C and O isotope compositions of modern fresh-water mollusc shells and river waters from Himalaya and Ganga plain

The aim of this paper is to unfold the relationship between O and C isotope compositions of modern fresh-water mollusc shells and water in order to refine the basis of interpretation for paleoenvironnemental reconstruction in the sub-Himalayan river basins. Large number of mollusc shells and associated host water from both running water and closed body of water were analysed including intra-shell variability in a few cases. The O isotopic compositions of river waters in the Himalayas and Ganga plain have a large range, from -18‰ in the north of the High range up to -8 to -4 ‰ in the Ganga plain. d18O of rivers are also seasonally variable, especially in foothills rivers whereas the seasonal contrast is smoothed out for main Himalayan rivers having large catchments. O isotopic compositions of bulk shells (Aragonite) vary between -15 and -5 ‰. Average d18OAra values are consistent with precipitation at equilibrium with host waters at a temperature range of 20-25°C suggesting that shell growth may be favoured during non-monsoon conditions. Shells collected along main Himalayan rivers have d18O values uniformly distributed within -11 and -6 ‰ reflecting the minimal seasonal contrast shown by these rivers. In contrast, O isotopic compositions of shells from foothills rivers vary only by 4‰. This shows that, depending on the type of river where the molluscs grow, the information in term of d18O amplitude will be different for identical climatic conditions. In closed or pond water bodies significant enrichment in 18O due to evaporation is observed. The C isotopic compositions of river dissolved inorganic carbon (DIC) decrease downstream from 0 to -10 ‰ reflecting input of soil derived alkalinity and plant productivity in the river. d13C of shells are systematically lower than compositions calculated for equilibrium with river DIC indicating that in addition to DIC, a significant fraction of carbon is derived from metabolic sources. Intra-shell d13C are stable compared to the seasonal variability of DIC suggesting that the pool of organic carbon changes throughout year

Green Edge ice camp campaigns : understanding the processes controlling the under-ice Arctic phytoplankton spring bloom

The Green Edge initiative was developed to investigate the processes controlling the primary productivity and fate of organic matter produced during the Arctic phytoplankton spring bloom (PSB) and to determine its role in the ecosystem. Two field campaigns were conducted in 2015 and 2016 at an ice camp located on landfast sea ice southeast of Qikiqtarjuaq Island in Baffin Bay (67.4797∘ N, 63.7895∘ W). During both expeditions, a large suite of physical, chemical and biological variables was measured beneath a consolidated sea-ice cover from the surface to the bottom (at 360 m depth) to better understand the factors driving the PSB. Key variables, such as conservative temperature, absolute salinity, radiance, irradiance, nutrient concentrations, chlorophyll a concentration, bacteria, phytoplankton and zooplankton abundance and taxonomy, and carbon stocks and fluxes were routinely measured at the ice camp. Meteorological and snow-relevant variables were also monitored. Here, we present the results of a joint effort to tidy and standardize the collected datasets, which will facilitate their reuse in other Arctic studies

Predominant floodplain over mountain weathering of Himalayan sediments (Ganga basin)

Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 84 (2012): 410-432, doi:10.1016/j.gca.2012.02.001.We present an extensive river sediment dataset covering the Ganga basin from the Himalayan front downstream to the Ganga mainstream in Bangladesh. These sediments were mainly collected over several monsoon seasons and include depth profiles of suspended particles in the river water column. Mineral sorting is the first order control on the chemical composition of river sediments. Taking into account this variability we show that sediments become significantly depleted in mobile elements during their transit through the floodplain. By comparing sediments sampled at the Himalayan front with sediments from the Ganga mainstream in Bangladesh it is possible to budget weathering in the floodplain. Assuming a steady state weathering regime in the floodplain, the weathering of Himalayan sediments in the Gangetic floodplain releases ca. (189 ± 92)109 and (69 ± 22)109 moles/yr of carbonate bound Ca and Mg to the dissolved load, respectively. Silicate weathering releases (53 ± 18)109 and (42 ± 13)109 moles/yr of Na and K while the release of silicate Mg and Ca is substantially lower, between ca. 0 and 20109 moles/yr. Additionally, we show that sediment hydration, [H2O+], is a sensitive tracer of silicate weathering that can be used in continental detrital environments, such as the Ganga basin. Both [H2O+] content and the D/H isotopic composition of sediments increases during floodplain transfer in response to mineral hydrolysis and neoformations associated to weathering reactions. By comparing the chemical composition of river sediments across the floodplain with the composition of the eroded Himalayan source rocks, we suggest that the floodplain is the dominant location of silicate weathering for Na, K and [H2O+]. Overall this work emphasizes the role of the Gangetic floodplain in weathering Himalayan sediments. It also demonstrates how detrital sediments can be used as weathering tracers if mineralogical and chemical sorting effects are properly taken into account.This work was supported by INSU program “Relief de la Terre” and ANR Calimero. Valier Galy was supported by the U.S. National Science Fundation (Grant OCE-0851015)

Macroinvertebrate delta 13C variability analysis for the assessment of lake trophic functioning

International audienceThe aim of this study was to better understand the relationships of within-and among-lake variability of macroinvertebrate carbon stable-isotope ratios with both lake trophic potential and lake trophic functioning

A high-resolution stable isotopic record from the Junggar Basin (NW China) : implications for the paleotopographic evolution of the Tianshan Mountains

This study presents high-resolution oxygen and carbon isotopic records of paleosol carbonates from fluvial sediments and lacustrine carbonates, sampled from the Jingou He and Kuitun He stratigraphic sections, located in the northern Tianshan piedmont. These sections expose remarkable outcrops of Junggar foreland basin sediments that have been previously dated by high-resolution magnetostratigraphy to between ∼23.6 and ∼1 Ma, and ∼10.5 and ∼3.1 Ma. A total of 216 samples of fluvio-lacustrine sediments were collected from which isotopic analyses yield δ18O (SMOW) values that range from 13.7‰ to 29.9‰ in the Jingou He section, and 16.3‰ to 21.0‰ in the Kuitun He section. δ13C (PDB) values range from −12.9‰ to 3.0‰ in the Jingou He section and from −7.8‰ to −4.0% in the Kuitun He section. δ18O values decrease between ∼25 and 23 Ma, and then remain relatively steady, with the exception of one period that contains samples with higher oxygen isotope values at ∼16 Ma. During the periods when there are samples that overlap in time from the Kuitun He and Jingou He sections, we observe a difference of ∼1.7% between values from the two locales. The δ13C values also decrease between ∼25 and 23 Ma, and then remain relatively steady until ∼10 Ma with, again, one short period of higher values at ∼16 Ma. Then, between ∼10 and 3.1 Ma, carbon isotope values progressively increase. We interpret that δ18O and δ13C isotopic values during lacustrine periods (∼25–23 Ma and ∼16 Ma) as largely controlled by evaporation and opening/closing of the lake to external inputs. We interpret the δ18O values of paleosol carbonate in the Junggar Basin to be influenced by the hypsometry of the high Tianshan range while the δ13C values may record the uplift history of the depositional area in the foreland basin itself as well as the isotopic composition of plants. Consequently, we conclude that the Jingou He and Kuitun He drainage basins in the Central Tianshan have remained at relatively unchanged elevations for the past ∼20 Ma. We also suggest that the elevation of the southern part of the foreland basin increased between ∼10 and ∼3.1 Ma, probably as a result of tectonic deformation in the piedmont and sedimentary filling of the sedimentary basin. The carbon isotope record remains relatively stable through time, and isotopic values suggest that there was little or no expansion of C4 plants in this region in the late Miocene

Particle absorption (aP) in the surface water of the Mackenzie Delta Region during 4 expeditions from spring to fall in 2019

Absorbance of particles retained on GF/F (0.7 µm) filters was measured using a Varian Cary 100 spectrophotometer equipped with an integrated sphere. Absorbance and reflectance spectra were measured by placing a sample filter in front and back of an integrating sphere, respectively (so-called Transmittance-Reflectance or T-R method; Tassan & Ferrari 1995; doi:10.4319/lo.1995.40.8.1358). An appropriate beta factor specific to the geometry of the instrument was used to calculate absorption coefficients of particles (Tassan & Ferrari 2002; doi:10.1093/plankt/24.8.757)

Stable water isotopes (δ18O, δD, d-excess) in the surface water of the Mackenzie Delta Region during 4 expeditions from spring to fall in 2019

Water samples for stable isotopes were collected untreated in 10 mL HDPE vials, sealed tightly, stored in the dark at 4°C. Measurements were conducted at the laboratory facility for stable isotopes at AWI Potsdam using a Finnigan MAT Delta-S mass spectrometer equipped with equilibration units for the online determination of hydrogen and oxygen isotopic composition. The data is given as δD and δ18O values, which is the per mille difference to standard V-SMOW. The deuterium excess (d-excess) is calculated by: d-excess=δD-8.*δ18O. The measurement accuracy for hydrogen and oxygen isotopes was better than ±0.8%¸ and ±0.1%, respectively (Meyer et al., 2000; doi:10.1080/10256010008032939)

Colored dissolved organic matter absorption (aCDOM) and spectal slopes (S) in the surface water of the Mackenzie Delta Region during 4 expeditions from spring to fall in 2019

Measurement of CDOM absorption was conducted from a water sample within 12 hours of collection using an UltraPath liquid waveguide system (World Precision Instruments, Inc.) over the wavelengths ranging from 200 to 722 nm (see also Matsuoka et al. (2012; doi:10.5194/bg-9-925-2012) for details). To minimize temperature effects, both the sample and the reference water were kept at 4 °C for at least 30 minutes prior to analysis. We followed the International Ocean Colour Coordinating Group (IOCCG) Ocean Optics and Biogeochemistry CDOM protocols (Mannino et al., 2019 (see further details)) with a few modifications: 1) reference water with salinity ±2 relative to the sample was prepared on site a few hours before sample analysis to minimize the effect of difference in refractive index between sample and reference; 2) aCDOM(λ) was measured in flow mode, meaning, a measurement was made while water was running using a peristaltic pump (Lefering et al., 2017; doi:10.1364/AO.56.006357). While the use of a long optical cell provides a good better signal particularly withinin the visible spectral domain essential to SOCRS, it necessarily suffers from light saturation in the UV domain. To overcome this issue, an optimal length of a cell (i.e. 10 cm or 200 cm) was selected following an empirical relationship between optical density observed at 350 and 443 nm based on Matsuoka et al. (2012; doi:10.5194/bg-9-925-2012). For each sample, measurements were done in triplicates of which each was visually inspected for quality control. CDOM measurements were fitted using following equation: a_CDOM (λ)=a_CDOM (λ_0 )*e^(-S(λ-λ_0)), where S is the spectral slope of aCDOM(λ) between 350 and 500 nm (Babin et al., 2003; doi:10.1029/2001JC000882 and Matsuoka et al., 2012; doi:10.5194/bg-9-925-2012)

Dissolved organic carbon (DOC) concentration in the surface water of the Mackenzie Delta Region during 4 expeditions from spring to fall in 2019

Water samples were filtered through 0.7 µm GF/F filter, and acidified with 25 µL Suprapur HCl (10 M) on the same day of sampling. DOC samples were stored and kept at 4°C in the dark during transport until further analysis. Concentration of DOC was measured using high-temperature catalytic oxidation (TOC-VCPH, Shimadzu) at the Alfred-Wegener-Institute (AWI) Potsdam, Germany. Blanks (Milli-Q water) and certified reference standards (Battle-02, Mauri-09 or Super-05 from the National Laboratory for Environmental Testing, Canada) were measured for quality control

Bacteria cells in the surface water of the Mackenzie Delta Region during 4 expeditions from spring to fall in 2019

Samples for bacterial abundance (1.5 mL) were preserved with glutaraldehyde (1% final concentration) and stored at -80°C. Samples were stained with SYBRTM Green I (Thermofisher Scientific) and analyzed on a flow cytometer (FACSCanto, BD Biosciences) as previously described (Gasol & Del Giorgio, 2000; doi:10.3989/scimar.2000.64n2197)