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  • 1
    Publication Date: 2019-01-26
    Type: Dataset
    Format: text/tab-separated-values, 108 data points
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  • 2
    Publication Date: 2019-01-26
    Type: Dataset
    Format: text/tab-separated-values, 72 data points
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  • 3
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    PANGAEA
    In:  Supplement to: Waterson, Amy; Edgar, Kirsty M; Schmidt, Daniela N; Valdes, Paul J (2017): Quantifying the stability of planktic foraminiferal physical niches between the Holocene and Last Glacial Maximum. Paleoceanography, https://doi.org/10.1002/2016PA002964
    Publication Date: 2019-04-30
    Description: The application of transfer functions on fossil assemblages to reconstruct past environments is fundamentally based on the assumption of stable environmental niches in both space and time. We quantitatively test this assumption for six dominant planktic foraminiferal species (Globigerinoides ruber (pink), G. ruber (white), Trilobatus sacculifer, Truncorotalia truncatulinoides, Globigerina bulloides and Neogloboquadrina pachyderma) by contrasting reconstructions of species realised and optimum distributions in the modern and during the Last Glacial Maximum (LGM) using an ecological niche model (ENM; MaxEnt) and ordination framework. Global ecological niche models calibrated in the modern ocean have high predictive performance when projected to the LGM for sub-polar and polar species, indicating that the environmental niches of these taxa are largely stable at the global scale across this interval. In contrast, ENM's had much poorer predictive performance for the optimal niche of tropical-dwelling species, T. sacculifer and G. ruber (pink). This finding is supported by independent metrics of niche margin change, suggesting that niche stability in environmental space was greatest for (sub)polar species, with greatest expansion of the niche observed for tropical species. We find that globally calibrated ENMs showed good predictions of species occurrences globally, whereas models calibrated in either the Pacific or Atlantic Oceans only and then projected globally performed less well for T. sacculifer. Our results support the assumption of environmental niche stability over the last ~21,000 years for most of our focal planktic foraminiferal species and thus, the application of transfer function techniques for palaeoenvironmental reconstruction during this interval. However, the lower observed niche stability for (sub)tropical taxa T. sacculifer and G. ruber (pink) suggests that (sub)tropical temperatures could be underestimated in the glacial ocean with the strongest effect in the equatorial Atlantic where both species are found today.
    Type: Dataset
    Format: text/tab-separated-values, 70 data points
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  • 4
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    PANGAEA
    In:  Supplement to: Stewart, Joseph A; Wilson, Paul A; Edgar, Kirsty M; Anand, Pallavi; James, Rachael H (2012): Geochemical assessment of the palaeoecology, ontogeny, morphotypic variability and palaeoceanographic utility of “Dentoglobigerina” venezuelana. Marine Micropaleontology, 84-85, 74-86, https://doi.org/10.1016/j.marmicro.2011.11.003
    Publication Date: 2019-01-27
    Description: To better understand the links between the carbon cycle and changes in past climate over tectonic timescales we need new geochemical proxy records of secular change in silicate weathering rates. A number of proxies are under development, but some of the most promising (e.g. palaeoseawater records of Li and Nd isotope change) can only be employed on such large samples of mono-specific foraminifera that application to the deep sea sediment core archive becomes highly problematic. "Dentoglobigerina" venezuelana presents a potentially attractive target for circumventing this problem because it is a typically large (〉 355 mm diameter), abundant and cosmopolitan planktic foraminifer that ranges from the early Oligocene to early Pliocene. Yet considerable taxonomic and ecological uncertainties associated with this taxon must first be addressed. Here, we assess the taxonomy, palaeoecology, and ontogeny of "D." venezuelana using stable isotope (oxygen and carbon) and Mg/Ca data measured in tests of late Oligocene to early Miocene age from Ocean Drilling Program (ODP) Site 925, on Ceara Rise, in the western equatorial Atlantic. To help constrain the depth habitat of "D." venezuelana relative to other species we report the stable isotope composition of selected planktic foraminifera species within Globigerina, Globigerinoides, Paragloborotalia and Catapsydrax. We define three morphotypes of "D." venezuelana based on the morphology of the final chamber and aperture architecture. We determine the trace element and stable isotope composition of each morphotype for different size fractions, to test the validity of pooling these morphotypes for the purposes of generating geochemical proxy datasets and to assess any ontogenetic variations in depth habitat. Our data indicate that "D." venezuelana maintains a lower thermocline depth habitat at Ceara Rise between 24 and 21 Ma. Comparing our results to published datasets we conclude that this lower thermocline depth ecology for the Oligo-Miocene is part of an Eocene-to-Pliocene evolution of depth habitat from surface to sub-thermocline for "D." venezuelana. Our size fraction data advocate the absence of photosymbionts in "D." venezuelana and suggest that juveniles calcify higher in the water column, descending into slightly deeper water during the later stages of its life cycle. Our morphotype data show that d18O and d13C variation between morphotypes is no greater than within-morphotype variability. This finding will permit future pooling of morphotypes in the generation of the "sample hungry" palaeoceanographic records.
    Type: Dataset
    Format: text/tab-separated-values, 564 data points
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  • 5
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Major ice sheets were permanently established on Antarctica approximately 34 million years ago, close to the Eocene/Oligocene boundary, at the same time as a permanent deepening of the calcite compensation depth in the world’s oceans. Until recently, it was thought that Northern ...
    Type of Medium: Electronic Resource
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  • 6
    Publication Date: 2017-03-01
    Description: Atmospheric carbon dioxide concentrations and climate are regulated on geological timescales by the balance between carbon input from volcanic and metamorphic outgassing and its removal by weathering feedbacks; these feedbacks involve the erosion of silicate rocks and organic-carbon-bearing rocks. The integrated effect of these processes is reflected in the calcium carbonate compensation depth, which is the oceanic depth at which calcium carbonate is dissolved. Here we present a carbonate accumulation record that covers the past 53 million years from a depth transect in the equatorial Pacific Ocean. The carbonate compensation depth tracks long-term ocean cooling, deepening from 3.0-3.5 kilometres during the early Cenozoic (approximately 55 million years ago) to 4.6 kilometres at present, consistent with an overall Cenozoic increase in weathering. We find large superimposed fluctuations in carbonate compensation depth during the middle and late Eocene. Using Earth system models, we identify changes in weathering and the mode of organic-carbon delivery as two key processes to explain these large-scale Eocene fluctuations of the carbonate compensation depth.
    Type: Article , PeerReviewed
    Format: text
    Format: text
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  • 7
    Publication Date: 2019-01-26
    Type: Dataset
    Format: text/tab-separated-values, 316 data points
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  • 8
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    PANGAEA
    In:  Supplement to: Edgar, Kirsty M; Pälike, Heiko; Wilson, Paul A (2013): Testing the impact of diagenesis on the d18O and d13C of benthic foraminiferal calcite from a sediment burial depth transect in the equatorial pacific. Paleoceanography, 28(3), 468-480, https://doi.org/10.1002/palo.20045
    Publication Date: 2019-02-13
    Description: Stable oxygen and carbon isotope (d18O and d13C) values measured in foraminiferal calcite are one of the primary tools used in paleoceanography. Diagenetic recrystallization of foraminiferal calcite can act to reset primary isotopic values, but its effects are typically poorly quantified. Here we test the impact of early stage diagenesis on stable isotope records generated from a suite of drill sites in the equatorial Pacific Ocean recovered during Ocean Drilling Program Leg 199 and Integrated Ocean Drilling Program Expedition 320. Our selected sites form paleowater and burial depth transects, with excellent stratigraphic control allowing us to confidently correlate our records. We observe large intersite differences in the preservation state of benthic foraminiferal calcite, implying very different recrystallization histories, but negligible intersite offsets in benthic d18O and d13C values. We infer that diagenetic alteration of benthic foraminiferal calcite (in sedimentary oozes) must predominantly occur at shallow burial depths (〈100 m) where offsets in both the temperature and isotopic composition of waters in which the foraminifera calcified and pore waters in which diagenesis occurs are small. Our results suggest that even extensive recrystallization of benthic foraminiferal calcite results in minimal shifts from primary d18O and d13C values. This finding supports the long-held suspicion that diagenetic alteration of foraminiferal calcite is less problematic in benthic than in planktic foraminifera and that in deep-sea sediments routinely employed for paleoceanographic studies benthic foraminifera are robust recorders of stable isotope values in the fossil record.
    Type: Dataset
    Format: application/zip, 5 datasets
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  • 9
    Publication Date: 2019-01-26
    Type: Dataset
    Format: text/tab-separated-values, 1245 data points
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  • 10
    Publication Date: 2019-01-26
    Type: Dataset
    Format: text/tab-separated-values, 72 data points
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