Temporal variations in ⁸⁷Sr/⁸⁶Sr and ε_Nd in sediments of the southeastern Arabian Sea: impact of monsoon and surface water circulation

Sr and Nd isotopic composition of silicate fractions of sediments have been measured in two well dated gravity cores from the eastern Arabian Sea archiving a depositional history of ∼29 and ∼40 ka. The 87Sr/86Sr and εNd in the northern core (SS-3104G; 12.8°N, 71.7°E) ranges from 0.71416 to 0.71840 and −8.8 to −12.8; these variations are limited compared to those in the southeastern core (SS-3101G; 6.0°N, 74.0°E), in which they vary from 0.71412 to 0.72069 and −9.0 to −15.2 respectively. This suggests that the variation in the relative proportions of sediments supplied from different sources to the core SS-3104G are limited compared to core SS-3101G. The 87Sr/86Sr and εNd profiles of SS-3101G exhibit two major excursions, ca. 9 ka and 20 ka, coinciding with periods of Holocene Intensified Monsoon Phase (IMP) and the Last Glacial Maximum (LGM) respectively with more radiogenic 87Sr/86Sr and lower εNd during these periods. These excursions have been explained in terms of changes in the erosion patterns in the source regions and surface circulation of the Northern Indian Ocean resulting from monsoon intensity variations. The intensification of North-East (NE) monsoon and associated strengthening of the East Indian Coastal Current in southwest direction during LGM transported sediments with higher 87Sr/86Sr and lower εNd from the western Bay of Bengal to the Arabian Sea. In contrast, enhanced South-West (SW) monsoon at ∼9 ka facilitated the transport of sediments from the northern Arabian Sea, particularly Indus derived, to the southeastern Arabian Sea. This study thus highlights the impact of monsoon variability on erosion patterns and ocean surface currents on the dispersal of sediments in determining the Sr and Nd isotopic composition of sediments deposited in the eastern Arabian Sea during the last ∼40 ka

Neodymium Isotope Constraints on the Origin of TTGs and High-K Granitoids in the Bundelkhand Craton, Central India : Implications for Archaean Crustal Evolution

The Bundelkhand craton in central India consists mainly of abundant high-K granitoids formed at the Archaean-Proterozoic boundary and several enclosed rafts of TTGs (tonalite-trondhjemite-granodiorites) up to 3.5 Ga. Therefore, the Bundelkhand craton is a key locality for studies on Archaean crustal growth and the emergence of multisource granitoid batholiths that stabilised a supercontinent at 2.5 Ga. Based on their geochemical characteristics, the high-K granitoids are divided into low silica-high Mg (sanukitoids and hybrids) and high silica-low Mg (anatectic) groups. We aim to provide new insights into the role of juvenile versus crustal sources in the evolution of the TTG, sanukitoid, hybrid, and anatectic granitoids of the Bundelkhand craton by comparing their key geochemical signatures with new Nd isotope evidence on crustal contributions and residence times. The ages and geochemical signatures as well as epsilon Nd(t) values and Nd model ages of TTGs point towards partial melting of a juvenile or short-lived mafic crust at different depths. Paleoarchaean TTGs show short crustal residence times and contributions from the newly formed crust, whereas Neoarchaean TTGs have long crustal residence times and contributions from the Paleoarchaean crust. This may reflect the transition from melting in a primitive oceanic plateau (3.4-3.2 Ga) in plume settings, resulting in a Paleoarchaean protocontinent, to 2.7 Ga subduction and island arc accretion along the protocontinent. The 2.5 Ga high-K granitoids formed at convergent subduction settings by partial melting of the mantle wedge and preexisting crust. Sanukitoids and hybrid granitoids originated in the mantle, the latter showing stronger crustal contributions, whereas abundant anatectic granitoids were products of pure crustal melting. Our Nd data and geochemical signatures support a change from early mafic sources to strong crust-mantle interactions towards the A-P boundary, probably reflecting the onset of supercontinent cycles.Peer reviewe

Tracing the Vedic Saraswati River in the Great Rann of Kachchh

© The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 7 (2017): 5476, doi:10.1038/s41598-017-05745-8.The lost Saraswati River mentioned in the ancient Indian tradition is postulated to have flown independently of the Indus River into the Arabian Sea, perhaps along courses of now defunct rivers such as Ghaggar, Hakra and Nara. The persistence of such a river during the Harappan Bronze Age and the Iron Age Vedic period is strongly debated. We drilled in the Great Rann of Kachchh (Kutch), an infilled gulf of the Arabian Sea, which must have received input from the Saraswati, if active. Nd and Sr isotopic measurements suggest that a distinct source may have been present before 10 ka. Later in Holocene, under a drying climate, sediments from the Thar Desert probably choked the signature of an independent Saraswati-like river. Alternatively, without excluding a Saraswati-like secondary source, the Indus and the Thar were the dominant sources throughout the post-glacial history of the GRK. Indus-derived sediment accelerated the infilling of GRK after ~6 ka when the Indus delta started to grow. Until its complete infilling few centuries ago, freshwater input from the Indus, and perhaps from the Ghaggar-Hakra-Nara, probably sustained a productive marine environment as well as navigability toward old coastal Harappan and historic towns in the region.The drilling effort and subsequent study of the cores was funded by Department of Science and Technology (DST), Government of India sponsored research project to DMM (Project No. SR/S4/ES-21/Kachchh Window/P1) under the science of Shallow Subsurface Programme (SSS). N. Khonde gratefully acknowledges Indo-US Post-doctoral Fellowship sponsored by SERB-IUSSTF for research work at Woods Hole Oceanographic Institution

Water circulation in Ryugu asteroid affected the distribution of nucleosynthetic isotope anomalies in returned sample

Studies of material returned from Cb asteroid Ryugu have revealed considerable mineralogical and chemical heterogeneity, stemming primarily from brecciation and aqueous alteration. Isotopic anomalies could have also been affected by delivery of exogenous clasts and aqueous mobilization of soluble elements. Here, we show that isotopic anomalies for mildly soluble Cr are highly variable in Ryugu and CI chondrites, whereas those of Ti are relatively uniform. This variation in Cr isotope ratios is most likely due to physicochemical fractionation between 54Cr-rich presolar nanoparticles and Cr-bearing secondary minerals at the millimeter-scale in the bulk samples, likely due to extensive aqueous alteration in their parent bodies that occurred 5:2þ11::84 Ma after Solar System birth. In contrast, Ti isotopes were marginally affected by this process. Our results show that isotopic heterogeneities in asteroids are not all nebular or accretionary in nature but can also reflect element redistribution by water

Rare earth elements and ⁸⁷Sr/⁸⁶Sr isotopic characterization of Indian Basmati rice as potential tool for its geographical authenticity

The increasing demand for premium priced Indian Basmati rice (Oryza sativa) in world commodity market causing fraudulent activities like adulteration, mislabelling. In order to develop authentication method for Indian Basmati rice, 87Sr/86Sr ratios and REEs composition of Basmati rice, soil and water samples were determined and evaluated their ability as geographical tracer in the present study. In addition, the possible source of Sr in rice plant has also been examined. Basmati rice samples (n = 82) showed 87Sr/86Sr ratios in the range 0.71143–0.73448 and concentrations of 10 REEs (La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Er, Yb) in ppb levels. Statistical analysis showed strong correlation between 87Sr/86Sr ratios of rice, silicate and carbonate fractions of soil. Good correlation and closeness of 87Sr/86Sr of rice with water indicate its uptake in rice from water. Rice grown in southern Uttar Pradesh contains higher 87Sr/86Sr compared to other region of Indo-Gangetic Plain due to higher 87Sr/86Sr of the Ganga compared to other rivers. 87Sr/86Sr ratios can be used as a tracer for differentiating Indian Basmati rice from the other country originated rice samples

Molybdenum isotopes in two Indian estuaries: mixing characteristics and input to oceans

The distributions of dissolved and particulate Mo and their isotope composition (δ⁹⁸Mo) have been measured in the Narmada and the Tapi estuaries draining into the Arabian Sea. During monsoon, the δ⁹⁸Mo of dissolved Mo in the Narmada estuary ranges from 0.49‰ to 2.19‰ in the salinity range 0–17.2 practical salinity unit (psu) quite similar to that in the Tapi estuary, 0.99–2.36‰, in the salinity range 0–20.3 psu. Mo concentration in suspended sediments of the Narmada estuary collected during monsoon average 512 ± 44 ng/g (range 459–602 ng/g) similar to that measured in one sample from the Tapi estuary 560 ng/g Mo. δ⁹⁸Mo of particulate Mo in the Narmada ranges from −0.21‰ to 0.48‰ with an average −0.03 ± 0.2‰. Dissolved Mo in the Narmada and the Tapi rivers display isotopically heavier Mο compared to that in basalts, the major lithology of their drainage. This could result from a variety of processes, preferential weathering of Mo rich sulphide minerals dispersed in the basalts, preferential removal of isotopically lighter Mo during transport or contribution from marine cyclic salts supplied via rain or chemical weathering of organic rich shales in the basins. The distribution of δ⁹⁸Mo in the Narmada and the Tapi estuaries with salinity does not follow the theoretical mixing line between river and seawater endmembers suggesting its non-conservative behavior. Particulate Mo and δ⁹⁸Mo show concomitant increase with salinity in the Narmada estuary indicating loss of dissolved Mo by adsorption onto Fe–Mn oxyhydroxide. Balancing the Mo budget along the course of these estuaries using inverse model suggests that in the Narmada estuary there could be loss up to 8% of the dissolved Mo and that in the Tapi supply from anthropogenic sources could be up to 27%. The results obtained in this study bring out the processes modifying riverine input of Mo and its δ98Mo in the estuaries, oxic sink in the Narmada and anthropogenic input in the Tapi. Repetitive adsorption and desorption of Mo in the Narmada estuary can modify the supply of dissolved Mo and its δ⁹⁸Mo relative to riverine supply by up to 40%, this can significantly impact the Mo isotope budget of the oceans. In contrast, in the Tapi estuary there is enhancement in the dissolved supply of Mo relative to that from river due to anthropogenic input of Mo. The investigations in these two estuaries underscore the importance of solute particle interactions and anthropogenic input in determining the Mo flux and its δ⁹⁸Mo to the open Arabian Sea

Anomalous sulfur isotope compositions of volcanic sulfate over the last millennium in Antarctic ice cores

International audienceThe reconstruction of past volcanism from glaciological archives is based on the measurement of sulfate concentrations in ice. This method does not allow a proper evaluation of the climatic impact of an eruption owing to the uncertainty in classifying an event between stratospheric or tropospheric. This work develops a new method, using anomalous sulfur isotope composition of volcanic sulfate in order to identify stratospheric eruptions over the last millennium. The advantages and limits of this new method are established with the examination of the 10 largest volcanic signals in ice cores from Dome C and South Pole, Antarctica. Of the 10, seven are identified as stratospheric eruptions. Among them, three have been known to be stratospheric (Tambora, Kuwae, the 1259 Unknown Event) and they exhibit anomalous sulfur isotope compositions. Three unknown events (circa 1277, 1230, 1170 A.D.) and the Serua eruption have been identified as stratospheric eruptions, which suggests for the first time that they could have had significant climatic impact. However, the Kuwae and the 1259 Unknown Event stratospheric eruptions exhibit different anomalous sulfur isotope compositions between South Pole and Dome C samples. Differences in sulfate deposition and preservation patterns between the two sites can help explain these discrepancies. This study shows that the presence of an anomalous sulfur isotope composition of volcanic sulfate in ice core indicates a stratospheric eruption, but the absence of such composition does not necessarily lead to the conclusion of a tropospheric process because of differences in the sulfate deposition on the ice sheet

Isotope signature study of the tea samples produced at four different regions in India

India ranks second in the world for tea production and is well known for Darjeeling tea, which has great demand in the world market due to its unique flavor. In the present study, the combination of isotopic composition of Sr (as 87Sr/86Sr) and C (as δ87C) was studied as geographic tracing signatures for Indian tea samples grown in different regions. Authentic tea leaves as well as soil samples were collected from different tea producing regions; namely, Assam, Darjeeling, Munnar and Kangra, which are geographically distinct from one another. Isotopic analyses were performed by Multi-Collector Inductively Coupled Plasma Mass Spectrometry and Elemental Analyzer-Isotope Ratio Mass Spectrometry for Sr and C, respectively. On the basis of Sr isotopic data, Darjeeling tea samples were found to be more radiogenic than the other tea samples, with changes in the 87Sr/86Sr ratio being an excellent geographic indicator. Variations in δ13C proved to be an excellent geographic indicator for Munnar and Kangra teas. The 87Sr/86Sr values were statistically identical in both the soil and the tea. Principal Component Analysis (PCA), using the combination of 87Sr/86Sr, δ13C and strontium concentration data, was used to effectively differentiate among different tea producing regions

Water circulation in Ryugu asteroid affected the distribution of nucleosynthetic isotope anomalies in returned sample

Studies of material returned from Cb asteroid Ryugu have revealed considerable mineralogical and chemical heterogeneity, stemming primarily from brecciation and aqueous alteration. Isotopic anomalies could have also been affected by delivery of exogenous clasts and aqueous mobilization of soluble elements. Here, we show that isotopic anomalies for mildly soluble Cr are highly variable in Ryugu and CI chondrites, whereas those of Ti are relatively uniform. This variation in Cr isotope ratios is most likely due to physicochemical fractionation between 54Cr-rich presolar nanoparticles and Cr-bearing secondary minerals at the millimeter-scale in the bulk samples, likely due to extensive aqueous alteration in their parent bodies that occurred 5.2₋₁.₄⁺¹.⁸ after Solar System birth. In contrast, Ti isotopes were marginally affected by this process. Our results show that isotopic heterogeneities in asteroids are not all nebular or accretionary in nature but can also reflect element redistribution by water.ISSN:2375-254