636 Goldschmidt2013 Conference Abstracts Discovery and characterization of Using isotopic analysis of copper to contrasting siderophores produced by assess copper transport and related nitrogen fixing bacteria using partitioning in wetland systems high resolution LC-MS I. BABCSANYI*, F. CHABAUX, V.M. GRANET AND G. IMFELD* OLIVER BAAR, DAVID H. PERLMAN, ANNE M. L. KRAEPIEL AND FRANÇOIS M. M. MOREL* Laboratory of Hydrology and Geochemistry of Strasbourg (LHyGeS), University of Strasbourg/ENGEES, CNRS, 1, Princeton University, Princeton, NJ, USA rue Blessig, 67 084 Strasbourg CEDEX (*correspondence: [email protected]) (*correspondence: [email protected], [email protected]) Azotobacter vinelandii (AV) and Azotobacter chroococcum (AC) are closely related N fixing bacteria. 2 Copper isotopes (65Cu/63Cu) are potentially powerful new Whereas the structures and physiological functions of geochemical proxies for transport and oxidation–reduction siderophores produced by AV have been much studied, those processes in hydromorphic soils, rivers and lake sediments. of AC remain unidentified beyond a general chemical However, the integrative signal of !65Cu has not been used so characterization. Here we have exploited the characteristic far to investigate the transport and partitioning of copper in iron isotopic fingerprint to identify known and unknown wetland systems with respect to both hydrological and siderophores and characterize them structurally using ultra- biogeochemical conditions. Here we used copper isotopes to sensitive high-resolution nano-flow UPLC-MS on an LTQ- investigate the copper cycling in a stormwater wetland (as a Orbitrap XL platform. ‘natural laboratory’) that regularly received copper- Interrogation of preliminary data for AV revealed many contaminated runoff from a 42 ha vineyard catchment putative Fe-chelators with high abundances, including those (Rouffach, Alsace, France). Runoff water, suspended solids, previously identified and other, yet unreported compounds. Siderophores produced by AC were unrelated to those of sediments and plants were regularly collected throughout the AV. Many AC siderophores possess aliphatic side chains of period of copper-based fungicides application (May to July variable length with corresponding changes in hydrophobicity. 2011) to establish the copper mass balance and study isotopic Current work investigates how these chemical differences in fractionations. siderophore production relate to different metal acquisition 60 to 93% of copper in runoff was associated with strategies and occupation of different ecological niches. suspended solids, which were efficiently retained by the wetland (93 to 96%). Copper bound to suspended solids had negative isotope signatures (-0.33 to -0.1 ± 0.1‰), whereas dissolved copper was enriched in 65Cu (0.23 to 1.35 ± 0.06‰). Dissolved copper retention largely varied (68 to 95%) and became depleted in 65Cu when passing through the wetland 65 65 (! Cuinlet-! Cuoutlet: 0.03 to 0.77 ± 0.08‰). This isotopic shift suggests that copper rapidely sorbed to organic matter or mineral phases of the wetland sediments. Under high-flow conditions, copper was less retained by the wetland and was likely mobilised from the wetland sediments. This was attested by a lower !65Cu value of the outflowing dissolved copper, thereby reflecting the contribution of sediment-bound copper (0.02 ± 0.1‰). Copper uptake by the vegetation (Phragmites australis, Cav.) was not a significant retention process in the wetland, and accounted for less than 1.5% of the total copper amount in the wetland. We anticipate our results to be a starting point for using copper isotopes in a comprehensive approach to evaluate processes affecting copper cycling in hydro-biogeochemically dynamic systems, such as wetlands or hyporheic zones. DOI:10.1180/minmag.2013.077.5.2 www.minersoc.org Downloaded from http://pubs.geoscienceworld.org/minmag/article-pdf/77/5/636/2920651/gsminmag.77.5.02-B.pdf by guest on 01 October 2021 Goldschmidt2013 Conference Abstracts 637 High-precision Nd isotope and HFSE U-Pb dating vs. Sr isotope analysis of Deccan Traps chemostratigraphy on weathering profiles Neoproterozoic carbonates: MICHAEL G. BABECHUK1*, MIKE WIDDOWSON2, Shedding light on blind dating? 3 1 MICHAEL MURPHY AND BALZ S. KAMBER 1 1 M. BABINSKI , G.M. PAULA-SANTOS ; 1Trinity College Dublin, Dublin, Ireland M. KUCHENBECKER 2, S. CAETANO-FILHO1, 2The Open University, Milton Keynes, United Kingdom R.I.F. TRINDADE3 AND A.C. PEDROSA-SOARES2 3 University College Dublin, Dublin, Ireland 1 Instituto de Geociências, Universidade de São Paulo, São Paulo, SP, Brazil. ([email protected]) Accurately quantifying the flux of elements from 2 Instituto de Geociências, Universidade Federal de Minas landmasses during pedogenesis necessitates knowledge of the Gerais, Belo Horizonte, MG, Brazil. parent rock chemistry and some control on whether 3Instituto de Geofísica, Universidade de São Paulo, São Paulo, allochthonous materials (e.g., dust) have beem added to the SP, Brazil. profile during exposure. This is important, for instance, in calculating weathering rates from U-series isotopes in young Sr isotope ratios of carbonate rocks have been extensively profiles or interpreting stable isotope depth signatures. The used for global correlations especially on Precambrian rocks Deccan Traps provide an ideal natural laboratory for studying due to lack of fossils and scarcity of dating targets to constrain chemical weathering due to the thick succession of mafic their depositional ages. This “blind dating” procedure has been flows which have been weathered to varying degrees on questioned before but it is still commonly used. Here we different time scales. In addition, the isotopic and elemental present a case study on carbonates from the basal units of the composition of the basalt parent rock contrasts significantly Bambuí Group (central Brazil) where Sr, C, and O with most potential dust sources (e.g., Archean-Proterozoic chemostratigraphy was combined with U-Pb ages from detrital crust of the Dravidian Shield). zircons recovered from pelitic intercalations. Our results show Deeply weathered laterite of the Deccan Traps has a strong incompatibility between 87Sr/86Sr ratios and the experienced significant accumulation of aeolian material detrital zircons record. during its long exposure history. For example, in a full laterite The Bambuí Group is composed of a carbonatic-pelitic profile near Bidar, an upward increase in Th concentration and sucession which overlies a glacial diamictite (Jequitaí Fm.) accompanying decrease in the Nb/Th ratio is evident from the correlated to the Sturtian or Marinoan ice-ages. U-Pb ages base to top. If Nb is assumed to be immobile during from detrital zircons from the diamictite sets the maximum pedogenesis and least affected by dust addition, Th is enriched depositional age at 875 Ma. The cap carbonate that overlies up to 400% relative to the parent rock in the most 13 this diamictite has ! C negative values and was dated at 740 contaminated samples. Variations in the Nb/Th ratio are well ±22 Ma, indicating a Sturtian age. Limestones and dolostones correlated with the 143Nd/144Nd ratio, implicating the source of overlying the cap carbonate show !13C values around 0 ‰. the contaminant as being incompatible element enriched and Upsection, carbonates are organic-rich limestones displaying less radiogenic than the Deccan basalt. 13 highly positive ! C values. All carbonates, including those Near Chhindwara, a sub-Recent weathering profile is overlying the diamitite, show 87Sr/86Sr ratios between 0.7074 exposed which spans across two identifiable basalt flows. The to 0.7076. These ratios are compatible with depositional ages individual flows can be fingerprinted with variations in their as old as 650 Ma according to the global Sr isotope evolution HFSE composition, highlighting another important curves available in the literature. However, detrital zircons consideration in mass balance calculations of a weathering yielded U-Pb ages as young as 540 Ma, pointing to profile. Even more interesting, however, are the uppermost depositional ages close to the Precambrian-Cambrian samples of the lower exposed flow with alkali element, HFSE boundary or even younger, when more radiogenic Sr isotopes ratios, and subtly less radiogenic Nd isotope values which ratios (ca. 0.7085) are expected. This may result from a again suggest contamination with an allochthonous restricted sea context for the Bambuí carbonate platform; component. This is interpreted to represent the entrainment of consequently their Sr isotope ratios do not correspond to that sediment in the lava flow top during emplacement or the of contemporaneous ocens. Several lines of evidence suggest accumulation of dust during post-eruption volcanic quiescence this is not an unusual scenario for Neoproterozoic carbonate prior to the emplacement of the overlying flow. platforms. Our work shows that worldwide correlations based only on Sr isotopes must be considered with caution. DOI:10.1180/minmag.2013.077.5.2 www.minersoc.org Downloaded from http://pubs.geoscienceworld.org/minmag/article-pdf/77/5/636/2920651/gsminmag.77.5.02-B.pdf by guest on 01 October 2021 638 Goldschmidt2013 Conference Abstracts Rocky constraints on catabolic Contaminant geochemistry and energy supply in the subseafloor migration in three different mine sites W. BACH1, W.-A. KAHL1, N. JÖNS1, A. TÜRKE1 in Finland – Comparison of AND O. PLÜMPER2 anthropogenic and geogenic