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  • 1
    Publikationsdatum: 2024-11-11
    Beschreibung: Bulk sediment δ15N records from the eastern tropical Pacific (ETP) extending back to the last ice age most often show low glacial δ15N, then a deglacial δ15N maximum, followed by a gradual decline to a late Holocene δ15N that is typically higher than that of the Last Glacial Maximum (LGM). The lower δ15N of the LGM has been interpreted to reflect an ice age reduction in water column denitrification. We report foraminifera shell‐bound nitrogen isotope (FB‐δ15N) measurements for the two species Neogloboquadrina dutertrei and Neogloboquadrina incompta over the last 35 ka in two sediment cores from the eastern equatorial Pacific (EEP), both of which have the typical LGM‐to‐Holocene increase in bulk sediment δ15N. FB‐δ15N contrasts with bulk sediment δ15N by not indicating a lower δ15N during the LGM. Instead, the FB‐δ15N records are dominated by a deglacial δ15N maximum, with comparable LGM and Holocene values. The lower LGM δ15N of the bulk sediment records may be an artifact, possibly related to greater exogenous N inputs and/or weaker sedimentary diagenesis during the LGM. The new data raise the possibility that the previously inferred glacial reduction in ETP water column denitrification was incorrect. A review of reconstructed ice age conditions and geochemical box model output provides mechanistic support for this possibility. However, equatorial ocean circulation and nitrate‐rich surface water overlying both core sites allow for other possible interpretations, calling for replication at non‐equatorial ETP sites.
    Beschreibung: Plain Language Summary: The 15N/14N ratio of sediments provides information on the past marine nitrogen (N) cycle through the production of N‐bearing organic matter in the surface ocean and its burial in the sediments. Previous measurements of the sedimentary 15N/14N ratio in the eastern equatorial Pacific (EEP) indicate lower values during the last ice age compared to the Holocene (the current warm period). This has been interpreted to reflect an ice age reduction in the oceanic N loss process known as “denitrification” that occurs between 200 and 500 m depth in this region of the ocean. However, the 15N/14N ratio measured on the whole sediment can be biased by biological and chemical processes in the sediments and by foreign N inputs. To avoid these complications, we measured the 15N/14N ratio of organic N embedded in the calcite shell of unicellular zooplankton (foraminifera) in two sediment cores from the EEP. We found similar foraminifera‐bound 15N/14N ratios during the last ice and the Holocene. This may argue against the long‐held interpretation of a reduction in denitrification during the last ice age. However, the oceanographic setting of these equatorial cores leaves open alternative interpretations, calling for further work at other eastern tropical Pacific sites.
    Beschreibung: Key Points: Foraminifera‐bound δ15N was similar during the last ice age and the Holocene in the eastern equatorial Pacific, unlike bulk sedimentary δ15N. Bulk sediment δ15N is likely biased to lower ice age values by foreign N inputs and weaker sedimentary diagenesis. The foraminifera‐bound δ15N data may reflect that water column denitrification was not reduced during the last glacial period.
    Beschreibung: Swiss National Science Foundation
    Beschreibung: US National Science Foundation
    Beschreibung: Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung http://dx.doi.org/10.13039/501100001711
    Beschreibung: National Science Foundation http://dx.doi.org/10.13039/100000001
    Schlagwort(e): ddc:551.9 ; Pacific Ocean ; nitrogen isotopes ; denitrification ; suboxia ; Last Glacial Maximum ; Holocene
    Sprache: Englisch
    Materialart: info:eu-repo/semantics/article , doc-type:article
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    facet.materialart.
    Unbekannt
    PANGAEA
    In:  Supplement to: Greenop, Rosanna; Hain, Mathis P; Sosdian, Sindia M; Oliver, Kevin I C; Goodwin, Philip; Chalk, Thomas B; Lear, Caroline H; Wilson, Paul A; Foster, Gavin L (2017): A record of Neogene seawate d11B reconstructed from paired d11B analyses on benthic and planktic foraminifera. Climate of the Past, 13(2), 149-170, https://doi.org/10.5194/cp-13-149-2017
    Publikationsdatum: 2024-07-19
    Beschreibung: The boron isotope composition (d11B) of planktic foraminiferal calcite, which reflects seawater pH, is a well-established proxy for reconstructing palaeo-atmospheric CO2 and seawater carbonate chemistry. However, to translate d11B measurements determined in calcareous fossils into pH we need to know the boron isotope composition of the parent seawater (d11Bsw). While a number of d11Bsw reconstructions exist, the discrepancies between them reveals uncertainties and deficiencies that need to be addressed. Here we present a new d11Bsw record based on the d11B difference between planktic and benthic foraminifera and an estimate of the pH gradient between surface and deep water. We then calculate d11Bsw two different ways. One variant of our method assumes that the pH gradient between surface and deep has remained the same as today over the past 23 Ma; the other uses the d13C gradient between surface and deep to represent change in the pH gradient through time. The results of these two methods of calculating d11Bsw are broadly consistency with each other, however, based on extensive carbon cycle modelling using CYCLOPS and GENIE we favour the d13C gradient method. In our favoured d11Bsw reconstruction, d11Bsw is around 2 per mil lower than today at ~37.5 per mil during the early and middle Miocene and increases to the modern value (39.61 per mil) by ~5 Ma. A similar pattern of change is evident in the seawater composition of three other stable isotope systems, Mg, Li and Ca. Concurrent shifts in the seawater isotopic composition of all four of these elements during the late Miocene, suggest a common forcing mechanism. We hypothesise the most likely cause of these shifts is a change in the isotopic composition of the riverine input, potentially driven by an increase in secondary mineral formation since ~15 Ma.
    Schlagwort(e): Ocean Drilling Program; ODP
    Materialart: dataset publication series
    Format: application/zip, 2 datasets
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Publikationsdatum: 2024-08-15
    Beschreibung: Previous paleoceanographic applications of the N isotopes in the eastern equatorial Pacific have used the N isotopic composition of the bulk sediment, which can be biased by diagenetic alteration or foreign N input. To avoid these biases, we measured foraminifera shell-bound d15N (FB-d15N) on the two species Neogloboquadrina dutertrei and Neogloboquadrina incompta in two sediment cores extending back to the last ice age. The datafile contains FB-d15N data measured on the two sediment cores ME0005-24JC (0°1.3' N, 86°27.8' W, 2941m) and ME0005-27JC (1°51.2' S, 82°47.2'W, 2203m) from the eastern equatorial Pacific, as well as updated age models for the two sediment cores. Moreover, it contains estimated changes in Pacific oxygen concentration from the LGM to the Holocene. The age models for both sediment cores have been updated by Dubois et al. (2014) and are based on (1) radiocarbon ages measured on the planktonic foraminifera N. dutertrei by accelerator mass spectrometry, (2) correlation of benthic foraminifera oxygen isotopes to the LR04 stack and (3) the identification of the Los Chocoyos Ash Layer in the sediment cores. In core ME0005-27JC, three additional 14C dates on N. dutertrei from Mekik (2014) were included. All radiocarbon ages were calibrated with Calib 7.1. and the marine calibration curve MARINE13, assuming a reservoir age of 467 years as given in Dubois et al. (2014). Ages were linearly interpolated between the stratigraphic tie points. Foraminifera-bound d15N (FB-d15N) was measured with the “persulfate-denitrifier” technique (Ren et al., 2009; Straub et al., 2013). In short, ~3-5 mg of foraminifera (N. dutertrei and N. incompta from the 300-600µm size fraction) were picked, cut open with a scalpel and underwent a chemical cleaning. The organic N bound within the calcite was then released by dissolution with HCl and converted to nitrate in a basic potassium persulfate solution. The nitrate concentration of the solution was determined by chemiluminescence, and an aliquot of the nitrate solution equivalent to 5nmol of N was converted to nitrous oxide (N2O) by denitrifying bacteria. The N isotopic composition of the N2O was measured with a custom continuous-flow system for N2O extraction and purification on-line to a Thermo MAT253 stable isotope mass spectrometer and referenced to air N2 using the international nitrate standards IAEA-N3 and USGS-34. The FB-d15N data were then corrected for the contribution of the oxidation procedural blank with an in-house aminocaproic acid standard of known isotopic composition. Changes in Pacific oxygen concentration from the LGM to the Holocene were calculated based on solubility changes as well as CYCLOPS box model results of Hain et al., (2010). Changes in oxygen saturation result from changes in temperature and salinity; changes in oxygen utilization result from a glacial shoaling of the Atlantic Meridional Overturning Circulation, enhanced nutrient consumption due to Subantarctic iron fertilization, reduced Antarctic surface-to-deep exchange and more complete Antarctic nutrient consumption. Oxygen utilization is calculated using O2:Pregenerated of -170:1 (Anderson and Sarmiento, 1994).
    Schlagwort(e): Eastern Equatorial Pacific; Foraminifera-bound nitrogen isotopes; Holocene; Last Glacial; suboxia; water column denitrification
    Materialart: dataset bundled publication
    Format: application/zip, 4 datasets
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Publikationsdatum: 2024-07-19
    Schlagwort(e): 165-999; AGE; Carbon dioxide; Caribbean Sea; COMPCORE; Composite Core; Joides Resolution; Leg165
    Materialart: dataset
    Format: text/tab-separated-values, 7494 data points
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Publikationsdatum: 2024-07-19
    Schlagwort(e): 165-999; AGE; Carbon dioxide; Caribbean Sea; COMPCORE; Composite Core; Joides Resolution; Leg165
    Materialart: dataset
    Format: text/tab-separated-values, 12198 data points
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Publikationsdatum: 2024-07-19
    Schlagwort(e): Comment; Eastern Equatorial Pacific; Foraminifera-bound nitrogen isotopes; Holocene; Last Glacial; Oxygen, change; suboxia; water column denitrification
    Materialart: dataset
    Format: text/tab-separated-values, 24 data points
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    facet.materialart.
    Unbekannt
    PANGAEA
    In:  Supplement to: Chalk, Thomas B; Hain, Mathis P; Foster, Gavin L; Rohling, Eelco J; Sexton, Philip F; Badger, Marcus P S; Cherry, Soraya G; Hasenfratz, Adam P; Haug, Gerald H; Jaccard, Samuel L; Martínez‐García, Alfredo; Pälike, Heiko; Pancost, Richard D; Wilson, Paul A (2017): Causes of ice age intensification across the Mid-Pleistocene Transition. Proceedings of the National Academy of Sciences, 114(50), 13114-13119, https://doi.org/10.1073/pnas.1702143114
    Publikationsdatum: 2025-01-10
    Beschreibung: During the Mid-Pleistocene Transition (MPT; 1,200-800 kya), Earth's orbitally paced ice age cycles intensified, lengthened from ~40,000 (~40 ky) to ~100 ky, and became distinctly asymmetrical. Testing hypotheses that implicate changing atmospheric CO2 levels as a driver of the MPT has proven difficult with available observations. Here, we use orbitally resolved, boron isotope CO2 data to show that the glacial to interglacial CO2 difference increased from ~43 to ~75 µatm across the MPT, mainly because of lower glacial CO2 levels. Through carbon cycle modeling, we attribute this decline primarily to the initiation of substantive dust-borne iron fertilization of the Southern Ocean during peak glacial stages. We also observe a twofold steepening of the relationship between sea level and CO2-related climate forcing that is suggestive of a change in the dynamics that govern ice sheet stability, such as that expected from the removal of subglacial regolith or interhemispheric ice sheet phase-locking. We argue that neither ice sheet dynamics nor CO2 change in isolation can explain the MPT. Instead, we infer that the MPT was initiated by a change in ice sheet dynamics and that longer and deeper post-MPT ice ages were sustained by carbon cycle feedbacks related to dust fertilization of the Southern Ocean as a consequence of larger ice sheets.
    Materialart: dataset publication series
    Format: application/zip, 6 datasets
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    facet.materialart.
    Unbekannt
    PANGAEA
    In:  Supplement to: Sosdian, Sindia M; Greenop, Rosanna; Hain, Mathis P; Foster, Gavin L; Pearson, Paul N; Lear, Caroline H (2018): Constraining the evolution of Neogene ocean carbonate chemistry using the boron isotope pH proxy. Earth and Planetary Science Letters, 498, 362-376, https://doi.org/10.1016/j.epsl.2018.06.017
    Publikationsdatum: 2025-04-05
    Beschreibung: Over the course of the Neogene, the Earth underwent profound climatic shifts from the sustained warmth of the middle Miocene to the development of Plio-Pleistocene glacial-interglacial cycles. Major perturbations in the global carbon cycle have occurred alongside these shifts, however the lack of long- term carbonate system reconstructions currently limits our understanding of the link between changes in CO2, carbon cycling, and climate over this time interval. Here we reconstruct continuous surface ocean pH, CO2, and surface ocean aragonite saturation state using boron isotopes from the planktonic foraminifer Trilobatus trilobus and we perform a sensitivity analysis of the key variables in our calculations (e.g. δ11Bsw, [Ca]sw, CCD). We show that the choice of δ11Bsw influences both seawater pH and CO2 while [Ca]sw reconstructed dissolved inorganic carbon exerts a significant influence only on CO2. Over the last 22 Myr, the lowest pH levels occurred in the Middle Miocene Climate Optimum (MMCO; 17-14 Myr ago) reaching ∼7.6 ± 0.1 units in all our scenarios. The extended warmth of the MMCO corresponds to mean CO2 and aragonite saturation state levels of 470-630 ppm and 2.7-3.5, respectively. Despite a general correspondence between our CO2 record and climate, all CO2 scenarios show a peak at ∼9 Ma not matched by corresponding changes in climate reconstructions. This may suggest decoupling (i.e. significant CO2 change without a discernible climate response) for a limited interval in the Late Miocene (11.6-8.5 Ma), although further refinement of our understanding of the temporal evolution of the boron isotopic composition of seawater is necessary to fully evaluate the nature of the relationship between CO2 and climate. Nonetheless, from our long-term view it is clear that low-latitude open ocean marine ecosystems are unlikely to have experienced sustained surface pH and saturation levels below 7.7 and 1.7, respectively, during the past 14 million years (66% CI).
    Schlagwort(e): boron isotopes; carbonate system; Foraminifera; Miocene; Neogene
    Materialart: dataset publication series
    Format: application/zip, 4 datasets
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    Publikationsdatum: 2025-04-05
    Schlagwort(e): 108-668; 122-761B; 144-872C; 154-926A; 165-1000A; 165-999; AGE; Alkalinity, total; Aragonite saturation state; boron isotopes; Calculated; Carbon, inorganic, dissolved; carbonate system; Carbon dioxide; Caribbean Sea; COMPCORE; Composite Core; DRILL; Drilling/drill rig; Event label; Foraminifera; Joides Resolution; Leg108; Leg122; Leg144; Leg154; Leg165; Miocene; Neogene; North Atlantic Ocean; North Pacific Ocean; Reconstructed; Reference/source; Sample comment; Site; South Indian Ridge, South Indian Ocean; Species
    Materialart: dataset
    Format: text/tab-separated-values, 15366 data points
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Publikationsdatum: 2025-04-05
    Schlagwort(e): 108-668; 122-761B; 144-872C; 154-926A; 165-1000A; 165-999; AGE; Alkalinity, total; Aragonite saturation state; boron isotopes; Calculated; Carbon, inorganic, dissolved; carbonate system; Carbon dioxide; Caribbean Sea; COMPCORE; Composite Core; DRILL; Drilling/drill rig; Event label; Foraminifera; Joides Resolution; Leg108; Leg122; Leg144; Leg154; Leg165; Miocene; Neogene; North Atlantic Ocean; North Pacific Ocean; Reconstructed; Reference/source; Sample comment; Site; South Indian Ridge, South Indian Ocean; Species
    Materialart: dataset
    Format: text/tab-separated-values, 15366 data points
    Standort Signatur Erwartet Verfügbarkeit
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