Research
At the Biogeochemistry Lab at IISER Pune, we employ stable isotopes as a tool to address various curiosity-driven research questions in the fields of geology, climate studies and biology.
Our research mainly deals with the characterization of the climate proxies and reconstruction of the past climate. Lately, we have also been interested in exploring the effects of climate change and understanding the feeding ecology and migration of birds using stable isotopes.
The research involves designing novel approaches (experimental and modeling) to answer specific research questions.
Isotope dendroclimatology
Highlights of the previous work
Isotopic composition tree-rings of trees from various parts of India have been analyzed to decipher past climatic variability. The major contributions of these studies are
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Teak from Kerala is suited for isotope-based precipitation reconstruction. Teak from central India shows a higher response to relative humidity than to the precipitation amount
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Reconstruction of past precipitation variability for southern India (for a period from 1743 to 1830 AD), and soil moisture stress variability for the western Himalaya (for a period from 439 to 2006 AD)
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The study (Managave et al., 2020) establishes the association between higher soil moisture stress and higher temperature in the western Himalaya. This will help the policymakers to formulate a strategy to mitigate the effects of climate change in the western Himalaya.
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There is a clear sign of the effects of the Little Ice Age on the climate of the western Himalaya.
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Demonstrated that the Karakoram Anomaly observed in the glacier mass balance rates in High Mountain Asia is the result of natural climate variability (Managave et al., 2020)
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It is shown that the simultaneous investigations of carbon and oxygen isotopic composition of tree-ring can be used to reconstruct past variations in the relative humidity (Managave et al., 2017).
The current investigations focus on reconstructing the relative strengths of westerlies and monsoon in the western Himalayas (PhD work: Sindoora P.).
Characterizing hydrogen isotopic composition of the leaf wax compounds
Assessing hydrogen isotopic fractionation between the leaf wax compounds and source water (Eapp) (Saishree et al., 2024, Paleoceanography and Paleoclimatology)
The hydrogen isotopic composition of leaf wax n‐alkanes and n‐alkanoic acids preserved in sediments have been used extensively for reconstructing past climate variability. However, whether these records reflect a climate of a specific season or an entire year is not known. In our experiment, we grew various tropical plants using normal water during early growing season and heavy water during later growing season. Lack of isotopic signal associated with the heavy water in leaf wax compounds suggested that the bulk of leaf wax production occurred during the early growing season of the leaves. As the hydrogen isotopic composition of the leaf wax compounds reflects ambient climatic conditions, our results suggested that the hydrogen isotope record of tropical leaf wax compounds reflects the climatic conditions prevailing during the early stages of leaf growth.
Assessing hydrogen isotopic fractionation between the leaf wax compounds and source water (Eapp) (Saishree et al., 2023, Organic Geochemistry)
Quantifying the hydrogen isotope fractionation between leaf wax compounds and source water (Eapp) is a prerequisite for hydrogen isotopic composition (dD) based paleo-hydrological studies. However, characterization of the Eapp values, mostly done in the field-based studies, are predominantly carried out in northern mid-latitude regions as compared to that in the tropics. Further, the Eapp values estimated in field-based studies are often associated with inherent uncertainties which could stem from (i) incorrect source water dD values, (ii) species-effect, and (iii) varying climatic conditions (as in transect studies).
Hence, to charaterize the Eapp values in tropics and to decouple the factors affecting the variability of Eapp, we conducted an outdoor experiment wherein four evergreen and three deciduous angiosperm trees were grown under similar climatic conditions for 85 days with water of known δD value (−2‰).
The Eapp values in the studied species were −119 ± 23‰ (n = 14) for n-alkanes and −126 ± 27‰ (n = 12) for n-alkanoic acids of chain lengths C31 and C30, respectively.
We observed inter-species variabilities in Eapp values that are consistent with previous field and transect studies. As the plants were grown under similar climatic conditions and irrigated with water of the same δD value, the variability in Eapp values observed here suggested that the species-specific hydrogen isotopic fractionation likely has a dominant control over the uncertainty in the community-averaged Eapp values.
The Eapp values of deciduous and evergreen species showed no systematic differences, suggesting that changes in the relative proportion of these taxa may not affect the community-averaged Eapp and the reconstructed dD values of paleo-precipitation in angiosperm tree dominated catchments.
Holocene precipitation hydrogen isotopic values on Nilgiri Plateau (southern India) suggest a combined effect of precipitation amount and transport paths (Managave et al., Holocene, 2023)
Soil organic carbon dynamics
Understanding how climate, geology and vegetation influence soil organic carbon stocks and their dynamics (PhD work: Salam Devi Maheshwori)
Stable isotopes and avian research
Application of hydrogen, carbon, nitrogen and sulfur isotopic studies to decipher diet and migration of birds (MSc Thesis: Yuvraj Date; PhD work: Shashank Sankpal)
Here, based on museum collections, we report the feather δ34S values of 13 avian species that included marine birds with expected 34S enriched feathers, resident birds throughout India and a single migratory species, Bar-headed Goose (Anser indicus). Feathers from the marine birds were the most enriched (20.6± 1.2‰, n=10; range=4.4‰) in 34S but terrestrial resident species also showed unexpectedly high δ34S values (11.7±4.8‰, n = 74; range=19.9‰) throughout most of India but the Himalayan region and Gangetic plain typically showed δ34S values less than 6.4‰. Our results show the utility of feather δ34S studies to decipher avian and other animal migration between these two regions.