The dominant role of extreme precipitation events in Antarctic snowfall variability

Antarctic snowfall consists of frequent clear‐sky precipitation and heavier falls from intrusions of maritime airmasses associated with amplified planetary waves. We investigate the importance of different precipitation events using the output of the RACMO2 model. Extreme precipitation events consisting of the largest 10% of daily totals are shown to contribute more than 40% of the total annual precipitation across much of the continent, with some areas receiving in excess of 60% of the total from these events. The greatest contribution of extreme precipitation events to the annual total is in the coastal areas and especially on the ice shelves, with the Amery Ice Shelf receiving 50% of its annual precipitation in less than the 10 days of heaviest precipitation. For the continent as a whole, 70% of the variance of the annual precipitation is explained by variability in precipitation from extreme precipitation events, with this figure rising to over 90% in some areas

Sr and ⁸⁷Sr/⁸⁶Sr in estuaries of western India: impact of submarine groundwater discharge

Dissolved Sr and 87Sr/86Sr are measured in the Narmada, Tapi and the Mandovi estuaries linked to the eastern Arabian Sea. The concentration of dissolved Sr and 87Sr/86Sr in the river water endmembers show significant differences reflecting the lithologies they drain. The distribution of Sr in all these estuaries shows a near perfect two endmember mixing between river water and seawater suggesting that there is no discernible net addition/removal of Sr from the estuarine waters. In contrast, 87Sr/86Sr shows non-conservative behaviour in all these estuaries, its distribution exhibits significant departure from the theoretical mixing lines. A likely mechanism for this difference in the behaviour between dissolved Sr and its 87Sr/86Sr is the discharge of submarine groundwater (SGD) which can modify the 87Sr/86Sr of the estuarine waters by exchange with sediments without causing measurable changes in Sr concentration. The impact of such an exchange process on the 87Sr/86Sr of the estuaries and therefore on the Sr isotope composition of dissolved Sr entering the Arabian Sea differs among the three estuaries and also between seasons in the Narmada. The non-conservative behaviour of 87Sr/86Sr provides a handle to estimate the quantum of SGD to these estuaries. The Sr concentration, 87Sr/86Sr ratio and salinity of the submarine groundwater and estimate of its fluxes to the Narmada estuary have been made using inverse model calculations. The model derived SGD flow rates are ∼5 and 280 cm/day during pre-monsoon and monsoon, respectively. The more radiogenic Sr isotope composition of SGD relative to the seawater suggests that SGD acts as an additional source of 87Sr to the Arabian Sea

Tracing paleoerosion in the Ganga Basin

The Ganga River supplies about ∼500-1000 tons of sediments (Galy and France-Lanord 2001; Hay 1998; Milliman and Syvitski 1992), from the Himalaya, predominantly the Higher Himalaya (Singh et al., 2008) to the Ganga plain and finally to the Bay of Bengal.Records of erosional process in the Himalaya over millennia time scales are preserved in sediments of the Ganga plain and can serve as an archive to study paleoerosion in the region. In this study an effort is made to track the variations in the provenance of the sediments in the Ganga Plain, through analysis of silicate fraction of sediments from a 50 m long core for Sr, Nd concentration and isotopic composition. The core was raised from IIT Kanpur campus (26030'77"N and 80014'1.87"E). The Sr and Nd isotope measurements were made following conventional procedures and using Isoprobe-T Thermal Ionisation Mass Spectrometer. The chronology of this core is available based on the OSL dating of feldspars. Sr concentration in the silicate phase from different depths of the core varies from 77 ppm to 225 ppm with 87Sr/86Sr ranges from 0.72701 to 0.76708 (Fig. 1). The Nd content of these sediments varies from 18 ppm to 42 ppm with ∈Nd values in the range of -16.6 to -14.4. The Nd and Sr isotopic composition of these sediments are determined by the mixing proportion of material derived from the Higher Himalaya (HH) and the Lesser Himalaya (LH), the two major sources of sediments to the Ganga Plain. The Higher Himalayan source,which includes the Tethyan Sedimentary Sequences (TSS) and the Higher Himalayan Crystallines (HHC), is characterized by lower 87Sr/86Sr, 0.71 to 0.79 and enriched ∈Nd, -16 to -12. The Lesser Himalaya consists of lithologies with more radiogenic Sr and depleted Nd isotope composition, in the range of 0.72 – 0.95 and -25 to -23 respectively (Singh et al. 2008). The shaded bands represent major excursion in 87Sr/86Sr and ∈Nd. The Sr and Nd isotope profiles of the sediment core show four excursions at ∼6.6, 17.4, 34 and 41m corresponding to the ages of ∼20, 35, 70 and 85 Ka (Fig.1). The trend in 87Sr/86Sr excursion is opposite to that of ∈Nd, i.e., increase in 87Sr/86Sr coincides with decrease in ∈Nd. These excursions can be interpreted in terms of variations in mixing proportion of HHLH derived sediments. Such variations in relative contribution of HH-LH can occur in response to climate/tectonic changes. The observation that two of the excursions, ∼20 Ka and ∼70 Ka, coincide with the two glacial maxima is an indication of the climate control on the sediment supply (Owen et al. 2002; Prell and Kutzbach 1987; Sharma and Owen 1996). Glacial periods being characterized by low precipitation and more extensive ice cover over the HH decreases the contribution of the sediments from the HH. Thus increases in the proportion of LH sediment supply to the plain. The LH, being high 87Sr/86Sr and depleted in ∈Nd, caused high 87Sr/86Sr and depleted ∈Nd in the sediment. This study underscores the importance of climate in controlling erosion in the Himalaya over 100 Ka time scale

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

Foraminifera boron isotope, sea surface temperature, salinity, pH and pCO2 data from the eastern Arabian Sea during the last glacial-interglacial interval

Data presented here are trace-elements and boron isotope composition of planktic foraminifera G. ruber (250-355 μm) along with reconstructed surface ocean temperature, salinity, pH and pCO2 for the past 136 Ka from the south-eastern Arabian Sea. Foraminifera cleaning was carried out using the method adopted from Barker et al. 2003. Boron was purified using the micro-distillation method (Misra et al., 2014a). Trace-element analysis (e.g. Mg/Ca) was carried out using the High-Resolution Inductively Coupled Plasma Mass Spectrometer (HR-ICPMS) (Misra et al., 2014b). Boron isotope analysis was carried out using Thermo Neptune Plus multi-collector inductively coupled plasma mass spectrometer (MC–ICPMS), following the method described in Tarique et al. 2021, and Lloyd et al. 2018. Sea surface temperature (SST) was calculated using the foraminifera Mg/Ca utilizing the method adapted from Gray and Evans 2019. Sea surface salinity (SSS) was calculated using the Mg/Ca derived SST, foraminifera d18O and regional seawater d18O and salinity relationship

Sr, C and O isotopes in carbonate nodules from the Ganga Plain: evidence for recent abrupt rise in dissolved <SUP>87</SUP>Sr/<SUP>86</SUP>Sr ratios of the Ganga

The evolution of <SUP>87</SUP>Sr/<SUP>86</SUP>Sr ratio of the Ganga water during the past ˜ 100 ka has been reconstructed in this study. The <SUP>87</SUP>Sr/<SUP>86</SUP>Sr, δ<SUP>13</SUP>C and δ<SUP>18</SUP>O values have been measured in carbonate nodules from different depths of two sediment cores raised from the Indian Institute of Technology Kanpur (IITK) campus (50 m long) and Jagdishpur (JP, 25 m long) respectively. The <SUP>87</SUP>Sr/<SUP>86</SUP>Sr ratios of the carbonate nodules range from 0.7142 to 0.7189 in the IITK and 0.7142 to 0.7367 in the JP cores. The nodules in general, display significantly lower <SUP>87</SUP>Sr/<SUP>86</SUP>Sr ratio compared to contemporary Ganga river water at Kanpur, however, values of <SUP>87</SUP>Sr/<SUP>86</SUP>Sr ratio are observed in the nodules of the JP core near the surface are consistent with that of the present day Ganga water at Kanpur as well as groundwater samples from adjacent areas indicate recent abrupt increase in <SUP>87</SUP>Sr/<SUP>86</SUP>Sr ratio of the Ganga. These findings are also consistent with the concomitant increase in <SUP>87</SUP>Sr/<SUP>86</SUP>Sr ratio of silicates in contemporary sediments of the Ganga at Kanpur compared to that of past ˜ 100 ka. The sudden rise of <SUP>87</SUP>Sr/<SUP>86</SUP>Sr ratio of the Ganga is probably due to increase in the relative proportion of Sr from the Lesser Himalaya containing silicates and carbonates with higher <SUP>87</SUP>Sr/<SUP>86</SUP>Sr ratio. The cause for the recent increase in Sr contribution from the Lesser Himalaya is not clear; this could be due to enhanced agricultural activities and deforestation and or climatic variability during recent times resulting in more erosion in the Lesser Himalaya. The δ<SUP>13</SUP>C and δ<SUP>18</SUP>O, measured in the nodules from the IITK core, vary from - 6.8 to + 1.6%. and - 8.3 to - 5.4%. respectively. The co-variation of δ<SUP>13</SUP>C and δ<SUP>18</SUP>O suggest the impact of paleoclimate/paleovegetation. Petrography and chemical composition of carbonate nodules indicate little or no diagenetic alteration. Research highlights:› <SUP>87</SUP>Sr/<SUP>86</SUP>Sr of the Ganga water was low during the last 100 ka except the recent past. › Recent increase in <SUP>87</SUP>Sr/<SUP>86</SUP>Sr could be due to recent climatic/anthropogenic impact. › These recent activities could have resulted more weathering in the Lesser Himalaya. › Role of Himalayan rivers towards marine <SUP>87</SUP>Sr/<SUP>86</SUP>Sr budget needs to be reevaluated. › This requires better constraint on the temporal variation in <SUP>87</SUP>Sr/<SUP>86</SUP>Sr of the Ganga