Pryer Helena V.

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Pryer
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Helena V.
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  • Preprint
    Multiple plant-wax compounds record differential sources and ecosystem structure in large river catchments
    ( 2016-04) Hemingway, Jordon D. ; Schefuß, Enno ; Dinga, Bienvenu J. ; Pryer, Helena V. ; Galy, Valier
    The concentrations, distributions, and stable carbon isotopes (δ13C) of plant waxes carried by fluvial suspended sediments contain valuable information about terrestrial ecosystem characteristics. To properly interpret past changes recorded in sedimentary archives it is crucial to understand the sources and variability of exported plant waxes in modern systems on seasonal to inter-annual timescales. To determine such variability, we present concentrations and δ13C compositions of three compound classes (n-alkanes, n-alcohols, n-alkanoic acids) in a 34-month time series of suspended sediments from the outflow of the Congo River. We show that exported plant-dominated n-alkanes (C25 – C35) represent a mixture of C3 and C4 end members, each with distinct molecular distributions, as evidenced by an 8.1 ± 0.7‰ (±1σ standard deviation) spread in δ13C values across chain-lengths, and weak correlations between individual homologue concentrations (r = 0.52 – 0.94). In contrast, plant-dominated n-alcohols (C26 – C36) and n-alkanoic acids (C26 – C36) exhibit stronger positive correlations (r = 0.70 – 0.99) between homologue concentrations and depleted δ13C values (individual homologues average ≤ -31.3‰ and -30.8‰, respectively), with lower δ13C variability across chain-lengths (2.6 ± 0.6‰ and 2.0 ± 1.1‰, respectively). All individual plant-wax lipids show little temporal δ13C variability throughout the time-series (1σ ≤ 0.9‰), indicating that their stable carbon isotopes are not a sensitive tracer for temporal changes in plant-wax source in the Congo basin on seasonal to inter-annual timescales. Carbon-normalized concentrations and relative abundances of n-alcohols (19 – 58% of total plant-wax lipids) and n-alkanoic acids (26 – 76%) respond rapidly to seasonal changes in runoff, indicating that they are mostly derived from a recently entrained local source. In contrast, a lack of correlation with discharge and low, stable relative abundances (5 – 16%) indicate that n-alkanes better represent a catchment-integrated signal with minimal response to discharge seasonality. Comparison to published data on other large watersheds indicates that this phenomenon is not limited to the Congo River, and that analysis of multiple plant-wax lipid classes and chain lengths can be used to better resolve local vs. distal ecosystem structure in river catchments.
  • Preprint
    Barium isotopes reveal role of ocean circulation on barium cycling in the Atlantic
    ( 2017-02-02) Bates, Stephanie L. ; Hendry, Katharine R. ; Pryer, Helena V. ; Kinsley, Christopher W. ; Pyle, Kimberley M. ; Woodward, E. Malcolm S. ; Horner, Tristan J.
    We diagnose the relative influences of local-scale biogeochemical cycling and regional-scale ocean circulation on Atlantic barium cycling by analyzing four new depth profiles of dissolved Ba concentrations and isotope compositions from the South and tropical North Atlantic. These new profiles exhibit systematic vertical, zonal, and meridional variations that reflect the influence of both local-scale barite cycling and large-scale ocean circulation. Previously reported epipelagic decoupling of Ba and Si in the tropics is also found to be associated with significant Ba isotope heterogeneity. We contend that this decoupling originates from the depth segregation of opal & barite formation but is exacerbated by weak vertical mixing, as in the tropics. Zonal influence from isotopically-‘heavy’ water masses in the western North Atlantic evidence the advective inflow of Ba-depleted Upper Labrador Sea Water, which is not seen in the eastern basin or the South Atlantic. Meridional variations in Atlantic Ba isotope systematics below 2,000 m appear entirely controlled by conservative mixing. Using an inverse isotopic mixing model, we calculate the Ba isotope composition of the Ba-poor northern end member as +0.45 ‰ and the Ba-rich southern end member +0.26 ‰, relative to NIST SRM 3104a. The near-conservative behaviour of Ba in the deep ocean indicates that Ba isotopes may serve as an independent tracer of the provenance of advected water masses in the Atlantic Ocean. The clearly resolved Ba-isotope signatures of northern- and southern-sourced waters may also prove useful in paleoceanographic studies, should appropriate sedimentary archives be identified. Overall, our results offer new insights into the controls on Ba cycling in seawater and thus the mechanisms that underpin the utility of Ba-based proxies in paleoceanography.
  • Article
    Barium isotope evidence for pervasive sediment recycling in the upper mantle
    (American Association for the Advancement of Science, 2018-07-11) Nielsen, Sune G. ; Horner, Tristan J. ; Pryer, Helena V. ; Blusztajn, Jerzy S. ; Shu, Yunchao ; Kurz, Mark D. ; Le Roux, Véronique
    The upper mantle, as sampled by mid-ocean ridge basalts (MORBs), exhibits significant chemical variability unrelated to mechanisms of melt extraction at ridges. We show that barium isotope variations in global MORBs vary systematically with radiogenic isotopes and trace element ratios, which reflects mixing between depleted and enriched MORB melts. In addition, modern sediments and enriched MORBs share similar Ba isotope signatures. Using modeling, we show that addition of ~0.1% by weight of sediment components into the depleted mantle in subduction zones must impart a sedimentary Ba signature to the overlying mantle and induce low-degree melting that produces the enriched MORB reservoir. Subsequently, these enriched domains convect toward mid-ocean ridges and produce radiogenic isotope variation typical of enriched MORBs. This mechanism can explain the chemical and isotopic features of enriched MORBs and provide strong evidence for pervasive sediment recycling in the upper mantle.
  • Article
    Publisher Correction : Pelagic barite precipitation at micromolar ambient sulfate
    (Nature Publishing Group, 2018-01-18) Horner, Tristan J. ; Pryer, Helena V. ; Nielsen, Sune G. ; Crockford, Peter W. ; Gauglitz, Julia M. ; Wing, Boswell A. ; Ricketts, Richard D.
    Correction to: Nature Communications https://doi.org/10.1038/s41467-017-01229-5, Article published online 07 November 2017
  • Article
    Pelagic barite precipitation at micromolar ambient sulfate
    (Nature Publishing Group, 2017-11-07) Horner, Tristan J. ; Pryer, Helena V. ; Nielsen, Sune G. ; Crockford, Peter W. ; Gauglitz, Julia M. ; Wing, Boswell A. ; Ricketts, Richard D.
    Geochemical analyses of sedimentary barites (barium sulfates) in the geological record have yielded fundamental insights into the chemistry of the Archean environment and evolutionary origin of microbial metabolisms. However, the question of how barites were able to precipitate from a contemporary ocean that contained only trace amounts of sulfate remains controversial. Here we report dissolved and particulate multi-element and barium-isotopic data from Lake Superior that evidence pelagic barite precipitation at micromolar ambient sulfate. These pelagic barites likely precipitate within particle-associated microenvironments supplied with additional barium and sulfate ions derived from heterotrophic remineralization of organic matter. If active during the Archean, pelagic precipitation and subsequent sedimentation may account for the genesis of enigmatic barite deposits. Indeed, barium-isotopic analyses of barites from the Paleoarchean Dresser Formation are consistent with a pelagic mechanism of precipitation, which altogether offers a new paradigm for interpreting the temporal occurrence of barites in the geological record.
  • Dataset
    Particulate multi-element geochemical concentrations, dissolved barium concentrations and barium-isotopic data collected during the R/V Blue Heron cruise BH15-11 in Lake Superior during August 2015
    (Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2017-02-03) Horner, Tristan J. ; Ricketts, Richard D. ; Pryer, Helena V.
    Particles are important vectors of nutrients, carbon, and several trace metals within large bodies of water. Broadly speaking, particle distributions can be classified into three major groups on the basis of their multi-element geochemistry: biogenic (organic matter-associated phases and tests); lithogenic (highly refractory rock-derived materials); and authigenic (formed in situ below the euphotic zone). We collected particulate samples spanning the full water column of Lake Superior at Stations FWM (46.998528, -91.246250) and WM (47.331611, -89.821389) during the height of 2015 summer thermal stratification (cruise BH15-11). We analyzed particle leachates for their multi-element geochemistry using ICP-MS (inductively-coupled plasma mass spectrometry) at the Woods Hole Oceanographic Institution Plasma Facility. We report elemental concentrations in Lake Superior particulate matter in (nano or pico) moles per liter, defined by a 0.44 um filter cutoff. Lithogenic cycles are resolved by Al, Fe, Ti, V, and Y; biogenic phases by Ca, Cd, P, and Sr; and authigenic processes by Ba, Cd, and Mn. Several elements exhibit hybrid-type distributions depending on the depth range under investigation. Also reported are stable barium-isotopic distributions for particulate and total dissolvable Ba, measured using multiple-collector ICP-MS and reported relative to NIST SRM 3104a in permill. For a complete list of measurements, refer to the supplemental document 'Field_names.pdf', and a full dataset description is included in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: http://www.bco-dmo.org/dataset/680091