Journal cover Journal topic
Climate of the Past An interactive open-access journal of the European Geosciences Union
doi:10.5194/cp-2016-132
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
20 Jan 2017
Review status
A revision of this discussion paper is under review for the journal Climate of the Past (CP).
Decreasing Indian summer monsoon in northern Indian sub-continent during the last 180 years: evidence from five tree cellulose oxygen isotope chronologies
Chenxi Xu1, Masaki Sano2, Ashok Dimri3, Rengaswamy Ramesh4, Takeshi Nakatsuka2, Feng Shi1, and Zhengtang Guo1,5,6 1Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
2Research Institute for Humanity and Nature, Kyoto 603-8047, Japan
3School of Environmental Sciences, Jawaharlal Nehru University, New Delhi 110067, India
4Geoscience Division, Physical Research Laboratory, Ahmedabad 380009, India
5CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China
6University of Chinese Academy of Sciences, Beijing 100049, China
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 north India and central Nepal and three published records from Northwest India, western Nepal and Bhutan. The record spans the interval from 1743–2008 CE. Correlation analysis reveals that the record is significantly negatively correlated with the three regional climatic indices: All India Rainfall (r = −0.5, p < 0.001, n = 138), Indian monsoon index (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 inter-annual and centennial variations. Inter-annual 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. Centennial changes in the regional tree ring δ18O record indicate a 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 1820 CE.

Citation: Xu, C., Sano, M., Dimri, A., Ramesh, R., Nakatsuka, T., Shi, F., and Guo, Z.: Decreasing Indian summer monsoon in northern Indian sub-continent during the last 180 years: evidence from five tree cellulose oxygen isotope chronologies, Clim. Past Discuss., doi:10.5194/cp-2016-132, in review, 2017.
Chenxi Xu et al.
Chenxi Xu et al.
Chenxi Xu et al.

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Short summary
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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