Genesis of uranium mineralization in the Singhbhum Shear Zone: constraints from geochemistry and geochronology of hydrothermal minerals
Abstract
The genesis of uranium mineralization in the Singhbhum Shear Zone (SSZ), including the sources of the hydrothermal fluids has consistently remained a subject of debate. The present research deals with the Mohuldih and Bagjata uranium mine along the SSZ, India. The chemical and isotopic studies on the accessory minerals such as tourmaline, magnetite, fluorapatite, and monazite from the aforementioned mines were conducted to understand the mineralizing history in the Singhbhum Shear Zone. This discussion will focus on the distinct hydrothermal events and associated mineralization processes, as inferred from chemical compositions, isotopic signatures, and age data.
Chemical compositions of the Ganga, Yamuna, Narmada and Tapi Rivers: An assessment of spatial and temporal variability
Abstract
Rivers are the major pathways which supplies metals from the continents to the oceans. The chemistry of these pathways plays a crucial role in riverine systems as they influence water quality and terrestrial biogeochemistry. Further, their riverine supply to ocean is crucial in regulating ocean productivity, influencing the oceanic biological pump, which modulates the atmospheric CO2 levels and global climatic variability. In this talk I will present a detailed investigation of the elemental chemistry in seasonally and spatially resolved samples from the Ganga, Yamuna, Narmada and Tapi rivers.
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.
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..
Factors affecting gas-particle partitioning of the NHx system
Abstract
Ammonia (NH3) and its particulate form ammonium (NH4⁺) together form the reactive nitrogen system NHx, which plays a key role in air quality, particulate matter formation, and nitrogen deposition. The gas-particle partitioning of NHx is influenced by several factors like meteorology (temperature and relative humidity) and atmospheric chemistry (pH and aerosol liquid water content (ALWC)) with a complex interplay between them. While low temperature and high RH promote the partitioning towards the particulate phase, higher temperature shift it back to the gas phase. Aerosol pH and ALWC further control this balance, by governing the effect of this partitioning on PM load. While pH and ALWC influence the partitioning of gases into their particulate counterparts, this partitioning in turn affects the aerosol pH, creating a two-way interaction between chemical composition and aerosol thermodynamics. Given the multifaceted importance of the NHx system, it is essential to understand how meteorology and aerosol chemistry together, shape the gas-particle partitioning. This seminar aims to provide a deeper insight into the gas-particle partitioning dynamics of NH3 and NH4+, focusing on the role of temperature, RH, pH, and ALWC under different conditions.
Dynamics of Dissolved Organic Matter in Regulated River Systems
Abstract
The dynamics of dissolved organic matter has always been complex because of their largely unexplored nature. Freshwater systems such as rivers are vital components of the global biogeochemical system as they act as conduits for transporting large quantities of dissolved organic matter (DOM) from terrestrial landscapes to the ocean. However, their role in DOM dynamics still remains underexplored, specifically from a biogeochemical perspective. Moreover, the anthropogenic alteration to it’s flow regime has put a limit to its transport mechanism-reducing its export.
In ths seminar, a basic review of a DOM in riverine system along with results obtained from regulated river systems in western India will be presented
Can CO2 outgassing explain the Lomagundi carbon isotope excursion?
Abstract
The Lomagundi-Jatuli excursion event (2.3-2.0 Ga) is one of grandest carbonate isotopic excursion events in the geological history, that is said to mark a global perturbation in carbon cycle. The canonical explanation given for this excursion attributes it to be the resultant of enhanced organic carbon burial. But, the lack of geological evidence for an enhanced organic matter accumulation prior to or synchronous with the excursion, leaves this event an unanswered puzzle.
Furthermore, recent insights from sedimentological facies-based studies challenges the presumed global extent of this excursion.
In this discussion we will evaluate the canonical organic burial mechanism and explore the possibility of CO2 outgassing as a potential driver responsible for this excursion.
Fate of Environmental Microplastics
Abstract
Microplastics (MPs) are omnipresent on the Earth, found everywhere from Mount Everest to the Mariana Trench, and from fishes to human body. MPs are known to affect human and environmental health directly/indirectly. However, research on MPs is in initial stage only with major focus on 'MPs in water bodies'. This talk will provide a brief overview on the MP research done in different environmental systems and future perspectives.
Corals as geochemical proxy for N:P ratio: Insight from modern corals
Abstract
Globally, phytoplankton typically maintain the Carbon:Nitrogen:Phosphorus (C:N:P) ratios close to the Redfield ratio (~106:16:1), which reflects the balance of nutrients required for their growth.
Therefore, these ratios serve as a baseline for assessing nutrient availability or limitation and carbon export efficiency. Understanding the future shifts in oceanic C:N:P ratios is essentially required for predicting the future trends of the biological pumps under the global climate change scenario. Recent studies reveal that the C:N:P ratios in the global ocean vary regionally, and their future projections are highly uncertain.
Understanding the past variability in the C:N:P ratios could improve predictions. However, no geochemical proxy for C:N:P ratios at present. In this context, we analyzed C:N:P stoichiometry as well as d13C and d15N in different layers of modern corals (including coral-mounted algal biofilms) and surrounding seawaters and particulate organic matter collected from the Gulf of Kutch. In this talk, I will share insights into C:N:P ratios in the global ocean, and key findings highlight the efficiency of corals in capturing marine nutrient signatures and the biogeochemical processes shaping elemental and isotopic patterns.
Magnitude and regulation of methane emission from tropical streams and rivers
Abstract
Inland waters, particularly fluvial systems, are significant sources of atmospheric methane (CH4), a greenhouse gas with 34 times the global warming potential of carbon dioxide. However, large uncertainties persist
regarding the extent and controls of CH4 emissions, especially in tropical river basins like those in Southeast Asia. Research work during my PhD addressed three critical knowledge gaps in understanding CH4 dynamics in
tropical fluvial systems: (1) the effect of land use changes on CH4 concentration and emissions, (2) the occurrence and regulation of oxic CH4 production (OMP), and (3) the extent and environmental controls of aerobic
CH4 oxidation (MOX), which will be discussed during the seminar.
Biogeochemical implications of Ocean Alkalinity Enhancement
Abstract
Over the past few centuries, anthropogenic activities have significantly altered the global carbon cycle, leading to a ~ 50% increase in atmospheric CO2 concentration relative to the pre-industrial levels. This rise has contributed to a global surface temperature increase of approximately 1.1°C (IPCC, 2023).
To limit the future warming, it is being widely acknowledged that in addition to immediate reduction in greenhouse gas emissions, excess CO₂ needs to be actively removed from the atmosphere through carbon dioxide removal (CDR) methods.
One promising CDR approach is Ocean Alkalinity Enhancement (OAE), which involves the addition of alkaline mineral to the ocean to enhance the oceanic uptake of atmospheric CO2 and is subsequently stored as dissolved inorganic carbon (DIC) over long periods. In addition to CO2 removal, OAE may also help mitigate ocean acidification by increasing the pH of water.
Despite its potential, significant uncertainties remain regarding the feasibility, effectiveness, and environmental implications of implementing OAE at a global scale. To address these knowledge gaps, we conducted mesocosm experiments in the coastal waters of the Arabian Sea.
These experiments aimed to investigate the effects of OAE on the carbon (C) and nitrogen (N) biogeochemical cycles within the marine ecosystem. In this seminar I will present some preliminary findings on how OAE influences carbon and nitrogen uptake rates in the coastal regions of the Arabian Sea.
Anatomy of Monsoon Break Spells: A Probabilistic Approach
Abstract
The Indian Summer Monsoon (ISM) is vital to India’s economy, and is intrinsically linked to the dreams and aspirations of over a billion people residing in the Indian subcontinent. Several causal mechanisms operating at differing spatio-temporal scales dictate the ISM performance, driving large inter-annual variability.
Since the turn of the century, there has also been a conspicuous rise in both the frequency as well as intensity of extreme events, marking a discernible shift from the climatological trends. Such events have significant consequences necessitting the need for improved understanding of the causal mechanisms, as well as improved forecast skill for efficient water resources management.
One such type of climatic extremes: the ‘monsoonal breaks’ are marked by a pause in the ISM synoptic system, resulting in reduced overall rainfall, and are accompanied by suppressed convection over the Monsoon Core Zone (MCZ), extended dry periods, heatwaves, and severe droughts as a direct consequence. However, the spatio-temporal pattern of rainfall distribution over the MCZ exhibit significant variability. Due to this inherent unpredictability and randomness, analyses often focus on aggregated rainfall data to discern broader trends and patterns.
In this study, we dmonstrate that the seemingly random pattern of rainfall, when analysed at small (1̊X1̊) spatial scales is indeed information rich, which can be efficiently churned out with the help of simple statistical tools. We find that the divergence of the rainfall distribution from the climatological trend exhibits symmetries. This information, which is otherwise averaged out can be leveraged to gain novel insights into the underlying causal mechanisms, thereby contributing to improved skill of forecasting extended monsoonal breaks.
We extend the analysis to map the rainfall anomalies to the corresponding anomalies in the mean wind field, thereby identifying the dominant pathways of anomaly propagation and further extending the possible scope of forecasting such precipitation extremes.
Habitat Selection by Early Humans in the Indian Subcontinent
Abstract
The dispersal of our species out of Africa is believed to have occurred in multiple phases from the middle to late Pleistocene. Earliest fossil evidences for this migration of Homo sapiens is documented around 200-100 kya. These dispersals are influenced by the climate shifts, which shaped their habitats during migration.
According to the Southern Dispersal Hypothesis, the dispersal of Homo sapiens from Africa into South Asia (130–75 kya) coincided with periods of favorable monsoon-driven green corridors, which influenced migration pathways and habitat selection.
In this seminar, we will explore hominin habitat selection patterns by reconstructing woody cover along these dispersal routes using pedogenic carbonates as a vegetation proxy, providing insights into the environments they might have encountered and adapted.
Banded Iron Formations: Archives of Precambrian ocean-atmospheric redox conditions
Abstract
Banded Iron Formations (BIFs) are chemical sedimentary rocks with alternating silica and iron-rich bands. The composition of well-preserved BIFs records the seawater composition from which they precipitated and hence, can be used to infer the evolution of Precambrian ocean, ocean-atmospheric redox conditions as well as the emergence of continental crust.
Based on associated litho units, BIFs are classified mainly into two variants, i.e., Algoma-type BIFs, that are associated with volcano-sedimentary sequences and Superior-type BIFs, that are associated with clastic sediments.
In this presentation, I’ll discuss about different views on BIFs, including the origin of their banding, primary mineralogy and post-depositional alteration, with a focus on trace element compositions of Superior-type BIF from the Bastar Craton and Algoma-type BIF from the Dharwar Craton.
The BIFs from the Bastar Craton records Archean seawater compositions, while those from the Dharwar have been significantly modified by post-depositional alteration.
Echoes of the Ancient Earth: A Quarter Century of Exploring the Vindhyan Basin’s Secrets
Abstract
The first known animal life on Earth dates back to 630 million years. However, in 1998, a couple of fossil discoveries shook the geoscience world with their spectacular claims of the presence of advanced animal life in rocks of the Vindhya mountains that were generally considered to be older than 1100 million years.
These findings sparked intense controversies about their legitimacy and the host rocks' ages. We took up the challenge of dating these rocks deposited in India's largest Proterozoic sedimentary basin.
In the last 25 years, we have not only been able to resolve the chronology of the Vindhyan Supergroup, but also made many significant contributions to the study of regional stratigraphy and environment, ocean chemistry and tectonics during the Proterozoic. In the talk, I shall share some of our important findings.
Health risks of air pollution in a warming climate: Current evidence and New directions
Abstract
Air pollution has been identified as the leading environmental health risk globally. In India, air pollution has been identified as the second largest health risk after maternal and child malnutrition. Health risks attributable to air pollution require robust exposure estimates, sociodemographic conditions and background disease rates.
The Global Burden of Disease (GBD) Study has provided a robust framework to estimate the health burden of air pollution. However, the current estimates, available at state levels, have two critical assumptions. First, the risk is considered to be uniform across the composition, neglecting the issue of particle toxicity. Second, the exposure-response functions are derived from cohorts primarily conducted in developed countries.
Lack of robust exposure data hindered the generation of India-specific exposure-response functions for non-communicable diseases. In this talk, I will demonstrate the recent advancements in exposure modelling and how such data is being used for health studies, addressing these two aspects.
I will also highlight the complex pathways between air pollution and climate and how the air pollution attributable burden is expected to change in future.
My talk will demonstrate the urgent need for a collaborative and systematic approach to understand and minimise environmental health risks in India.
Biogeochemistry of the Arabian Sea since JGOFS
Abstract
The Arabian Sea is one of the most productive oceanic basins of the world. Most of our understanding related to physical, chemical and biological aspects of the Arabian Sea was developed during the Joint Global Ocean Flux Studies (JGOFS) program in the early 90s. This talk will delve upon some of the landmark findings of that era and progress made, if at all, since then.
Exploring the Dynamics of Oxygen Minimum Zones in the Bay of Bengal over the last 25 ka
Abstract
Anthropogenic warming has significantly reduced oceanic oxygen levels,
raising concerns about the expansion of Oxygen Minimum Zones (OMZs) and
their impact on marine habitats. The northern Indian Ocean hosts one of
the world's three major OMZs, with pronounced oxygen-deficient conditions
in the northeastern Arabian Sea. In this region, dissolved oxygen levels
drop below 10 nM at intermediate depths, intensifying anaerobic processes
such as denitrification and ammonium oxidation (anammox). These processes
contribute to the loss of bioavailable nitrogen and nitrous oxide
production—a potent greenhouse gas. In contrast, while dissolved oxygen
concentrations in the Bay of Bengal fall below 20 μM, evidence for
nitrogen loss processes remains inconclusive. However, the Bay of Bengal
OMZ is considered to be at a geochemical tipping point, where further
oxygen depletion—driven by anthropogenic nutrient input or climate
change—could amplify its role in the marine nitrogen cycle by triggering
nitrogen loss processes. Natural mechanisms influencing OMZ variability,
aside from global warming, remain poorly understood, likely due to limited
observations that are already influenced by anthropogenic signals.
Therefore, it is essential to explore long-term OMZ variations under
diverse climatic conditions through paleo reconstructions, which can
provide crucial insights into the natural variability of OMZs, aiding in
more accurate future predictions.
In this talk, I will discuss the current understanding of OMZ dynamics in
the northern Indian Ocean and highlight key research gaps in the field.
Organic Matter Sulfurization Dynamics in Natural Systems
Abstract
The sulfurization of organic matter is a globally significant biogeochemical process with far-reaching implications for the Earth's carbon, sulfur, and oxygen cycles. This process has been a subject of intense investigation due to its role in several critical areas: (1) petroleum formation and quality, (2) the coupled global biogeochemical cycles of carbon, sulfur, and oxygen, (3) sedimentary microbial activity, and (4) the preservation of organic matter and its application in molecularly based paleoenvironmental reconstructions. Despite its significance, our understanding of organic matter sulfurization remains incomplete. One major challenge in unraveling the sulfurization process is the immense diversity of organic sulfur compounds in nature, which form via various pathways.
Sulfur can be incorporated intramolecularly into organic molecules, forming cyclo-sulfur compounds such as thiophenes or thianes. Alternatively, sulfur can be added intermolecularly, leading to macromolecular moieties linked by C-Sx-C bonds. This diversity complicates efforts to establish universal mechanisms for organic sulfur formation. Another critical challenge lies in the complexity of sedimentary sulfur cycling, which involves both biological and abiological processes.
The precise source of sulfur incorporated into organic matter is not well understood. Whether pore-water sulfide, polysulfides, elemental sulfur, or a combination of these sources contributes to the sulfurization process remains unclear. The interactions among these sulfur pools and organic substrates further add to the complexity of the system. The sulfurization process is particularly significant in anoxic environments, such as marine sediments, where sulfate-reducing bacteria generate hydrogen sulfide. This reactive sulfide interacts with organic matter, stabilizing it by forming sulfur-rich compounds. These compounds, such as thiophenes, are resistant to degradation and play a vital role in the long-term preservation of organic matter in sediments. Furthermore, sulfurization contributes to the formation of sulfur-rich petroleum and coal, such as the Paleogene Superhigh-Organic-Sulfur Coals of Meghalaya, India.
Recent advancements in analytical techniques are opening new avenues for understanding the mechanisms of organic matter sulfurization. The use of sophisticated tools such as GC-MS/FID/FPD for organic sulfur compound identification, coupled with compound-specific sulfur isotope analysis (CSIA), enables researchers to trace sulfur fractionation at the molecular level. These techniques
help establish precursor-product relationships and provide insights into the pathways of sulfur incorporation into organic matter.
Are humans now the dominant geological agent?
Abstract
The Anthropocene is a term that has been proposed to account for the arguably ‘dominant’, ‘overriding’ or ‘overwhelming’ role of human activities in shaping the Earth’s geological record. Some academics have argued that we have now exited from the Holocene (the present interglacial time division) and entered a new geological age, one now defined by humanity’s profound influence on Earth’s atmospheric, biological, and earth surface processes.
Although a subcommittee of the International Commission on Stratigraphy (ICS) has recently decided that the Anthropocene will not become an official epoch in Earth’s geological timeline, the term itself will endure because for many people it encapsulates the sense that humans are now a fundamental part of the Earth system and integral to its processes.
The Anthropocene proposal has many philosophical, ethical, moral and practical implications, and will continue to generate lively academic debate across the natural sciences, social sciences, humanities and arts, while also providing scope for greater public engagement with environmental decision making.
Adopting a geoscience perspective, this talk will outline the case for and against an Anthropocene, and outline ways in which we might compare landscape shaping by human activities and natural processes.
Loss Pathway of organic Carbon in the Himalayan Permafrost Region
Abstract
Soil organic carbon (SOC) stored in permafrost regions represents a
critical component of the global carbon cycle. Climate change
significantly influences the distribution and dynamics of carbon across
Earth's systems. It is widely believed that climate change is driving
substantial carbon loss from high-latitude and high-altitude soils,
including permafrost areas. However, the pathways through which soil
organic matter is lost remain poorly understood, and the extent of older
organic matter degradation, particularly in the high-altitude Himalayan
permafrost regions, is not well quantified. To address this gap, we
measured radiocarbon content in soil organic carbon, soil CO2, and soil
CH4 across various depths of a peat profile located at approximately 4500
meters above mean sea level in the Sikkim Himalayas. In this talk I will
discuss about the basics of mountain permafrost, radiocarbon dating of
soil methane, and loss pathway of organic carbon in the permafrost region.