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  • 1
    ISSN: 1432-1041
    Keywords: nicotine ; epinephrine ; cigarette smoking ; total forearm blood flow ; muscle blood flow ; plethysmography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary In 9 healthy subjects the effect of smoking one cigarette (nicotine content 0.9 mg) on blood pressure, heart rate and total and muscle blood flow in the forearm was measured. Blood flow was measured by a new noninvasive plethysmographic method that simultaneously gives quantitative data about total and muscle blood flow. Smoking the cigarette did not significantly affect blood pressure or heart rate. Total blood flow in the forearm did not change but the flow to the muscle was increased and resistance in this vascular bed was decreased. The pattern of haemodynamic changes in the forearm indicates that epinephrine may be the mediator of the circulatory effects of nicotine.
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 2019-01-02
    Description: Even though it is well accepted that the Earth's surface topography has been affected by mantle-convection induced dynamic topography, its magnitude and time-dependence remain controversial. The dynamic influence to topographic change along continental margins is particularly difficult to unravel, because their stratigraphic record is dominated by tectonic subsidence caused by rifting. We follow a three-fold approach to estimate dynamic topographic change along passive margins based on a set of seven global mantle convection models. We first demonstrate that a geodynamic forward model that includes adiabatic and viscous heating in addition to internal heating from radiogenic sources, and a mantle viscosity profile with a gradual increase in viscosity below the mantle transition zone, provides a greatly improved match to the spectral range of residual topography end-members as compared with previous models at very long wavelengths (spherical degrees 2–3). We then combine global sea level estimates with predicted surface dynamic topography to evaluate the match between predicted continental flooding patterns and published paleo-coastlines by comparing predicted versus geologically reconstructed land fractions and spatial overlaps of flooded regions for individual continents since 140 Ma. Modelled versus geologically reconstructed land fractions match within 10% for most models, and the spatial overlaps of inundated regions are mostly between 85% and 100% for the Cenozoic, dropping to about 75–100% in the Cretaceous. Regions that have been strongly affected by mantle plumes are generally not captured well in our models, as plumes are suppressed in most of them, and our models with dynamically evolving plumes do not replicate the location and timing of observed plume products. We categorise the evolution of modelled dynamic topography in both continental interiors and along passive margins using cluster analysis to investigate how clusters of similar dynamic topography time series are distributed spatially. A subdivision of four clusters is found to best reveal end-members of dynamic topography evolution along passive margins and their hinterlands, differentiating topographic stability, long-term pronounced subsidence, initial stability over a dynamic high followed by moderate subsidence and regions that are relatively proximal to subduction zones with varied dynamic topography histories. Along passive continental margins the most commonly observed process is a gradual motion from dynamic highs towards lows during the fragmentation of Pangea, reflecting the location of many passive margins now over slabs sinking in the lower mantle. Our best-fit model results in up to 500 (± 150) m of total dynamic subsidence of continental interiors while along passive margins the maximum predicted dynamic topographic change over 140 million years is about 350 (± 150) m of subsidence. Models with plumes exhibit clusters of transient passive margin uplift of about 200 ± 200 m, but are mainly characterised by long-term subsidence of up to 400 m. The good overall match between predicted dynamic topography to geologically mapped paleo-coastlines makes a convincing case that mantle-driven topographic change is a critical component of relative sea level change, and indeed the main driving force for generating the observed geometries and timings of large-scale continental inundation through time.
    Type: Article , PeerReviewed
    Format: text
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  • 3
    Publication Date: 2018-10-22
    Description: An International Ocean Discovery Program (IODP) workshop was held at Sydney University, Australia, from 13 to 16 June 2017 and was attended by 97 scientists from 12 countries. The aim of the workshop was to investigate future drilling opportunities in the eastern Indian Ocean, southwestern Pacific Ocean, and the Indian and Pacific sectors of the Southern Ocean. The overlying regional sedimentary strata are underexplored relative to their Northern Hemisphere counterparts, and thus the role of the Southern Hemisphere in past global environmental change is poorly constrained. A total of 23 proposal ideas were discussed, with 12 of these deemed mature enough for active proposal development or awaiting scheduled site survey cruises. Of the remaining 11 proposals, key regions were identified where fundamental hypotheses are testable by drilling, but either site surveys are required or hypotheses need further development. Refinements are anticipated based upon regional IODP drilling in 2017/2018, analysis of recently collected site survey data, and the development of site survey proposals. We hope and expect that this workshop will lead to a new phase of scientific ocean drilling in the Australasian region in the early 2020s.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
    Format: application/pdf
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  • 4
    Publication Date: 2013-03-19
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 5
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    Geological Society of America
    In:  In: Evolution and Dynamics of the Australian Plate. GSA Special Paper, 372 . Geological Society of America, Boulder, Colo., pp. 343-359.
    Publication Date: 2017-06-06
    Description: We present a revised model for the formation of southwest Pacific backarc basins from 120 Ma to the present day. Our aim is to improve our understanding of the tectonic regime operating in the region and its consequences for global plate motions. Such an understanding helps explain present-day structures observed on the continental and oceanic lithosphere and the underlying mantle. Regional plate reconstructions were created using gravity and magnetic data from backarc basins, plate-circuit closure, global tomography and existing geological data. Our model predicts convergence between the Australian and Pacific Plates along the Norfolk Ridge from 120 to 100 Ma, followed by the fragmentation of East Gondwana. East-dipping subduction east of Australia was initiated at ca 90 Ma along the Loyalty-Three Kings Ridge and may have trapped Cretaceous quiet-zone crust In the Norfolk Basin. The inception of this subduction system may have provided a driving mechanism for the opening of the Tasman Sea by means of slab pull. A jump in subduction to the east was subsequently initiated along a west-dipping subduction system at ca 45 Ma driven by the collision of the Loyalty Arc with New Caledonia. Consequently, spreading in the North Loyalty Basin occurred by anticlockwise rotation of the subduction hinge between chrons 20 and 16 (43.8–35.3 Ma). This was concurrent to Norfolk Basin opening and formation of the Cook Fracture Zone. Backarc-basin formation then transferred to the South Fiji Basin where magnetic anomalles from chron 12 to 7N (30.9–25.2 Ma) have been identified as two contemporaneous triple junctions. The complex spreading regime witnessed in the South Fiji Basin appears analogous to the North Fiji Basin and may represent the surface expression of a hot, shallow mantle consistent in character to a superswell. The South Fiji Basin ceased forming at ca 25 Ma in response to a major plate reorganisation coinciding with the inception of the Alpine Fault, docking of the Ontong Java Plateau with the Melaneslan Arc and transpressional obduction of the Northland ophiollte. A lull in basin formation throughout most of the Miocene was followed by the reinitiation of backarc basin formation in the Lau Basin (during the past ∼7 million years) and North Fiji Basin (during the past ∼10 million years). All these apparent episodes of backarc-basin formation during the past 45 million years are possibly related to mantle-slab interaction at the 670 km discontinuity.
    Type: Book chapter , NonPeerReviewed
    Format: text
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  • 6
    Publication Date: 2019-09-23
    Description: Large tectonic plates are known to be susceptible to internal deformation, leading to a range of phenomena including intraplate volcanism. However, the space and time dependence of intraplate deformation and its relationship with changing plate boundary configurations, subducting slab geometries, and absolute plate motion is poorly understood. We utilise a buoyancy driven Stokes flow solver, BEM-Earth, to investigate the contribution of subducting slabs through time on Pacific Plate motion and plate-scale deformation, and how this is linked to intraplate volcanism. We produce a series of geodynamic models from 62 to 42 Ma in which the plates are driven by the attached subducting slabs and mantle drag/suction forces. We compare our modelled intraplate deformation history with those types of intraplate volcanism that lack a clear age progression. Our models suggest that changes in Cenozoic subduction zone topology caused intraplate deformation to trigger volcanism along several linear seafloor structures, mostly by reactivation of existing seamount chains, but occasionally creating new volcanic chains on crust weakened by fracture zones and extinct ridges. Around 55 Ma subduction of the Pacific-Izanagi ridge reconfigured the major tectonic forces acting on the plate by replacing ridge push with slab pull along its north-western perimeter, causing lithospheric extension along pre-existing weaknesses. Large scale deformation observed in the models coincides with the seamount chains of Hawaii, Louisville, Tokelau, and Gilbert during our modelled time period of 62 to 42 Ma. We suggest that extensional stresses between 72 and 52 Ma are the likely cause of large parts of the formation of the Gilbert chain and that localised extension between 62 and 42 Ma could cause late-stage volcanism along the Musicians Volcanic Ridges. Our models demonstrate that early Cenozoic changes in Pacific plate driving forces only cause relatively minor changes in Pacific absolute plate motions, and cannot be responsible for the Hawaii-Emperor Bend (HEB), confirming previous interpretations that the 47 Ma HEB does not reflect an absolute plate motion event.
    Type: Article , PeerReviewed
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  • 7
    Publication Date: 2019-09-23
    Description: The origin of the Christmas Island Seamount Province in the northeast Indian Ocean is enigmatic. The seamounts do not form the narrow, linear and continuous trail of volcanoes that would be expected if they had formed above a mantle plume1, 2. Volcanism above a fracture in the lithosphere3 is also unlikely, because the fractures trend orthogonally with respect to the east–west trend of the Christmas Island chain. Here we combine 40Ar/39Ar age, Sr, Nd, Hf and high-precision Pb isotope analyses of volcanic rocks from the province with plate tectonic reconstructions. We find that the seamounts are 47–136 million years old, decrease in age from east to west and are consistently 0–25 million years younger than the underlying oceanic crust, consistent with formation near a mid-ocean ridge. The seamounts also exhibit an enriched geochemical signal, indicating that recycled continental lithosphere was present in their source. Plate tectonic reconstructions show that the seamount province formed at the position where West Burma began separating from Australia and India, forming a new mid-ocean ridge. We propose that the seamounts formed through shallow recycling of delaminated continental lithosphere entrained in mantle that was passively upwelling beneath the mid-ocean ridge. We conclude that shallow recycling of continental lithosphere at mid-ocean ridges could be an important mechanism for the formation of seamount provinces in young ocean basins.
    Type: Article , PeerReviewed
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  • 8
    Publication Date: 2019-10-10
    Description: Contourite drifts are anomalously high sediment accumulations that form due to reworking by bottom currents. Due to the lack of a comprehensive contourite database, the link between vigorous bottom water activity and drift occurrence has yet to be demonstrated on a global scale. Using an eddy-resolving ocean model and a new georeferenced database of 267 contourites, we show that the global distribution of modern contourite drifts strongly depends on the configuration of the world’s most powerful bottom currents, many of which are associated with global meridional overturning circulation. Bathymetric obstacles frequently modify flow direction and intensity, imposing additional finer-scale control on drift occurrence. Mean bottom current speed over contourite-covered areas is only slightly higher (2.2cm/s) than the rest of the global ocean (1.1cm/s), falling below proposed thresholds deemed necessary to re-suspend and redistribute sediments (10–15cm/s). However, currents fluctuate more frequently and intensely over areas with drifts, highlighting the role of intermittent, high-energy bottom current events in sediment erosion, transport, and subsequent drift accumulation. We identify eddies as a major driver of these bottom current fluctuations, and we find that simulated bottom eddy kinetic energy is over three times higher in contourite-covered areas in comparison to the rest o.f the ocean. Our work supports previous hypotheses which suggest that contourite deposition predominantly occurs due to repeated acute events as opposed to continuous reworking under average-intensity background flow conditions. This suggests that the contourite record should be interpreted in terms of a bottom current’s susceptibility to experiencing periodic, high-speed current events. Our results also highlight the potential role of upper ocean dynamics in contourite sedimentation through its direct influence on deep eddy circulation.
    Type: Article , PeerReviewed
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  • 9
    Publication Date: 1998-01-01
    Electronic ISSN: 1087-3562
    Topics: Geography , Geosciences , Physics
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  • 10
    Publication Date: 1998-01-01
    Electronic ISSN: 1087-3562
    Topics: Geography , Geosciences , Physics
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