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  • 1
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    Impact of diagenetic alteration on brachiopod shell magnesium isotope (δ26Mg) signatures: Experimental versus field data (2016)
    Elsevier
    In:  Chemical Geology, 440 . pp. 191-206.
    Details
    Publication Date: 2019-02-01
    Description: Due to their thermodynamically stable low-Mg calcite mineralogy, the shells of brachiopods are often counted among the most reliable archives of the physicochemical conditions that occurred during the Phanerozoic in marine waters. Consequently, traditional and non-traditional isotope and elemental proxy data from brachiopod valves have been analyzed in numerous studies and results obtained have been placed in context with ancient seawater properties. This paper tests the sensitivity of brachiopod shell magnesium isotope (δ26Mg) data to diagenetic alteration. We apply a dual approach by: (i) performing hydrothermal alteration experiments using meteoric, marine, and burial reactive fluids; and (ii) comparing these data to naturally altered, ancient brachiopod shells. The degree of alteration of individual shells is assessed by a combination of fluorescence and cathodoluminescence microscopy. The absence of luminescence might indicate both well-preserved shell material, but also the secondary enrichment of quenching elements such as iron along diagenetic pathways. Complementary oxygen isotope data provide insight into the question of open versus closed system behavior of brachiopod shells. Brachiopod shell magnesium isotope values respond to differential fluid temperature, chemistry, and experiment durations. The patterns observed are complicated by the interplay of kinetic and thermodynamic patterns and the presence of variable amounts of water soluble and water insoluble organic matter within these biominerals. Generally, the range in bulk δ26Mg from experimentally altered (1.52‰) and that of bulk samples from ancient, diagenetically altered brachiopod valves (1.53‰) exceed the geochemical variability of δ26Mgbrachiopod bulk values of most recent specimens (1.26‰) in the lower and upper range. More 26Mg enriched (0.8‰) and more 26Mg depleted (0.7‰) values, respectively, are found in altered shells in comparison to unaltered ones. The data shown here are considered significant for those aiming to reconstruct palaeoenvironmental parameters based on brachiopod archives. Consequently, we propose tentative guidelines for magnesium isotope research applied to ancient carbonates.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1016/j.chemgeo.2016.07.020
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Response of the coccolithophores Emiliania huxleyi and Coccolithus braarudii to changing seawater Mg2+ and Ca2+ concentrations: Mg/Ca, Sr/Ca ratios and δ44/40Ca, δ26/24Mg of coccolith calcite (2011)
    Elsevier
    In:  Geochimica et Cosmochimica Acta, 75 (8). pp. 2088-2102.
    Details
    Publication Date: 2019-09-23
    Description: Calcium and magnesium concentrations in seawater have varied over geological time scales. On short time scales, variations in the major ion composition of seawater influences coccolithophorid physiology and the chemistry of biogenically produced coccoliths. Validation of those changes via controlled laboratory experiments is a crucial step in applying coccolithophorid based paleoproxies for the reconstruction of past environmental conditions. Therefore, we examined the response of two species of coccolithophores, Emiliania huxleyi and Coccolithus braarudii, to changes in the seawater Mg/Ca ratio (≈0.5 to 10 mol/mol) by either manipulating the magnesium or calcium concentration under controlled laboratory conditions. Concurrently, seawater Sr/Ca ratios were also modified (≈2 to 40 mmol/mol), while keeping salinity constant at 35. The physiological response was monitored by measurements of the cell growth rate as well as the production rates of particulate inorganic and organic carbon, and chlorophyll a. Additionally, coccolithophorid calcite was analyzed for its elemental composition (Sr/Ca and Mg/Ca) as well as isotope fractionation of calcium and magnesium (Δ44/40Ca and Δ26/24Mg). Our results reveal that physiological rates were substantially influenced by changes in seawater calcium rather than magnesium concentration within the range estimated to have occurred over the past 250 million years when coccolithophores appear in the fossil record. All physiological rates of E. huxleyi decreased at a calcium concentration above 25 mmol L−1, whereas C. braarudii displayed a higher tolerance to increased seawater calcium concentrations. Partition coefficient of Sr was calculated as 0.36 ± 0.04 (±2σ) independent of species. Partition coefficient of Mg2+ increased with increasing seawater Ca2+ concentrations in both coccolithophore species. Calcium isotope fractionation was constant at 1.1 ± 0.1‰ (±2σ) and not altered by changes in seawater Mg/Ca ratio. There is a well-defined inverse linear relationship between calcium isotope fractionation and partition coefficient of Sr2+ in all experiments, suggesting similar controls on both proxies in the investigated species. Magnesium isotope ratios were relatively stable for seawater Mg/Ca ratios ranging from 1 to 5, with a higher degree of fractionation in Emiliania huxleyi (by ≈0.2‰ in Δ26/24Mg). Although Mg/Ca ratios in the calcite of coccolithophores and foraminifera are similar, the former have considerably higher Δ26/24Mg (by 〉+3‰), presumably due to differences in calcification mechanisms between the two taxa. These observations suggest, a physiological control over magnesium elemental and isotopic fractionation during the process of calcification in coccolithophores.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1016/j.gca.2011.01.035
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Isotope ratios, trace elements and ultrastructure results of Mytilus galloprovincialis shells and experimental site data off Ischia (Italy)
    PANGAEA
    In:  Supplement to: Hahn, Sabine; Rodolfo-Metalpa, Riccardo; Griesshaber, Erika; Schmahl, Wolfgang W; Buhl, Dieter; Hall-Spencer, Jason M; Baggini, Cecilia; Fehr, Karl T; Immenhauser, Adrian (2012): Marine bivalve shell geochemistry and ultrastructure from modern low pH environments: environmental effect versus experimental bias. Biogeosciences, 9, 1897-1914, https://doi.org/10.5194/bg-9-1897-2012
    Details
    Publication Date: 2023-05-12
    Description: Bivalve shells can provide excellent archives of past environmental change but have not been used to interpret ocean acidification events. We investigated carbon, oxygen and trace element records from different shell layers in the mussels Mytilus galloprovincialis combined with detailed investigations of the shell ultrastructure. Mussels from the harbour of Ischia (Mediterranean, Italy) were transplanted and grown in water with mean pHT 7.3 and mean pHT 8.1 near CO2 vents on the east coast of the island. Most prominently, the shells recorded the shock of transplantation, both in their shell ultrastructure, textural and geochemical record. Shell calcite, precipitated subsequently under acidified seawater responded to the pH gradient by an in part disturbed ultrastructure. Geochemical data from all test sites show a strong metabolic effect that exceeds the influence of the low-pH environment. These field experiments showed that care is needed when interpreting potential ocean acidification signals because various parameters affect shell chemistry and ultrastructure. Besides metabolic processes, seawater pH, factors such as salinity, water temperature, food availability and population density all affect the biogenic carbonate shell archive.
    Keywords: BIOACID; Biological Impacts of Ocean Acidification; Mediterranean Sea Acidification in a Changing Climate; MedSeA
    Type: Dataset
    Format: application/zip, 4 datasets
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    DATA PANGAEA
  • 4
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    (Table S1) Results of isotope analysis from shells of Mytilus galloprovincialis at the experimental site B1 and control site C
    PANGAEA
    Details
    Publication Date: 2023-05-12
    Keywords: East coast of Ischia, Italia; ES; Event label; HAND; Ischia_B1; Ischia_C; Mediterranean Sea Acidification in a Changing Climate; MedSeA; Mytilus galloprovincialis, distance from commissure; OS; Sample code/label; Sample type; Sampling by hand; δ13C; δ13C, standard deviation; δ18O, carbonate; δ18O, standard deviation
    Type: Dataset
    Format: text/tab-separated-values, 1190 data points
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    DATA PANGAEA
  • 5
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    (Table 1) Seawater chemistry calculated over the experiment period at the experimental site B1 and control site C
    PANGAEA
    Details
    Publication Date: 2023-05-12
    Keywords: Aragonite saturation state; Aragonite saturation state, standard deviation; Bicarbonate, standard deviation; Bicarbonate ion; Calcite saturation state; Calcite saturation state, standard deviation; Carbon, inorganic, dissolved; Carbon, inorganic, dissolved, standard deviation; Carbonate ion; Carbonate ion, standard deviation; Carbon dioxide; Carbon dioxide, partial pressure; Carbon dioxide, partial pressure, standard deviation; Carbon dioxide, standard deviation; DEPTH, water; East coast of Ischia, Italia; ES; Event label; HAND; IP; Ischia_B1; Ischia_C; Ischia_harbour; Mediterranean Sea Acidification in a Changing Climate; MedSeA; OS; pH; pH, standard deviation; Sampling by hand; Temperature, standard deviation; Temperature, water; δ13C; δ13C, standard deviation; δ18O, maximum; δ18O, minimum; δ18O, standard deviation; δ18O, water
    Type: Dataset
    Format: text/tab-separated-values, 72 data points
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    DATA PANGAEA
  • 6
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    (Table 2) Thickness characteristics of different shell layers of Mytilus galloprovincialis at the experimental site B1 and control site C
    PANGAEA
    Details
    Publication Date: 2023-05-12
    Keywords: Comment; East coast of Ischia, Italia; ES; Event label; HAND; Ischia_B1; Ischia_C; Layer description; Mediterranean Sea Acidification in a Changing Climate; MedSeA; Mytilus galloprovincialis, layer thickness; OS; pH; Sampling by hand
    Type: Dataset
    Format: text/tab-separated-values, 131 data points
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    DATA PANGAEA
  • 7
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    (Table S2) Results of microprobe analysis maps (total area) of Mytilus galloprovincialis at the experimental site B1
    PANGAEA
    Details
    Publication Date: 2023-05-12
    Keywords: Barium; Barium, standard deviation; Calcium; Calcium, standard deviation; Chlorine; Chlorine, standard deviation; East coast of Ischia, Italia; ES; HAND; Iron; Iron, standard deviation; Ischia_B1; Magnesium; Magnesium, standard deviation; Manganese; Manganese, standard deviation; Mediterranean Sea Acidification in a Changing Climate; MedSeA; Phosphorus; Phosphorus, standard deviation; Sample code/label; Sampling by hand; Silicon; Silicon, standard deviation; Sodium; Sodium, standard deviation; Strontium; Strontium, standard deviation
    Type: Dataset
    Format: text/tab-separated-values, 357 data points
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    DATA PANGAEA
  • 8
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    Marine bivalve shell geochemistry and ultrastructure from modern low pH environments: environmental effect versus experimental bias (2012)
    PANGAEA
    Details
    Publication Date: 2024-03-15
    Keywords: Alkalinity, total; Animalia; Aragonite saturation state; Aragonite saturation state, standard deviation; Benthic animals; Benthos; Bicarbonate ion; Bicarbonate ion, standard deviation; Calcification/Dissolution; Calcite saturation state; Calcite saturation state, standard deviation; Calculated using seacarb after Nisumaa et al. (2010); Carbon, inorganic, dissolved; Carbon, inorganic, dissolved, standard deviation; Carbonate ion; Carbonate ion, standard deviation; Carbonate system computation flag; Carbon dioxide; Carbon dioxide, standard deviation; CO2 vent; Coast and continental shelf; Distance; East coast of Ischia, Italia; Elements; ES; Event label; Field experiment; Fugacity of carbon dioxide (water) at sea surface temperature (wet air); Growth/Morphology; HAND; IP; Ischia_B1; Ischia_C; Ischia_harbour; Layer description; Mediterranean Sea; Mollusca; Mytilus galloprovincialis; North Atlantic; OA-ICC; Ocean Acidification International Coordination Centre; OS; Partial pressure of carbon dioxide, respiration, standard deviation; Partial pressure of carbon dioxide (water) at sea surface temperature (wet air); Percentage; Percentage, standard deviation; pH; pH, standard deviation; Salinity; Sample code/label; Sample type; Sampling by hand; Shell length; Single species; Site; Species; Table; Temperate; Temperature, water; Temperature, water, standard deviation; Thickness; δ13C; δ13C, standard deviation; δ18O, carbonate; δ18O, maximum; δ18O, minimum; δ18O, standard deviation; δ18O, water
    Type: Dataset
    Format: text/tab-separated-values, 10106 data points
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    DATA PANGAEA
  • 9
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    Testing the preservation potential of early diagenetic dolomites as geochemical archives (2021)
    Details
    Publication Date: 2021-07-05
    Description: Early marine diagenetic dolomite is a rather thermodynamically‐stable carbonate phase and has potential to act as an archive of marine porewater properties. However, the variety of early to late diagenetic dolomite phases that can coexist within a single sample can result in extensive complexity. Here, the archive potential of early marine dolomites exposed to extreme post‐depositional processes is tested using various types of analyses, including: petrography, fluid inclusion data, stable δ13C and δ18O isotopes, 87Sr/86Sr ratios, and U‐Pb age dating of various dolomite phases. In this example, a Triassic carbonate platform was dissected and overprinted (diagenetic temperatures of 50 to 430°C) in a strike‐slip zone in Southern Spain. Eight episodes of dolomitization, a dolostone cataclasite and late stage meteoric/vadose cementation were recognized. The following processes were found to be diagenetically relevant: (i) protolith deposition and fabric‐preservation, and marine dolomitization of precursor aragonite and calcite during the Middle–Late Triassic; (ii) intermediate burial and formation of zebra saddle dolomite and precipitation of various dolomite cements in a Proto‐Atlantic opening stress regime (T ca 250°C) during the Early–Middle Jurassic; (iii) dolomite cement precipitation during early Alpine tectonism, rapid burial to ca 15 km, and high‐grade anchizone overprint during Alpine tectonic evolution in the Early Eocene to Early Miocene; (iv) brecciation of dolostones to cataclasite during the onset of the Carboneras Fault Zone activity during the Middle Miocene; and (v) late‐stage regression and subsequent meteoric overprint. Data shown here document that, under favourable conditions, early diagenetic marine dolomites and their archive data may resist petrographic and geochemical resetting over time intervals of 108 or more years. Evidence for this preservation includes preserved Late Triassic seawater δ13CDIC values and primary fluid inclusion data. Data also indicate that oversimplified statements based on bulk data from other petrographically‐complex dolomite archives must be considered with caution.
    Description: DFG http://dx.doi.org/10.13039/501100001659
    Keywords: 551.9 ; Diagenesis ; dolomite ; dolomitization ; fluid inclusions ; geochemistry ; petrography ; tectonic overprint ; U‐Pb dating
    Type: article
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    CITATION GEO-LEO
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