Lithospheric flexure on Venus     

Catherine L. Johnson  David T. Sandwell 《Geophysical Journal International》1994,119(2):627-647

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Genetic structure of bay anchovy (Anchoa mitchilli) populations in Chesapeake Bay     

Raymond P. Morgan  Bruce M. Baker  James H. Howard 《Estuaries and Coasts》1995,18(3):482-493

To determine the genetic structure of the bay anchovy (Anchoa mitchilli) within Chesapeake Bay, 16 isozyme systems encoding 21 loci for 20 population were examined using horizontal starch gel electrophoresis. Contingency Chisquare analysis revealed significant allelic frequency differences at nine loci (AAT-1, AAT-2, ALD-1, CPK-2, GAP-1, GLY-1, LDH-1, MDH-1, and MDH-2). Two loci, ALD-1 and MDH-1, were responsible for nine of 14 tests not conforming to Hardy-Weinberg expectations, with some of these deviations attributed to possible scoring and/or sampling error. Estimates for mean average heterozygosity were relatively high, ranging from 0.40 to 0.096, with 33–57% of the loci polymorphic. A low F_st value (0.041) along with high genetic identity estimates (I=0.997) indicated little substructuring of bay anchovy populations within Chesapeake Bay.  相似文献   

Miocene-Pliocene half-graben evolution, detachment faulting and late-stage core complex uplift from reflection seismic data in south-east Arizona     

J. M. Kruger  R. A. Johnson  B. B. Houser† 《Basin Research》1995,7(2):129-149

Reflection seismic data show that the late Cenozoic Safford Basin in the Basin and Range of south-eastern Arizona, is a 4.5-km-deep, NW-trending, SW-dipping half graben composed of middle Miocene to upper Pliocene sediments, separated by a late Miocene sequence boundary into lower and upper basin-fill sequences. Extension during lower basin-fill deposition was accommodated along an E-dipping range-bounding fault comprising a secondary breakaway zone along the north-east flank of the Pinaleño Mountains core complex. This fault was a listric detachment fault, active throughout the mid-Tertiary and late Cenozoic, or a younger fault splay that cut or merged with the detachment fault. Most extension in the basin was accommodated by slip on the range-bounding fault, although episodic movement along antithetic faults temporarily created a symmetric graben. Upper-plate movement over bends in the range-bounding fault created rollover structures in the basin fill and affected deposition within the half graben. Rapid periods of subsidence relative to sedimentation during lower basin-fill deposition created thick, laterally extensive lacustrine or alluvial plain deposits, and restricted proximal alluvian-fan deposits to the basin margins. A period of rapid extension and subsidence relative to sediment influx, or steepening of the upper segment of the range-bounding fault at the start of upper basin-fill deposition resulted in a large downwarp over a major fault bend. Sedimentation was restricted to this downwarp until filled. Episodic subsidence during upper basin-fill deposition caused widespread interbedding of lacustrine and fluvial deposits. Northeastward tilting along the south-western flank of the basin and north-eastward migration of the depocentre during later periods of upper basin-fill deposition suggest decreased extension rates relative to late-stage core complex uplift.  相似文献   

Formal inversion of ISC arrival times for mantle P-velocity structure     

D. W. Vasco  R. Jay Pulliam  Lane R. Johnson 《Geophysical Journal International》1993,113(3):586-606

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The biogeochemical sulfur cycle in the marine boundary layer over the Northeast Pacific Ocean   总被引：1，自引：0，他引：1  

T. S. Bates  J. E. Johnson  P. K. Quinn  P. D. Goldan  W. C. Kuster  D. C. Covert  C. J. Hahn 《Journal of Atmospheric Chemistry》1990,10(1):59-81

The major components of the marine boundary layer biogeochemical sulfur cycle were measured simultaneously onshore and off the coast of Washington State, U.S.A. during May 1987. Seawater dimethylsulfide (DMS) concentrations on the continental shelf were strongly influenced by coastal upwelling. Concentration further offshore were typical of summer values (2.2 nmol/L) at this latitude. Although seawater DMS concentrations were high on the biologically productive continental shelf (2–12 nmol/L), this region had no measurable effect on atmospheric DMS concentrations. Atmospheric DMS concentrations (0.1–12 nmol/m³), however, were extremely dependent upon wind speed and boundary layer height. Although there appeared to be an appreciable input of non-sea-salt sulfate to the marine boundary layer from the free troposphere, the local flux of DMS from the ocean to the atmosphere was sufficient to balance the remainder of the sulfur budget.  相似文献   

Regional hydrogeological screening characteristics used for siting near-surface waste-disposal facilities in Oklahoma,U.S.A.     

Kenneth S. Johnson 《Environmental Geology》1991,17(1):3-7

The Oklahoma Geological Survey has developed several maps and reports for preliminary screening of the state of Oklahoma to identify areas that are generally acceptable or unacceptable for disposal of a wide variety of waste materials. These maps and reports focus on the geologic and hydrogeologic parameters that must be evaluated in the screening process. One map (and report) shows the outcrop distribution of 35 thick shale or clay units that are generally suitable for use as host rocks for surface disposal of wastes. A second map shows the distribution of unconsolidated alluvial and terrace-deposit aquifers, and a third map shows the distribution and hydrologic character of bedrock aquifers and their recharge areas. These latter two maps show the areas in the state where special attention must be exercised in permitting storage or disposal of waste materials that could degrade the quality of groundwater. State regulatory agencies and industry are using these maps and reports in preliminary screening of the state to identify potential disposal sites. These maps in no way replace the need for site-specific investigations to prove (or disprove) the adequacy of a site to safely contain waste materials.  相似文献   

Implications of CO2 global warming on great lakes ice cover     

Raymond A. Assel 《Climatic change》1991,18(4):377-395

Statistical ice cover models were used to project daily mean basin ice cover and annual ice cover duration for Lakes Superior and Erie. Models were applied to a 1951–80 base period and to three 30-year steady double carbon dioxide (2 × CO₂) scenarios produced by the Geophysical Fluid Dynamics Laboratory (GFDL), the Goddard Institute of Space Studies (GISS), and the Oregon State University (OSU) general circulation models. Ice cover estimates were made for the West, Central, and East Basins of Lake Erie and for the West, East, and Whitefish Bay Basins of Lake Superior. Average ice cover duration for the 1951– 80 base period ranged from 13 to 16 weeks for individual lake basins. Reductions in average ice cover duration under the three 2 × CO₂ scenarios for individual lake basins ranged from 5 to 12 weeks for the OSU scenario, 8 to 13 weeks for the GISS scenario, and 11 to 13 weeks for GFDL scenario. Winters without ice formation become common for Lake Superior under the GFDL scenario and under all three 2 × CO₂ scenarios for the Central and East Basins of Lake Erie. During an average 2 × CO₂ winter, ice cover would be limited to the shallow areas of Lakes Erie and Superior. Because of uncertainties in the ice cover models, the results given here represent only a first approximation and are likely to represent an upper limit of the extent and duration of ice cover under the climate change projected by the three 2 × CO₂scenarios. Notwithstanding these limitations, ice cover projected by the 2 × CO₂ scenarios provides a preliminary assessment of the potential sensitivity of the Great Lakes ice cover to global warming. Potential environmental and socioeconomic impacts of a 2 × CO₂ warming include year-round navigation, change in abundance of some fish species in the Great Lakes, discontinuation or reduction of winter recreational activities, and an increase in winter lake evaporation.  相似文献   

Ocean-atmosphere CO2 exchange: An accessible lab simulation for considering biological effects     

David A. Noever  Helen C. Matsos  Raymond J. Cronise  Loren L. Looger  Rachna A. Relwani  Vladimir I. Nikora 《Climatic change》1994,27(3):299-320

Phytoplankton is considered a key component mediating the ocean-atmospheric exchange of carbon dioxide and oxygen. Lab simulations which model biological responses to atmospheric change are difficult to translate into natural settings owing in part to the vertical migration of phytoplankton. In the sea this vertical migration acts to regulate actual carbon dioxide consumption. To capture some critical properties of this vertical material transfer, we monitored the effects of atmospheric CO₂ on dense suspensions of bioconvecting microorganisms. Bioconvection refers to the spontaneous patterns of circulation which arise among such upwardly swimming cells as alga, protozoa, zoospore and large bacteria. Gravity, phototaxis and chemotaxis have all been implicated as affecting pattern-forming ability. The ability of a biologically active suspension to detect atmospheric changes offers a unique method to quantify organism adjustment and vertical migration. With increasing CO₂, bioconvection patterns in alga (P. parva) and protozoa (T. pyriformis) lose their robustness, and surface cell populations retreat from the highest CO₂ regions. Cell movement (both percent motile and mean velocity) generally diminishes. A general program of image analysis yields statistically significant variations in macroscopic migration patterns; both fractal dimension and various crystallographic parameters correlate strongly with carbon dioxide content.  相似文献   

(White) papering over the regional problem: unemployment in Geelong and the federal government response     

Louise Johnson  Steve Wright 《The Australian geographer》1994,25(2):121-125

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On the excitation of short-term variations in the length of the day and polar motion     

Raymond Hide 《Surveys in Geophysics》1985,7(2):163-167

Variations in the distribution of mass within the atmosphere, and changes in the pattern of winds produce fluctuations in all three components of the angular momentum of the atmosphere on time-scales upwards of a few days. It, has been shown that variations in theaxial component of atmospheric angular momentum during the Special Observing Periods in the recent First GARP Global Experiment (FGGE, where GARP is the Global Atmospheric Research Programme) are well correlated with short-term changes in the length of the day. They are consistent with the total angular momentum of the atmosphere and solid Earth being conserved on short timescales (allowing for lunar and solar effects), without requiring significant angular momentum transfer between the Earth's liquid core and solid mantle on timescales of weeks or months. It has also been shown that fluctuations, in the equatorial components of atmospheric angular momentum make a major contribution to the observed wobble of the instantaneous pole of the Earth's rotation with respect to the Earth's crust. A necessary step in the investigation was a re-examination of the underlying theory of non-rigid body rotational dynamics and angular momentum exchange between the atmosphere and solid Earth. Since only viscous or topographic coupling between the atmosphere and solid Earth can transfer angular momentum, no atmospheric flow that everywhere satisfied inviscid equations (including, but not solely, geostrophic flow) could affect the rotation of a spherical solid Earth. New effective angular momentum functions were introduced in order to exploit the available data and allow for rotational and surface loading deformation of the Earth. A theoretical basis has now been established for future routine determinations of atmopheric, angular momentum fluctuations for the purpose of meteorological and geophysical research, including the assessment of the extent to which movements in the solid Earth associated with very large earthquakes contribute to the excitation of the Chandlerian wobble.  相似文献