Moumita Das

Solar forcing of the Indian summer monsoon variability during the Allerod period

Rapid climatic shifts across the last glacial to Holocene transition are pervasive feature of the North Atlantic as well as low latitude proxy archives. Our decadal to centennial scale record of summer monsoon proxy Globigerina bulloides from rapidly accumulating sediments from Hole 723A, Arabian Sea shows two distinct intervals of weak summer monsoon wind coinciding with cold periods within Ållerød inerstadial of the North Atlantic named here as IACP-A1 and IACP-A2 and dated (within dating uncertainties) at 13.5 and 13.3 calibrated kilo years before the present (cal kyr BP), respectively. Spectral analysis of the Globigerina bulloides time series for the segment 13.6–13.1 kyr (Ållerød period) reveals a strong solar 208-year cycle also known as de Vries or Suess cycle, suggesting that the centennial scale variability in Indian summer monsoon winds during the Ållerød inerstadial was driven by changes in the solar irradiance through stratospheric-tropospheric interactions.

Mahanadi: The Great River

Mahanadi, the ‘Great River’, is a major rain-fed peninsular river in East Central India that flows through states of Chhattisgarh and Odisha and meets the water requirement for irrigation, domestic and industrial purposes in part of these states. The farthest headwater of the river lies on Sihawa hills. It splits into various channels at Naraj in Odisha, and emerge into an arcuate shaped delta. Progressive shifting of the Mahanadi river course and its coastline can be observed at different stages in the Mahanadi delta. The upstream part of the river is dominated by Proterozoic sedimentary rocks of Chhattisgarh basin while downstream part by silicate rocks of Eastern Ghat Mobile belt. A large number of minor to major projects have already commenced or are under construction and the canals that come out from these projects regulate the agriculture practices in the basin. This river is very vulnerable to climate change as the spatial distribution of regional rainfall pattern enhances the chance of flood in its downstream sub-catchments, while the upstream sub-catchments face threats of draught. The deteriorating water quality of the Mahanadi and its seasonal variability is also a cause of concern.