Abstract
As one of the most prominent seasonally recurring atmospheric circulation patterns, the Asian summer monsoon (ASM) plays a vital role for the life and livelihood of about one-third of the global population. Changes in the strength and seasonality of the ASM significantly affect the ASM region, yet the drivers of change and the varied regional responses of the ASM are not well understood. In the last two decades, there were a number of studies reconstructing the ASM using stalagmite-based proxies such as oxygen isotopes (δ18O). Such reconstructions allow examination of ASM drivers and responses, increasing monsoon predictability. In this review paper, we focus on stalagmite δ18O records from India at the proximal end of the ASM region. Indian stalagmite δ18O records show well-dated, high-amplitude changes in response to the dominant drivers of the ASM on orbital to multi-centennial timescales, and indicate the magnitude of monsoon variability in response to these drivers. We examine Indian stalagmite records collated in the Speleothem Isotope Synthesis and AnaLysis version 1 (SISAL_v1) database (http://researchdata.reading.ac.uk/139/) and support the database with a summary of record quality and regional climatic interpretations of the δ18O record during different climate states. We highlight current debates and suggest the most useful time periods (climatic events) and locations for further work using tools such as data-model comparisons, spectral analysis methods, multi-proxy investigations, and monitoring.
Highlights
The Indian summer monsoon (ISM) is part of the Asian summer monsoon (ASM) and provides ca. 70% of India’s annual precipitation
A pronounced temperature gradient between Central Asia and the Indian Ocean is accompanied by a northward shift of the Intertropical Convergence Zone (ITCZ), resulting in the southeast trade winds turning westerly due to Coriolis forces as they cross the equator
Paired analysis of Global Network of Isotopes in Precipitation (GNIP) δ18 Orainfall data collected at Delhi and low-level wind trajectory patterns show that δ18 O variability in northern India is linked to periods of strong ISM circulation [10]
Summary
The Indian summer monsoon (ISM) is part of the Asian summer monsoon (ASM) and provides ca. 70% of India’s annual precipitation. Reconstruction of past sub-continental climate variability is hampered by insufficient understanding of proxy-influencing factors, record quality, lack of adequate spatial and temporal coverage, and lack of synthesis of records that would enable pan-regional comparisons. This collation and synthesis of stalagmite δ18 O records was made available by the Speleothem Isotope Synthesis and AnaLysis (SISAL) database. The following review complements the SISAL database by introducing the geography and modern climate of the ISM region (Section 2), describing the spatial and temporal distribution and quality of stalagmite δ18 O records in the ISM region (Section 3), providing regional interpretations of the δ18 O records (Section 4), and discussing specific climate events and underlying forcings in the ISM region (Section 5)
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