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  • 2020-2024  (22)
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  • 1
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    Authigenic Formation of Clay Minerals in the Abyssal North Pacific (2022)
    Details
    Publication Date: 2023-07-19
    Description: Present estimates of the biogeochemical cycles of calcium, strontium, and potassium in the ocean reveal large imbalances between known input and output fluxes. Using pore fluid, incubation, and solid sediment data from North Pacific multi‐corer cores we show that, contrary to the common paradigm, the top centimeters of abyssal sediments can be an active site of authigenic precipitation of clay minerals. In this region, clay authigenesis is the dominant sink for potassium and strontium and consumes nearly all calcium released from benthic dissolution of calcium carbonates. These observations support the idea that clay authigenesis occurring over broad regions of the world ocean may be a major buffer for ocean chemistry on the time scale of the ocean overturning circulation, and key to the long‐term stability of Earth's climate.
    Description: Key Points: North Pacific red clay sediments are a sink for marine calcium, strontium, and potassium. Authigenic formation of clay minerals is prevalent in pelagic sediments throughout the North Pacific. The main mechanism for clay formation is recrystallization of aluminosilicates, neoformation can occur in biogenic silica rich sediments.
    Description: EC H2020 PRIORITY “Excellent science” H2020 European Research Council http://dx.doi.org/10.13039/100010663
    Description: Blavatnik Family Foundation http://dx.doi.org/10.13039/100011643
    Description: Isaac Newton Trust http://dx.doi.org/10.13039/501100004815
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: National Science Foundation http://dx.doi.org/10.13039/100000001
    Description: https://doi.pangaea.de/10.1594/PANGAEA.946881
    Keywords: ddc:549 ; reverse weathering ; clay authigenesis ; calcium ; potassium ; porewater ; strontium
    Language: English
    Type: doc-type:article
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    CITATION GEO-LEO
  • 2
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    Glacial influence on the iron and sulfur cycles in Arctic fjord sediments (Svalbard) (2020)
    Elsevier
    Details
    Publication Date: 2023-02-08
    Description: Arctic fjord sediments of Svalbard receive terrestrial material from glacial runoff and organic matter from marine primary productivity. Organic carbon mineralization proceeds primarily through sulfate and iron reduction in the fjord sediment. The ongoing retreat of glaciers in the high Arctic is altering the input of glacial material to the fjords, with unknown consequences for the iron and sulfur cycles in the fjord sediments. We measured sulfate reduction rates in sediment cores and analyzed porewater geochemistry, then compared these results to long-term sediment incubations to determine the rates of iron reduction and sulfide oxidation in three glacially influenced fjords on the west coast of Spitsbergen, Svalbard. Despite an abundance of glacially-sourced Fe(III)-oxide minerals, active sulfate reduction took place throughout the sediment. Analyses of the sulfur and oxygen isotopic composition of porewater sulfate and sulfate concentrations suggest that sulfide produced from biological sulfate reduction is reoxidized to sulfate. Long-term sediment incubations indicated sulfide oxidation at all three stations. The rate of sulfide oxidation was controlled by both the rate of sulfate reduction and the quantity and reactivity of Fe(III)-oxides. In our experimental incubations, we detected a decrease in Fe(III) content of the 0.5 M HCl and ascorbate-extractable fractions, but not in the 6 M HCl fraction, indicating that the highly reactive Fe(III) fraction is utilized by microorganisms and serves as the oxidant for sulfide oxidation. Our results show that sulfide oxidation in glacially-influenced fjord sediments is a wide-spread geochemical process. Further warming will drive glacial retreat onto land, where sediment-laden glacial meltwater will be altered during flow through proglacial streams and lakes before entering the marine environment. Fjord sediments will likely become more sulfidic, as glaciers deliver less particulate, highly-reactive metal oxides to the marine environment.
    Type: Article , PeerReviewed
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    PAPER (OCEANREP)
  • 3
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    Dissolved Strontium, Sr/Ca Ratios, and the Abundance of Acantharia in the Indian and Southern Oceans (2020)
    ACS (American Chemical Society)
    Details
    Publication Date: 2023-02-08
    Description: We report measurements of strontium concentrations and Sr/Ca ratios in the Indian and Southern Oceans, which show that subtle geochemical variations along the main thermocline are the product of calcium carbonate (CaCO3) and celestite (SrSO4) precipitation and dissolution. Our calculations suggest that celestite skeletons precipitated by Acantharia contribute up to 10 mol % of the combined amount of carbonate and celestite shells precipitated in the Indian Ocean. The data suggest that the distribution of the concentration of strontium in the global ocean is governed by the different modes of deep-water formation in the Southern Ocean and North Atlantic. The formation of Antarctic bottom waters from strontium-rich, upwelled deep waters forms a southern end member contrasted with the strontium depleted North Atlantic deep water. The difference in strontium concentrations and Sr/Ca ratios of the different water masses reported here is maintained by precipitation, export, and dissolution of CaCO3 and SrSO4. These preformed strontium concentrations correlate linearly with nitrate and phosphate concentrations in the Indian Ocean, but this correlation is weaker in low latitudes, where the mixotrophic lifestyle of Acantharia allows them to thrive in nutrient-depleted environments.
    Type: Article , PeerReviewed
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    PAPER (OCEANREP)
  • 4
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    Assessing Sedimentary Boundary Layer Calcium Carbonate Precipitation and Dissolution Using the Calcium Isotopic Composition of Pore Fluids (2021)
    Frontiers
    Details
    Publication Date: 2024-02-07
    Description: We present pore fluid geochemistry, including major ion and trace metal concentrations and the isotopic composition of pore fluid calcium and sulfate, from the uppermost meter of sediments from the Gulf of Aqaba (Northeast Red Sea) and the Iberian Margin (North Atlantic Ocean). In both the locations, we observe strong correlations among calcium, magnesium, strontium, and sulfate concentrations as well as the sulfur isotopic composition of sulfate and alkalinity, suggestive of active changes in the redox state and pH that should lead to carbonate mineral precipitation and dissolution. The calcium isotope composition of pore fluid calcium (δ 44 Ca) is, however, relatively invariant in our measured profiles, suggesting that carbonate mineral precipitation is not occurring within the boundary layer at these sites. We explore several reasons why the pore fluid δ 44 Ca might not be changing in the studied profiles, despite changes in other major ions and their isotopic composition, including mixing between the surface and deep precipitation of carbonate minerals below the boundary layer, the possibility that active iron and manganese cycling inhibits carbonate mineral precipitation, and that mineral precipitation may be slow enough to preclude calcium isotope fractionation during carbonate mineral precipitation. Our results suggest that active carbonate dissolution and precipitation, particularly in the diffusive boundary layer, may elicit a more complex response in the pore fluid δ 44 Ca than previously thought.
    Type: Article , PeerReviewed
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    Format: archive
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    PAPER (OCEANREP)
  • 5
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    On calcium-to-alkalinity anomalies in the North Pacific, Red Sea, Indian Ocean and Southern Ocean (2021)
    Elsevier
    Details
    Publication Date: 2024-02-07
    Description: An important factor for predicting the effect of increased CO2 on future acidification of the ocean is a proper understanding of the interactions controlling production and dissolution of calcium carbonate minerals (CaCO3). The production and dissolution of CaCO3 in the ocean can be assessed over large spatial scales by measuring seawater calcium concentrations and total alkalinity (AT), yet past studies suggest that there could be large discrepancies between calcium and AT-based balances of the CaCO3 cycle in the North Pacific and Indian Oceans. Here, we analyse water column samples collected along transects in the North Pacific, Southern Ocean, tropical Indian Ocean and Red Sea for their concentrations of calcium, nutrients, and AT. We find that there is an excess calcium over AT anomaly in the top 1000 m of the tropical Indian Ocean water-column. The source of this anomaly is the dissolution of subsurface gypsum deposits in the Red Sea. We find no evidence for calcium-over-AT anomalies in the North Pacific, in contrast to previous studies. Our results show that, in most cases, calcium and AT data agree well and can be used to reconstruct the marine CaCO3 cycle.
    Type: Article , PeerReviewed
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  • 6
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    Trace Element Geochemistry in North Pacific Red Clay Sediment Porewaters and Implications for Water‐Column Studies (2023)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2024-02-07
    Description: Geochemical analyses of trace elements in the ocean water column have suggested that pelagic clay‐rich sediments are a major source of various elements to bottom‐waters. However, corresponding high‐quality measurements of trace element concentrations in porewaters of pelagic clay‐rich sediments are scarce, making it difficult to evaluate the contributions from benthic processes to global oceanic cycles of trace elements. To bridge this gap, we analyzed porewater and bulk sediment concentrations of vanadium, chromium, cobalt, nickel, copper, arsenic, molybdenum, barium and uranium, as well as concentrations of the major oxidants nitrate, manganese, iron, and sulfate in the top 30 cm of cores collected along a transect from Hawaii to Alaska. The data show large increases in porewater concentrations of vanadium, manganese, cobalt, nickel, copper, and arsenic within the top cm of the sediment, consistent with the release of these elements from remineralized organic matter. The sediments are a sink for sulfate, uranium, and molybdenum, even though conditions within the sampled top 30 cm remain aerobic. Porewater chromium concentrations generally increase with depth due to release from sediment particles. Extrapolated to the global aerial extent of pelagic clay sediment, the benthic fluxes in mol yr −1 are Ba 3.9 ± 3.6 × 10 9 , Mn 3.4 ± 3.5 × 10 8 , Co 2.6 ± 1.3 × 10 7 , Ni 9.6 ± 8.6 × 10 8 , Cu 4.6 ± 2.4 × 10 9 , Cr 1.7 ± 1.1 × 10 8 , As 6.1 ± 7.0 × 10 8 , V 6.0 ± 2.5 × 10 9 . With the exception of vanadium, calculated fluxes across the sediment–water interface are consistent with the variability in bottom‐water concentrations and ocean residence time of the studied elements.
    Type: Article , PeerReviewed
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  • 7
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    A quantification of the effect of diagenesis on the paleoredox record in mid-Proterozoic sedimentary rocks (2021)
    GSA (Geological Society of America)
    Details
    Publication Date: 2024-02-07
    Description: Iron speciation in ancient sedimentary rocks is widely used to reconstruct oceanic redox conditions over geological time, specifically to assess the extent of oxic, euxinic (anoxic containing sulfide), and ferruginous (anoxic containing iron) conditions. We explore how post-depositional sedimentary processes can skew particular geochemical signals in the rock record. One such process is when aqueous sulfide—including that produced in the sediment column—reacts with sedimentary iron, converting non-sulfide, highly reactive iron minerals to iron-sulfide minerals; this can lead to increased preservation of iron as pyrite and an overestimation of seafloor euxinia. We show that sedimentary rocks with higher (〉5 wt%) total iron content are more buffered to this effect and thus are a more reliable indicator of true water-column euxinia. When considering this effect in the geological past, we estimate that true euxinia in the mid-Proterozoic may have been as much as fourfold less than previously thought—more in line with other recent paleoredox proxies not based on iron minerals. Marine iron and sulfate concentrations were more equivalent in Proterozoic–Neoproterozoic oceans, suggesting this time period was particularly susceptible to this post-depositional alteration, explaining the extent of euxinia suggested for this geological interval.
    Type: Article , PeerReviewed
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  • 8
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    Authigenic formation of clay minerals in the abyssal North Pacific (2022)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2024-02-07
    Description: Present estimates of the biogeochemical cycles of calcium, strontium and potassium in the ocean reveal large imbalances between known input and output fluxes. Using pore fluid, incubation and solid sediment data from North Pacific multi-corer cores we show that, contrary to the common paradigm, the top centimetres of abyssal sediments can be an active site of authigenic precipitation of clay minerals. In this region, clay authigenesis is the dominant sink for potassium and strontium and consumes nearly all calcium released from benthic dissolution of calcium carbonates. These observations support the idea that clay authigenesis occurring over broad regions of the world ocean may be a major buffer for ocean chemistry on the time scale of the ocean overturning circulation, and key to the long-term stability of Earth’s climate. Key Points North Pacific red clay sediments are a sink for marine calcium, strontium and potassium Authigenic formation of clay minerals is prevalent in pelagic sediments throughout the North Pacific The main mechanism for clay formation is recrystallisation of aluminosilicates, neoformation can occur in biogenic silica rich sediments
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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  • 9
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    Early diagenesis of sulfur in Bornholm Basin sediments: The role of upward diffusion of isotopically “heavy” sulfide (2021)
    Elsevier
    Details
    Publication Date: 2021-11-01
    Print ISSN: 0016-7037
    Electronic ISSN: 1872-9533
    Topics: Chemistry and Pharmacology , Geosciences
    Published by Elsevier
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    PAPER CURRENT
  • 10
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    (Table S3) Electron microprobe measurements analysis for hardgrounds (2020)
    PANGAEA
    Details
    Publication Date: 2023-12-11
    Keywords: 1; 10; 11; 13; 14; 15; 16; 17; 2; 3; 4; 5; 6; 7; 8; 9; Age, comment; Avon Park Formation, USA; carbonate hard grounds; CHC-01; CHC-02; CHC-03; CHC-04; CHC-05; CHC-06; CHC-07; CHC-08; CHC-09; CHC-10; CHC-11; CHC-13; CHC-14; CHC-15; CHC-16; CHC-17; Electron microprobe (EMP); Enewetak Atoll, Marshalls Islands; Eskett Limestones, England; Event label; Furongian, Banff National Park; Geological sample; GEOS; Gerecse Mts. Of Hungary; Holder formation, New Mexico; Intertidal Zone, Persian Gulf, UAE; Kanosh Formation, Utah; Latemar Formation; Latitude of event; Longitude of event; Magnesium; Magnesium/Calcium ratio; Manganese/Strontium ratio; Marjuman, Banff National Park; Meerssen Member, the Netherlands; Mg/Ca ratios; Mussafah Channel Hardground, UAE; Qishn Formation, Oman; Sample ID; Strontium; Suwannee Limestone, USA; Upper Greensands, Devon, UK
    Type: Dataset
    Format: text/tab-separated-values, 1602 data points
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    DATA PANGAEA
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