• R V Krishnamurthy

      Articles written in Journal of Earth System Science

    • Palaeoclimate, stratigraphy and prehistory in north and west Rajasthan

      D P Agrawal P S Datta Zahid Hussain R V Krishnamurthy V N Misra S N Rajaguru P K Thomas

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      Quaternary formations in western Rajasthan are of fluvial, locustrinal and aeolian origins. Fossil gravel ridge of Jayal in Nagaur District is one of the earliest quaternary formations so far recorded in the region. A rich lower palaeolithic habitation-cum-workshop site has been discovered in association with the gravel ridge. Multiple evidence for climatic change in the area during the quaternary period is discussed.

    • Oxygen and hydrogen isotopic ratios in groundwaters and river waters from India

      S K Bhattacharya S K Gupta R V Krishnamurthy

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      A comprehensive set of measurements of oxygen and hydrogen isotopic ratios in groundwaters as well as waters from rivers, lakes, hot springs etc. taken from a variety of locations in India has been carried out for the first time. Isotopically the most depleted samples occur in the high altitude precipitations in the Himalayas e.g. in the lakes of Bhutan and the source water of the Ganga. The shallow groundwater data display a continental effect where the heavy isotope content decreases with distance from the coast (about 4 to 6 per mil decrease in δ18O per 1000 km). The δ D and δ18O of these fresh waters are linearly related and an analysis of this relation vis-a-vis the meteoric water line shows the unambiguous effect of enrichment due to evaporation from soils.

    • Late Glacial and Holocene Paleolimnology of two temperate lakes inferred from sediment organic δ13C chronology

      N A Lovan R V Krishnamurthy

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      The stable carbon isotope (δ13C) and elemental C/N ratios in Total Organic Carbon (TOC) extracted from radiometrically dated cores from two Midwestern USA lakes were determined to investigate the factors that control these values in temperate lakes. The range of δ13C values (-26 to -32%) and C/N ratios (mean value ∼10.8) are typical of values reported for other temperate lake organic matter in this region. In the core from Lake Winnebago, Wisconsin, a negative correlation was seen between the TOC and δ13C, which can be interpreted in terms of a re-mixing and consumption of sedimented organic carbon along with rapid equilibration throughout the water column. No correlation was seen between the TOC and δ13C in the record from Ladd Lake, Ohio, implying that in this latter lake productivity alone was not a singular process controlling the isotope ratio. Here, it is suggested that equilibrium conditions are maintained such that the DIC of the water is never depleted of aqueous CO2 during high organic production and the resulting δ13C of the organic carbon lacks correlation with the TOC. Further, in this lake a fine resolution analysis was carried out which indicated a possible anthropogenic influence on the isotope ratio around times when human settlement (∼300 yrs ago) and enhanced agricultural practices (∼80 yrs ago) were significant. The study shows that carbon isotope studies are useful in paleolimnologic investigations.

    • Is there a stable isotope evidence for the CO2 fertilization effect?

      R V Krishnamurthy M Machavaram

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      It has been suggested that part of the so-called “missing sink” of carbon dioxide introduced into the atmosphere by anthropogenic activities, that is the imbalance between estimated anthropogenic carbon dioxide emissions and oceanic uptake, may be stored in the vegetation in midlatitudes. Precise mechanisms of abstraction of additional carbon dioxide by vegetation, also known as the “fertilization effect”, are poorly understood. Stable carbon and hydrogen isotope ratios of cellulose extracted from annual growth rings (covering the time period 1980–1993) in an oak tree from Kalamazoo, SW Michigan provide a basis to investigate at a physiological level how the fertilization effect may operate. The carbon isotope ratios show that the intercellular concentration of carbon dioxide increased due to an increase in stomatal opening. Although increased intercellular concentration of carbon dioxide translated to increased Water Use Efficiency and assimilation rates, it also resulted in increased transpiration rate as shown by higher D/H of the fixed carbon. The two-fold significance of the isotope data are: first, they provide the first field evidence based on isotope studies for excess CO2 induced biomass production and second, they suggest that this mechanism is likely to operate only in limited environments. Vegetation in regions where moisture availability is not restricted so that there can be a gain in water use efficiency despite increased leaf evaporation are best suited to sequester excess carbon from the atmosphere.

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