Schmidt hammer exposure‐age dating (SHD) of late Quaternary fluvial terraces in New Zealand     

Timothy Stahl  Stefan Winkler  Mark Quigley  Mark Bebbington  Brendan Duffy  Daniel Duke 《地球表面变化过程与地形》2013,38(15):1838-1850

Schmidt hammer (SH) R‐values are reported for surface clasts from numerically dated Holocene and Pleistocene fluvial terraces in the South Island of New Zealand. The R‐values are combined with previously obtained weathering rind, radiocarbon, terrestrial cosmogenic nuclide and luminescence terrace ages to derive SH R‐value chronofunctions for greywacke clasts from four distinct locations. Our results show that different weathering rates affect the form of the SH R‐value versus Age curve, however a fundamental dependency between the two remains constant over timescales ranging from 10² to 10⁵ years. Power law scaling constants suggest changes in clast weathering rates are primarily affected by climatic (precipitation and temperature) and sedimentologic variables (source terrane petrology). Age uncertainties of ~22% of the surface age suggest that Schmidt hammer exposure‐age dating (SHD) is a reliable calibrated‐age dating technique for fluvial terraces. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

The transport of cosmic rays in self-excited magnetic turbulence     

B. Reville  S. O'Sullivan  P. Duffy  J. G. Kirk 《Monthly notices of the Royal Astronomical Society》2008,386(1):509-515

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Evidence of summer parturition in shortfin mako (Isurus oxyrinchus) sharks from New Zealand waters     

Clinton Duffy  Malcolm P. Francis 《新西兰海洋与淡水研究杂志》2013,47(2):319-324

A litter of eight near‐term shortfin mako (Isurus oxyrinchus Rafinesque 1810) embryos is described from a 317.5 cm total length (TL) female caught off Hawke Bay, south‐east North Island, New Zealand on 5 February 1999. The embryos (3 males and 5 females) were 67.2–77.0 cm TL. Embryo length, condition, hepato‐somatic indices, and mass of yolk in their stomachs all indicate they were close to birth. This is the first shortfin mako litter reported from New Zealand and is outside the late winter‐early spring parturition period predicted from estimated embryonic and juvenile growth rates. Uterine width data from four mature non‐pregnant females and age‐0+ length‐at‐capture data suggest parturition occurs from September to late February (late winter‐mid summer) but is infrequent after January. We suggest that shortfin makos have an extended parturition period, possibly year‐round, with peak parturition occurring in late winter‐spring.  相似文献   

Deformation of lower-mantle ferropericlase (Mg,Fe)O across the electronic spin transition   总被引：2，自引：1，他引：1  

Jung-Fu Lin  Hans-Rudolf Wenk  Marco Voltolini  Sergio Speziale  Jinfu Shu  Thomas S. Duffy 《Physics and Chemistry of Minerals》2009,36(10):585-592

Recent high-pressure studies have shown that an electronic spin transition of iron in ferropericlase, an expected major phase of Earth’s lower mantle, results in changes in its properties, including density, incompressibility, radiative thermal conductivity, electrical conductivity, and sound velocities. To understand the rheology of ferropericlase across the spin transition, we have used in situ radial X-ray diffraction techniques to examine ferropericlase, (Mg_0.83,Fe_0.17)O, deformed non-hydrostatically in a diamond cell up to 81 GPa at room temperature. Compared with recent quasi-hydrostatic studies, the range of the spin transition is shifted by approximately 20 GPa as a result of the presence of large differential stress in the sample. We also observed a reduction in incompressibility and in the unit cell volume of 3% across the spin transition. Our radial X-ray diffraction results show that the {0 0 1} texture is the dominant lattice preferred orientation in ferropericlase across the spin transition and in the low-spin state. Viscoplastic self-consistent polycrystal plasticity simulations suggest that this preferred orientation pattern is produced by {1 1 0}<1–10> slip. Analyzing our radial X-ray diffraction patterns using lattice strain theory, we evaluated the lattice d-spacings of ferropericlase and Mo as a function of the ψ angle between the compression direction and the diffracting plane normal. These analyses give the ratio between the uniaxial stress component (t) and the shear modulus (G) under constant stress condition, which represents a proxy for the supported differential stress and elastic strength. This ratio in the mixed-spin and low-spin states is lower than what is expected from previous studies of high-spin ferropericlase, indicating that the spin transition results in a reduced differential stress and elastic strength along with the volume reduction. The influence of the spin transition on the differential stress and strength of ferropericlase is expected to be less dominant across the wide spin transition zone at high pressure–temperature conditions relevant to the lower mantle.  相似文献   

High-resolution simulations of global climate, part 1: present climate   总被引：2，自引：1，他引：1  

P. B. Duffy  B. Govindasamy  J. P. Iorio  J. Milovich  K. R. Sperber  K. E. Taylor  M. F. Wehner  S. L. Thompson 《Climate Dynamics》2003,21(5-6):371-390

We examine simulations of today's climate performed with a global atmospheric general circulation model run at spectral truncations of T42, T170, and T239, corresponding to grid cell sizes of roughly 310 km, 75 km, and 55 km, respectively. The simulations were forced with observed sea-surface temperatures and sea-ice concentrations. The T42 simulations and initial simulations at T170 and T239 were performed using a model version that was carefully "tuned" to optimize results at T42; subsequent simulations at T170 and T239 used a model version that was partly re-tuned to improve results at T170. On the scales of a T42 grid cell and larger, nearly all quantities we examined in all the T170 and T239 simulations agree better with observations, at least in terms of spatial patterns, than in the T42 simulations. In some cases the improvements are very substantial. Improvements are seen in all-season, global domain results, and in results pertaining to most seasons and latitude bands. Increasing the model resolution from T42 introduces biases (errors in the mean) into some simulated quantities; the worst of these were removed by the partial retuning we performed at T170. This retuning has little effect on the spatial patterns of results, except in Northern Hemisphere winter at T170, where it tends to bring improvements. We discuss aspects of simulated regional climates, and their dependence on model resolution.  相似文献   

Shelf-edge deltas and drowned barrier–island complexes on the northwest Florida outer continental shelf     

J.V. Gardner  P. Dartnell  L.A. Mayer  J.E. Hughes Clarke  B.R. Calder  G. Duffy   《Geomorphology》2005,64(3-4):133-166

A high-resolution multibeam survey of the northwest Florida shelf mapped six relict shelf-edge deltas, each with a drowned barrier–island system developed on its south and southwestern rims. The deltas appear to have formed during periods of sea-level stasis that occurred between 58,000 and 28,000 years ago. The barrier islands formed on the deltas during periods of slow regression during this same time interval. Large fields of asymmetric dunes are found on the delta surfaces as well as on the south and southwestern flanks of the deltas. The asymmetry and orientation of the dunes suggest that a northward-flowing current was sheared by the presence of the delta topography, and as a result, the upper layer of the flow continued to the north, whereas the lower layer was steered by the topography. The topographic steering accelerated the northward flow around the south and southwestern flanks with speeds adequate to form large dunes. The flow slowed after rounding southwestern flank but accelerated again as it encountered the next delta flank to the north. The age of the dune formation is unknown, and no northward-flowing geostrophic flow has been reported in the literature from this area.  相似文献   

Effects of model resolution and subgrid-scale physics on the simulation of precipitation in the continental United States   总被引：4，自引：0，他引：4  

J. P. Iorio  P. B. Duffy  B. Govindasamy  S. L. Thompson  M. Khairoutdinov  D. Randall 《Climate Dynamics》2004,23(3-4):243-258

We analyze simulations of the global climate performed at a range of spatial resolutions to assess the effects of horizontal spatial resolution on the ability to simulate precipitation in the continental United States. The model investigated is the CCM3 general circulation model. We also preliminarily assess the effect of replacing cloud and convective parameterizations in a coarse-resolution (T42) model with an embedded cloud-system resolving model (CSRM). We examine both spatial patterns of seasonal-mean precipitation and daily time scale temporal variability of precipitation in the continental United States. For DJF and SON, high-resolution simulations produce spatial patterns of seasonal-mean precipitation that agree more closely with observed precipitation patterns than do results from the same model (CCM3) at coarse resolution. However, in JJA and MAM, there is little improvement in spatial patterns of seasonal-mean precipitation with increasing resolution, particularly in the southeast USA. This is because of the dominance of convective (i.e., parameterized) precipitation in these two seasons. We further find that higher-resolution simulations have more realistic daily precipitation statistics. In particular, the well-known tendency at coarse resolution to have too many days with weak precipitation and not enough intense precipitation is partially eliminated in higher-resolution simulations. However, even at the highest resolution examined here (T239), the simulated intensity of the mean and of high-percentile daily precipitation amounts is too low. This is especially true in the southeast USA, where the most extreme events occur. A new GCM, in which a cloud-resolving model (CSRM) is embedded in each grid cell and replaces convective and stratiform cloud parameterizations, solves this problem, and actually produces too much precipitation in the form of extreme events. However, in contrast to high-resolution versions of CCM3, this model produces little improvement in spatial patterns of seasonal-mean precipitation compared to models at the same resolution using traditional parameterizations.  相似文献   

Controls on landscape and drainage evolution in regions of distributed normal faulting: Perachora Peninsula,Corinth Rift,Central Greece          下载免费PDF全文

O. B. Duffy  S. H. Brocklehurst  R. L. Gawthorpe  M. R. Leeder  E. Finch 《Basin Research》2015,27(4):473-494

Zones of distributed faulting with narrow (2–3 km) across‐strike spacing form a common structural style within rifts, especially in accommodation zones, and contrast with crustal‐scale half‐grabens, where strain is localised on normal faults spaced 10–30 km apart. These contrasting styles are likely to have a significant impact on geomorphic development, sediment routing and the stratigraphic record. Perachora Peninsula, in the eastern part of the active Corinth Rift, Greece, is one such zone of distributed faulting. We analyse the topography and drainage networks developed around these closely spaced normal faults, and compare our results with published studies from crustal‐scale half‐grabens. We subdivide the Perachora Peninsula into a series of drainage domains and examine the tectono‐geomorphic evolution of three domains that best represent the range of topographic characteristics, base levels and drainage network styles. We interpret that the perched, endorheic nature of the Asprokampos domain developed due to uplift and backtilt on offshore faults. The Pisia West domain, which drains the valley between the Skinos and Pisia Faults and responds to a perched base level, is interpreted to have experienced a complex base‐level history with episodic connections to sea level. The Skinos Relay domain drains to sea level, lying on the relay ramp between the closely spaced Kamarissa and Skinos Faults. Here, interaction between the displacement fields associated with each of the closely spaced faults controls the rate and style of landscape evolution. In contrast to crustal‐scale half‐grabens, observations from Perachora Peninsula suggest that zones of distributed faulting may be characterised by: (i) perched, internal sediment sinks at different elevations, responding to multiple base levels; (ii) minimal fault‐transverse sediment transport; (iii) interaction of uplift and subsidence fields associated with closely spaced faults, which modulate the rate and style of landscape response; and (iv) complex erosion and sedimentation histories, the evidence for which may have low preservation potential in the stratigraphic record.  相似文献   

Tectonic geomorphology and hydrocarbon induced topography of the Mid-Channel Anticline, Santa Barbara Basin, California     

E.A. Keller  Marlene Duffy  J.P. Kennett  T. Hill 《Geomorphology》2007,89(3-4):274-286

The geomorphology of the western sector of the Mid-Channel Anticline (MCA), Santa Barbara, southern California suggests the actively growing fold is laterally propagating to the west. The presence of fold scarps and cross faults that segment the structure suggests that buried faults that are producing the folding are present at shallow depths. The summit area of the anticline at the Last Glacial Maximum (22 to 19 ka) was probably a small late Pleistocene island. Evidence for presence of the island includes what appears to be terrestrial erosion and is supported by assumption of sea level change and rates of uplift and subsidence.Pockmarks and domes ranging in diameter from  10 to 100 m, and several meters deep are present along the crest and flanks of the MCA. These features appear to be the result of hydrocarbon emission. Their formation has significantly modified the surface features, producing simple to complex erosional and/or constructional topography. A large pockmark near the anticline crest dated by two calibrated AMS radiocarbon dates of 25.3 and 36.9 ka continues to emit hydrocarbon gases. We term the topography produced by hydrocarbon emission as Hydrocarbon Induced Topography (HIT).  相似文献   

The UVic earth system climate model: Model description,climatology, and applications to past,present and future climates     

Andrew J. Weaver  Michael Eby  Edward C. Wiebe  Cecilia M. Bitz  Phil B. Duffy  Tracy L. Ewen 《大气与海洋》2013,51(4):361-428

Abstract

A new earth system climate model of intermediate complexity has been developed and its climatology compared to observations. The UVic Earth System Climate Model consists of a three‐dimensional ocean general circulation model coupled to a thermodynamic/dynamic sea‐ice model, an energy‐moisture balance atmospheric model with dynamical feedbacks, and a thermomechanical land‐ice model. In order to keep the model computationally efficient a reduced complexity atmosphere model is used. Atmospheric heat and freshwater transports are parametrized through Fickian diffusion, and precipitation is assumed to occur when the relative humidity is greater than 85%. Moisture transport can also be accomplished through advection if desired. Precipitation over land is assumed to return instantaneously to the ocean via one of 33 observed river drainage basins. Ice and snow albedo feedbacks are included in the coupled model by locally increasing the prescribed latitudinal profile of the planetary albedo. The atmospheric model includes a parametrization of water vapour/planetary longwave feedbacks, although the radiative forcing associated with changes in atmospheric CO₂ is prescribed as a modification of the planetary longwave radiative flux. A specified lapse rate is used to reduce the surface temperature over land where there is topography. The model uses prescribed present‐day winds in its climatology, although a dynamical wind feedback is included which exploits a latitudinally‐varying empirical relationship between atmospheric surface temperature and density. The ocean component of the coupled model is based on the Geophysical Fluid Dynamics Laboratory (GFDL) Modular Ocean Model 2.2, with a global resolution of 3.6° (zonal) by 1.8° (meridional) and 19 vertical levels, and includes an option for brine‐rejection parametrization. The sea‐ice component incorporates an elastic‐viscous‐plastic rheology to represent sea‐ice dynamics and various options for the representation of sea‐ice thermodynamics and thickness distribution. The systematic comparison of the coupled model with observations reveals good agreement, especially when moisture transport is accomplished through advection.

Global warming simulations conducted using the model to explore the role of moisture advection reveal a climate sensitivity of 3.0°C for a doubling of CO₂, in line with other more comprehensive coupled models. Moisture advection, together with the wind feedback, leads to a transient simulation in which the meridional overturning in the North Atlantic initially weakens, but is eventually re‐established to its initial strength once the radiative forcing is held fixed, as found in many coupled atmosphere General Circulation Models (GCMs). This is in contrast to experiments in which moisture transport is accomplished through diffusion whereby the overturning is reestablished to a strength that is greater than its initial condition.

When applied to the climate of the Last Glacial Maximum (LGM), the model obtains tropical cooling (30°N‐30°S), relative to the present, of about 2.1°C over the ocean and 3.6°C over the land. These are generally cooler than CLIMAP estimates, but not as cool as some other reconstructions. This moderate cooling is consistent with alkenone reconstructions and a low to medium climate sensitivity to perturbations in radiative forcing. An amplification of the cooling occurs in the North Atlantic due to the weakening of North Atlantic Deep Water formation. Concurrent with this weakening is a shallowing of, and a more northward penetration of, Antarctic Bottom Water.

Climate models are usually evaluated by spinning them up under perpetual present‐day forcing and comparing the model results with present‐day observations. Implicit in this approach is the assumption that the present‐day observations are in equilibrium with the present‐day radiative forcing. The comparison of a long transient integration (starting at 6 KBP), forced by changing radiative forcing (solar, CO₂, orbital), with an equilibrium integration reveals substantial differences. Relative to the climatology from the present‐day equilibrium integration, the global mean surface air and sea surface temperatures (SSTs) are 0.74°C and 0.55°C colder, respectively. Deep ocean temperatures are substantially cooler and southern hemisphere sea‐ice cover is 22% greater, although the North Atlantic conveyor remains remarkably stable in all cases. The differences are due to the long timescale memory of the deep ocean to climatic conditions which prevailed throughout the late Holocene. It is also demonstrated that a global warming simulation that starts from an equilibrium present‐day climate (cold start) underestimates the global temperature increase at 2100 by 13% when compared to a transient simulation, under historical solar, CO₂ and orbital forcing, that is also extended out to 2100. This is larger (13% compared to 9.8%) than the difference from an analogous transient experiment which does not include historical changes in solar forcing. These results suggest that those groups that do not account for solar forcing changes over the twentieth century may slightly underestimate (～3% in our model) the projected warming by the year 2100.  相似文献