Grid transformation for incorporating the Arctic in a global ocean model   总被引：2，自引：0，他引：2  

Michael Eby  Greg Holloway 《Climate Dynamics》1994,10(4-5):241-247

A grid transformation is described which isolates the Arctic and North Atlantic, rotates the spherical grid to pass an equator up the Atlantic through the north pole and remaps the Coriolis parameter. Boundary condition information is exchanged along the equatorial Atlantic so that the Arctic-Atlantic model is dynamically coupled to a model of the rest of the global ocean (which remains on the geographic spherical grid). The transform produces a more regular grid over the Arctic and eliminates the need for filtering or special treatment at the pole. The transform has been implemented in the GFDL Modular Ocean Model. After testing with idealized geometry, a 300 y global integration is compared to an integration using the geographic spherical grid and Fourier filtering. Results are similar, with differences in the Arctic and western North Atlantic regions leading to smaller air-sea heat flux near the Gulf Stream separation latitude for the transform case. Use of the transform also leads to a reduction in computation time.  相似文献   

Diagenetic overprinting of the sphaerosiderite palaeoclimate proxy: are records of pedogenic groundwater δ18O values preserved?     

David F. Ufnar  Luis A. González†‡  Greg A. Ludvigson‡§¶  Robert L. Brenner¶  Brian J. Witzke§¶ 《Sedimentology》2004,51(1):127-144

Meteoric sphaerosiderite lines (MSLs), defined by invariant δ¹⁸O and variable δ¹³C values, are obtained from ancient wetland palaeosol sphaerosiderites (millimetre‐scale FeCO₃ nodules), and are a stable isotope proxy record of terrestrial meteoric isotopic compositions. The palaeoclimatic utility of sphaerosiderite has been well tested; however, diagenetically altered horizons that do not yield simple MSLs have been encountered. Well‐preserved sphaerosiderites typically exhibit smooth exteriors, spherulitic crystalline microstructures and relatively pure (> 95 mol% FeCO₃) compositions. Diagenetically altered sphaerosiderites typically exhibit corroded margins, replacement textures and increased crystal lattice substitution of Ca²⁺, Mg²⁺ and Mn²⁺ for Fe²⁺. Examples of diagenetically altered Cretaceous sphaerosiderite‐bearing palaeosols from the Dakota Formation (Kansas), the Swan River Formation (Saskatchewan) and the Success S2 Formation (Saskatchewan) were examined in this study to determine the extent to which original, early diagenetic δ¹⁸O and δ¹³C values are preserved. All three units contain poikilotopic calcite cements with significantly different δ¹⁸O and δ¹³C values from the co‐occurring sphaerosiderites. The complete isolation of all carbonate phases is necessary to ensure that inadvertent physical mixing does not affect the isotopic analyses. The Dakota and Swan River samples ultimately yield distinct MSLs for the sphaerosiderites, and MCLs (meteoric calcite lines) for the calcite cements. The Success S2 sample yields a covariant δ¹⁸O vs. δ¹³C trend resulting from precipitation in pore fluids that were mixtures between meteoric and modified marine phreatic waters. The calcite cements in the Success S2 Formation yield meteoric δ¹⁸O and δ¹³C values. A stable isotope mass balance model was used to produce hyperbolic fluid mixing trends between meteoric and modified marine end‐member compositions. Modelled hyperbolic fluid mixing curves for the Success S2 Formation suggest precipitation from fluids that were < 25% sea water.  相似文献   

Chemical and isotopic evaluation of water sources to the fens of South Park,Colorado   总被引：1，自引：0，他引：1  

Jenny B. Chapman  Brent Lewis  Greg Litus 《Environmental Geology》2003,43(5):533-545

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Tectonic wedging along the rear of the offshore Taiwan accretionary prism     

Wu-Cheng Chi  Donald L. Reed  Greg Moore  Tuan Nguyen  Char-Shine Liu  Neil Lundberg 《Tectonophysics》2003,374(3-4):199-217

The structural geometry, kinematics and density structure along the rear of the offshore Taiwan accretionary prism were studied using seismic reflection profiling and gravity modeling. Deformation between the offshore prism and forearc basin at the point of incipient collision, and southward into the region of subduction, has been interpreted as a tectonic wedge, similar to those observed along the front of mountain ranges. This tectonic wedge is bounded by an east-dipping roof thrust and a blind, west-dipping floor thrust. An east-dipping sequence of forearc-basin strata in the hanging wall of the roof thrust reaches a thickness in excess of 4 km near the tip of the interpreted tectonic wedge. Section restoration of the roof sequence yields an estimate of 4 km of shortening, which is small compared with that inferred in the collision area to the north, based on the variation in distance between the apex of the prism and the island arc.Previous studies propose that either high-angle normal faulting or backfolding has exhumed the metamorphic rocks along the eastern flank of the Central Range in the collision zone on land. To better constrain the initial crustal configuration, we tested 350 crustal models to fit the free-air gravity anomaly data in the offshore region to study the density structure along the rear of the accretionary prism in the subduction and initial collision zones before the structures become more complex in the collision zone on land. The gravity anomaly, observed in the region of subduction (20.2°N), can be modeled with the arc basement forming a trenchward-dipping backstop that is overlain by materials with densities in the range of sedimentary rocks. Near the point of incipient collision (20.9°N), however, the free-air gravity anomaly over the rear of the prism is approximately 40 mgal higher, compared with the region of subduction, and requires a significant component of high density crustal rocks within the tectonic wedge. These results suggest that the forearc basement may be deformed along the rear of the prism, associated with the onset of collision, but not in the subduction region further to the south.  相似文献   

Climatic regions as an indicator of forest coarse and fine woody debris carbon stocks in the United States   总被引：2，自引：0，他引：2  

Christopher W Woodall  Greg C Liknes 《Carbon balance and management》2008,3(1):5

Background  

Coarse and fine woody debris are substantial forest ecosystem carbon stocks; however, there is a lack of understanding how these detrital carbon stocks vary across forested landscapes. Because forest woody detritus production and decay rates may partially depend on climatic conditions, the accumulation of coarse and fine woody debris carbon stocks in forests may be correlated with climate. This study used a nationwide inventory of coarse and fine woody debris in the United States to examine how these carbon stocks vary by climatic regions and variables.  相似文献   

Evaluation of osmium isotopes and iridium as paleoflux tracers in pelagic carbonates     

Tarun K. Dalai  Greg Ravizza 《Geochimica et cosmochimica acta》2006,70(15):3928-3942

New osmium (Os) isotope and platinum group element (PGE) concentration data are used in conjunction with published ³He and Th isotope data to determine the relative proportions of lithogenic, extraterrestrial and hydrogenous iridium (Ir) in a Pacific pelagic carbonate sequence from the Ocean Drilling Program (ODP) Site 806 on the Ontong Java Plateau (OJP). These calculations demonstrate that lithogenic and extraterrestrial contributions to sedimentary Ir budget are minor, while hydrogenous Ir accounts for roughly 85% of the total Ir. Application of analogous partitioning calculations to previously reported data from a North Pacific red clay sequence (LL44-GPC3) yields very similar results. Total Ir burial fluxes at Site 806 and LL44-GPC3 are also similar, 45 and 30 pg cm⁻² kyr⁻¹, respectively. Average Ir/³He and Ir/xs²³⁰Th_initial ratios calculated from the entire Site 806 data set are similar to those reported earlier for Pacific sites. In general, down-core profiles of Ir, ³He and xs²³⁰Th_initial, are not well correlated with one another. However, all three data sets show similar variance and yield sediment mass accumulation rate estimates that agree within a factor of two. While these results indicate that Ir concentration has potential as a point-paleoflux tracer in pelagic carbonates, Ir-based paleoflux estimates are likely subject to uncertainties that are similar to those associated with Co-based paleoflux estimates. Consequently, local calibration of Ir flux in space and time will be required to fully assess the potential of Ir as a point paleoflux tracer. Measured ¹⁸⁷Os/¹⁸⁸Os of the OJP sediments are systematically lower than the inferred ¹⁸⁷Os/¹⁸⁸Os of contemporaneous seawater and a clear glacial-interglacial ¹⁸⁷Os/¹⁸⁸Os variation is lacking. Mixing calculations suggest Os contributions from lithogenic sources are insufficient to explain the observed ¹⁸⁷Os/¹⁸⁸Os variations. The difference between the ¹⁸⁷Os/¹⁸⁸Os of bulk sediment and that of seawater is interpreted in terms of subtle contributions of unradiogenic Os carried by particulate extraterrestrial material. Down-core variations of ¹⁸⁷Os/¹⁸⁸Os with Pt/Ir and Os/Ir also point to contributions from extraterrestrial particles. Mixing calculations for each set of several triplicate analyses suggest that the unradiogenic Os end member cannot be characterized by primary extraterrestrial particles of chondritic composition. It is noteworthy that in efforts aimed at determining the effect of extraterrestrial contributions, ¹⁸⁷Os/¹⁸⁸Os of pelagic carbonates has greater potential compared to abundances of PGE. An attempt has been made for the first time to estimate sediment mass accumulation rates based on amount of extraterrestrial Os in the OJP samples and previously reported extraterrestrial Os flux. Throughout most of the OJP record, Os isotope-based paleoflux estimates are within a factor of two of those derived using other constant flux tracers. Meaningful flux estimates cannot be made during glacial maxima because the OJP sediments do not record the low ¹⁸⁷Os/¹⁸⁸Os reported previously. We speculate that this discrepancy may be related to focusing of extraterrestrial particles at the OJP, as has been suggested to explain down-core ³He variations.  相似文献   

Occurrence of Almandine, and Its Implications for Ancient High Temperature Activity of the Orakeikorako Geothermal Field, Taupo Volcanic Zone, New Zealand     

Greg BIGNALL 《Resource Geology》2000,50(2):131-135

Abstract: Exploration drilling at Orakeikorako provides information on the hydrologic and thermal regime of the geothermal system, which is presently as high as 265C. The presence of almandine in Drillhole OK–1, at 1312. 5m drilled depth, is the only known occurrence of hydrothermal garnet in an active geothermal system from New Zealand. The formation temperature of the almandine, is not consistent with measured (bore) temperatures, but does coincide with fluid inclusion data and temperatures inferred from other secondary minerals, which suggest it formed at >240C, and possibly as much as 310C. Almandine is an important mineral geothermometer in active hydrothermal systems, and implications for its occurrence should not be discounted in fossil (mineralised) epithermal-type hydrothermal systems.  相似文献   

Deformations of accreting neutron star crusts and gravitational wave emission   总被引：1，自引：0，他引：1  

Greg Ushomirsky  †  Curt Cutler  Lars Bildsten 《Monthly notices of the Royal Astronomical Society》2000,319(3):902-932

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An improved practical approach for estimating catchment-scale response functions through wavelet analysis     

Ravindra Dwivedi  Christopher Eastoe  John F. Knowles  Lejon Hamann  Thomas Meixner  Paul A. “Ty” Ferre  Christopher Castro  William E. Wright  Guo-Yue Niu  Rebecca Minor  Greg A. Barron-Gafford  Nathan Abramson  Bhaskar Mitra  Shirley A. Papuga  Michael Stanley  Jon Chorover 《水文研究》2021,35(3):e14082

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Polar orbits around binary stars     

Greg Egan 《Celestial Mechanics and Dynamical Astronomy》2018,130(1):5

Oks proposes the existence of a new class of stable planetary orbits around binary stars, in the shape of a helix on a conical surface whose axis of symmetry coincides with the interstellar axis, and rotates with the same orbital frequency as the binary pair. We show that this claim relies on the inappropriate use of an effective potential that is only applicable when the stars are held motionless. We also present numerical evidence that the only planetary orbits whose planes are initially orthogonal to the interstellar axis that remain stable on the time scale of the stellar orbit are ordinary polar orbits around one of the stars, and that the perturbations due to the binary companion do not rotate the plane of the orbit to maintain a fixed relationship with the axis.  相似文献