Geosciences Seminars

Modern human evolution cannot be understood from archaeological evidence alone; it requires placing human behaviour within its environmental and geological context. This seminar presents an interdisciplinary approach that integrates Palaeolithic archaeology with geoscience to reconstruct the landscapes occupied by early modern humans in Peninsular India during the Late Pleistocene. By combining archaeological investigations with sedimentology, geomorphology, geochronology, palaeoecology, archaeology, and palaeontology, this research examines site formation processes, landscape evolution, environmental change, and their influence on human adaptation. Drawing on case studies from southern India, the talk highlights how geological archives and archaeological records together provide new insights into the interactions among climate, landscapes, ecosystems, and modern human populations, demonstrating the value of bridging geosciences and archaeology in studies of human evolution.

The northern permafrost regions store vast amounts of organic carbon in frozen soils, representing one of the largest terrestrial carbon reservoirs on Earth. Ongoing Arctic warming poses a significant threat to the stability of this long-preserved carbon pool, potentially accelerating the release of greenhouse gases and creating positive feedback to climate change. However, the size, age, and vulnerability of carbon stored both as soil organic carbon and as gaseous carbon species remain insufficiently constrained. To investigate the dynamics and turnover of these carbon pools under contemporary climatic conditions, we conducted radiocarbon and stable carbon isotope analyses of soils, soil-air CO2 and CH4, and surface-emitted gases collected from peat and mineral soil profiles at multiple depths in the High Arctic region of Svalbard. In this seminar, I will present our latest findings on the sources, age, and mobilization of carbon in Arctic permafrost ecosystems and discuss their implications.

Sulfuric acid-mediated carbonate weathering in mountainous regions serves as a dominant CO2 source, counterbalancing the carbon sequestration via silicate weathering. In this study, we investigated the intensity and controlling factors for sulfide oxidation for some major Himalayan Rivers (the Teesta, the Ganga and the Yamuna) draining the eastern to central Himalaya, using dissolved major ions, and δ34SSO4 and δ13CDIC data. The water samples examined in this study include spatial collections from the mainstream and tributaries during pre-monsoon (2018; the Teesta), monsoon (2022; the Yamuna), and biweekly samples collected at the mountain front (at Paonta Sahib and Rishikesh) of the Yamuna and Ganga Rivers, respectively for a duration of one year (2022-23). The spatial δ13CDIC data vary between -7.4‰ and 4.3‰ for the Yamuna and from -11.9‰ to -3.8‰ for the Teesta River. Similarly, the temporal δ13CDIC compositions fluctuates between -10.3‰ to 4.9‰ (for Yamuna) and -12.2‰ to 2.0‰ (for Ganga), which are intermediate between carbonic acid-mediated silicate weathering (-24‰ ± 2‰) and sulfuric acid-mediated carbonate weathering (0‰ ± 2‰) values. At the spatial scale, the average SO42- concentration of the Yamuna (~300 μM) and Teesta (~92 μM) are higher than that of the Ganga (~58 μm) and Brahmaputra (~78 μM) outflows, and global rivers (~88 μM). The corresponding δ 34SSO4 data of the Yamuna water vary between 2.3‰ and 25.5‰, with an average value of 13.0‰. The δ34SSO4 values for the mountainous samples are more depleted than those from the floodplains, hinting at intense sulfuric acid-mediated weathering in the mountainous region. The δ34SSO4 values for the Yamuna also exhibit strong seasonal variations, with more depleted δ34SSO4 signatures (14.1‰ ± 1.0‰) during the monsoon compared to those for the non-monsoon (17.0‰ ± 1.3‰) period. However, for the Ganga River, the average monsoon and non-monsoon δ34SSO4 compositions are similar (6.8‰ ± 2.3‰). The observed discrepancy in the seasonal difference for the Yamuna and the Ganga Rivers suggest that fluctuation in hydrology and oxygen availability influence the oxidation reactions at subsurface level. Our preliminary observation indicates intense sulfide oxidation in this mountainous catchment, possibly triggered by basin lithology and oxygen vailability. These results show that in the Himalayan Rivers, the CO2 release (through H2SO4-mediated carbonate weathering) is balancing ~80% of CO2 uptake (through H2CO3-mediated silicate weathering). 

Silicon is a moderately volatile, lithophile, and major rock-forming element in the Solar System. It occurs predominantly as SiO2; in silicate minerals, as gaseous SiO and SiS in the solar nebula, and as metallic Si under highly reducing conditions. Under mantle and crustal conditions on Earth, silicon exists primarily in the tetravalent state (Si4+). Owing to its abundance and relatively conservative geochemical behavior, silicon serves as a key reference element for comparing elemental abundances among diverse Solar System materials and investigating planetary formation processes. Variations in silicon isotopic compositions among Earth, meteorites, and other planetary bodies provide valuable insights into nebular condensation, accretion, core formation, and planetary differentiation, making Si isotopes a powerful tracer of the origin and evolution of rocky planets. 

The ocean’s biological carbon pump encompasses a suite of biologically mediated processes by which photosynthetically fixed carbon is exported from the sunlit surface ocean (the euphotic zone) to the ocean interior. A fraction of the organic matter produced in the euphotic zone is exported below as particulate organic carbon (POC). As the exported POC sinks through the mesopelagic zone, the majority is remineralized, and only a fraction reaches the deep ocean below ~1000 m. This residual flux, called the deep-sea POC flux, governs long-term carbon sequestration by the ocean, with residence time spanning 1,000 years to millennial scales. The Northern Indian Ocean (NIO), comprising the Arabian Sea and the Bay of Bengal, hosts one of the most intense biological carbon pumps globally. However, sparse sediment-trap deployments and limited BGC-Argo time-series data limit the estimation of deep-sea POC fluxes at basin-wide scales. Moreover, differences in measurement techniques and regional and seasonal variability across the NIO introduce significant uncertainty into the flux estimates. These limitations motivate a need for machine learning-based modeling capable of resolving complex, multi-scale processes under sparse observation constraints, thereby enabling improved estimates of the basin-wide carbon sequestration. The ratio of deep-sea POC flux to euphotic-zone POC flux, termed the transfer efficiency, provides a normalized metric for basin-wide comparison and analysis. In this talk, we will discuss the factors governing transfer efficiency and its variability, outline the associated modeling challenges, and explore how interpretable and physics-informed machine learning can provide insight into the dominant controls of transfer efficiency and deep-sea POC fluxes in the NIO. 

Speleothems, secondary carbonates precipitated in karst regions, have been widely used to reconstruct past variations in Indian Summer Monsoon Rainfall on centennial to millennial timescales. Previous studies have shown that the oxygen isotopic composition (δ18O) of speleothem reflects integrated rainfall along the moisture transport pathway rather than local rainfall. However, it can be difficult to deconvolve the δ18O signal into its individual components, including possible cave kinetic effects, temperature, precipitation amount, moisture source and transport processes, potentially leading to a biased climatic signal. Triple oxygen isotopes systematic (Δ’17O), based on mass-dependent deviations from the expected proportionality between δ18O and δ17O during equilibrium and kinetic processes, can provide additional constraints on hydrological processes. To explore this potential, we have established in-house setups for Δ’17O measurements in carbonates using the Pt-catalysed CO2-O2 exchange method. In this seminar, I will present preliminary results of triple oxygen isotope measurements from Indian caves. These observations provide initial insights into the behaviour of Δ’17O in the regional hydrological cycle and highlight its potential in disentangling the processes recorded in speleothems.

This study integrates hydrogeological, geochemical, and isotopic approaches to assess groundwater quality and identify recharge zones in the Viswamitri River Basin (Gujarat, India). The basin hosts complex confined and unconfined aquifers with diverse recharge sources. Groundwater chemistry is primarily controlled by carbonate dissolution, rock-water interaction, and ion exchange, while elevated heavy metals (Li, Mn, Mo, Sr, Th, V, Zn) indicate anthropogenic contamination. Approximately 78% of the area falls under medium to poor drinking water quality and high salinity and SAR values limit its suitability for irrigation in many areas. Industrial indices suggest significant corrosion and scaling risks. Stable isotope ratios (δ2H, δ18O) reveal recharge sources and interaction between surface water and groundwater systems. Suitability mapping indicates that only ~18% of the basin is appropriate for water harvesting structures. Key findings on groundwater quality and recharge potential will be presented.

This study integrates hydrogeological, geochemical, and isotopic approaches to assess groundwater quality and identify recharge zones in the Viswamitri River Basin (Gujarat, India). The basin hosts complex confined and unconfined aquifers with diverse recharge sources. Groundwater chemistry is primarily controlled by carbonate dissolution, rock-water interaction, and ion exchange, while elevated heavy metals (Li, Mn, Mo, Sr, Th, V, Zn) indicate anthropogenic contamination. Approximately 78% of the area falls under medium to poor drinking water quality and high salinity and SAR values limit its suitability for irrigation in many areas. Industrial indices suggest significant corrosion and scaling risks. Stable isotope ratios (δ2H, δ18O) reveal recharge sources and interaction between surface water and groundwater systems. Suitability mapping indicates that only ~18% of the basin is appropriate for water harvesting structures. Key findings on groundwater quality and recharge potential will be presented.

Organic geochemical/environmental markers/tracers encode a remarkable narrative of origin, transformation and persistence across natural and extraterrestrial systems. Here, I present an analytical framework analyzing two classes of compounds, including sugars and lipids, using the most trusted instrumental platforms (GC-MS and LC-MS/MS) in organic geochemistry. Within this framework, I correct isomeric assignments of monosaccharide anhydrides or anhydrosugars (levoglucosan, mannosan and galactosan) using LC-MS/MS, resolving ambiguities inherent in earlier protocols. While GC-MS is employed as a complementary technique to substantiate these refined isomeric assignments and to evaluate the loss of silyl (TMS) derivatives of anhydrosugars, a critical constraint in many analytical workflows analyzing polar analytes. Building upon this corrected molecular correction, the framework extends to structurally more complex and recalcitrant lipid-derived markers, including polycyclic aromatic hydrocarbons (PAHs), to further constrain biomass burning signatures and chemotaxonomic controls in different environmental archives. This progression, from resolving fundamental analytical uncertainties to investigating higher-order molecular complexity, enables a robust and coherent interpretation of source-specific inputs and post-depositional transformations. Importantly, these molecular tracers provide key insights into the nature and variability of fire regimes, capturing information on fuel type, combustion conditions and their environmental imprint. Such an integrated approach not only refines overall interpretations within complex environmental matrices but also demonstrates a tested applicability across a broad spectrum of environmental settings, including extraterrestrial systems. By coupling insights from analogous environments with remote and in situ analysis of organic matter, these molecular frameworks offer a pathway to investigate prebiotic chemistry and the evolution of life beyond our planet. In doing so, this work highlights the broader relevance of organic geochemistry in connecting molecular-level observations to overarching questions of environmental dynamics and the distribution of organic matter across the cosmos.

This presentation reveals that Himalayan hot springs are key to understanding the region's carbon cycle, with geochemical analysis showing that fault-controlled meteoric water circulation drives metamorphic CO2 degassing. Water penetrates to depths of ~5 km, creating pathways for deep-sourced CO2 to reach the surface. The hot springs release significant amounts of CO2, which is comparable to the region's silicate weathering sink. The degassed CO2 is primarily derived from metamorphic decarbonation (~78%) reactions, and can turn the orogen into a net source of CO2 on million-year time scales.

Transformers have rapidly become the backbone of modern day forecasting - from the language models reshaping how we interact with information, to Earth system predictors that now rival decades of numerical weather modelling. Yet despite this power, most transformer architectures remain agnostic to the physical structure of geoscientific data. They lack awareness of sensor identity, carry no representation of directed physical influence between variables, and impose no built-in sense of the diverse rhythms that characterise Earth system processes - from diurnal cycles and seasonal variability to longer climate modes such as ENSO. Despite this, the fact that models like GraphCast and Pangu-Weather achieve remarkable forecasting skill even without this inherent physical awareness speaks to the framework's fundamental strength. It also raises a pointed question: what becomes possible when that structure is built in deliberately?
We introduce CRISP, a 22 million parameter transformer architecture specifically designed in-house at PRL, for multivariate geoscientific forecasting. CRISP models observations as collections of distinct sensors - each with its own dynamics and directed, time-lagged influence on others, and constructs faithful context vectors so that every token encodes a single variable’s structured, lagged history. This guarantees physical homogeneity of tokens and simultaneously widens the temporal receptive field before any attention is applied. Temporal structure and sensor identity are encoded jointly through dual rotary positional encodings with learnable frequencies that adapt to dominant periodicities in the data. Finally, an explicit channel-mixing block learns asymmetric, directed cross-sensor interactions without imposing artificial symmetry, while sparse ProbAttention provides scalable long-range interaction across time.
Across multiple standard benchmarks, CRISP achieves state-of-the-art predictive skill relative to leading transformer, MLP, and state-space models and crucially, produces interpretable influence structures that allow Earth scientists to diagnose the physical relationships driving each prediction.

The diverse geochemical composition of Ganga-Brahmaputra floodplain sediments found in the inland aquifers of the Bengal Basin, and their impact on groundwater chemistry over a seasonal timescale, has been poorly investigated yet. This study combines seasonal groundwater geochemistry with isotope-based mass-balance modelling to constrain the controls on dissolved Sr and 87Sr/86Sr in depth-bound inland groundwater from the western Bengal Basin (West Bengal, India) located within the Ganga (Hooghly) floodplain. To further understand the spatial variations in the inland groundwater composition across the Bengal floodplain, the present groundwater database has been compared with available inland groundwater data from the eastern Bengal Basin (Bangladesh) located in both the Ganga and Brahmaputra drainage basins. The shallow groundwater in western Bengal Basin exhibits variable hydrogeochemistry and radiogenic 87Sr/86Sr with limited seasonal variability; however, showing higher solute loads during pre-monsoon period. Comparing with available geochemical data on the Ganga River bedload sediments-water, we suggest detrital radiogenic calcite dissolution (74 - 93%) from the Ganga floodplain sediments and a subordinate localized contribution from silicate mineral weathering may drive heterogeneous Sr release with radiogenic 87Sr/86Sr in the seasonal shallow groundwater, which may further undergo secondary interactions with exchangeable clay-sediment fractions.

The challenge in predicting monsoon is difficult to overcome by relying on instrumental data from only the past few decades. Palaeomonsoon reconstructions help us understand and predict the sensitivity and response of monsoon to forcings on multi-decadal-centennial timescale. Numerous palaeomonsoon reconstructions based on oxygen-18 in speleothems have been done in India to investigate the drivers of Indian Summer Monsoon Rainfall (ISMR). However, it can be difficult to deconvolve the δ18O signal into individual components, including possible kinetic isotope effects, temperature, precipitation amount, moisture source and transport, which can lead to an overstated climatic signal. In such a case, the extent to which the variability in ISMR in the instrumental period reflects natural variability, still remains debatable. In this seminar, I will discuss how triple oxygen isotope systematics can provide a way to identify kinetic effects and delineate the influencing processes. I will present results from in-house setup that have resolved the existing theoretical-experimental gap and interlaboratory inconsistencies, crucial in standardising triple oxygen measurements in carbonates. I will also present preliminary investigations of paired speleothem-dripwater samples from Indian caves.

The Pliocene was the last significant sustained warm period on Earth. Atmospheric carbon dioxide and global temperatures during this interval can be comparable to those modeled and proposed for the near future. Considering a similar continental and oceanic positioning to the present, it is possible to assume that the oceanic and atmospheric circulation patterns were also comparable to those of today. Current data on the Pliocene, and the transition to the cooling conditions of the Pleistocene, mostly arrive from marine archives, thus leaving the continental regions mostly barren of reliable and continuous information. Therefore, continental climate archives from this interval are highly valuable for comprehending the impact of climate change on terrestrial areas and serve as good analogues for understanding present conditions without the influence of humans. 
In the present study, a multi-proxy approach was applied to both sediment cores and outcrop samples retrieved from three different lacustrine formations exposed in the Near East, which are chronologically constrained to the Pliocene and Early Pleistocene. The multi-proxy analyses indicate major fluctuations in the lakes hypsometry, transitions from anoxic to oxic conditions in the sediment-water interface, and major changes in the limnic states, indicating a response of the lake systems to changing conditions in the precipitation patterns through time. It appears that the different lakes responded to orbital-scale forcing, which may have played a key role in governing the dry-wet climate cycles in the Near East. Results from this study provide an important understanding of the hydrological conditions that may have dominated the region during a warmer climate phase, challenging previous estimations, while concurrently providing clues to the role of the climate system in greening the path of early hominin migrations out of Africa through the region.