Jaishri Sanwal

Stalagmite Inferred High Resolution Climatic Changes throughPleistocene-Holocene Transition in Northwest Indian Himalaya

Investigated for d18O and d13C isotopes, mineralogy and growth rate, a 20 cm long and 230Th-dated calcite stalagmite from Kalakot (Jammu and Kashmir Himalaya), has recorded high resolution precipitation variability during the Pleistocene-Holocene transition. At present, the study area is influenced by both the Indian Summer Monsoon (ISM) and Westerlies. The StalAge model indicates that the stalagmite grew between 16.3 ka to 9.5 ka BP under the ideal isotopic equilibrium conditions as revealed by the Hendy test results. The d18O and d13C values range from -5.41 to -8.82% and -7.09 to -10.84% respectively. Although the U/Th chronology is poor due to low Uranium content in the samples resulting in relatively large errors, the first stalagmite inferred precipitation variability reconstructed from NW Indian Himalaya makes this study significant. The near footprints of three global events, e.g., Older Dryas (OD), Allerod period and Younger Drays (YD) can be noticed at ~14.3-13.9, 13.9-12.7 and 12.7-12.2 ka BP. The precipitation strength was weaker during the OD and YD, but was stronger during the Allerod interstadial. By the termination of YD interval, the climate seems fluctuating in the NW Himalaya. There seems variation in commencement, duration and termination of the above mentioned events in different parts of the globe due to latitude location and response time.

Adsorption of actinides within speleothems

Abstract Stalagmites and stalactites, as observed within natural caves, may develop inside geological repositories during constructional and post-operational periods. It is therefore important to understand actinide sorptionwithin such materials. Towards this, experimental studies were carried out with 233U, 238Np (VI), 238Np (IV), 239Pu and 241Am radiotracers using natural speleothem samples collected from the Dharamjali cave of the Kumaon Lesser Himalayas, India. Petrological/mineralogical studies showed that natural speleothems have three general domains: (1) columnar calcite; (2) microcrystalline calcite; and (3) botryoidal aragonite - each with ferruginous materials. Results showed that all domains of speleothems can take up >99% actinides, irrespective of valence state and pH (1-6 range) of the solution. However, distribution coefficients were found to be at a maximum in aragonite for most of the actinides. Such data are very important for long-term performance and safety assessments of the deep geological repositories planned for the disposal of high-level nuclear wastes.

Sorption of Cs and Sr radionuclides within natural carbonates

Understanding the mobility of radiocesium and radiostrontium within geological environment is important from ‘deep geological repository system’—safety assessment point of view. Cs and Sr radionuclide sorption studies have been carried out with a stalagmite sample collected from Lesser—Himalayas. Detailed microstructural studies, backed up by micro-Raman and LIBS analyses, identified three different domains within the sample; constituted of microcrystalline calcite, botryoidal aragonite and palisadic calcite respectively. Experimental studies showed that both the radionuclides exhibit moderate to low sorption coefficients within all the different domains of stalagmite under acidic environment.

Adsorption of Ru, Ce and Eu radionuclides within naturally precipitated polycrystalline calcium carbonate under acidic environment

Abstract106Ru, 144Ce and 152+154Eu radiotracers sorption experiments (pH: 1–6) have been carried out with polycrystalline columnar/microcrystalline calcite and aragonite obtained from a stalagmite of Dharamjali cave, India. The different domains of the sample were powdered and thoroughly studied using electron microscopic and X-ray spectroscopic techniques. Both 106Ru and 144Ce exhibited higher sorption within calcite varieties compared to aragonite and increased with rising pH, while it showed reverse relation in case of 152+154Eu. Further, it is noted that aragonite offers the highest Kd values for 152+154Eu, whereas 106Ru and 144Ce prefer calcite.