Title : Sediment Connectivity in India’s Large River Basins under Climate and Human-Induced Stress

Abstract

Currently, large river systems are under increasing stress due to climate-driven extreme events, floods, human interventions, and concerns over delta sustainability. These systems span diverse geomorphological, climatic, and lithological domains, each contributing uniquely to the basin’s sediment dispersal processes. These domains are activated or suppressed in response to external forcings such as climate extremes and human activities. In this talk, I will discuss these factors in the context of three major Indian river basins: the Brahmaputra, the Ganga, and the Godavari. I will show how the alluvial plains, particularly in the Ganga and Brahmaputra basins, may be highly sensitive to seasonal-scale fluctuations, which in turn influence sediment budgets and provenance signals. At the same time, climate-driven extreme events are leaving far-reaching and persistent imprints, with sediment signals traceable as far downstream as the Bengal delta. I will also explore how human interventions, particularly dams, have disrupted sediment connectivity within these river systems. Almost all of the observed reduction in sediment load can be attributed to reservoir storage, placing parts of the delta at risk of sinking. In conclusion, while climate-driven forces are significant, human-induced interventions are leaving equally, if not more, profound imprints on the sediment dynamics of India’s large river systems. A carefully integrated methodological approach is essential to effectively address these complex interactions.

Title : Mineralogical Characterization of Mare Australe: A Unique Region on the Moon

Abstract

Mare Australe (47.77°S, 91.99°E) is a volcanic province ~1000 km in diameter at the eastern nearside and farside boundary of the Moon. It consists of 248 mapped basaltic patches arranged in a more-or-less circular pattern. Initially classified as a “distinct” basin, it was later considered a “no topographic basin” due to a lack of identifiable topographic features. The results from the GRAIL mission, did not confirm the presence of a basin coinciding with the previously proposed one. Instead, GRAIL suggested the presence of a ~880 km diameter impact structure northwards named the Australe North Basin centered at 35.5°S, 96°E. In the earlier study geological evidences were provided to further establish the presence of the Australe North Basin. Volcanic activity at Lacus Solitudinis and Bowditch Crater, once thought to be isolated, is now linked to Australe North Basin. Based on the re-defined basin boundaries in the region a significant part of Mare Australe’s basalts lie outside the boundaries of Australe North. These basaltic units of Mare Australe remain largely uncharacterized. In this seminar, I will present a detailed investigation into the mineralogical diversity of the Mare Australe region. This study aims to shed light on the nature and origin of the distinctive style of volcanism in the region, highlighting the unique geological setting of Mare Australe and its implications for lunar volcanic evolution.

Title : Atmosphere Characterization of the Hot-Jupiter Exoplanets

Abstract

Hot Jupiters, tidally locked to their host stars, exhibit extreme day–night temperature contrasts that drive vigorous atmospheric circulation. In my recent work, I analytically and numerically quantified how this heat redistribution shapes their temperature–pressure (T–P) profiles and dayside emission spectra. Using discrete space theory radiative transfer simulations, I demonstrated that reduced heat redistribution leads to hotter daysides, stronger thermal inversions, and higher emission fluxes. Application to exoplanet XO-1b revealed near-complete heat redistribution, resolving key degeneracies in its atmospheric characterization. Beyond circulation, my research also addresses two crucial aspects: • Radius Inflation: Ionized atmospheric flows coupled with magnetic fields generate Ohmic dissipation within the radiative and convective zones. MESA evolutionary simulations, parameterized by atmospheric flow velocities, successfully reproduce the observed inflated radii of hot Jupiters through this internal heating mechanism. • Spectral Separation: I have generalized Chandrasekhar’s diffuse reflection theory to unify thermal emission and scattering, allowing precise separation of planetary spectra from stellar contamination in ultra-hot Jupiters. In future work, I plan to integrate equilibrium and non-equilibrium chemistry into circulation models to better capture day–night variations in chemical abundances to study the effect of atmospheric heat redistribution on the atmospheric chemistry and finally its imprints on the emission spectra. Additionally, I aim to extend these frameworks to lower-mass, potentially habitable tidally locked terrestrial planets to inform climate and habitability studies. I also plan to develop improved radiative transfer tools that can simultaneously handle complex emission, scattering, and chemical processes, providing stronger predictive power for upcoming JWST and ARIEL observations.

Title : Palaeoceanographic implications of single planktonic foraminiferal isotopic analysis

Abstract

Planktonic foraminifera have the ability to archive geochemical signatures of seasonal scale due to their short life spans. We utilized stable isotopes in individual foraminiferal tests to reconstruct sur-face ocean conditions and climate fluctuations over the past few thousand years in the Northern In-dian Ocean. We developed a state-of-the-art methodology for measuring the clumped isotope com-position (Δ47) of individual foraminiferal tests, marking the first such attempt. This approach holds the potential to reconstruct past ocean temperatures, offering unprecedented insights into short-term climate dynamics. We also analyzed δ13C and δ18O isotopic ratios in single foraminifera to resolve vertical habitat signals and understand the variation in mixed layer depths. These multi-isotope da-tasets allow us to better understand the physical and chemical structure of the upper ocean and its response to past climate change. In this talk, I will present preliminary results from this novel single-foram clumped and conventional isotope analysis, and discuss their implications..