Continental flood basalt (CFB) provinces represent large-scale fissure eruptions fed by dykes. Tholeiitic dykes of the Vikramgad-Murbad dyke swarm, in the western Deccan Traps CFB province, are up to 40 km long, and mainly trend NS, E–W, NE–SW and NW–SE. They are potential feeders of the kilometers-thick Western Ghats volcanic sequence forming the type section of the Deccan Traps. Plagioclase separates from one dyke of each orientation yield 40Ar/39Ar ages of 66.43 ± 0.26 to 65.95 ± 0.39 Ma (2σ, full uncertainty including decay constants), all indistinguishable within uncertainty, indicating rapid swarm emplacement and matching the Western Ghats volcanic sequence in age. Bulk-rock major and trace element and SrNd isotopic data ((87Sr/86Sr)t = 0.70400–0.71302, εNd(t) = +5.4 to −13.5) on 58 samples representing 53 dykes indicate variable degrees of magma contamination by Precambrian crustal sources, and a much larger overall geochemical variability than encountered in any single section such as the Western Ghats. Thirty-five of the 53 dykes are geochemically correlatable with specific stratigraphic formations, members, or lavas forming the Western Ghats sequence, and are interpreted as probable feeders. Eighteen dykes show geochemical characteristics shared by two or more stratigraphic units, or isotopic ratios outside the range of the lavas analysed thus far. Feeder dykes of some formations show preferred orientations, whereas others do not. Frequent switches in crustal stress fields in a relatively short time interval (< 1 Myr) are indicated; partial control by structural architecture of the Precambrian basement is also likely.

Dykes transport magmas from the Earth's interior to the surface, feeding eruptions. Many dykes are single magma injections, but multiple dykes are also common. The growth of multiple dykes in active volcanoes can be studied using field and geophysical data (e.g., ground deformation, migration of magma-generated seismicity, eruptions). However, none of these can be used in inactive volcanoes. In this study of the Kinhavli multiple dyke, in the similar to 65.5 Ma Deccan Traps continental flood basalt province, we use outcrop features and rock textures, mineral chemistry, and whole-rock geochemistry to infer its progressive growth. The dyke, with five distinct columnar rows, is a moderately evolved (Mg# 61.6-58.8), uniformly quartz-normative tholeiitic basalt. It contains phenocrystic olivine (Fo(81.6-70.4)), groundmass clinopyroxene (Mg# 81.8-69.8), plagioclase (An(68.3-55.7)) and Fe-Ti oxides, and interstitial silicic glass. The five rows are also extremely uniform in trace element composition (Zr/Y = 5.04-5.24, Zr/Nb = 14.56-14.71, La-N/Lu-N = 5.02-5.17). They also have closely similar Sr-Nd isotopic ratios, with (Sr-87/Sr-86)(t) of 0.70599-0.70605 (+/- 0.00001, 2 sigma) and epsilon(Nd)(t) of -5.5 to -5.8 (+/- 0.2, 2 sigma) for four rows, and 0.70591 and -4.5 for the fifth. Thermobarometry shows crystallisation of olivine (1282-1274 +/- 29 degrees C, 1 sigma error), clinopyroxene (1185-1150 +/- 38 degrees C) and plagioclase (1146-1143 +/- 20 degrees C) at pressures of 2.1-0.5 (+/- 1.9, 1 sigma) kbar, suggesting a shallow-level source magma chamber. Co-existing titanomagnetite-ilmenite pairs yielded temperatures ranging from 1114 to 924 degrees C and log fO(2) values ranging from -10.42 to -13.07 that plot on or slightly below the quartz-fayalite-magnetite (QFM) buffer, typical for flood basalts. The textural features and geochemical data cannot be explained by rock alteration, mantle heterogeneity, or magma mixing, but are consistent with magma contamination by similar to 5% of ancient granitic basement crust. However, the inter-row geochemical differences do not support a simple model of three successive axial magma injections. Instead, the dyke formed from (i) a homogeneous magma chamber producing four successive magma injections which were progressively less crustally contaminated by wall rocks during ascent, or (ii) from five successive magma injections from a source magma chamber getting progressively more contaminated with time. The geochemical approach used here could be usefully applied to infer the probable growth manner of all ancient multiple dykes.

Antarctic sea ice is a critical component of the global ocean and climate system, undergoing significant changes over recent decades. The forcing factors and mechanisms driving these changes remain poorly understood due to a lack of long-term observational records. Here, we present an annually resolved high-resolution reconstruction of sea ice concentration (SIC) in the Weddell Sea spanning 1809–2013 CE, based on d-excess record derived from δ18O and δD measurements in an ice core from Dronning Maud Land, East Antarctica. This proxy-based SIC reconstruction combined with satellite record (1809–2022 CE) reveals a persistent dominant ∼40-year periodicity throughout the record, along with a notable increase in high-frequency variability within 16–20 and 2–8 year bands in recent decades. These decadal to interannual variations suggest a strong link to Pacific oscillations. Our investigations further reveal relatively stable SIC until the mid-20th century, followed by a threefold increase in variability since the 1970s, marking an unprecedented shift in recent sea ice dynamics over the last two centuries. In addition to tropical Pacific forcing, the Southern Annular Mode (SAM) exerts a strong extratropical influence on Weddell Sea ice. The recent shift of SAM toward positive phase likely intensified circumpolar westerlies, enhanced wind-driven upwelling, and strengthened the Weddell Sea Gyre, thereby increasing sea-surface temperatures contributing to the sea ice decline and amplified variability. We suggest that this pronounced recent shift in sea ice variability reflects SAM and enhanced remote teleconnections, particularly the growing influence of high-frequency Pacific oscillations.

Lead (Pb) concentrations and isotopic ratios (206Pb/207Pb and 208Pb/207Pb) in Antarctic snow serve as unique tracers of atmospheric pollution transport into the Southern Hemisphere. We investigated Pb sources and transport pathways to coastal Dronning Maud Land (cDML), East Antarctica, through the analysis of nine surface snow cores collected from three different ice rises. To isolate the atmospherically derived fractions, snow samples were subjected to 60-day weak-acid leaching prior to trace-element and Pb isotope analyses. The Pb concentrations range from 9.97-29.8 pg g-1 (mean = 18.7 ± 6.4 pg g-1). Enrichment factors for Pb in the operationally defined labile fraction (EFPb=70-110; mean = 93) calculated relative to upper continental crust values (Pb/Ba ≈ 0.03), indicate substantial non-crustal enrichment, consistent with anthropogenic Pb input. The 206Pb/207Pb ratios ranges from 1.13 to 1.16, and 208Pb/207Pb ratios from 2.41 to 2.43 are consistent with dominant contributions from South American emission sources. A five source Bayesian isotope mixing model (MixSIAR) was employed to quantify the relative contributions of major Pb sources to the cDML region. Model estimates that Argentina (∼40%) and Brazil (∼36%) together account for 74-82% of Pb deposition across the three ice rises, with smaller contributions from Chile (∼15%), Australia (∼5%), and local Antarctic sources (Skarvsnes; ∼4%). These results demonstrate that cDML snow archives hemispheric-scale industrial emissions, with South America as the primary contributor. The findings provide a regionally constrained modern baseline for monitoring global pollution transport and highlight Antarctica's sensitivity to anthropogenic atmospheric contamination in the Southern Hemisphere.

The Erinpura granites, occurring extensively to the west of the Neoproterozoic South Delhi Fold Belt and east of the younger Sirohi orogenic belt, occupy a pivotal tectonic position between two closely-spaced and closely-timed orogenic events, recording key Neoproterozoic magmatic activity. An integrated approach combining petrography, major- and trace-element geochemistry, SrNd isotopes, and zircon trace-element profiles is employed to constrain their petrogenesis. Petrography reveals sporadic presence of amphibole and muscovite in otherwise predominantly biotite granites. Most Erinpura Granite samples are weakly to moderately peraluminous (A/CNK > 1.0), indicating a dominant S-type affinity, although a few samples plot near the metaluminous-peraluminous boundary. Occurrence of mafic enclaves in plutons, occassional presence of amphibole-biotite assemblage and geochemical signatures such as marginally metaluminous character (A/CNK approximate to 0.99) and elevated Na2O suggest that minor I-type characteristics are locally present. Erinpura granites exhibit epsilon(Nd) (t = 870 Ma) from +3.0 to -7.2, with two-stage depleted mantle model ages of 1.4 to 2.5 Ga. While high Sr-87/Sr-86 ratios suggest evolved crustal contributions or post-magmatic disturbance of the RbSr system, positive epsilon(Nd) in amphibole bearing and some biotite granites point to juvenile input. The amphibole-bearing granite yields Sr-87/Sr-86 ratio of 0.77246 and a positive epsilon(Nd) (+0.7), reflecting mantle input, whereas the muscovite-bearing granite exhibits strongly negative epsilon(Nd) (-7.2) coupled with a high Sr-87/Sr-86 ratio of 1.17377, indicative of a crustal origin. Collectively, these results reveal a mixed petrogenetic history characterized by both S-type and I-type signatures. This reflects crustal anatexis of heterogeneous sources with evidence of mantle-derived inputs, shedding light on the complex tectono-magmatic evolution of the region during the Neoproterozoic.

The Mumbai area in the western Deccan continental flood basalt (CFB) province is well known for large-scale, compositionally diverse, Danian-age (post-K/Pg boundary) Deccan magmatism, coinciding with or slightly postdating the 62.5 Ma India-Seychelles continental breakup. The late-Deccan Mumbai magmatic suite contains subaerial tholeiitic lavas, subaqueous spilitic pillow lavas, "intertrappean" sediments (with substantial volcanic ash input), rhyolitic lavas and tuffs, a tholeiitic dyke swarm, gabbro-granophyre intrusions, and trachyte intrusions containing alkali basalt enclaves. We present new geological and compositional data on the vitrophyre forming the hillock of Gandhi Tekdi, in the Sanjay Gandhi National Park and forest reserve, in Mumbai City. The vitrophyre is traversed throughout by a polyhedral fracture network, and has an upper surface covered with loose primary blocks reflecting active crustal brecciation. The vitrophyre is texturally extremely uniform, containing abundant crystal aggregates and phenocrysts of andesine to oligoclase feldspar and augite, with minor Fe-Ti oxides, in a glassy groundmass rich in anorthoclase microlites. In major element composition it varies from (mainly) rhyolite to trachyte and trachydacite, all of metaluminous character, due to slightly variable crystal cargoes. In trace element (including rare earth element) composition it bridges the Mumbai trachytes and rhyolites, indicating a compositional continuum. Its relatively low (87Sr/86Sr)t ratios (0.70516-0.70596) and moderately low epsilon Ndt values (-3.1 to -3.3) indicate considerable isotopic homogeneity, and likely derivation from closed-system fractional crystallisation of known isotopically matched Mumbai tholeiites. The rhyolitic groundmass (glass + microlites) of the vitrophyre represents the residual liquid extracted from a dioritic cumulate mush, which is represented by the vitrophyre's crystal cargo. Based on its major outcrop features we interpret the Gandhi Tekdi vitrophyre as a lava dome, the first identified silicic lava dome in the entire Deccan Traps, which expands the varied styles of silicic magmatism recognised in this continental flood basalt province.

This study is focussed on understanding of molybdenum (Mo) cycling in the mesotidal to macrotidal estuary of the Ganga (Hooghly) River in India. Our investigation encompasses the composition of water and suspended particulate matter (SPM) samples collected in three separate periods (pre-monsoon: PrM, monsoon: M and postmonsoon: PoM) over two consecutive years, surface sediments, exchangeable phases of surface and suspended sediments, one sediment core, urban and industrial effluent waters and ground waters. The observed dissolved Mo concentrations in the estuary are in excess of those expected from conservative mixing of seawater and river water. The "excess" Mo values, observed in the mid-to-high salinity regions (4-27 parts per thousand) for four out of the six study periods, are the highest in the monsoon samples. The bulk and exchangeable phase compositions are supportive of release of Mo from the Fe-Mn oxyhydroxide phases of the SPM and surface sediments in the estuary. Mass balance calculations indicate that Mo release from the SPM and surface sediments can account for up to 40 % of the median value of the "excess" Mo in the estuary. The compositions of the sediment core provide evidence for the mobilization of Mo and its release to porewater due to reductive dissolution of Fe-Mn oxyhydroxides. The tidally induced sediment resuspension likely facilitates the transport of porewater Mo to the overlying water. Mass balance calculations indicate that Mo loss from the sediment column can account for the bulk of the "excess" Mo in the estuary waters. This study further demonstrates that industrial effluents, urban waste waters and groundwaters do not constitute significant sources of dissolved Mo in the estuary. The average annual Mo flux from the estuary is ( 2-3) x 106 mol, of which 30-50 % of Mo is due to estuarine addition. More significantly, Mo contribution from the Hooghly River estuary, accounting for 0.7-1.0 % of the global riverine Mo flux, is 3-4 folds higher than its water contribution ( 0.25 %) to the global river water flux. Our study highlights the role of interactions between oxyhydroxide phases and estuarine water, diagenetic mobilization of elements in the sediment column and porewater transport in the cycling of Mo in a monsoon-dominated tropical estuary with high sediment loads. We also demonstrate that the mobilization of Mo through chemical weathering is driven by physical weathering in the catchments of the South Asian Rivers.

Antarctic ice cores provide past atmospheric composition beyond the timeframe of the instrumental records. Here, we examine the record of copper (Cu), a trace metal contaminant, from an ice core record spanning the past 200 years (1809–2012 CE) from the coastal Dronning Maud Land (cDML), East Antarctica (71.5° S, 10.25° E). We observed two-phase variability in Cu flux, first with no discernible trend (slope = − 0.0001, p = 0.27), and marked by a few high flux periods related to El Niño Southern Oscillations (ENSO) events during 1809–1942 (average = 0.05 µg cm−2 a−1), and second phase with an exponentially increasing trend that started around 1943 (R2 = 0.424, average = 0.09 µg cm−2 a−1), resulting in the doubling of Cu deposition after 1985 (average = 0.14 µg cm−2 a−1). Our study reveals that the dramatic increase of Cu deposition since 1985 can be attributed to the combined role of 42-fold increase in Cu production from Chilean Cu mines and favorable atmospheric transport by a deepened low-pressure anomaly and stronger westerlies associated with the positive phase of the Southern Annular Mode (SAM). A comparable trend was observed for antimony (Sb), a trace element often associated with primary copper minerals, further supporting the attribution of elevated Cu deposition at the core site to historical mining activities. Our investigation on the Cu flux record revealed strong linkages with climate modes such as SAM and ENSO in controlling the variability of the Cu deposition flux. Further, examining the specific peaks and dips in the Cu flux record during 1985–2012, peak years showed an average wind intensification of 0.45–1.05 ms−1 compared to dip years, which contributed to the doubling of Cu deposition over the region. Considering this increasing trend in Cu deposition in this region, elevated copper levels may pose a long-term risk to phytoplankton growth and primary productivity in the Southern Ocean due to potential Cu toxicity.

Accurate prediction of a West Antarctic Ice Sheet (WAIS) collapse and its impact on sea level in a future warmer climate remains uncertain. Here, we provide evidence for the transition from a smaller-sized WAIS during the warm Pliocene to an expanded ice sheet closer to its modern configuration during the Pleistocene based on geochemical records from the proximity to the current maximum ice loss in the Amundsen Sea. In contrast to Pliocene ice sheet dynamics, the WAIS exhibited a relatively muted response throughout the Pleistocene despite substantial glacial-interglacial variations in atmospheric CO₂ levels, temperature, and orbital forcing. Our data suggest that critical tipping points for WAIS growth occurred under atmospheric-oceanic conditions of the Pliocene-Pleistocene transition. These findings highlight the importance of the Pliocene-Pleistocene transition in establishing the modern configuration of the WAIS and its importance as a key interval for understanding ice sheet stability under the changing climate.

The Paleoproterozoic Mangalwar Complex (MC) comprises various lithologies, including granitoids, amphibolites, metasediments and basement gneisses. Limited geochemical data have made the provenance, paleoweathering conditions and tectonic setting of the MC ambiguous. Addressing these issues, we present the first comprehensive geochemical and Sr-Nd isotopic study of metasediments, along with the geochemistry of amphibolites. Field observations reveal that amphibolites occur as isolated bodies, as intrusive dykes, and as intercalated with studied metasediments. Petrographic studies indicate that both lithologies underwent metamorphism to amphibolite facies. The amphibolites are tholeiites, which are derived from high-degree partial melting of a depleted mantle at shallow depths. Geochemistry and detailed field observations suggest that the amphibolites were emplaced in a continental rift setting, and the studied metasediments were deposited in this rift basin. The geographically nearby situated provenance suggests rapid and short-distance deposition, consistent with low chemical weathering despite globally warm, humid conditions during the Paleoproterozoic. Elemental and isotopic ratios, including Na2O/K2O, SiO2/Al2O3, Al2O3/TiO2, La/Sc, Cr/Th, Th/Co, Th/Sc, Zr/Sc, 87Sr/86Sr and 143Nd/144Nd, and the REE patterns coupled with field observations, indicate that the sediments were derived dominantly from a felsic igneous source with insignificant mafic contribution. The negative epsilon Nd(1.7 Ga) (-15.1 to -4.9) values and T CHUR ages (2.10 to 3.18 Ga) suggest that the provenance of the studied metasediments was a felsic crust. Earlier studies suggested a subduction-related arc setting and an Archean provenance; however, our findings contrast with earlier studies and indicate that the metasedimentary rocks were deposited in a continental rift setting, and the Paleoproterozoic granitoids and ortho-gneisses belonging to the MC served as the provenance.

The Pb/Ca ratio of coralline aragonite is a recognized archive of marine lead (Pb) pollution, while the isotopic composition (Pb-20X/Pb-207) enables source tracing. The critical analytical challenge of Pb analyses is the extremely low concentration of aragonite lattice bound Pb (10(-9) mol mol(-1)). The extremely low levels of Pb in natural corals render the determination of Pb/Ca and Pb isotope ratios susceptible to potential contamination from preexisting detrital matter like clay and organic substances or during laboratory processing. We present a novel method for the accurate and precise determination of Pb/Ca and Pb isotopes (Pb-20X/Pb-207) from <2 mg of coralline CaCO3 by triple quadrupole inductive coupled plasma mass spectrometry (Agilent (R) ICP-QQQ-MS). The external precision of our Pb/Ca ratio determination is better than 2% (n = 56, 2 sigma); whereas the Pb isotope ratios, determined on similar to 50 pg of column purified Pb, have precision better than +/- 0.0008 (1.23%, 2 sigma), +/- 0.0043 (0.38%, 2 sigma), and +/- 0.0042 (0.17%, 2 sigma) for Pb-204/Pb-207, Pb-206/Pb-207, and Pb-208/Pb-207 ratios respectively. The determination of metals/Ca ratios of multiple trace metals (viz. Li/Ca, B/Ca, Mg/Ca, Sr/Ca, U/Ca, etc.) is also possible during the same instrumental session. Our Pb/Ca determination method utilizes matrix matching coupled with external calibration, whereas the Pb isotope method is based on concentration matching and standard-sample bracketing. Overall, the total mass of chemically cleaned coralline CaCO3 required for Pb/Ca and Pb isotope determination is similar to 2-3 mg. Our novel method addresses the key analytical challenges associated with the determination of the Pb concentration and isotope ratio in the coralline archive and outlines a simple method with key advantages compared to the other traditional methods for extremely low Pb concentration and high Ca matrix samples.

Erosion of the Himalaya Mountain and subsequent deposition of sediments in the flood plains, and distal fans are primarily regulated by tectonics, climates, lithology, and relief of the region. These eroded sediments preserve their chemical and isotopic compositions in their depositional archive, which can be used to trace the erosion processes and assess the relative role of controlling factors and their spatio-temporal variations. The present study has analysed the 87Sr/86Sr and epsilon Nd of in silicate phase of sediment recovered from a - 40 m long sedimentary core representing -8 ky of sediment accumulation in the Teesta River mega fan. The lithostratigraphy of the core indicates rapid aggradational nature of the Teesta mega fan. The 87Sr/86Sr and epsilon Nd display large variability with depth, which ranges from 0.75700 to 0.89294 and - 15.1 to -25.0, respectively. The observed 87Sr/86Sr and epsilon Nd values in the core sediments have been interpreted in terms of differential sediment contribution from the Higher and the Lesser Himalayan lithology. The 87Sr/86Sr and epsilon Nd isotope profiles and estimated fractional sediment contributions identify the Lesser Himalaya as the major sediment contributor to the Teesta basin since the mid-Holocene, unlike the other Himalayan River basins, dominated by sediments from the Higher Himalaya after the Last Glacial Maximum. The rapid exhumation and erosion of the tectonically active Rangeet window with the focused precipitation and presence of rock types vulnerable to weathering in the Lesser Himalaya of the basin appear to be the major factors resulting in the sedimentary budget of the Teesta River basin over at least last 8 ky. Our assessment suggests that tectonic activity and climate have a competitive effect on the observed sedimentary budget, with an additional role of lithology. The study infers a major control of active tectonics, precipitation, and lithology on the sedimentary budget of the Himalayan River basins.

Despite the rapid industrial growth and urban expansion along the coastline of the Western Indian Ocean, knowledge of both historical and current levels of anthropogenic lead (Pb) contamination, as well as its impact on the biosphere, remains limited compared to other industrialized regions. We present a twenty-four year long coralline record (1989-2013) of Pb/Ca ratio and Pb isotopes from the Lakshadweep coral reef in the Western Indian Ocean. This new record provides critical insight into source(s), possible transport pathways, and temporal trends in Pb deposition during the studied interval. The long-term trend in the surface seawater Pb concentration ([Pb]SW), reconstructed from the coralline Pb/Ca record, reveals almost doubling in [Pb]SW from ~50 pmol/kg in the year 1990 to ~107 pmol/kg in the year 2013. Bayesian mixing model calculations reveal that among the potential Pb polluting sources to this region, anthropogenic aerosol from the hinterland of the continents was the dominant contributor of Pb (23-89 %). A compilation of available Pb records from the Indian Ocean reveals that Pb isotope distribution patterns in the western and central equatorial Indian Oceans are distinctly different from those observed in the eastern Indian Ocean. The western Indian Ocean records exhibit lower Pb isotope ratios (206Pb/207Pb and 208Pb/207Pb) compared to the East Indian Ocean, suggesting a greater influence of anthropogenic Pb on seawater concentration. These findings highlight the spatio-temporally spread of anthropogenic Pb pollution and its potential impact on the biosphere in the Indian Ocean and therefore emphasize the urgent need for region-specific environmental management strategies. PLAIN LANGUAGE SUMMARY: This study reconstructs the history of lead (Pb) pollution in the Western Indian Ocean. We analyzed a specimen of coral, collected from Lakshadweep, to create a 24-year-long (years 1989 to 2013) for Pb concentration and isotopic composition of seawater in the Western Indian Ocean. Using the coralline Pb/Ca ratio and Pb isotope data, we have reconstructed surface ocean Pb concentration ([PbSW]) and isotopic composition to understand the sources, transport pathways, and temporal depositional trends over the western Indian Ocean during the past two decades. This reconstruction of [PbSW] reveals a doubling from ~50 pmol/kg in the year 1990 to ~107 pmol/kg in the year 2013. Our investigations to fingerprint the Pb source(s) to our study area reveal that majority of the anthropogenic Pb has been contributed by aerosol deposition sourced from the hinterland of the surrounding continents. Our investigation also revealed that the western Indian Ocean is more contaminated by anthropogenic Pb compared to the eastern Indian Ocean. These findings highlight the need for region-specific monitoring efforts in the Indian Ocean as well as the formulation of environmental strategies to mitigate the impact of Pb pollution.

AbstractNitrate (NO3−) deposition in polar ice sheets archives valuable information on past solar activity. However, interpretation of Antarctic ice core NO3− records as a proxy for past solar activity remains challenging due to multiple sources and processes controlling NO3− variability in ice core records. Here, we present a new high‐resolution ice core NO3− record (1905–2005 CE) from coastal Dronning Maud Land, East Antarctica, to investigate the solar signal and other forcing factors/processes in controlling ice core NO3− variability. Our record exhibits significant periodicity in the range of 8–12 years frequency band during 1940–2005 CE, apparently identified as the signal of ∼11 year sunspot cycle; however, such signal was not detected in the previous interval during 1905–1940 CE. To address the discontinuous and/or obscured signals in the present ice core record and inconsistency among various Antarctica ice core records, we extended our investigations to 10 ice core NO3− records from various regions of Antarctica. Analysis of seven records for the common interval from 1738 to 1990 CE reveals dominant periodicities of 8–12 years, indicating solar forcing as a primary driver, followed by precipitation modulated by El Niño‐Southern Oscillation and Pacific Decadal Oscillation. Further, our investigation reveals that the solar signal extracted from multiple records becomes undetectable when mean annual hemispheric sunspot numbers larger than 140, suggesting this is a threshold limit for detecting the solar signal. These findings will improve our present understanding of ice core NO3− records as a proxy for past solar activity.

The present study focuses on the petrographic studies, XRD patterns, whole-rock geochemical data and Nd isotopic data of the clastic rocks of the Paleoproterozoic Mahakoshal Basin which includes meta-argillites, meta-greywackes and quartzites to characterize their provenance, tectonic setting, weathering intensity, and paleoclimate condition. Geochemically, the rock samples of meta-argillite and meta-greywacke in the bivariate plot Log Na2O/K2O vs. Log SiO2/Al2O3 are classified as litharenite and greywacke. The samples of quartzite fall in the fields from the sublitharenite to quartzarenite. The weathering indices such as CIA, α _Ca^Al , α _Na^Al , α _K^Al , α _Sr^Al , α _Ba^Al and Th/U suggest that the clastic rocks have undergone moderate to intense chemical weathering and show K-metasomatism. Chondrite normalized REE patterns, discriminant diagrams of La–Th–Sc and Ni–V–10*Th and various transition elements ratio such as Cr/Th, Th/Co, Th/Sc, and La/Sc support the mixing of the mafic, intermediate and felsic sources. The Eu anomaly is highly variable and ranges from 0.29 to 1.08 and supports that the sediments have been derived from the heterogeneous source. TCHUR model ages are consistent with 1.98–2.92 Ga possible provenance. εNd(t) and f(Sm/Nd) values overlap with the arc and the Archean crust signatures indicating that the sediments are derived from a Paleoproterozoic arc and older Archean crust (TTG gneisses and Archean granite). The opening of the Mahakoshal Basin is characterized by the retreating accretionary orogen and the closure of the basin is due to switching retreating accretionary orogen into advancing accretionary orogen which is contemporaneous to the assembly of the Columbia Supercontinent (∼1.8 Ga).

Recent technological advancement has revolutionized the field of non-traditional stable metal and metalloid isotopes for their wide applications for the study of earth surface processes, reconstructing past oceanic environments, tracing contaminants, and biomedical investigations. Beyond the conventional stable isotopes (H, C, O, N, S), this field has led to a wide exploration of stable isotopes (e.g., Li, B, Mg, Si, Ca, K, V, Cr, Ni, Fe, Cu, Zn, Sr, Mo, Cd, Ba, Hg, U) and their potential applications. This review delves into the applications of stable metal and metalloid isotopes as an important tool for tracing sources and elucidating various processes within the realm of earth, ocean, and environmental studies. The fundamental concept of mass-dependent and -independent isotope fractionations are introduced firstly; the selected "emerging" stable isotopes like Li isotopes (δ7Li), B isotopes (δ11B), and Mo isotopes (δ98Mo) are discussed; their applications as a proxy for earth surface processes, paleo-ocean pH, and paleo-redox conditions in oceans are highlighted respectively; various measurement techniques and their advantages/disadvantages are presented, including chemical extractions of elements and their isotope measurements using a Multi-Collector Inductively Coupled Plasma Mass Spectrometer (MC-ICPMS). Finally, this article highlights the caveats and limitations, challenges, and scopes for future research of the stable isotopes.

The study investigates the sources of metals in urban road dusts using elemental concentration and Pb isotopic ratios. The elemental concentrations are also utilized to determine the present heavy metal emissions as well as projected emissions till 2045. Bayesian mixing model for source apportionment highlights the significant contributions of both exhaust and non-exhaust sources to the metal enriched urban road dusts, with each contributing approximately 40%. Emission analysis reveals that India’s projected electric vehicle (EV) penetration may not be sufficient to suppress the metal emissions from vehicular exhausts. Further challenge is posed by high metal concentrations in the non-exhaust sources, that dominates the emission of some metals compared to exhaust sources. If the metal concentrations remain unchanged, the emission analysis predicts alarming increases in total emissions from all the exhaust and non-exhaust sources by 174%, 176%, 163% and 184% for Ni, Cu, Zn and Pb, respectively, from 2022 to 2045. Thus, it is crucial to reduce the metal concentrations in traffic emission sources and also impose better regulatory measures to improve the urban metal pollution scenario.

The age of emplacement and geochemistry of the lamprophyres are of tectonic significance as they have potential to unravel global scale geodynamic processes. We present petrology, U-Pb SHRIMP apatite and titanite ages and bulk-rock Sr-Nd isotope data for an unmetamorphosed and undeformed lamprophyre dyke from the Simdega area of the Chhotanagpur Gneissic Complex (CGC) which is a component of the E-W trending Central Indian Tectonic Zone (CITZ), India. The CITZ is a major intercontinental suture which separates the northern Indian and the southern Indian blocks whose polarity of their subduction is a contentious issue. The lamprophyre exhibits a strong porphyritic-panidiomorphic texture imparted by the megacrysts/phenocrysts of mica and amphibole with feldspar, apatite, titanite, zircon and opaques confined to the groundmass. Based on combined mineralogy and geochemistry, the lamprophyre is classified to be of calc-alkaline variety (minette) with shoshonitic affinities. Mg# (70.7-78.2) contents highlight the primitive melt character whereas incompatible trace element ratios exclude crustal contamination and are indistinguishable from those of the subduction-related global as well as Eastern Dharwar craton (southern India) calc-alkaline lamprophyres. U-Pb dating of apatite gave an emplace-ment age of 944 +/- 82 Ma which is indistinguishable, within the error limits, from the U-Pb titanite age of 942.1 +/- 5 Ma demonstrating a Neoproterozoic magmatic emplacement age of the lamprophyre synchronous with the Rodinia assembly. Bulk-rock 87Sr/86Srinitial (0.707239 and 0.708910) and epsilon Ndinitial (-8.9 to-8.3) highlights the involvement of an enriched mantle source. Calculated Paleoproterozoic model ages (Nd depleted mantle) of 2.1 Ga of the lamprophyre are indistinguishable from those of the co-spatial amphibolite dykes. Petrogenetic modeling involving rare earth elements reveals that the derivation of the lamprophyre magma from 2 to 3% partial melting of a mixed garnet (70%) and spinel (30%) lherzolitic mantle source with minor phlogopite. Our study highlights that the western part of the CGC was less affected, relative to the eastern part, by the M3 regional amphibolite grade metamorphic event (ca. 920-880 Ma) and also supports the geodynamic models involving northward-directed subduction of the Southern Indian block under the Northern Indian block.-

Atmospheric CO 2 variability on the glacial–interglacial (G–IG) timescale reflects a balance between oceanic and terrestrial processes involving carbon uptake and release. The Southern Ocean CO 2 uptake is considered as an important modulator for the G–IG atmospheric CO 2 variability, while the role of tropical ocean ventilation remains enigmatic. We present critical evidence for CO 2 ventilation from the tropical Indian Ocean through the reconstruction of the Arabian Sea‐surface p CO 2 for the past ∼136 ka utilizing boron isotope (δ 11 B) record of planktic foraminifera, Globigerinoides ruber . Our site in the Arabian Sea presently acts as a significant source of CO 2 . The reconstructed Δ p CO 2 (Δ p CO 2 = p CO 2 Seawater − p CO 2 Atmosphere ) record shows an enhanced CO 2 degassing up to ∼50 ppm during the major cooling events, such as the Last Glacial Maximum, Younger Dryas, and Heinrich‐Stadials. Our investigation based on multiproxy records of sea‐surface temperature, salinity, and productivity suggests that the northward invasion and shoaling of southern source CO 2 ‐rich water, coupled with stronger upwelling, resulted in CO 2 degassing during these cold intervals. This finding is in align with the tropical Atlantic which also demonstrated an enhanced CO 2 degassing during the cold intervals; however, most of the upwelled CO 2 was consumed as the water moved away from the upwelling sites. Therefore, our finding, when considered alongside tropical Atlantic records, suggests that tropical oceans played a minor role in reducing atmospheric CO 2 levels during the cold intervals of the last glacial cycle, supporting the prevailing hypothesis.

During the Southwest monsoon (SWM), aeolian dust is mainly supplied via wet deposition over the northeast Arabian Sea (NEAS). To understand their impact on the biogeochemistry of the Arabian Sea, it is important to identify their sources and characteristics. In this context, wet deposit particulate (WDP) samples were collected at a coastal station (Goa; 15.4° N, 73.8° E) in the NEAS during the SWM for three years. These samples were used to characterize and identify mineral dust sources using mineralogical, elemental, and isotopic (Sr and Nd) signatures. The WDP samples were classified as Beginning of Monsoon (BM, June samples), Mid Monsoon (MM, July-August samples) and End of Monsoon (EM, September samples). Clay mineralogical composition indicate high palygorskite content during BM, which subsequently found to decrease in MM, and almost negligible in EM. However, smectite is highest during MM, with moderate presence of palygorskite during this period. The considerable variation in the relative percentages of clay minerals suggests significant temporal variability in dust sources which is further corroborated by the radiogenic isotopic composition. A strong seasonality in the isotopic composition is observed with 87Sr/86Sr ratio being relatively less radiogenic during MM than the BM and highly radiogenic at the EM. Whereas ƐNd values show an opposite trend to 87Sr/86Sr ratios throughout the monsoon, with more radiogenic ƐNd in the MM, and less radiogenic at the EM. End member mixing plot indicate dominant contribution of dust from the Arabian Peninsula (ARB) and Northeast African (NEA) sources during BM and MM, while a shift towards the Thar desert and Southwest Asian (SWA) sources at the EM. Trace elements associated with different sources were quantified and suggest high Fe concentration is associated with NEA dust sources, despite ARB being major supplier of aeolian dust to the Arabian Sea.