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  • 2020-2024  (9)
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  • 1
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    Characteristics, elevations and ages of various mid-late Holocene features collected from twelve islands in French Polynesia (2021)
    PANGAEA
    Details
    Publication Date: 2024-01-25
    Description: Characteristics, elevations and ages of 165 samples from various mid-late Holocene features, such as in situ Porites microatolls, in situ reef flats, conglomerates and reworked reef blocks, collected from twelve islands in French Polynesia. This table complements the database on which the mid-late Holocene sea-level curve has been initially reconstructed (Hallmann et al., 2018). Δ modern-fossil represents the difference in elevation between modern and Holocene microatolls at the same study site and in a similar environment (maximum vertical error is of ± 2 cm). NGPF = altimetric reference of French Polynesia. The elevations have been corrected for subsidence based on rates of 0.14 mm/yr for Moorea, 0.05 mm/yr for Bora Bora and Tahaa as well as 0.03 mm/yr for Maupiti, the Gambier Islands and Raivavae. Error values for ages and elevations are 2-sigma. Uncertainties for measured elevations related to NGPF are ± 14 cm for samples from Bora Bora, Maupiti, Raivavae, Tikehau and the Gambier Islands; ± 22 cm for samples from Fakarava, Hao, Makemo, Manihi, Moorea, Rangiroa and Tahaa. Uncertainties for estimated elevations are ± 10 cm for Δ modern-fossil and ± 22 cm for NGPF elevations.
    Keywords: AGE; Age, dated standard deviation; Aragonite; Bora Bora; Calculated; Corrected; Diameter; Difference; ELEVATION; Event label; Fakarava; French_Polynesia_BOB; French_Polynesia_FAK; French_Polynesia_GAM; French_Polynesia_HAO; French_Polynesia_MAK; French_Polynesia_MAN; French_Polynesia_MAU; French_Polynesia_MOO; French_Polynesia_RAI; French_Polynesia_RAN; French_Polynesia_TAA; French_Polynesia_TIK; French Polynesia; Gambier; HAND; Hao; LATITUDE; Location; LONGITUDE; low-lying islands; Makemo; Manihi; Maupiti; mid-late Holocene sea level; Moorea; Porites microatolls; Raivavae; Rangiroa; reef development; Sample comment; Sample ID; Sampling by hand; storm deposits; Tahaa; Tikhau; U-series dating
    Type: Dataset
    Format: text/tab-separated-values, 1068 data points
    Location Call Number Limitation Availability
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    DATA PANGAEA
  • 2
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    Uranium/Thorium isotopic composition of various mid-late Holocene features collected from twelve islands in French Polynesia (2021)
    PANGAEA
    Details
    Publication Date: 2024-01-25
    Description: Uranium/Thorium isotopic composition of 165 samples from various mid-late Holocene features, such as in situ Porites microatolls, in situ reef flats, conglomerates and reworked reef blocks, collected from twelve islands in French Polynesia. Recommendations of Dutton et al. (2017) were followed for the presentation of U/Th age data. For each parameter, the first column contains the value and the second column the statistical error. All statistical errors are two standard deviations of the mean (2σ mean). All samples have been corrected for initial 230Th by using a 230Th/232Th activity ratio of 0.66 ± 0.2 (Fietzke et al., 2005). Non-reported data consist of 230Th/232Th ratios which became negative due to background corrections. 238U Concentrations are not corrected for the background.
    Keywords: Age, dated; Age, dated standard deviation; Age, Uranium-Thorium; Bora Bora; Calculated; Event label; Fakarava; French_Polynesia_BOB; French_Polynesia_FAK; French_Polynesia_GAM; French_Polynesia_HAO; French_Polynesia_MAK; French_Polynesia_MAN; French_Polynesia_MAU; French_Polynesia_MOO; French_Polynesia_RAI; French_Polynesia_RAN; French_Polynesia_TAA; French_Polynesia_TIK; French Polynesia; Gambier; HAND; Hao; LATITUDE; LONGITUDE; low-lying islands; Makemo; Manihi; Maupiti; mid-late Holocene sea level; Moorea; Porites microatolls; Raivavae; Rangiroa; reef development; Sample ID; Sampling by hand; storm deposits; Tahaa; Thorium-230; Thorium-230, standard deviation; Thorium-230/Thorium-232 activity ratio; Thorium-230/Thorium-232 activity ratio, standard deviation; Thorium-230/Uranium-238 activity ratio; Thorium-230/Uranium-238 activity ratio, error, relative; Thorium-232; Thorium-232, standard deviation; Tikhau; Uranium-234/Uranium-238 activity ratio; Uranium-234/Uranium-238 activity ratio, standard deviation; Uranium-238; Uranium-238, standard deviation; Uranium-238/Thorium-232 activity ratio; Uranium-238/Thorium-232 activity ratio, standard deviation; U-series dating
    Type: Dataset
    Format: text/tab-separated-values, 3111 data points
    Location Call Number Limitation Availability
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    DATA PANGAEA
  • 3
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    Inverse response of 231Pa/230Th to variations of the Atlantic meridional overturning circulation in the North Atlantic intermediate water (2020)
    Springer
    Details
    Publication Date: 2023-02-08
    Description: This study aims to provide a more detailed understanding of the behavior of 231Pa/230Th under varying ocean circulation regimes. The North Atlantic provides a unique sedimentary setting with its ice-rafted detritus (IRD) layers deposited during glacial times. These layers have been found north of 40° N (Ruddiman Belt) and are most pronounced during Heinrich Stadials. Most of these sediments have been recovered from the deep North Atlantic basin typically below 3000 m water depth. This study reports sedimentological and sediment geochemical data from one of the few sites at intermediate depth of the open North Atlantic (core SU90-I02, 45° N 39° W, 1965 m water depth) within the Ruddiman Belt. The time periods of Heinrich Stadials 1 and 2 of this core were identified with the help of the major element composition by XRF scanning and by IRD counting. Along the core profile, the sedimentary 231Pa/230Th activity ratio has been measured as a kinematic proxy for the circulation strength. The 231Pa/230Th record shows highest values during the Holocene and Last Glacial Maximum, above the natural production ratio of these isotopes. During Heinrich Stadials 1 and 2, when Atlantic meridional overturning circulation was most reduced, the 231Pa/230Th record shows overall lowest values below the production ratio. This behavior is contrary to classical findings of 231Pa/230Th from the northwestern Atlantic where a strong Holocene circulation is associated with low values. However, this behavior at the presented location is in agreement with results from simulations of the 231Pa/230Th-enabled Bern3D Earth system model.
    Type: Article , PeerReviewed
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    Format: other
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    The impact of MC-ICP-MS plasma conditions on the accuracy and precision of stable isotope measurements evaluated for barium isotopes (2020)
    Elsevier
    Details
    Publication Date: 2023-02-08
    Description: Highlights • Improved understanding of the behaviour of instrumental mass fractionation (IMF). • The effect of matrix elements on IMF is largely associated with plasma conditions that can be quantified with the NAI. • Matrix effects can be systematically and significantly attenuated by tuning of instrumental operating parameters. • A matrix tolerance plasma state is defined for stable barium isotope analysis. • The suggested analytical protocol is expected to be applicable to other stable isotope measurements with MC-ICP-MS. Abstract Stable barium isotope measurements with multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) remain an analytical challenge and can be considerably affected by the presence of matrix elements, even when applying double spiking. Therefore significant efforts were invested in previous studies to develop efficient barium purification methods. However, due to the high variability in matrix/barium ratios for diverse sample matrices, potential matrix effects can still not be excluded. While a lot of effort has been invested into improving the chemical separation protocols, the impact of plasma conditions on the accuracy and precision of stable isotope measurements has rarely been considered. Here we present a systematic investigation of the relationship between plasma conditions, instrumental mass fractionation (IMF) and impurity (i.e. matrix) concentrations. The Normalised Ar Index (NAI) and Matrix-Ar Index (MA) are used to quantify MC-ICP-MS plasma conditions and plasma mass loading, respectively. Our results show that the effect of matrix elements on IMF is largely linked to plasma conditions (i.e. NAI) and behaves as a linear function of mass loading (i.e. MA). Accordingly, the matrix effects can be significantly attenuated by increasing the NAI thereby minimising the risk of plasma “over-loading”. The improved understanding of the behaviour of the matrix-induced IMF allows us to define a matrix tolerance plasma state for barium isotope analysis. The accuracy of this recommended method is further assessed by analyses of two well-studied reference materials, the GEOTRACES seawater reference sample SAFe D2 and the carbonate reference material JCp-1. We expect that the analytical protocol described in this study is applicable not only to barium isotope analysis, but also to a wide range of other stable isotope measurements with MC-ICP-MS.
    Type: Article , PeerReviewed
    Format: archive
    Format: text
    Location Call Number Limitation Availability
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Minimal cobalt metabolism in the marine cyanobacterium Prochlorococcus (2020)
    National Academy of Sciences (Washington, DC)
    Details
    Publication Date: 2023-02-08
    Description: Despite very low concentrations of cobalt in marine waters, cyanobacteria in the genus Prochlorococcus retain the genetic machinery for the synthesis and use of cobalt-bearing cofactors (cobalamins) in their genomes. We explore cobalt metabolism in a Prochlorococcus isolate from the equatorial Pacific Ocean (strain MIT9215) through a series of growth experiments under iron- and cobalt-limiting conditions. Metal uptake rates, quantitative proteomic measurements of cobalamin-dependent enzymes, and theoretical calculations all indicate that Prochlorococcus MIT9215 can sustain growth with less than 50 cobalt atoms per cell, ∼100-fold lower than minimum iron requirements for these cells (∼5,100 atoms per cell). Quantitative descriptions of Prochlorococcus cobalt limitation are used to interpret the cobalt distribution in the equatorial Pacific Ocean, where surface concentrations are among the lowest measured globally but Prochlorococcus biomass is high. A low minimum cobalt quota ensures that other nutrients, notably iron, will be exhausted before cobalt can be fully depleted, helping to explain the persistence of cobalt-dependent metabolism in marine cyanobacteria.
    Type: Article , PeerReviewed
    Format: text
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Seawater Pb isotopes record early Miocene to modern circulation dynamics in the Pacific sector of the Southern Ocean (2023)
    Details
    Publication Date: 2023-12-14
    Type: Conference or Workshop Item , NonPeerReviewed
    Format: text
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    OceanRep: Poster
  • 7
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    Living on the edge: environmental variability of a shallow late Holocene cold-water coral mound (2022)
    Springer
    Details
    Publication Date: 2024-02-07
    Description: Similar to their tropical counterparts, cold-water corals (CWCs) are able to build large three-dimensional reef structures. These unique ecosystems are at risk due to ongoing climate change. In particular, ocean warming, ocean acidification and changes in the hydrological cycle may jeopardize the existence of CWCs. In order to predict how CWCs and their reefs or mounds will develop in the near future one important strategy is to study past fossil CWC mounds and especially shallow CWC ecosystems as they experience a greater environmental variability compared to other deep-water CWC ecosystems. We present results from a CWC mound off southern Norway. A sediment core drilled from this relatively shallow (~ 100 m) CWC mound exposes in full detail hydrographical changes during the late Holocene, which were crucial for mound build-up. We applied computed tomography, 230Th/U dating, and foraminiferal geochemical proxy reconstructions of bottom-water-temperature (Mg/Ca-based BWT), δ18O for seawater density, and the combination of both to infer salinity changes. Our results demonstrate that the CWC mound formed in the late Holocene between 4 kiloannum (ka) and 1.5 ka with an average aggradation rate of 104 cm/kiloyears (kyr), which is significantly lower than other Holocene Norwegian mounds. The reconstructed BWTMg/Ca and seawater density exhibit large variations throughout the entire period of mound formation, but are strikingly similar to modern in situ observations in the nearby Tisler Reef. We argue that BWT does not exert a primary control on CWC mound formation. Instead, strong salinity and seawater density variation throughout the entire mound sequence appears to be controlled by the interplay between the Atlantic Water (AW) inflow and the overlying, outflowing Baltic-Sea water. CWC growth and mound formation in the NE Skagerrak was supported by strong current flow, oxygen replenishment, the presence of a strong boundary layer and larval dispersal through the AW, but possibly inhibited by the influence of fresh Baltic Water during the late Holocene. Our study therefore highlights that modern shallow Norwegian CWC reefs may be particularly endangered due to changes in water-column stratification associated with increasing net precipitation caused by climate change.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    Reef response to sea-level and environmental changes in the Central South Pacific over the past 6000 years (2020)
    Elsevier
    Details
    Publication Date: 2023-05-16
    Description: Highlights • Coral reef responses to slow-rate, low-amplitude, high-frequency sea-level changes. • Continuous reef development over the last 6000 years in optimal conditions. • Mid-late Holocene coral assemblages similar to their modern counterparts. • Facies distribution governed by variations in accommodation space. • Prominent role played by reef deposits in the formation and shaping of modern islands. Geological records of coastal system evolution during past higher and/or rising sea levels provide an important baseline for developing projections regarding the response of modern coastal systems to future sea-level rise. The mid-late Holocene corresponds to the most recent window into natural variability prior to the Anthropocene and involves slow-rate and low-amplitude sea-level changes that were mostly governed by a limited glacio-eustatic contribution, most likely sourced from Antarctica, and ‘glacial isostatic adjustment’ processes. This paper documents in unprecedented detail the response of coral reefs and coastal systems to changing accommodation space in relation to mid-late Holocene sea-level changes in French Polynesia. The sea-level curve that underpins this study has a global significance and documents a single short-lived sea-level highstand between 4.10 and 3.40 kyr BP. The amplitude of the highstand is less than one metre, within the range of the predicted sea level at the end of the current century. The reported relative sea-level changes are characterized by slow rates ranging from a few tens of millimetres per year to up to 2.5 mm/yr and by significant sea-level stability (stillstands) lasting more than a century and up to 250 years, defining a step-like pattern. Sea-level variability probably driven by climatic oscillations on interannual to millennial time scales is evidenced during the entire time window. The detailed reconstruction of reef development over the last 6000 years brings valuable information regarding coral reef dynamics and coastal processes during periods of higher sea level and wave energy regimes. The persistence of stable and optimal depositional environments over the last 6000 years is demonstrated by the constant overall composition and diversity of reef communities and the almost continuous development of coral microatolls. The facies distribution as well as the lateral extension and shift of facies belts have been governed by variations in accommodation space, which are controlled by relative sea-level changes and antecedent topography. The widespread development of mid-late Holocene reef deposits in coastal areas suggests that they have played a prominent role in global processes related to the formation and shaping of modern islands.
    Type: Article , PeerReviewed
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 9
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    A commentary on holocene relative sea-level histories of far-field islands in the mid-Pacific by F. Tan, N. S. Khan, T. Li, A. J. Meltzner, J. Majewski, N. Chan, P. M. Chutcharavan, N. Cahill, M. Vacchi, D. Peng, B. P. Horton, [Quat. Sci. Rev. 310: 107995; https://doi.org/10.1016/j.quascirev.2023.107995] (2024)
    Elsevier
    Details
    Publication Date: 2024-05-13
    Type: Article , NonPeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - without review
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