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  • AGU (American Geophysical Union)  (3)
  • American Physical Society (APS)  (2)
  • Oxford University Press  (1)
  • 1
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    Late Cenozoic tephrostratigraphy offshore the southern Central American Volcanic Arc: 1. Tephra ages and provenance (2016)
    AGU (American Geophysical Union) | Wiley
    In:  Geochemistry, Geophysics, Geosystems, 17 (11). pp. 4641-4668.
    Details
    Publication Date: 2019-02-01
    Description: We studied the tephra inventory of 18 deep sea drill sites from six DSDP/ODP legs (Legs 84, 138, 170, 202, 205, 206) and two IODP legs (Legs 334 and 344) offshore the southern Central American Volcanic Arc (CAVA). Eight drill sites are located on the incoming Cocos plate and ten drill sites on the continental slope of the Caribbean plate. In total we examined ∼840 ash-bearing horizons and identified ∼650 of these as primary ash beds of which 430 originated from the CAVA. Correlations of ash beds were established between marine cores and with terrestrial tephra deposits, using major and trace element glass compositions with respect to relative stratigraphic order. As a prerequisite for marine-terrestrial correlations we present a new geochemical data set for significant Neogene and Quaternary Costa Rican tephras. Moreover, new Ar/Ar ages for marine tephras have been determined and marine ash beds are also dated using the pelagic sedimentation rates. The resulting correlations and provenance analyses build a tephrochronostratigraphic framework for Costa Rica and Nicaragua that covers the last 〉8 Myr. We define 39 correlations of marine ash beds to specific tephra formations in Costa Rica and Nicaragua; from the 4.15 Ma Lower Sandillal Ignimbrite to the 3.5 ka Rincón de la Vieja Tephra from Costa Rica, as well as another 32 widely distributed tephra layers for which their specific region of origin along Costa Rica and Nicaragua can be constrained.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1002/2016GC006503
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Late Cenozoic tephrostratigraphy offshore the southern Central American Volcanic Arc: 2. Implications for magma production rates and subduction erosion (2016)
    AGU (American Geophysical Union) | Wiley
    In:  Geochemistry, Geophysics, Geosystems, 17 (11). pp. 4585-4604.
    Details
    Publication Date: 2019-02-01
    Description: Pacific drill sites offshore Central America provide the unique opportunity to study the evolution of large explosive volcanism and the geotectonic evolution of the continental margin back into the Neogene. The temporal distribution of tephra layers established by tephrochonostratigraphy in Part 1 indicates a nearly continuous highly explosive eruption record for the Costa Rican and the Nicaraguan volcanic arc within the last 8 M.y. The widely distributed marine tephra layers comprise the major fraction of the respective erupted tephra volumes and masses thus providing insights into regional and temporal variations of large-magnitude explosive eruptions along the southern Central American Volcanic Arc (CAVA). We observe three pulses of enhanced explosive magmatism between 0-1 Ma at the Cordillera Central, between 1-2 Ma at the Guanacaste and at 〉3 Ma at the Western Nicaragua segments. Averaged over the long-term the minimum erupted magma flux (per unit arc length) is ∼0.017 g/ms. Tephra ages, constrained by Ar-Ar dating and by correlation with dated terrestrial tephras, yield time-variable accumulation rates of the intercalated pelagic sediments with four prominent phases of peak sedimentation rates that relate to tectonic processes of subduction erosion. The peak rate at 〉2.3 Ma near Osa particularly relates to initial Cocos Ridge subduction which began at 2.91±0.23 Ma as inferred by the 1.5 M.y. delayed appearance of the OIB geochemical signal in tephras from Barva volcano at 1.42 Ma. Subsequent tectonic re-arrangements probably involved crustal extension on the Guanacaste segment that favored the 2-1 Ma period of unusually massive rhyolite production.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1002/2016GC006504
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Central American Subduction System (2007)
    AGU (American Geophysical Union)
    In:  Eos, Transactions American Geophysical Union, 88 (44). p. 459.
    Details
    Publication Date: 2019-09-23
    Description: Workshop to Integrate Subduction Factory and Seismogenic Zone Studies in Central America, Heredia, Costa Rica, 18–22 June 2007 The driving force for great earthquakes and the cycling of water and climate-influencing volatiles (carbon dioxide, sulfur, halogens) across the convergent margin of Central America have been a focus of international efforts for over 8 years, as part of the MARGINS program of the U.S. National Science Foundation, the Collaborative Research Center (SFB 574) of the German Science Foundation, and the Central American science community. Over 120 scientists and students from 10 countries met in Costa Rica to synthesize this intense effort spanning from land to marine geological and geophysical studies.
    Type: Article , NonPeerReviewed
    Format: text
    DOI: 10.1029/2007EO440006
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    OceanRep: Article in a Scientific Journal - without review
  • 4
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    RNA dimerization plays a role in ribosomal frameshifting of the SARS coronavirus (2013)
    Oxford University Press
    Details
    Publication Date: 2013-02-20
    Description: Messenger RNA encoded signals that are involved in programmed -1 ribosomal frameshifting (-1 PRF) are typically two-stemmed hairpin (H)-type pseudoknots (pks). We previously described an unusual three-stemmed pseudoknot from the severe acute respiratory syndrome (SARS) coronavirus (CoV) that stimulated -1 PRF. The conserved existence of a third stem–loop suggested an important hitherto unknown function. Here we present new information describing structure and function of the third stem of the SARS pseudoknot. We uncovered RNA dimerization through a palindromic sequence embedded in the SARS-CoV Stem 3. Further in vitro analysis revealed that SARS-CoV RNA dimers assemble through ‘kissing’ loop–loop interactions. We also show that loop–loop kissing complex formation becomes more efficient at physiological temperature and in the presence of magnesium. When the palindromic sequence was mutated, in vitro RNA dimerization was abolished, and frameshifting was reduced from 15 to 5.7%. Furthermore, the inability to dimerize caused by the silent codon change in Stem 3 of SARS-CoV changed the viral growth kinetics and affected the levels of genomic and subgenomic RNA in infected cells. These results suggest that the homodimeric RNA complex formed by the SARS pseudoknot occurs in the cellular environment and that loop–loop kissing interactions involving Stem 3 modulate -1 PRF and play a role in subgenomic and full-length RNA synthesis.
    Print ISSN: 0305-1048
    Electronic ISSN: 1362-4962
    Topics: Biology
    Published by Oxford University Press
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  • 5
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    Inherently unstable networks collapse to a critical point (2015)
    American Physical Society (APS)
    Details
    Publication Date: 2015-07-09
    Description: Author(s): M. Sheinman, A. Sharma, J. Alvarado, G. H. Koenderink, and F. C. MacKintosh Nonequilibrium systems that are driven or drive themselves towards a critical point have been studied for almost three decades. Here we present a minimalist example of such a system, motivated by experiments on collapsing active elastic networks. Our model of an unstable elastic network exhibits a c… [Phys. Rev. E 92, 012710] Published Wed Jul 08, 2015
    Keywords: Biological Physics
    Print ISSN: 1539-3755
    Electronic ISSN: 1550-2376
    Topics: Physics
    Published by American Physical Society (APS)
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  • 6
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    Anomalous Discontinuity at the Percolation Critical Point of Active Gels (2015)
    American Physical Society (APS)
    Details
    Publication Date: 2015-03-05
    Description: Author(s): M. Sheinman, A. Sharma, J. Alvarado, G. H. Koenderink, and F. C. MacKintosh We develop a percolation model motivated by recent experimental studies of gels with active network remodeling by molecular motors. This remodeling was found to lead to a critical state reminiscent of random percolation (RP), but with a cluster distribution inconsistent with RP. Our model not only c... [Phys. Rev. Lett. 114, 098104] Published Wed Mar 04, 2015
    Keywords: Polymer, Soft Matter, Biological, and Interdisciplinary Physics
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
    Published by American Physical Society (APS)
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