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  • 1
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    Interlaboratory study for coral Sr/Ca and other element/Ca ratio measurements (2013)
    Wiley
    In:  EPIC3Geochemistry Geophysics Geosystems, Wiley, 14(9), pp. 3730-3750, ISSN: 1525-2027
    Details
    Publication Date: 2015-10-21
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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    PAPER (OA)
  • 2
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    Constraining past environmental changes of cold‐water coral mounds with geochemical proxies in corals and foraminifera (2019)
    Wiley
    Details
    Publication Date: 2019-12-05
    Electronic ISSN: 2055-4877
    Topics: Geosciences
    Published by Wiley
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    PAPER CURRENT
  • 3
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    Assessment of Chalk as an Archive for the Lithium Isotope Composition of Seawater (2024)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2024-02-23
    Description: The understanding of silicate weathering and its role as a sink for atmospheric CO 2 is important to get a better insight into how the Earth shifts from warm to cool climates. The lithium isotope composition (δ 7 Li) of marine carbonates can be used as a proxy to track the past chemical weathering of silicates. A high‐resolution δ 7 Li record would be helpful to evaluate the role of silicate weathering during the late Cretaceous climate cooling. Here, we assess chalk as a potential archive for reconstructing Late Cretaceous seawater Li isotope composition by comparing Maastrichtian chalk from Northern Germany (Hemmoor, Kronsmoor) to a Quaternary coccolith ooze from the Manihiki Plateau (Pacific Ocean) as a lithological analog to modern conditions. We observe a negative offset of 3.9 ± 0.6‰ for the coccolith ooze relative to the modern seawater Li isotope composition (+31.1 ± 0.3‰; 2SE; n = 54), a value that falls in the range of published offsets for modern core‐top samples and for brachiopod calcite. Further, the negative offset between the Li isotope compositions of Manihiki coccolith ooze and modern planktonic foraminifera is 2.3 ± 0.6‰. Although chalk represents a diagenetically altered modification of pelagic nannofossil ooze, manifested by changes in the composition of trace elements, we observe a consistent offset of Li isotope data between Maastrichtian chalk and Maastrichtian planktonic foraminiferal data (−1.4 ± 0. 5‰) that lies within the uncertainty of modern values. We therefore suggest that chalk can be used as a reliable archive for δ 7 Li reconstructions. Key Points Chalk is a reliable archive for the Li isotope composition of seawater Coccolith ooze has a negative offset of 3.9 ± 0.6‰ from modern seawater for Li isotope ratios The estimated mean value for the late Maastrichtian seawater Li isotope composition is +27.5 ± 1.0‰
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  • 4
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    Accurate measurement of K/Ca in low‐[K] carbonate samples using laser‐ablation sector‐field inductively coupled plasma mass spectrometry (2024)
    Wiley
    Details
    Publication Date: 2024-03-15
    Description: Rationale Potassium (K) is a major component of several silicate minerals and seawater, and, therefore, constraining past changes in the potassium cycle is a promising way of tracing large‐scale geological processes on Earth. However, [K] measurement using inductively coupled plasma mass spectrometry (ICP‐MS) is challenging due to an ArH + interference, which may be of a similar magnitude to the K + ion beam in samples with 〈0.1% m/m [K]. Methods In this work, we investigated the effect of the ArH + interference on K/Ca data quality by comparing results from laser‐ablation (LA)‐ICP‐MS measured in medium and high mass resolution modes and validating our LA results via solution ICP‐optical emission spectroscopy (OES) and solution ICP‐MS measurements. To do so, we used a wide range of geological reference materials, with a particular focus on marine carbonates, which are potential archives of past changes in the K cycle but are typically characterised by [K] 〈 200 μg/g. In addition, we examine the degree to which trace‐element data quality is driven by downhole fractionation during LA‐ICP‐MS measurements. Results Our results show that medium mass resolution (MR) mode is sufficiently capable of minimising the effect of the ArH + interference on K + . However, the rate of downhole fractionation for Na and K varies between different samples as a result of their differing bulk composition, resulting in matrix‐specific inaccuracy. We show how this can be accounted for via downhole fractionation corrections, resulting in an accuracy of better than 1% and a long‐term reproducibility (intermediate precision) of 〈6% (relative standard deviation) in JCp‐1NP using LA‐ICP‐MS in MR mode. Conclusion Our [K] measurement protocol is demonstrably precise and accurate and applicable to a wide range of materials. The measurement of K/Ca in relatively low‐[K] marine carbonates is presented here as a key example of a new application opened up by these advances.
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  • 5
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    Interlaboratory study for coral Sr/Ca and other element/Ca ratio measurements (2013)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2024-03-22
    Description: The Sr/Ca ratio of coral aragonite is used to reconstruct past sea surface temperature (SST). Twentyone laboratories took part in an interlaboratory study of coral Sr/Ca measurements. Results show interlaboratory bias can be significant, and in the extreme case could result in a range in SST estimates of 7°C. However, most of the data fall within a narrower range and the Porites coral reference material JCp- 1 is now characterized well enough to have a certified Sr/Ca value of 8.838 mmol/mol with an expanded uncertainty of 0.089 mmol/mol following International Association of Geoanalysts (IAG) guidelines. This uncertainty, at the 95% confidence level, equates to 1.5°C for SST estimates using Porites, so is approaching fitness for purpose. The comparable median within laboratory error is 〈0.5°C. This difference in uncertainties illustrates the interlaboratory bias component that should be reduced through the use of reference materials like the JCp-1. There are many potential sources contributing to biases in comparative methods but traces of Sr in Ca standards and uncertainties in reference solution composition can account for half of the combined uncertainty. Consensus values that fulfil the requirements to be certified values were also obtained for Mg/Ca in JCp-1 and for Sr/Ca and Mg/Ca ratios in the JCt-1 giant clam reference material. Reference values with variable fitness for purpose have also been obtained for Li/Ca, B/Ca, Ba/Ca, and U/Ca in both reference materials. In future, studies reporting coral element/Ca data should also report the average value obtained for a reference material such as the JCp-1.
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  • 6
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    Paleoseawater density reconstruction and its implication for cold-water coral carbonate mounds in the northeast Atlantic through time (2016)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2024-03-22
    Description: Carbonate buildups and mounds are impressive biogenic structures throughout Earth history. In the recent NE Atlantic, cold-water coral (CWC) reefs form giant carbonate mounds of up to 300 m of elevation. The expansion of these coral carbonate mounds is paced by climatic changes during the past 2.7 Myr. Environmental control on their development is directly linked to controls on its main constructors, the reef-building CWCs. Seawater density has been identified as one of the main controlling parameter of CWC growth in the NE Atlantic. One possibility is the formation of a pycnocline above the carbonate mounds, which is increasing the hydrodynamic regime, supporting elevated food supply, and possibly facilitating the distribution of coral larvae. The potential to reconstruct past seawater densities from stable oxygen isotopes of benthic foraminifera has been further developed: a regional equation gives reliable results for three different settings, peak interglacials (e.g., Holocene), peak glacials (e.g., Last Glacial Maximum), and intermediate setting (between the two extremes). Seawater densities are reconstructed for two different NE Atlantic CWC carbonate mounds in the Porcupine Seabight indicating that the development of carbonate mounds is predominantly found at a seawater density range between 27.3 and 27.7 kg m−3 (σΘ notation). Comparable to recent conditions, we interpret the reconstructed density range as a pycnocline serving as boundary layer, on which currents develop, carrying nutrition and possibly coral larvae. The close correlation of CWC reef growth with reconstructed seawater densities through the Pleistocene highlights the importance of pycnoclines and intermediate water mass dynamics.
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  • 7
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    Sea surface and subsurface circulation dynamics off equatorial Peru during the last ~17 kyr (2015)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2024-03-22
    Description: The complex deglacial to Holocene oceanographic development in the Gulf of Guayaquil (Eastern Equatorial Pacific) is reconstructed for sea surface and subsurface ocean levels from (isotope) geochemical proxies based on marine sediment cores. At sea surface, southern sourced Cold Coastal Water and tropical Equatorial Surface Water/Tropical Surface Water are intimately related. In particular since ~10 ka, independent sea surface temperature proxies capturing different seasons emphasize the growing seasonal contrast in the Gulf of Guayaquil, which is in contrast to ocean areas further offshore. Cold Coastal Water became rapidly present in the Gulf of Guayaquil during the austral winter season in line with the strengthening of the Southeast Trades, while coastal upwelling off Peru gradually intensified and expanded northward in response to a seasonally changing atmospheric circulation pattern affecting the core locations intensively since 4 ka BP. Equatorial Surface Water, instead, was displaced and Tropical Surface Water moved northward together with the Equatorial Front. At subsurface, the presence of Equatorial Under Current-sourced Equatorial Subsurface Water was continuously growing, prominently since ~10–8 ka B.P. During Heinrich Stadial 1 and large parts of the Bølling/Allerød, and similarly during short Holocene time intervals at ~5.1–4 ka B.P. and ~1.5–0.5 ka B.P., the admixture of Equatorial Subsurface Water was reduced in response to both short-term weakening of Equatorial Under Current strength from the northwest and emplacement by tropical Equatorial Surface Water, considerably warming the uppermost ocean layers.
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  • 8
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    Environmental constraints on Holocene cold-water coral reef growth off Norway: Insights from a multi-proxy approach (2016)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2024-03-22
    Description: High-latitude cold-water coral (CWC) reefs are particularly susceptible due to enhanced CO2 uptake in these regions. Using precisely dated (U/Th) CWCs (Lophelia pertusa) retrieved during research cruise POS 391 (Lopphavet 70.6°N, Oslofjord 59°N) we applied boron isotopes (δ11B), Ba/Ca, Li/Mg and U/Ca ratios to reconstruct the environmental boundary conditions of CWC reef growth. The sedimentary record from these CWC reefs reveals a lack of corals between ∼ 6.4 and 4.8 ka. The question remains if this phenomenon is related to changes in the carbonate system or other causes. The initial postglacial setting had elevated Ba/Ca ratios, indicative of meltwater fluxes showing a decreasing trend towards cessation at 6.4 ka with a oscillation pattern similar to continental glacier fluctuations. Downcore U/Ca ratios reveal an increasing trend, which is outside the range of modern U/Ca variability in L. pertusa, suggesting changes of seawater pH near 6.4 ka. The reconstructed BWT at Lopphavet reveals a striking similarity to Barent Sea-Surface and sub-Sea-Surface-Temperature records. We infer that meltwater pulses weakened the North Atlantic Current system resulting in southward advances of cold and CO2 rich Arctic waters. A corresponding shift in the δ11B record from ∼ 25.0‰ to ∼ 27.0 ‰ probably implies enhanced pH-up regulation of the CWCs due to the higher pCO2 concentrations of ambient seawater, which hastened Mid-Holocene CWC reef decline on the Norwegian Margin.
    Type: Article , PeerReviewed
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