscience Division, Physical Research Laboratory, Navrangpura, Ahmedabad 380009, India
  • 7School of Earth and Planetary Sciences, National Institute of Science Education and Research, Odisha 752050, India
  • 8University of Chinese Academy of Sciences, Beijing, China
  • deceased, April 2018

Abstract. We have constructed a regional tree-ring cellulose oxygen isotope (δ18O) record for the northern Indian sub-continent based on two new records from northern India and central Nepal and three published records from northwestern India, western Nepal and Bhutan. The record spans the common interval from 1743 to 2008CE. Correlation analysis reveals that the record is significantly and negatively correlated with the three regional climatic indices: all India rainfall (AIR; r = −0.5, p < 0.001, n = 138), Indian monsoon index (IMI; r = −0.45, p < 0.001, n = 51) and the intensity of monsoonal circulation (r = −0.42, p < 0.001, n = 51). The close relationship between tree-ring cellulose δ18O and the Indian summer monsoon (ISM) can be explained by oxygen isotope fractionation mechanisms. Our results indicate that the regional tree-ring cellulose δ18O record is suitable for reconstructing high-resolution changes in the ISM. The record exhibits significant interannual and long-term variations. Interannual changes are closely related to the El Niño–Southern Oscillation (ENSO), which indicates that the ISM was affected by ENSO in the past. However, the ISM–ENSO relationship was not consistent over time, and it may be partly modulated by Indian Ocean sea surface temperature (SST). Long-term changes in the regional tree-ring δ18O record indicate a possible trend of weakened ISM intensity since 1820. Decreasing ISM activity is also observed in various high-resolution ISM records from southwest China and Southeast Asia, and may be the result of reduced land–ocean thermal contrasts since 1820CE.

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We have constructed a regional tree ring cellulose oxygen isotope record using a total of five chronologies obtained from the Himalaya. Centennial changes in the regional tree ring record indicate a trend of weakened Indian summer monsoon (ISM) intensity since 1820. Decreasing ISM activity is also observed in various high-resolution ISM records from southwest China and Southeast Asia, and may be the result of reduced land–ocean thermal contrasts since 1820.
We have constructed a regional tree ring cellulose oxygen isotope record using a total of five...
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