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  • 1
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    A large West Antarctic Ice Sheet explains early Neogene sea-level amplitude (2021)
    In:  EPIC3Nature, 600(7889), pp. 450-455, ISSN: 0028-0836
    Details
    Publication Date: 2022-01-20
    Description: Early to Middle Miocene sea-level oscillations of approximately 40–60 m estimated from far-field records1–3 are interpreted to reflect the loss of virtually all East Antarctic ice during peak warmth2. This contrasts with ice-sheet model experiments suggesting most terrestrial ice in East Antarctica was retained even during the warmest intervals of the Middle Miocene4,5. Data and model outputs can be reconciled if a large West Antarctic Ice Sheet (WAIS) existed and expanded across most of the outer continental shelf during the Early Miocene, accounting for maximum ice-sheet volumes. Here we provide the earliest geological evidence proving large WAIS expansions occurred during the Early Miocene (~17.72–17.40 Ma). Geochemical and petrographic data show glacimarine sediments recovered at International Ocean Discovery Program (IODP) Site U1521 in the central Ross Sea derive from West Antarctica, requiring the presence of a WAIS covering most of the Ross Sea continental shelf. Seismic, lithological and palynological data reveal the intermittent proximity of grounded ice to Site U1521. The erosion rate calculated from this sediment package greatly exceeds the long-term mean, implying rapid erosion of West Antarctica. This interval therefore captures a key step in the genesis of a marine-based WAIS and a tipping point in Antarctic ice-sheet evolution.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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    PAPER (OA)
  • 2
    Electronic Resource
    Electronic Resource
    Gastric mucus secretion in normal subjects and patients with gastric ulcer, gastric carcinoma, and pernicious anemia (1965)
    Springer
    Digestive diseases and sciences 10 (1965), S. 411-419 
    Details
    ISSN: 1573-2568
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The mucus secretion of a series of patients with gastric ulcer, gastric carcinoma, and pernicious anemia, studied in regard to concentration, output and constituent sugars in basal gastric secretion, showed few differences between the groups of patients. Pernicious anemia patients showed high mucus concentrations due to their low secretory volume. Gastric ulcer patients had a mucus output and concentration similar to control subjects. The only obvious difference in mucus secretion appeared to be that in gastric carcinoma patients; in this group, the amount of glucose in proportion to other sugars was high.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02233717
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    Paper (German National Licenses)
    Fulltext
  • 3
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    Seawater calcium isotope ratios across the Eocene-Oligocene transition (2011)
    GSA, Geological Society of America
    In:  Geology, 39 (7). pp. 683-686.
    Details
    Publication Date: 2019-09-23
    Description: During the Eocene-Oligocene transition (EOT, ca. 34 Ma), Earth's climate cooled significantly from a greenhouse to an icehouse climate, while the calcite (CaCO3) compensation depth (CCD) in the Pacific Ocean increased rapidly. Fluctuations in the CCD could result from various processes that create an imbalance between calcium (Ca) sources to, and sinks from, the ocean (e.g., weathering and CaCO3 deposition), with different effects on the isotopic composition of dissolved Ca in the oceans due to differences in the Ca isotopic composition of various inputs and outputs. We used Ca isotope ratios (δ44/40Ca) of coeval pelagic marine barite and bulk carbonate to evaluate changes in the marine Ca cycle across the EOT. We show that the permanent deepening of the CCD was not accompanied by a pronounced change in seawater δ44/40Ca, whereas time intervals in the Neogene with smaller carbonate depositional changes are characterized by seawater δ44/40Ca shifts. This suggests that the response of seawater δ44/40Ca to changes in weathering fluxes and to imbalances in the oceanic alkalinity budget depends on the chemical composition of seawater. A minor and transient fluctuation in the Ca isotope ratio of bulk carbonate may reflect a change in isotopic fractionation associated with CaCO3 precipitation from seawater due to a combination of factors, including changes in temperature and/or in the assemblages of calcifying organisms.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1130/G31872.1
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Influences on the fractionation of calcium isotopes in planktonic foraminifera (2008)
    Elsevier
    In:  Earth and Planetary Science Letters, 268 . pp. 124-136.
    Details
    Publication Date: 2017-02-09
    Description: For paleoceanographic studies, it is important to understand the processes that influence the calcium (Ca) isotopic composition of foraminiferal calcite tests preserved in the sediment record. Seven species of planktonic foraminifera from coretop sediments collectively exhibited a Ca temperature dependent fractionation of 0.013‰ per °C. This is in agreement with previously published estimates for most species of planktonic foraminifera as well as biogenic and inorganic calcite and aragonite. Four species of planktonic foraminifera collected from a sediment trap showed a considerable amount of scatter and no consistent temperature dependent fractionation. Analyzed size fractions of coretop samples show no significant relationship with δ44/40Ca. However, preliminary results suggest that the symbiotic and spinose foraminifera Globigerinoides sacculifer might exhibit a relationship between test size and δ44/40Ca. A one-box model in which Ca isotopes are allowed to fractionate by Rayleigh distillation from a biomineralization reservoir (internal pool) was used to constrain the isotopic composition of the original biomineralization Ca reservoir, assuming around 85% of the Ca reservoir is precipitated and the fractionation factor during precipitation is 0.9985 + 0.00002(T °C). To explain the foraminiferal Ca isotope data, this model indicates that the Ca isotopic composition of the biomineralization reservoir is offset from seawater (approximately − 0.8‰).
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.epsl.2008.01.006
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Peak intervals of equatorial Pacific export production during the middle Miocene climate transition (2016)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2016-10-19
    Description: The middle Miocene climate transition (MMCT) is characterized by an abrupt 1 increase in benthic foraminiferal oxygen isotopes at ca. 13.8 Ma, marking expansion of the Antarctic Ice Sheet and transition of Earth’s climate to a cooler, relatively stable glacial state. Also occurring during this period is a globally recognized positive carbon isotope excursion (16.9–13.5 Ma) in benthic and planktonic foraminifera with shorter carbon isotope maxima (CM) events, linking hypotheses for climate change at the time with the carbon cycle. In order to test whether export production in the eastern equatorial Pacific is related to the largest such event (CM6), coincident with Antarctic Ice Sheet expansion, a high-resolution (〈5 k.y.) record of export production at Integrated Ocean Drilling Program Site U1337 spanning the MMCT (14.02–13.43 Ma) was produced using marine pelagic barite mass accumulation rates. Export production is elevated with an extended period of more than double present-day values. These variations are not orbitally paced and provide evidence for a reorganization of nutrients supplied to the eastern equatorial Pacific in the Miocene and intensification of upwelling. If such changes are representative of the entire region, then this mechanism could sequester enough carbon to have a significant effect on atmospheric p CO 2 . However, continual delivery of nutrients to the surface waters of the eastern equatorial Pacific is required in order to sustain export production without depleting the surface ocean of limiting nutrients. This might be accomplished by a change in ocean circulation or a combination of other processes requiring further study.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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