32 results found
Horner TJ, Little SH, Conway TM, et al., 2021, Bioactive Trace Metals and Their Isotopes as Paleoproductivity Proxies: An Assessment Using GEOTRACES-Era Data, GLOBAL BIOGEOCHEMICAL CYCLES, Vol: 35, ISSN: 0886-6236
Little SH, Wilson DJ, Rehkämper M, et al., 2021, Cold-water corals as archives of seawater Zn and Cu isotopes, Chemical Geology, Vol: 578, Pages: 1-20, ISSN: 0009-2541
Traditional carbonate sedimentary archives have proven challenging to exploit for Zn and Cu isotopes, due to the high concentrations of trace metals in potential contaminants (e.g., Fe-Mn coatings) and their low concentrations in carbonate. Here, we present the first dataset of δ66ZnJMC-Lyon and δ65CuSRM 976 values for cold-water corals and address their potential as a seawater archive. Extensive cleaning experiments carried out on two corals with well-developed Fe-Mn rich coatings demonstrate that thorough physical and chemical cleaning can effectively remove detrital and authigenic contaminants. Next, we present metal/Ca ratios and δ66Zn and δ65Cu values for a geographically diverse sample set of Holocene age cold-water corals. Comparing cold-water coral δ66Zn values to estimated ambient seawater δ66Zn values (where Δ66Zncoral-sw = δ66Zncoral – δ66Znseawater), we find Δ66Zncoral-sw = +0.03 ± 0.17‰ (1SD, n = 20). Hence, to a first order, cold-water corals record seawater Zn isotope compositions without fractionation. The average Holocene coral Cu isotope composition is +0.59 ± 0.23‰ (1SD, n = 15), similar to the mean of published deep seawater δ65Cu values at +0.66 ± 0.09‰, but with considerable variability. Finally, δ66Zn and δ65Cu data are presented for a small subset of four glacial-age corals. These values overlap with the respective Holocene coral datasets, hinting at limited glacial-interglacial changes in oceanic Zn and Cu cycling.
Little SH, Archer C, Chatterjee A, et al., 2021, Towards balancing the oceanic Ni budget (vol 547, 116461, 2020), EARTH AND PLANETARY SCIENCE LETTERS, Vol: 557, ISSN: 0012-821X
Sherman DM, Little SH, 2020, Isotopic disequilibrium of Cu in marine ferromanganese crusts: Evidence from ab initio predictions of Cu isotope fractionation on sorption to birnessite, EARTH AND PLANETARY SCIENCE LETTERS, Vol: 549, ISSN: 0012-821X
Wang Q, Zhou L, Little SH, et al., 2020, The geochemical behavior of Cu and its isotopes in the Yangtze River, Science of The Total Environment, Vol: 728, Pages: 1-12, ISSN: 0048-9697
Copper (Cu) isotopes can be a useful tool to constrain the interaction of water and the environment, but they have not been widely applied to riverine research in the preceding decades. Isotopically heavy Cu in rivers (global average: about +0.7‰) compared to rocks (at about 0‰) has been attributed to: a) the mobilization of heavy Cu during oxidative weathering, and b) partitioning between an isotopically heavy, organically complexed dissolved pool, and an isotopically light pool adsorbed to particulates. Here, we report Cu concentrations and isotope ratios of the main stream of the Yangtze River and its several tributaries. We find that the Yangtze River exhibits anomalously heavy Cu isotope compositions compared to other rivers: δ65CuNIST 976 of dissolved Cu for the main stream, from Chongqing to Nanjing, ranges from +0.59 to +1.65‰, while the tributaries vary from +0.48 to +1.20‰. A negative correlation is observed between Cu concentrations and Cu isotope compositions.We attribute the anomalous Cu isotope geochemistry of the Yangtze River to two key features of the basin: first, the influence of the Three Gorges Dam (TGD), and second, the presence of extensive Cu sulphide deposits close to the lower reaches of the river. In the upper reaches, downstream towards the TGD, δ65Cu values increase as Cu concentrations decrease, reflecting the preferential adsorption of light Cu by sedimenting particulate phases. δ65Cu values continue to increase to a maximum of +1.65‰ in the middle reaches, at Guangxingzhou. The lower reaches, from Jiujiang to Tongling, are characterized by less positive values of δ65Cu (at about +0.60‰), due to the oxidative weathering of Cu sulphide deposits. The overall Cu-δ65Cu trend in the river reflects mixing of these waters from the lower reaches, influenced by Cu sulphides, with waters from upstream, which have lower Cu concentrations and elevated δ65Cu values.
Little S, 2020, Message in a fossil? Lessons from the last plants on Antarctica, Weather, Vol: 75, Pages: 30-31, ISSN: 0043-1656
Little SH, Munson S, Prytulak J, et al., 2019, Cu and Zn isotope fractionation during extreme chemical weathering, GEOCHIMICA ET COSMOCHIMICA ACTA, Vol: 263, Pages: 85-107, ISSN: 0016-7037
Pratt N, Chen T, Li T, et al., 2019, Temporal distribution and diversity of cold-water corals in the southwest Indian Ocean over the past 25,000 years, Deep Sea Research Part I: Oceanographic Research Papers, Vol: 149, ISSN: 0967-0637
Fossil cold-water corals can be used to reconstruct physical, chemical, and biological changes in the ocean because their skeleton often preserves ambient seawater signatures. Furthermore, patterns in the geographic and temporal extent of cold-water corals have changed through time in response to environmental conditions. Here we present taxonomic and dating results from a new collection of subfossil cold-water corals recovered from seamounts of the Southwest Indian Ocean Ridge. The area is a dynamic hydrographic region characterised by eastward flow of the Agulhas Return Current and the northernmost fronts of the Antarctic Circumpolar Current. In total, 122 solitary scleractinian corals and 27 samples of colonial scleractinian material were collected from water depths between 172 and 1395 m, corresponding to subtropical waters, Antarctic Intermediate Water (AAIW), and Upper Circumpolar Deep Water (UCDW). Fifteen species were identified, including eight species new to the region. The assemblage reflects the position of the seamounts in a transition zone between Indo-Pacific and Subantarctic biogeographic zones. Morphological variation in caryophyllids and the restriction of dendrophylliids to the southern seamounts could result from genetic isolation or reflect environmental conditions. Uranium-series dating using both rapid laser ablation and precise isotope dilution methods reveals their temporal distribution from the Last Glacial Maximum to the present day. Only one specimen of glacial age was found, while peaks in abundance occur around Heinrich Stadial 1 and the Younger Dryas, times at which ocean chemistry and food supply were likely to have presented optimal conditions for cold-water corals. A widespread regional preference of cold-water corals for UCDW over AAIW depths during the deglacial, the reverse of the modern situation, could be explained by higher dissolved oxygen concentrations and a temperature inversion that persisted into the early Holocene.
Little SH, Archer C, Milne A, et al., 2018, Paired dissolved and particulate phase Cu isotope distributions in the South Atlantic, Chemical Geology, Vol: 502, Pages: 29-43, ISSN: 0009-2541
Copper (Cu) is both an essential micronutrient and toxic to photosynthesizing microorganisms at low concentrations. Its dissolved vertical distribution in the oceans is unusual, being neither a nutrient-type nor scavenged-type element. This distribution is attributed to biological uptake in the surface ocean with remineralisation at depth, combined with strong organic complexation by dissolved ligands, scavenging onto particles, and benthic sedimentary input. We present coupled dissolved and particulate phase Cu isotope data along the UK-GEOTRACES South Atlantic section, alongside higher resolution dissolved and particulate phase Cu concentration measurements. Our dissolved phase isotope data contribute to an emerging picture of homogeneous deep ocean δ65Cu, at about +0.65‰ (relative to NIST SRM 976). We identify two pools of Cu in the particulate phase: a refractory, lithogenic pool, at about 0‰, and a labile pool accessed via a weak acidic leach, at about +0.4‰. These two pools are comparable to those previously observed in sediments. We observe deviations towards lighter δ65Cu values in the dissolved phase associated with local enrichments in particulate Cu concentrations along the continental slopes, and in the surface ocean. Copper isotopes are thus a sensitive indicator of localised particle-associated benthic or estuarine Cu inputs. The measurement of Cu isotopes in seawater is analytically challenging, and we call for an intercalibration exercise to better evaluate the potential impacts of UV-irradiation, storage time, and different analytical procedures.
Hayes CT, Anderson RF, Cheng H, et al., 2018, Replacement Times of a Spectrum of Elements in the North Atlantic Based on Thorium Supply, GLOBAL BIOGEOCHEMICAL CYCLES, Vol: 32, Pages: 1294-1311, ISSN: 0886-6236
Howarth S, Prytulak J, Little SH, et al., 2018, Thallium concentration and thallium isotope composition of lateritic terrains, Geochimica et Cosmochimica Acta, Vol: 239, Pages: 446-462, ISSN: 0016-7037
Continental weathering plays a key role in modifying the geochemical budget of terrestrial reservoirs. Laterites are the products of extreme sub-aerial continental weathering. This study presents the first investigation of thallium (Tl) abundances and stable isotopic compositions of lateritic terrains. Two laterite profiles from India of differing protolith and age are studied. Thallium concentrations range between 7 – 244 ng/g for a basalt-based lateritic profile and 37 – 652 ng/g within a greywacke lateritic profile. The average Tl stable isotope composition of the two profiles is similar to many typical igneous materials, however, the intense tropical weathering causes a small but resolvable fractionation of Tl stable isotopes towards heavy values in the residual soils. The profiles are dominated by significant positive isotope excursions (reported as ε205Tl relative to standard NBS997) of + 3.5 ± 0.5 2sd and + 6.2 ± 0.5 2sd at the inferred palaeowater tables within both laterite profiles. These signatures likely reflect combined changes in redox state and mineralogy. Extensive mineral dissolution under through-flowing fluids alongside the formation of new phases such as phyllosilicates and Mn- and Fe- oxides and hydroxides likely account for some of the Tl mobilisation, sorption and coprecipitation. In the case of laterites, the formation of the new phases and role of surface sorption likely contribute to stable Tl isotope fractionation. The identification of strong isotope excursions at inferred palaeowater tables encourages future research to determine specific mineral phases that may drive significant fractionation of Tl stable isotopes. This study showcases the magnitude of natural variation possible in terrestrial soils. Such information is key to the nascent applications of Tl isotope compositions as tracers of anthropogenic pollution.
The GEOTRACES Intermediate Data Product 2017 (IDP2017) is the second publicly available data product of the international GEOTRACES programme, and contains data measured and quality controlled before the end of 2016. The IDP2017 includes data from the Atlantic, Pacific, Arctic, Southern and Indian oceans, with about twice the data volume of the previous IDP2014. For the first time, the IDP2017 contains data for a large suite of biogeochemical parameters as well as aerosol and rain data characterising atmospheric trace element and isotope (TEI) sources. The TEI data in the IDP2017 are quality controlled by careful assessment of intercalibration results and multi-laboratory data comparisons at crossover stations. The IDP2017 consists of two parts: (1) a compilation of digital data for more than 450 TEIs as well as standard hydrographic parameters, and (2) the eGEOTRACES Electronic Atlas providing an on-line atlas that includes more than 590 section plots and 130 animated 3D scenes. The digital data are provided in several formats, including ASCII, Excel spreadsheet, netCDF, and Ocean Data View collection. Users can download the full data packages or make their own custom selections with a new on-line data extraction service. In addition to the actual data values, the IDP2017 also contains data quality flags and 1-σ data error values where available. Quality flags and error values are useful for data filtering and for statistical analysis. Metadata about data originators, analytical methods and original publications related to the data are linked in an easily accessible way. The eGEOTRACES Electronic Atlas is the visual representation of the IDP2017 as section plots and rotating 3D scenes. The basin-wide 3D scenes combine data from many cruises and provide quick overviews of large-scale tracer distributions. These 3D scenes provide geographical and bathymetric context that is crucial for the interpretation and assessment of tracer plumes near ocean margins or alo
de Souza GF, Khatiwala SP, Hain MP, et al., 2018, On the origin of the marine zinc–silicon correlation, Earth and Planetary Science Letters, Vol: 492, Pages: 22-34, ISSN: 0012-821X
The close linear correlation between the distributions of dissolved zinc (Zn) and silicon (Si) in seawater has puzzled chemical oceanographers since its discovery almost forty years ago, due to the apparent lack of a mechanism for coupling these two nutrient elements. Recent research has shown that such a correlation can be produced in an ocean model without any explicit coupling between Zn and Si, via the export of Zn-rich biogenic particles in the Southern Ocean, consistent with the observation of elevated Zn quotas in Southern Ocean diatoms. Here, we investigate the physical and biological mechanisms by which Southern Ocean uptake and export control the large-scale marine Zn distribution, using suites of sensitivity simulations in an ocean general circulation model (OGCM) and a box-model ensemble. These simulations focus on the sensitivity of the Zn distribution to the stoichiometry of Zn uptake relative to phosphate (PO4), drawing directly on observations in culture. Our analysis reveals that OGCM model variants that produce a well-defined step between relatively constant, high Zn:PO4 uptake ratios in the Southern Ocean and low Zn:PO4 ratios at lower latitudes fare best in reproducing the marine Zn–Si correlation at both the global and the regional Southern Ocean scale, suggesting the presence of distinct Zn-biogeochemical regimes in the high- and low-latitude oceans that may relate to differences in physiology, ecology or (micro-)nutrient status. Furthermore, a study of the systematics of both the box model and the OGCM reveals that regional Southern Ocean Zn uptake exerts control over the global Zn distribution via its modulation of the biogeochemical characteristics of the surface Southern Ocean. Specifically, model variants with elevated Southern Ocean Zn:PO4 uptake ratios produce near-complete Zn depletion in the Si-poor surface Subantarctic Zone, where upper-ocean water masses with key roles in the global oceanic circulation are formed. By setting th
Vance D, Archer C, Little SH, et al., 2018, The oceanic cycles of the transition metals and their isotopes (vol 36, pg 359, 2017), ACTA GEOCHIMICA, Vol: 37, Pages: 151-151, ISSN: 2096-0956
Vance D, Archer C, Little SH, et al., 2017, The oceanic cycles of the transition metals and their isotopes, Acta Geochimica, Vol: 36, Pages: 359-362, ISSN: 2096-0956
The stable isotope systems of the transition metals potentially provide constraints on the current and past operation of the biological pump, and on the state of ocean redox in Earth history. Here we focus on two exemplar metals, nickel (Ni) and zinc (Zn). The oceanic dissolved pool of both elements is isotopically heavier than the known inputs, implying an output with light isotope compositions. The modern oceanic cycle of both these elements is dominated by biological uptake into photosynthesised organic matter and output to sediment. It is increasingly clear, however, that such uptake is associated with only very minor isotope fractionation. We suggest that the isotopic balance is instead closed by the sequestration of light isotopes to sulphide in anoxic and organic-rich sediments, so that it is ocean chemistry that controls these isotope systems, and suggesting a different but equally interesting array of questions in Earth history that can be addressed with these systems.
Little SH, Vance D, McManus J, et al., 2017, Copper isotope signatures in modern marine sediments, Geochimica et Cosmochimica Acta, Vol: 212, Pages: 253-273, ISSN: 1872-9533
The development of metal stable isotopes as tools in paleoceanography requires a thorough understanding of their modern marine cycling. To date, no Cu isotope data has been published for modern sediments deposited under low oxygen conditions. We present data encompassing a broad spectrum of hydrographic and redox regimes, including continental margin and euxinic (sulphide-containing) settings. Taken together with previously published data from oxic settings, these data indicate that the modern oceanic sink for Cu has a surprisingly homogeneous isotopic composition of about +0.3‰ (δ65Cu, relative to NIST SRM976). We suggest that this signature reflects one of two specific water-column processes: (1) an equilibrium isotope fractionation between soluble, isotopically heavy, Cu complexed to strong organic ligands and an isotopically light pool sorbed to particles that deliver Cu to the sediment, or (2) an equilibrium isotope fractionation between the same isotopically heavy ligand-bound pool and the particle reactive free Cu2+ species, with the latter being scavenged by particulates and thereby delivered to the sediment. An output flux of about +0.3‰ into sediments is isotopically light relative to the known inputs to the ocean (at around +0.6‰) and the seawater value of +0.6 to +0.9‰, suggesting the presence of an as yet unidentified isotopically light source of Cu to the oceans. We hypothesize that this source may be hydrothermal, or may result from the partial dissolution of continentally derived particles.
Vance D, Little SH, De Souza GF, et al., 2017, Silicon and zinc biogeochemical cycles coupled through the Southern Ocean, Nature Geoscience, Vol: 10, Pages: 202-206, ISSN: 1752-0908
Zinc is vital for the physiology of oceanic phytoplankton. The striking similarity of the depth profiles of zinc to those of silicate suggests that the uptake of both elements into the opaline frustules of diatoms, and their regeneration from these frustules, should be coupled. However, the zinc content of diatom opal is negligible, and zinc is taken up into and regenerated from the organic parts of diatom cells. Thus, since opaline frustules dissolve deep in the water column while organic material is regenerated in the shallow subsurface ocean, there is little reason to expect the observed close similarity between zinc and silicate, and the dissimilarity between zinc and phosphate. Here we combine observations with simulations using a three-dimensional model of ocean circulation and biogeochemistry to show that the coupled distribution of zinc and silicate, as well as the decoupling of zinc and phosphate, can arise in the absence of mechanistic links between the uptake of zinc and silicate, and despite contrasting regeneration length scales. Our simulations indicate that the oceanic zinc distribution is, in fact, a natural result of the interaction between ocean biogeochemistry and the physical circulation through the Southern Ocean hub. Our analysis demonstrates the importance of uptake stoichiometry in controlling ocean biogeochemistry, and the utility of global-scale elemental covariation in the ocean in understanding these controls.
Vance D, Little SH, Archer C, et al., 2016, The oceanic budgets of nickel and zinc isotopes: the importance of sulfidic environments as illustrated by the Black Sea, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol: 374, ISSN: 1364-503X
Isotopic data collected to date as part of the GEOTRACES and other programmes show that the oceanic dissolved pool is isotopically heavy relative to the inputs for zinc (Zn) and nickel (Ni). All Zn sinks measured until recently, and the only output yet measured for Ni, are isotopically heavier than the dissolved pool. This would require either a non-steady-state ocean or other unidentified sinks. Recently, isotopically light Zn has been measured in organic carbon-rich sediments from productive upwelling margins, providing a potential resolution of this issue, at least for Zn. However, the origin of the isotopically light sedimentary Zn signal is uncertain. Cellular uptake of isotopically light Zn followed by transfer to sediment does not appear to be a quantitatively important process. Here, we present Zn and Ni isotope data for the water column and sediments of the Black Sea. These data demonstrate that isotopically light Zn and Ni are extracted from the water column, probably through an equilibrium fractionation between different dissolved species followed by sequestration of light Zn and Ni in sulfide species to particulates and the sediment. We suggest that a similar, non-quantitative, process, operating in porewaters, explains the Zn data from organic carbon-rich sediments.This article is part of the themed issue ‘Biological and climatic impacts of ocean trace element chemistry’.
van de Flierdt T, Griffiths AM, Lambelet M, et al., 2016, Neodymium in the oceans: a global database, a regional comparison and implications for palaeoceanographic research, Journal: Philosophical Transactions A: Mathematical, Physical and Engineering Sciences, Vol: 374, ISSN: 1471-2962
The neodymium (Nd) isotopic composition of seawater has been used extensively to reconstruct ocean circulation on a variety of time scales. However, dissolved neodymium concentrations and isotopes do not always behave conservatively, and quantitative deconvolution of this non-conservative component can be used to detect trace metal inputs and isotopic exchange at ocean–sediment interfaces. In order to facilitate such comparisons for historical datasets, we here provide an extended global database for Nd isotopes and concentrations in the context of hydrography and nutrients. Since 2010, combined datasets for a large range of trace elements and isotopes are collected on international GEOTRACES section cruises, alongside classical nutrient and hydrography measurements. Here, we take a first step towards exploiting these datasets by comparing high-resolution Nd sections for the western and eastern North Atlantic in the context of hydrography, nutrients and aluminium (Al) concentrations. Evaluating those data in tracer–tracer space reveals that North Atlantic seawater Nd isotopes and concentrations generally follow the patterns of advection, as do Al concentrations. Deviations from water mass mixing are observed locally, associated with the addition or removal of trace metals in benthic nepheloid layers, exchange with ocean margins (i.e. boundary exchange) and/or exchange with particulate phases (i.e. reversible scavenging). We emphasize that the complexity of some of the new datasets cautions against a quantitative interpretation of individual palaeo Nd isotope records, and indicates the importance of spatial reconstructions for a more balanced approach to deciphering past ocean changes.
Little SH, Vance D, McManus J, et al., 2016, Key role of continental margin sediments in the oceanic mass balance of Zn and Zn isotopes, Geology, Vol: 44, Pages: 207-210, ISSN: 0091-7613
Zinc is an essential micronutrient and its concentration and isotopic composition in marine sediments represent promising tracers of the ocean carbon cycle. However, gaps remain in our understanding of the modern marine cycle of Zn, including an explanation of the heavy Zn isotopic composition of seawater relative to the known inputs, and the identity of a required missing sink for light Zn isotopes. Here we present Zn isotope data for organic-rich and trace metal–rich continental margin sediments from the east Pacific margins that together provide the first observational evidence for the previously hypothesized burial of light Zn in such settings. In turn, this light Zn output flux provides a means to enrich the seawater dissolved pool in heavy isotopes. The size and isotopic composition of the margin sink are controlled by the uptake of Zn into organic matter in the photic zone and the fixation of this pool, probably in the form of Zn sulfides, in sediments. An estimate of its significance to the overall Zn oceanic mass balance, both in terms of flux and isotopic composition, indicates that such settings can fulfill the requirements of the missing Zn sink. Taken together, these observations have important implications for the interpretation of Zn isotope data for marine sediments in the geologic record.
Sherman DM, Little SH, Vance D, 2015, Reply to comment on "Molecular controls on Cu and Zn isotopic fractionation in Fe-Mn crusts", EARTH AND PLANETARY SCIENCE LETTERS, Vol: 411, Pages: 313-315, ISSN: 0012-821X
Little SH, Vance D, Lyons TW, et al., 2015, Controls on trace metal authigenic enrichment in reducing sediments: insights from modern oxygen-deficient settings, American Journal of Science: an international earth science journal, Vol: 315, Pages: 77-119, ISSN: 0002-9599
Any effort to reconstruct Earth history using variations in authigenic enrichments of redox-sensitive and biogeochemically important trace metals must rest on a fundamental understanding of their modern oceanic and sedimentary geochemistry. Further, unravelling the multiple controls on sedimentary enrichments requires a multi-element approach. Of the range of metals studied, most is known about the behavior of Fe, Mn, and Mo. In this study, we compare the authigenic enrichment patterns of these elements with a group whose behavior is not as well defined (Cd, Cu, Zn, and Ni) in three oxygen-poor settings: the Black Sea, the Cariaco Basin (Venezuela), and the Peru Margin. These three settings span a range of biogeochemical environments, allowing us to isolate the different controls on sedimentary enrichment. Our approach, relying on the covariation of elemental enrichment factors [EF, defined for element X as: EFX = (X/Al)sample/(X/Al)lithogenic], has previously been applied to Mo and U to elucidate paleoenvironmental information on, for example, benthic redox conditions, the particulate shuttle, and the evolution of water mass chemistry. We find two key controls on trace metal enrichment. First, the concentration of an element in the lithogenic background sediment (used in calculating EFX) controls the magnitude of potential enrichment. Maximum enrichment factors of 376 and 800 are calculated for Mo (∼1 ppm in detrital sediments) and Cd (∼0.3 ppm), respectively, compared to values not greater than 17 in any setting for the other five metals (∼45 ppm to ∼4.5 wt.% in detrital sediments). Second, there is a relationship between the aqueous concentration of the element in overlying seawater and its degree of enrichment in the sediment. We further identify four important processes for delivery of trace metals to the sediment. These are: (1) cellular uptake (especially important for Zn and Cd), (2) interaction/co-precipitation with sulfide (Mo, Cu, and Cd)
Andersen MB, Romaniello S, Vance D, et al., 2014, A modern framework for the interpretation of U-238/U-235 in studies of ancient ocean redox, EARTH AND PLANETARY SCIENCE LETTERS, Vol: 400, Pages: 184-194, ISSN: 0012-821X
Little SH, Sherman DM, Vance D, et al., 2014, Molecular controls on Cu and Zn isotopic fractionation in Fe-Mn crusts, EARTH AND PLANETARY SCIENCE LETTERS, Vol: 396, Pages: 213-222, ISSN: 0012-821X
Little SH, Vance D, Siddall M, et al., 2013, A modeling assessment of the role of reversible scavenging in controlling oceanic dissolved Cu and Zn distributions, Global Biogeochemical Cycles, Vol: 27, Pages: 780-791, ISSN: 0886-6236
The balance of processes that control elemental distributions in the modern oceans is important in understanding both their internal recycling and the rate and nature of their eventual output to sediment. Here we seek to evaluate the likely controls on the vertical profiles of Cu and Zn. Though the concentrations of both Cu and Zn increase with depth, Cu increases in a more linear fashion than Zn, which exhibits a typical “nutrient-type” profile. Both elements are bioessential, and biological uptake and regeneration has often been cited as an important process in controlling their vertical distribution. In this study, we investigate the likely importance of another key vertical process, that of passive scavenging on sinking particles, via a simple one-dimensional model of reversible scavenging. We find that, despite the absence of lateral or vertical water advection, mixing, diffusion, or biological uptake, our reversible scavenging model is very successful in replicating dissolved Cu concentration profiles on a range of geographic scales. We provide preliminary constraints on the scavenging coefficients for Cu for a spectrum of particle types (calcium carbonate, opal, particulate organic carbon, and dust) while emphasizing the fit of the shape of the modeled profile to that of the tracer data. In contrast to Cu, and reaffirming the belief that Zn behaves as a true micronutrient, the scavenging model is a poor match to the shape of oceanic Zn profiles. Modeling a single vertical process simultaneously highlights the importance of lateral advection in generating high Zn concentrations in the deep Pacific.
Little SH, Vance D, Walker-Brown C, et al., 2013, The oceanic mass balance of copper and zinc isotopes, investigated by analysis of their inputs, and outputs to ferromanganese oxide sediments, Geochimica et Cosmochimica Acta, Vol: 125, Pages: 673-693, ISSN: 1872-9533
The oceanic biogeochemical cycles of the transition metals have been eliciting considerable attention for some time. Manyof them have isotope systems that are fractionated by key biological and chemical processes so that significant informationabout such processes may be gleaned from them. However, for many of these nascent isotopic systems we currently know toolittle of their modern oceanic mass balance, making the application of such systems to the past speculative, at best. Here weinvestigate the biogeochemical cycling of copper (Cu) and zinc (Zn) isotopes in the ocean. We present estimates for the isotopiccomposition of Cu and Zn inputs to the oceans based on new data presented here and published data. The bulk isotopiccomposition of dissolved Cu and Zn in the oceans (d65Cu +0.9&, d66Zn +0.5&) is in both cases heavier than their respectiveinputs (at around d65Cu = +0.6& and d66Zn = +0.3&, respectively), implying a marine process that fractionates themand a resulting isotopically light sedimentary output. For the better-known molybdenum isotope system this is achieved bysorption to Fe–Mn oxides, and this light isotopic composition is recorded in Fe–Mn crusts. Hence, we present isotopic datafor Cu and Zn in three Fe–Mn crusts from the major ocean basins, which yield d65Cu = 0.44 ± 0.23& (mean and 2SD) andd66Zn = 1.04 ± 0.21&. Thus for Cu isotopes output to particulate Fe–Mn oxides can explain the heavy isotopic compositionof the oceans, while for Zn it cannot. The heavy Zn in Fe–Mn crusts (and in all other authigenic marine sediments measuredso far) implies that a missing light sink is still to be located. These observations are some of the first to place constraints on themodern oceanic mass balance of Cu and Zn isotopes.
Horner T, Little S, Conway T, et al., Bioactive trace metals and their isotopes as paleoproductivity proxies: An assessment using GEOTRACES-era data
Little S, van De Flierdt T, Wilson D, et al., Zn isotopes in deep sea corals: a useful palaeoceanographic archive?
<jats:p> &lt;p&gt;Zinc (Zn) is an important bioessential trace element. Its distribution in the modern oceans reflects a combination of biological uptake, remineralization and the physical ocean circulation. Furthermore, the partitioning behaviour of Zn (D&lt;sub&gt;Zn&lt;/sub&gt;) and its isotopes (&amp;#948;&lt;sup&gt;66&lt;/sup&gt;Zn) in carbonates has been linked to ambient seawater carbonate chemistry [1-3].&lt;/p&gt;&lt;p&gt;Development of Zn isotopes in carbonates as a palaeoceanographic tool has been hampered by the high concentrations of Zn in contaminating material, such as lithogenic or authigenic (e.g. Fe-Mn oxide) phases. However, deep-sea corals are large enough to be subjected to aggressive physical and chemical cleaning, enabling effective removal of contaminating phases. They also have several other advantages over traditional palaeoclimate archives, including the ability to assign precise absolute ages to individual specimens based on uranium-series dating .&lt;/p&gt;&lt;p&gt;Here we present Zn/Ca and &amp;#948;&lt;sup&gt;66&lt;/sup&gt;Zn data for a suite of modern and recent (&lt;1000 yr) deep sea corals from six ocean regions spanning the far North Atlantic to the Tasman Sea. We observe what appears to be species-specific Zn partitioning behaviour, but no clear links between D&lt;sub&gt;Zn&lt;/sub&gt; or coral &amp;#948;&lt;sup&gt;66&lt;/sup&gt;Zn and ambient seawater carbonate chemistry. Overall, there is good agreement between measured or best-guess modern seawater &amp;#948;&lt;sup&gt;66&lt;/sup&gt;Zn and coral aragonite &amp;#948;&lt;sup&gt;66&lt;/sup&gt;Zn values, suggesting that
Maters E, Appiah F, Lawrence A, et al., Are diverse geochemists retained and thriving on the UK academic ladder?
<jats:p>&lt;p&gt;Evaluating Diversity and Inclusion within the (geochemistry) Academic Ladder (E-DIAL), funded by the UK&amp;#8217;s Natural Environment Research Council, provides a snapshot of diversity and identifies barriers resulting in underrepresentation among intersectional identity groups across the UK geochemistry community. The project emphasis is on the academic ladder within UK higher education institutions (HEIs). As a multi-faceted discipline, geochemistry is central to Earth, environmental and planetary sciences, yet the first specific geochemistry workforce data is only now being collected (e.g., through the 2022 Global Geochemistry Community Survey launched by the European Association of Geochemistry and Geochemical Society). In complement to this timely society-led effort serving the international geochemistry community, our project collects original data and evidence through a UK-wide survey that captures coupled diversity and academic progression and retention data. These data are vital to catalyse policies that actively improve geochemistry career prospects for diverse talents, given that a community&amp;#8217;s scientific potential can only be reached by including everyone. Specifically, the UK-wide survey data examines information on past and recent rates of appointment, progression and retention of both majority and under-represented groups across all levels of seniority, including research students, within UK HEIs.&lt;/p&gt;&lt;p&gt;In profiling geochemists&amp;#8217; career pathways and evidencing lived experiences (e.g., among postdocs), exclusionary obstacles are identified with resultant understanding driving revision of prevailing policies, attitudes and practices while assessing implementation effectiveness at HEIs with, for example, differing diversity certifications (e.g., Athena Swan or Race Equality Charters). Findings will test the hypothesis that &a
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