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  • 1
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    Contribution of changes in opal productivity and nutrient distribution in the coastal upwelling systems to Late Pliocene/Early Pleistocene climate cooling (2012)
    Copernicus Publications (EGU)
    In:  Climate of the Past, 8 (5). pp. 1435-1445.
    Details
    Publication Date: 2019-09-23
    Description: The global Late Pliocene/Early Pleistocene cooling (~3.0–2.0 million years ago – Ma) concurred with extremely high diatom and biogenic opal production in most of the major coastal upwelling regions. This phenomenon was particularly pronounced in the Benguela upwelling system (BUS), off Namibia, where it is known as the Matuyama Diatom Maximum (MDM). Our study focuses on a new diatom silicon isotope (δ30Si) record covering the MDM in the BUS. Unexpectedly, the variations in δ30Si signal follow biogenic opal content, whereby the highest δ30Si values correspond to the highest biogenic opal content. We interpret the higher δ30Si values during the MDM as a result of a stronger degree of silicate utilisation in the surface waters caused by high productivity of mat-forming diatom species. This was most likely promoted by weak upwelling intensity dominating the BUS during the Late Pliocene/Early Pleistocene cooling combined with a large silicate supply derived from a strong Southern Ocean nutrient leakage responding to the expansion of Antarctic ice cover and the resulting stratification of the polar ocean 3.0–2.7 Ma ago. A similar scenario is hypothesized for other major coastal upwelling systems (e.g. off California) during this time interval, suggesting that the efficiency of the biological carbon pump was probably sufficiently enhanced in these regions during the MDM to have significantly increased the transport of atmospheric CO2 to the deep ocean. In addition, the coeval extension of the area of surface water stratification in both the Southern Ocean and the North Pacific, which decreased CO2 release to the atmosphere, led to further enhanced atmospheric CO2 drawn-down and thus contributed significantly to Late Pliocene/Early Pleistocene cooling.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.5194/cp-8-1435-2012
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    The acceleration of oceanic denitrification during deglacial warming (2013)
    Nature Publishing Group
    In:  Nature Geoscience, 6 (7). pp. 579-584.
    Details
    Publication Date: 2019-09-23
    Description: Over much of the ocean’s surface, productivity and growth are limited by a scarcity of bioavailable nitrogen. Sedimentary δ15N records spanning the last deglaciation suggest marked shifts in the nitrogen cycle during this time, but the quantification of these changes has been hindered by the complexity of nitrogen isotope cycling. Here we present a database of δ15N in sediments throughout the world’s oceans, including 2,329 modern seafloor samples, and 76 timeseries spanning the past 30,000 years. We show that the δ15N values of modern seafloor sediments are consistent with values predicted by our knowledge of nitrogen cycling in the water column. Despite many local deglacial changes, the globally averaged δ15N values of sinking organic matter were similar during the Last Glacial Maximum and Early Holocene. Considering the global isotopic mass balance, we explain these observations with the following deglacial history of nitrogen inventory processes. During the Last Glacial Maximum, the nitrogen cycle was near steady state. During the deglaciation, denitrification in the pelagic water column accelerated. The flooding of continental shelves subsequently increased denitrification at the seafloor, and denitrification reached near steady-state conditions again in the Early Holocene. We use a recent parameterization of seafloor denitrification to estimate a 30–120% increase in benthic denitrification between 15,000 and 8,000 years ago. Based on the similarity of globally averaged δ15N values during the Last Glacial Maximum and Early Holocene, we infer that pelagic denitrification must have increased by a similar amount between the two steady states.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1038/ngeo1832
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Mid-Holocene Antarctic sea-ice increase driven by marine ice sheet retreat (2021)
    Copernicus Publications (EGU)
    Details
    Publication Date: 2024-02-07
    Description: Over recent decades Antarctic sea-ice extent has increased, alongside widespread ice shelf thinning and freshening of waters along the Antarctic margin. In contrast, Earth system models generally simulate a decrease in sea ice. Circulation of water masses beneath large-cavity ice shelves is not included in current Earth System models and may be a driver of this phenomena. We examine a Holocene sediment core off East Antarctica that records the Neoglacial transition, the last major baseline shift of Antarctic sea ice, and part of a late-Holocene global cooling trend. We provide a multi-proxy record of Holocene glacial meltwater input, sediment transport, and sea-ice variability. Our record, supported by high-resolution ocean modelling, shows that a rapid Antarctic sea-ice increase during the mid-Holocene (∼ 4.5 ka) occurred against a backdrop of increasing glacial meltwater input and gradual climate warming. We suggest that mid-Holocene ice shelf cavity expansion led to cooling of surface waters and sea-ice growth that slowed basal ice shelf melting. Incorporating this feedback mechanism into global climate models will be important for future projections of Antarctic changes.
    Type: Article , PeerReviewed
    Format: text
    Format: archive
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Pliocene-Pleistocene variability of upwelling activity, productivity and nutrient cycle in the Benguela Upwelling System and the Eastern Equatorial Pacific (2009)
    Details
    Publication Date: 2024-03-22
    Description: The focus of this study is to explore the long term Plio-Pleistocene variability of coastal and open ocean upwelling systems by reconstructing for the last ~3.5 Ma, sea surface temperature (SST), primary productivity and nutrient cycling in the Benguela Upwelling System (BUS) and the Eastern Equatorial Pacific (EEP), two areas particularly sensible and influential to climate change.
    Type: Thesis , NonPeerReviewed
    Format: text
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    OceanRep: Thesis - not published by a publisher
  • 5
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    Antarctic Sea Ice Proxies from Marine and Ice Core Archives Suitable for Reconstructing Sea Ice over the Past 2000 Years (2019)
    In:  EPIC3Geosciences, 9(12), pp. 506, ISSN: 2076-3263
    Details
    Publication Date: 2020-05-25
    Description: Dramatic changes in sea ice have been observed in both poles in recent decades. However, the observational period for sea ice is short, and the climate models tasked with predicting future change in sea ice struggle to capture the current Antarctic trends. Paleoclimate archives, from marine sedimentary records and coastal Antarctic ice cores, provide a means of understanding sea ice variability and its drivers over decadal to centennial timescales. In this study, we collate published records of Antarctic sea ice over the past 2000 years (2 ka). We evaluate the current proxies and explore the potential of combining marine and ice core records to produce multi-archive reconstructions. Despite identifying 92 sea ice reconstructions, the spatial and temporal resolution is only sufficient to reconstruct circum-Antarctic sea ice during the 20th century, not the full 2 ka. Our synthesis reveals a 90 year trend of increasing sea ice in the Ross Sea and declining sea ice in the Bellingshausen, comparable with observed trends since 1979. Reconstructions in the Weddell Sea, the Western Pacific and the Indian Ocean reveal small negative trends in sea ice during the 20th century (1900–1990), in contrast to the observed sea ice expansion in these regions since 1979.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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    PAPER (OA)
  • 6
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    Mid-Holocene Antarctic sea-ice increase driven by marine ice sheet retreat (2021)
    European Geosciences Union
    Details
    Publication Date: 2022-05-26
    Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Ashley, K. E., McKay, R., Etourneau, J., Jimenez-Espejo, F. J., Condron, A., Albot, A., Crosta, X., Riesselman, C., Seki, O., Mass, G., Golledge, N. R., Gasson, E., Lowry, D. P., Barrand, N. E., Johnson, K., Bertler, N., Escutia, C., Dunbar, R., & Bendle, J. A. Mid-Holocene Antarctic sea-ice increase driven by marine ice sheet retreat. Climate of the Past, 17(1), (2021): 1-19, https://doi.org/10.5194/cp-17-1-2021.
    Description: Over recent decades Antarctic sea-ice extent has increased, alongside widespread ice shelf thinning and freshening of waters along the Antarctic margin. In contrast, Earth system models generally simulate a decrease in sea ice. Circulation of water masses beneath large-cavity ice shelves is not included in current Earth System models and may be a driver of this phenomena. We examine a Holocene sediment core off East Antarctica that records the Neoglacial transition, the last major baseline shift of Antarctic sea ice, and part of a late-Holocene global cooling trend. We provide a multi-proxy record of Holocene glacial meltwater input, sediment transport, and sea-ice variability. Our record, supported by high-resolution ocean modelling, shows that a rapid Antarctic sea-ice increase during the mid-Holocene (∼ 4.5 ka) occurred against a backdrop of increasing glacial meltwater input and gradual climate warming. We suggest that mid-Holocene ice shelf cavity expansion led to cooling of surface waters and sea-ice growth that slowed basal ice shelf melting. Incorporating this feedback mechanism into global climate models will be important for future projections of Antarctic changes.
    Description: This research has been supported by the Natural Environment Research Council (CENTA PhD; NE/L002493/1 and Standard Grant Ne/I00646X/1), Japanese Society for the Promotion of Science (JSPS/FF2/60 no. L-11523), NZ Marsden Fund (grant nos. 18-VUW-089 and 15-VUW-131), NSF (grant nos. PLR-1443347 and ACI-1548562), the U.S. Dept. of Energy (grant no. DE-SC0016105), ERC (StG ICEPROXY, 203441; ANR CLIMICE, FP7 Past4Future, 243908), L'Oréal-UNESCO New Zealand For Women in Science Fellowship, University of Otago Research Grant, the IODP U.S. Science Support Program, Spanish Ministry of Science and Innovation (grant no. CTM2017-89711-C2-1-P), and the European Union (FEDER).
    Repository Name: Woods Hole Open Access Server
    Type: Article
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    PAPER (OA)
  • 7
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    Sporomorph counts, diversity, DCA and climate estimate calculations from ODP Hole 113-696B (2021)
    PANGAEA
    Details
    Publication Date: 2023-01-30
    Description: A total of 35 samples from the late-middle Eocene to earliest Oligocene (643.73-520.88 mbsf) were analysed for their pollen and spore content. Slides were analysed using a Leica DM500 and Leica DM2000 transmitted light microscopes at 200x and 1000x magnification. Where possible, counts of 300 (excluding reworked grains) sporomorphs were made. Only samples containing 50 or more in situ sporomorphs were used for further analysis and evaluation. Sporomorph diversity was measured using both the Shannon–Wiener index and the observed number of taxa. A rarefaction method for sums of ≥50 and ≥100 grains was applied, so that the effect caused by differences in the sample size may be removed allowing the estimation of the number of sporomorph species at a constant sample size. Detrended Correspondence Analysis (DCA) was performed, with downweighting of rare species by removing pollen types whose representation is 〈5%. Estimates for terrestrial mean annual temperature (MAT), mean annual precipitation (MAP), warmest month mean temperature (WMMT) and coldest month mean temperature (CMMT) were obtained using the NLR approach in conjunction with the Probability Density Function (PDF) method.
    Keywords: Antarctica; Drake Passage; Eocene-Oligocene Transition; palynology
    Type: Dataset
    Format: application/zip, 3 datasets
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    DATA PANGAEA
  • 8
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    Raw pollen and sporen counts from ODP Hole 113-696B (2021)
    PANGAEA
    Details
    Publication Date: 2023-06-27
    Keywords: 113-696B; Acaena spp.; AGE; Alisporites cf. Australis; Antarctica; Araucariacites australis; Arecipites spp.; Baculatisporites comaumensis; Beaupreaidites cf. verrucosus; Beaupreaidites diversiformis; Camarozonosporites sp.; Ceratosporites cf. equalis; Chenopodipollis chenopodiaceoides; Clavatipollenites ascarinoides; Coptospora archangelskyi; Counting, light microscope; Cupanieidites orthoteichus; Cyathidites australis; Cyathidites minor; Cyathidites splendens; Cyathidites subtilis; Dacrydiumites florinii; DEPTH, sediment/rock; Dictyophyllidites arcuatus; Dilwynites granulatus; Drake Passage; DRILL; Drilling/drill rig; DSDP/ODP/IODP sample designation; Eocene-Oligocene Transition; Ericipites cf. scabratus; Foveotriletes lacunosus; Gleicheniidites spp.; Integricorpus sp.; Ischyosporites gremius; Joides Resolution; Laevigatosporites major; Laevigatosporites ovatus; Lateropora glabra; Leg113; Ligulifloridites sp.; Liliacidites intermedius; Lymingtonia cf. cenozoica; Malvacipollis cf. subtilis; Microalatidites paleogenicus; Microcachryidites antarcticus; Monolites alveolatus; Myricipites harrisii; Myrtaceidites cf. mesonesus; Nothofagidites asperus complex; Nothofagidites brachyspinulosus complex; Nothofagidites emarcidus complex; Nothofagidites flemingii; Nothofagidites lachlaniae complex; Nothofagidites rocaensis complex; Nothofagidites spp.; Osmundacidites cf. wellmanii; palynology; Parsonsidites psilatus; Peninsulapollis gillii; Periporopollenites polyoratus; Peromonolites cf. densus; Phyllocladidites cf. mawsonii; Phyllocladidites mawsonii; Podocarpidites cf. exiguus; Podocarpidites marwickii complex; Podocarpidites rugulatus complex; Podocarpidites spp.; Podosporites cf. brevisaccatus; Podosporites cf. ohikaensis; Podosporites parvus; Pollen and spores; Polycolporopollenites; Polypodiisporites cf. radiatus; Proteacidites adenanthoides; Proteacidites cf. amolosexinus; Proteacidites cf. Lewalanipollis trycheros; Proteacidites cf. Scabratriporites spp.; Proteacidites minimus; Proteacidites obscurus; Proteacidites parvus; Proteacidites reticuloscabratus; Proteacidites scaboratus; Proteacidites sp.; Proteacidites spiniferus; Proteacidites tenuiexinus; Proteacidites tuberculatus; Retitriletes spp.; Rugulatisporites spp.; Sample code/label; Scabramonoletes; Sparganiaceaepollenites barungensis; Stereisporites antiquasporites; Stereisporites regium; Trichotomosulcites subgranulatus; Tricolpites cf. asperamarginis; Tricolpites cf. brevicolpus; Tricolpites cf. delicatulus; Tricolpites fissilis; Tricolpites inargutus; Tricolpites lilliei; Tricolpites reticulatus; Tricolpites sp.; Tricolpites spp.; Tricolporites cf. scabratus; Tricolporites sp.; Triorites sp.; Tripunctisporis maastrichtiensis; Weddell Sea
    Type: Dataset
    Format: text/tab-separated-values, 3535 data points
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    DATA PANGAEA
  • 9
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    Reworked pollen and sporen counts from ODP Hole 113-696B (2021)
    PANGAEA
    Details
    Publication Date: 2023-06-27
    Keywords: 113-696B; AGE; Antarctica; Biretisporites cf. labruplenus; Brevitriletes bulliensis; Brevitriletes sp.; Calamospora spp.; Cibotiumspora cf. intrastriatus; Cicatricosisporites sp.; Classopollis spp.; Clavatipollenites hughesii; Coptospora striata; Counting, light microscope; Cyatheacidites annulatus; DEPTH, sediment/rock; Dictyophyllidites cf. harrisii; Drake Passage; DRILL; Drilling/drill rig; DSDP/ODP/IODP sample designation; Eocene-Oligocene Transition; Granulatisporites trisinus; Joides Resolution; Leg113; Leptolepidites verrucatus; Lycopodiacidites cf. bullerensis; Lycopodiacidites cristatus; Lycopodiumsporites pseudoreticulatus; palynology; Pollen, bisaccate undifferentiated; Pollen and spores; Protohaploxypinus cf. samoilovichii; Protohaploxypinus spp.; Retitriletes cf. eminulus; Retitriletes cf. reticulumsporites; Rugulatisporites cf. trisinus; Sample code/label; Spores, trilete undifferentiated; Tricolpites cf. pachyexinus; Trilites verrucatus; Weddell Sea
    Type: Dataset
    Format: text/tab-separated-values, 945 data points
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    DATA PANGAEA
  • 10
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    Radiocarbon ages, geochemistry, biomarkers and diatoms from the marine sediment core PS97/72-1, Bransfield Strait, Western Antarctic Peninsula (2023)
    PANGAEA
    Details
    Publication Date: 2023-07-01
    Description: The data set of the marine sediment core PS97/72-1 from the Bransfield Strait, Antarctic Peninsula, contains data from analyses of a 1012 cm core covering the age from recent to 13.8 ka BP. The piston core was retrieved 2016 during R/V Polarstern cruise PS97. The purpose of this data was a study for the reconstruction of Deglacial and Holocene sea ice and climate dynamics in the Bransfield Strait, Northern Antarctic Peninsula, which was published in Climate of the Past. Dataset 1 contains details of the radiocarbon ages. Dataset 2 are the geochemical bulk parameters including sedimentation rate, total organic carbon, biogenic opal, C/N ration, d13C of organic carbon, branched and isoprenoid tetraether index BIT and ice rafted debris. Dataset 3 is information on biomarkers with highly branched isoprenoids diene and triene (IPSO25), the phytoplankton biomarker IPSO25 index, d13C of IPSO25, branched and isoprenoid tetraether index BIT, sub-surface ocean temperature (based on branched GDGTs), diatom derived sea ice probability and diatom derived summer sea surface temperature. Dataset 4 contains all diatom counts including groupings of diatoms indication seasonal sea ice and open ocean cold and warm species.
    Keywords: Antarctica; Biomarker; Holocene; IPSO25; Marine Sediment Core; Sea ice
    Type: Dataset
    Format: application/zip, 4 datasets
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    DATA PANGAEA
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