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  • 1
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    Rhenium-osmium isotope systematics and platinum group element concentrations in oceanic crust (2012)
    Geological Society of America (GSA)
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    Publication Date: 2012-03-01
    Description: Knowledge of the 187Os/188Os ratio as well as the inventories of rhenium and platinum group elements (PGE) in oceanic crust allows quantification of the proportion of recycled oceanic crust in oceanic basalt sources. Our knowledge is limited by the availability of well-characterized sections of oceanic crust, specifically of the plutonic, lower portion that has not been drilled in situ to the Moho. Here we report new data for plutonic rocks that compose the bottom 4680 m of an ocean crust section from the Oman ophiolite. Major and trace element data as well as mineral analyses indicate that Oman gabbros are primitive cumulates from melts similar to typical mid-oceanic ridge basalt. The mean weighted composition of this section (Re: 427 pg/g; Os: 55 pg/g; Ir: 182 pg/g; Pd: 2846 pg/g; Pt: 4151 pg/g; initial 187Os/188Os: 0.142) indicates significantly higher Os and lower Re concentrations than previously analyzed partial sections of ocean crust that lack cumulate lower crust [Deep Sea Drilling Project–Ocean Drilling Program (DSDP-ODP) Hole 504B, ODP Hole 735B], emphasizing that the lower, cumulate oceanic crust dominates the Os budget of oceanic crust. Analyses of mineral grain size fractions indicate that rhenium, PGE, and lead are enriched in the sulfur-rich, fine fraction. This corroborates the notion that small accessory phases, and the melt migration processes affecting them, control these elements’ budgets, distributions, and susceptibilities to alteration. The Re-Os-PGE inventories of a hypothetical 6.5-km-thick composite section that consists of 1825 m of DSDP Hole 504B-like upper oceanic crust and 4680 m of Oman-like lower ocean crust (Re: 736 pg/g; Os: 45 pg/g; Ir: 133 pg/g; Pd: 2122 pg/g; Pt: 2072 pg/g; initial 187Os/188Os: 0.146) provide a new comprehensive assessment of oceanic crust composition. Upon recycling and mixing with reasonable proportions of mantle peridotite, this composite requires at least 2 G.y. to develop sufficiently radiogenic 187Os/188Os to generate high µ (HIMU: µ = 238U/204Pb) basalts.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 2
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    Tracing river chemistry in space and time : dissolved inorganic constituents of the Fraser River, Canada (2014)
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    Publication Date: 2022-05-25
    Description: Author Posting. © The Author(s), 2013. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 124 (2014): 283-308, doi:10.1016/j.gca.2013.09.006.
    Description: The Fraser River basin in southwestern Canada bears unique geologic and climatic features which make it an ideal setting for investigating the origins, transformations and delivery to the coast of dissolved riverine loads under relatively pristine conditions. We present results from sampling campaigns over three years which demonstrate the lithologic and hydrologic controls on fluxes and isotope compositions of major dissolved inorganic runoff constituents (dissolved nutrients, major and trace elements, 87Sr/86Sr, δD). A time series record near the Fraser mouth allows us to generate new estimates of discharge-weighted concentrations and fluxes, and an overall chemical weathering rate of 32 t km-2 y-1. The seasonal variations in dissolved inorganic species are driven by changes in hydrology, which vary in timing across the basin. The time series record of dissolved 87Sr/86Sr is of particular interest, as a consistent shift between higher (“more radiogenic”) values during spring and summer and less radiogenic values in fall and winter demonstrates the seasonal variability in source contributions throughout the basin. This seasonal shift is also quite large (0.709 – 0.714), with a discharge-weighted annual average of 0.7120 (2 s.d. = 0.0003). We present a mixing model which predicts the seasonal evolution of dissolved 87Sr/86Sr based on tributary compositions and water discharge. This model highlights the importance of chemical weathering fluxes from the old sedimentary bedrock of headwater drainage regions, despite their relatively small contribution to the total water flux.
    Description: This work was supported by the WHOI Academic Programs Office and MIT PAOC Houghton Fund to BMV, a WHOI Arctic Research Initiative grant to ZAW, NSF-ETBC grant OCE-0851015 to BPE and TIE, and NSF grant EAR-1226818 to BPE.
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  • 3
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    Land2Sea database of river drainage basin sizes, annual water discharges, and suspended sediment fluxes (2010)
    American Geophysical Union
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 10 (2009): Q06014, doi:10.1029/2008GC002356.
    Description: The Land2Sea database contains data on the sizes of 1519 exorheic river drainage basins (79% of the exorheic land area), annual suspended sediment fluxes (593 rivers, 63% of the exorheic land area), and water discharges (1272 rivers, 76% of the exorheic land area) that have been compiled from a variety of sources. The database extends earlier compilations, such as GEMS/GLORI. The river basins are grouped into 19 large-scale drainage regions to investigate the regional variability in freshwater and sediment fluxes to various ocean basins. The annual suspended sediment flux to the coastal ocean (~18.5 × 109 tons) is dominated by east Asia (6.1 × 109 tons); Arabia, India, and southeast Asia (4.3 × 109 tons); and eastern South America (2.4 × 109 tons). Small topical islands of Oceania support the highest annual sediment fluxes per drainage area (~9650 t km−2 a−1). Annual freshwater discharge to the coastal ocean (~38,857 km3) is dominated by runoff from eastern South America (11,199 km3); east Asia (7114 km3); and Arabia, India, and southeast Asia (4384 km3). The empirical data agree well with results from global models (ART and BQART) that have been trained on a subset of the data compiled here.
    Description: The Woods Hole Oceanographic Institution, the U.S. National Science Foundation (grants EAR-0519387 and OCE-0851015), and the French CNRS (Observatoire Midi- Pyre´ne´es in Toulouse, France) funded this work.
    Keywords: River ; Database ; Water discharge ; Runoff ; Suspended sediment ; Drainage basin area
    Repository Name: Woods Hole Open Access Server
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  • 4
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    Multiproxy analysis of a new terrestrial and a marine Cretaceous–Paleogene (K–Pg) boundary site from New Zealand (2011)
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    Publication Date: 2022-05-25
    Description: Author Posting. © The Author(s), 2010. 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 75 (2011): 657-672, doi:10.1016/j.gca.2010.10.016.
    Description: An integrated study of palynology, Mössbauer spectroscopy, mineralogy and osmium isotopes has led to the detection of the first K-Pg boundary clay layer in a Southern Hemisphere terrestrial setting. The K-Pg boundary layer was independently identified at centimetre resolution by all the above mentioned methods at the marine K-Pg boundary site of mid-Waipara and the terrestrial site of Compressor Creek (Greymouth coal field), New Zealand. Mössbauer spectroscopy shows an anomaly of Fe-containing particles in both K-Pg boundary sections: jarosite at mid-Waipara and goethite at Compressor Creek. This anomaly coincides with a turnover in vegetation indicated by an interval dominated by fern spores and extinction of key pollen species in both sections. In addition to the terrestrial floristic changes, the mid-Waipara section reveals a turnover in the dinoflagellate assemblages and the appearance of global earliest Danian index species. Geochemical data reveal relatively small iridium enrichments in the boundary layers of 321 pg/g at mid-Waipara and 176 pg/g at Compressor Creek. Unradiogenic 187Os/188Os values of the boundary clay reveal the presence of a significant extraterrestrial component. We interpret the accumulation of Fe nano-phases at the boundary as originating from both the impactor and the crystalline basement target rock. The goethite and jarosite are interpreted as secondary phases formed by weathering and diagenesis. The primary phases were probably controlled by the initial composition of the vapor plume and condensation kinetics rather than condensation thermodynamics. This investigation indicates that identification of Fe in nano-phases by Mössbauer spectroscopy is an accurate and cost-effective method for identifying impact event horizons and it efficiently complements widely used biostratigraphic and geochemical methods.
    Description: V. Vajda acknowledges the financial support provided by the Swedish Royal Academy of Sciences through the Knut & Alice Wallenbergs Foundation and from the Crafoord Foundation. P.S. Willumsen acknowledges financial support from the Carlsberg Foundation no.2008_01_0404.
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  • 5
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    Atmospheric mercury and fine particulate matter in coastal New England : implications for mercury and trace element sources in the northeastern United States (2013)
    Elsevier B.V.
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    Publication Date: 2022-05-25
    Description: This paper is not subject to U.S. copyright. The definitive version was published in Atmospheric Environment 79 (2013): 760–768, doi:10.1016/j.atmosenv.2013.07.031.
    Description: Intensive sampling of ambient atmospheric fine particulate matter was conducted at Woods Hole, Massachusetts over a four-month period from 3 April to 29 July, 2008, in conjunction with year-long deployment of the USGS Mobile Mercury Lab. Results were obtained for trace elements in fine particulate matter concurrently with determination of ambient atmospheric mercury speciation and concentrations of ancillary gasses (SO2, NOx, and O3). For particulate matter, trace element enrichment factors greater than 10 relative to crustal background values were found for As, Bi, Cd, Cu, Hg, Pb, Sb, V, and Zn, indicating contribution of these elements by anthropogenic sources. For other elements, enrichments are consistent with natural marine (Na, Ca, Mg, Sr) or crustal (Ba, Ce, Co, Cs, Fe, Ga, La, Rb, Sc, Th, Ti, U, Y) sources, respectively. Positive matrix factorization was used together with concentration weighted air-mass back trajectories to better define element sources and their locations. Our analysis, based on events exhibiting the 10% highest PM2.5 contributions for each source category, identifies coal-fired power stations concentrated in the U.S. Ohio Valley, metal smelting in eastern Canada, and marine and crustal sources showing surprisingly similar back trajectories, at times each sampling Atlantic coastal airsheds. This pattern is consistent with contribution of Saharan dust by a summer maximum at the latitude of Florida and northward transport up the Atlantic Coast by clockwise circulation of the summer Bermuda High. Results for mercury speciation show diurnal production of RGM by photochemical oxidation of Hg° in a marine environment, and periodic traverse of the study area by correlated RGM-SO2(NOx) plumes, indicative of coal combustion sources.
    Description: We acknowledge support of the USGS Toxic Substances Hydrology Program, the USGS Energy Resources Program, the National Science Foundation Small Grants for Exploratory Research Program, and for initial support, the USGS Mendenhall Postdoctoral Program.
    Keywords: Trace elements ; PM2.5 ; Mercury speciation ; Source attribution ; Saharan dust ; Transport of pollutants ; Woods Hole ; Cape Cod ; Massachusetts ; Coastal New England
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  • 6
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    Dissolved strontium in the subterranean estuary- implications for the marine strontium isotope budget (2013)
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    Publication Date: 2022-05-25
    Description: Author Posting. © The Author(s), 2013. 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 117 (2013): 33-52, doi:10.1016/j.gca.2013.03.021.
    Description: Submarine groundwater discharge (SGD) to the ocean supplies Sr with less radiogenic 87Sr/86Sr than seawater, and thus constitutes an important term in the Sr isotope budget in the modern ocean. However, few data exist for Sr in coastal groundwater or in the geochemically dynamic subterranean estuary (STE). We examined Sr concentrations and isotope ratios from nine globally-distributed coastal sites and characterized the behavior of Sr in the STE. Dissolved Sr generally mixed conservatively in the STE, although large differences were observed in the meteoric groundwater end-member Sr concentrations among sites (0.1 – 24 μM Sr). Strontium isotope exchange was observed in the STE at five of the sites studied, and invariably favored the meteoric groundwater end-member signature. Most of the observed isotope exchange occurred in the salinity range 5-15, and reached up to 40% exchange at salinity 10. Differences in fresh groundwater Sr concentrations and isotope ratios (87Sr/86Sr = 0.707-0.710) reflected aquifer lithology. The SGD end-member 87Sr/86Sr must be lower than modern seawater (i.e., less than 0.70916) in part because groundwater Sr concentrations are orders of magnitude higher in less-carbonate and volcanic island aquifers. A simple lithological model and groundwater Sr data compiled from the literature were used to estimate a global average groundwater end-member of 2.9 μM Sr with 87Sr/86Sr = 0.7089. This represents a meteoric-SGD-driven Sr input to the ocean of 0.7-2.8 × 1010 mol Sr y-1. Meteoric SGD therefore accounts for 2-8% of the oceanic Sr isotope budget, comparable to other known source terms, but is insufficient to balance the remainder of the budget. Using reported estimates for brackish SGD, the estimated volume discharge at salinity 10 (7-11 × 1015 L y-1) was used to evaluate the impact of isotope exchange in the STE on the brackish SGD Sr flux. A moderate estimate of 25% isotope exchange in the STE gives an SGD Sr end-member 87Sr/86Sr of 0.7091. The brackish SGD Sr flux thus accounts for 11-23% of the marine Sr isotope budget, but does not appear sufficient to balance the ~40% remaining after other known sources are included. Substantial uncertainties remain for estimating the SGD source of Sr to the global ocean, especially in the determination of the volume flux of meteoric SGD, and in the paucity of measurements of groundwater Sr isotope composition in major SGD regions such as Papua New Guinea, the South America west coast, and West Africa. Consequently, our global estimate should be viewed with some caution. Nevertheless, we show that the combined sources of meteoric SGD and brackish SGD coupled with isotope exchange in the STE may constitute a substantial component (~13-30%) of the modern oceanic 87Sr/86Sr budget, likely exceeding less radiogenic Sr inputs by sedimentary diagenesis and hydrothermal circulation through the mid-ocean ridge system. Temporal variation in SGD Sr fluxes and isotope composition may have contributed to fluctuations in the oceanic 87Sr/86Sr ratio over geologic time.
    Description: This project was supported by funding from the WHOI Coastal Ocean 670 Institute and the Tropical Research Initiative, and NSF OCE-0751525 to MAC. BPE acknowledges financial support from NSF ETBC-85101500 and a WHOI Coastal Ocean Institute Fellowship.
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  • 7
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    Continental bedrock and riverine fluxes of strontium and neodymium isotopes to the oceans (2010)
    American Geophysical Union
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2010. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 11 (2010): Q03016, doi:10.1029/2009GC002869.
    Description: Realistic models of past climate and ocean chemistry depend on reconstructions of the Earth's surface environments in the geologic past. Among the critical parameters is the geologic makeup of continental drainage. Here we show, for the present, that the isotope composition of dissolved strontium in rivers increases linearly with the age of bedrock in drainage basins, with the notable exception of the drainage area of Arabia, India, and Southeast Asia that is affected by unusually radiogenic dissolved Sr from the Himalaya. We also demonstrate that the neodymium isotope compositions of suspended matter in rivers as well as clastic sediments deposited along the ocean margins decrease linearly with the bedrock ages of river drainage basins and large-scale continental drainage regions, as determined from digital geologic maps. These correlations are used to calculate the present-day input of dissolved Sr (4.7 × 1010 mol yr−1, 87Sr/86Sr of ∼0.7111) and particulate Nd isotopes (ɛNd of approximately −7.3 ± 2.2) to the oceans. The fact that the regionally averaged ɛNd of the global detrital input to the global coastal ocean is identical to globally averaged seawater (ɛNd of −7.2 ± 0.5) lends credence to the importance of “boundary exchange” for the Nd isotope composition of water masses. Regional biases in source areas of detrital matter and runoff are reflected by the observation that the average age of global bedrock, weighted according to the riverine suspended sediment flux, is significantly younger (∼336 Myr) than the age of global bedrock weighted according to water discharge (394 Myr), which is younger than the average bedrock age of the nonglaciated, exorheic portions of the continents (453 Myr). The observation that the bedrock age weighted according to Sr flux is younger (339 Myr) than that weighted according to water flux reflects the disproportionate contribution from young sedimentary and volcanic rocks to the dissolved Sr load. Neither the isotope composition of the dissolved nor the particulate continental inputs to the ocean provide unbiased perspectives of the lithologic makeup of the Earth's surface. Temporal changes in bedrock geology as well as the shifting focal points of physical erosion and water discharge will undoubtedly have exerted strong controls on temporal and spatial changes in the isotope chemistry of past global runoff and thus seawater.
    Description: NSF grants EAR‐ 0125873, EAR‐0519387, and OCE‐0851015 to B.P.‐E. and a CNRS‐funded “poste rouge” position for B.P.‐E. at the Observatoire Midi‐Pyrénées in Toulouse supported this work.
    Keywords: Seawater ; River ; Strontium ; Neodymium ; Isotope ; Continental runoff
    Repository Name: Woods Hole Open Access Server
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  • 8
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    A fossil winonaite-like meteorite in Ordovician limestone : a piece of the impactor that broke up the L-chondrite parent body? (2014)
    Elsevier
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    Publication Date: 2022-05-26
    Description: © The Author(s), 2014. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Earth and Planetary Science Letters 400 (2014): 145-152, doi:10.1016/j.epsl.2014.05.034.
    Description: About a quarter of all meteorites falling on Earth today originate from the breakup of the L-chondrite parent body ∼470 Ma∼470 Ma ago, the largest documented breakup in the asteroid belt in the past ∼3 Ga∼3 Ga. A window into the flux of meteorites to Earth shortly after this event comes from the recovery of about 100 fossil L chondrites (1–21 cm in diameter) in a quarry of mid-Ordovician limestone in southern Sweden. Here we report on the first non-L-chondritic meteorite from the quarry, an 8 cm large winonaite-related meteorite of a type not known among present-day meteorite falls and finds. The noble gas data for relict spinels recovered from the meteorite show that it may be a remnant of the body that hit and broke up the L-chondrite parent body, creating one of the major asteroid families in the asteroid belt. After two decades of systematic recovery of fossil meteorites and relict extraterrestrial spinel grains from marine limestone, it appears that the meteorite flux to Earth in the mid-Ordovician was very different from that of today.
    Description: This study was supported by an European Research Council Advanced Grant to B.S., in part by NASA grant NNX08AE08G to K.K., and a grant to M.M. from the Swiss National Science Foundation.
    Keywords: Fossil meteorite ; Asteroid breakup ; Winonaite ; Ordinary chondrite ; Asteroid family ; Meteorite flux
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  • 9
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    Determining the impactor of the Ordovician Lockne crater : oxygen and neon isotopes in chromite versus sedimentary PGE signatures (2011)
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    Publication Date: 2022-05-26
    Description: 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 Earth and Planetary Science Letters 306 (2011): 149-155, doi:10.1016/j.epsl.2011.04.028.
    Description: Abundant chromite grains with L-chondritic composition in the resurge deposits of the Lockne impact crater (458 Myr old; dia. ~10 km) in Sweden have been inferred to represent relict fragments of an impactor from the break-up of the L-chondrite parent body at 470 Ma. This view has been challenged based on Ir/Cr and platinum group element (PGE) patterns of the same resurge deposits, and a reinterpretation of the origin of the chromite grains. An impactor of the non-magmatic iron meteorite type was proposed instead. Here we show that single-grain oxygen and noble-gas isotope analyses of the chromite grains from the resurge deposits further support an origin from an L-chondritic asteroid. We also present PGE analyses and Ir/Cr ratios for fossil L-chondritic meteorites found in mid-Ordovician marine limestone in Sweden. The L-chondritic origin has been confirmed by several independent methods, including major element and oxygen isotopic analyses of chromite. Although the meteorites show the same order-of-magnitude PGE and Cr concentrations as recent L chondrites, the elements have been redistributed to the extent that it is problematic to establish the original meteorite type from these proxies. Different PGE data processing approaches can lead to highly variable results, as also shown here for the Lockne resurge deposits. We conclude that the Lockne crater was formed by an L-chondritic impactor, and that considerable care must be taken when inferring projectile type from PGEs in sedimentary ejecta deposits.
    Description: The WiscSIMS Lab is partially funded by NSF-EAR (0319230, 0516725, 0744079). The Robert A. Pritzker Center for Meteoritics and Polar Studies is supported by the Tawani Foundation.
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