Rainfall seasonality changes in northern India across the 4.2 ka event
- 1Department of Earth Sciences, University of Cambridge, Cambridge, UK
- 2Department of Geography and Environmental Engineering, Northumbria University, Newcastle upon Tyne, UK
- 3Potsdam Institute for Climate Impact Research, Potsdam, Germany
- 4Environmental Research Institute, School of Science, Waikato University, Hamilton, New Zealand
- 5Helmholtz-Centre Potsdam, German Research Centre for Geosciences, Potsdam, Germany
- 6California Institute of Technology, Pasadena, USA
- 7Max-Planck-Institute for Chemistry, Mainz, Germany
- 8Department of Archaeology, University of Cambridge, Cambridge, UK
Despite intensive research efforts by archaeologists, geomorphologists, and palaeoclimatologists, the climatic and environmental changes accompanying the societal changes in the wider Indus/Thar region c. 4000 years ago remain puzzling. In particular, rainfall seasonality might be an important determinant for societal well-being. A major hurdle to a more detailed understanding of climate-human interaction is the relative scarcity of well-dated and highly resolved proxy records.
We present a multi-proxy record from aragonitic stalagmite DHAR-1 collected in Dharamjali Cave, Uttarakhand, India, that spans c. 1600 years between c. 4.25 and 2.6 ka BP. The stalagmite has been dated with 13 U/Th dates with average uncertainties of <18 years (2σ). In addition to c. 1600 oxygen and carbon isotope samples, element ratios (X/Ca) were measured using high resolution μXRF and laser ablation ICPMS at 25 μm resolution.
The DHAR-1 record represents the most precisely dated speleothem record to date from northern India, covering the mid-Holocene 4.2 ka BP event and the millennium thereafter. The attained sub-decadal to seasonal resolution allows robust assessment of both regional and local hydrological changes, and changes in amount and temporal distribution of summer and winter rainfall.
The speleothem record reveals decadal-scale trends that can be related to changes in seasonality. The δ18O record reveals a 220-year period of weakened ISM from 4.2 to 3.98 ka BP. A contemporaneous increase in δ13C, and decrease in U/Ca, Ba/Ca, and Sr/Ca point to increased prior aragonite precipitation (PAP) resulting from increased aridity above the cave extending throughout the dry season. The ISM intensified after c. 3.7 ka BP while dry seasons remained dry, with a resultant increase in seasonality. Lower PAP after c. 3.4 ka BP can be interpreted as sign of reduced rainfall seasonality.
We compare the results with available records from the wider region, and discuss potential implications of the suggested changes in seasonality for agriculture-based societies.
How to cite: Giesche, A., Breitenbach, S. F. M., Marwan, N., Hartland, A., Plessen, B., Adkins, J. F., Haug, G. H., French, A., Petrie, C. A., and Hodell, D. A.: Rainfall seasonality changes in northern India across the 4.2 ka event, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16898, https://doi.org/10.5194/egusphere-egu2020-16898, 2020.
