Shoreline erosion rates along barrier islands of the north central gulf of Mexico     

Stephen V. Shabica  Robert Dolan  Suzette May  Paul May 《Environmental Geology》1983,5(3):115-126

Rates of shoreline change and overwash penetration distances were calculated for barrier islands along the Louisiana, Mississippi, and Alabama coasts with the orthogonal grid mapping system (OGMS). Average rates of shoreline change are exceptionally high in Louisiana, being of the order ?4.7 to ?7.4 m yr^?1. Mississippi and Alabama recession rates are lower and range from ?2.0 to ?3.1 m yr^?1 over the period of record. Erosion rates along the shorelines of these islands have remained relatively constant over the period of study with five exceptions in coastal Louisiana and the Chandeleur-Breton Islands Arc, and two exceptions along the Mississippi-Alabama barrier islands where they have accelerated. Mean overwash penetration is greatest along Dauphin Island, Alabama, and Cat Island, Mississippi: 207.6 and 197.9 m, respectively. The Chandeleur-Brenton Islands Arc range from 88.1 m at the central barrier to 180.4 along the flanks. The Mississippi islands range from 105.2 m on Ship Island to 200.5 m along central Horn Island. Mean overwash penetration along the Louisiana barriers is highly variable: 46.3 to 211.4 m.  相似文献   

Reservoir geochemistry of South Pass 61 Field, Gulf of Mexico: compositional heterogeneities reflecting filling history and biodegradation   总被引：1，自引：0，他引：1  

A.G. Holba  L.I.P. Dzou  J.J. Hickey  S.G. Franks  S.J. May  T. Lenney 《Organic Geochemistry》1996,24(12):1179-1198

Cluster analysis of GC data for gasoline and mid-range hydrocarbon ratios from fifty-one South Pass 61 Field oils reveals geochemically similar oil clusters corresponding to geographically coherent groups. Insight into the groupings is obtained from examination of indicators of geochemical processes, e.g., anaerobic biodegradation, aerobic biodegradation and extensive remigration of light ends. Six duplicate samples collected in 1986 and 1992 as well as replicate runs on a single sample showed excellent analytical reproducibility.Subtle but consistent differences in both gasoline and oil-range hydrocarbon maturity indicators are observed between the east, west, and far west flanks of the field, suggesting filling of different segments of the reservoir from different kitchens at slightly different stages of thermal maturity or with slightly different chemical character. The west flank of the salt dome was charged with slightly more thermally mature petroleum than the east flank. The stratigraphically oldest and deepest sand on the far west flank has received the most mature petroleum. Different fluid contacts and GORs are observed in different sands and different fault blocks. The stacked pay geometry of the field and widespread faulting have led to considerable remigration of gas and condensate as observed in other fields in the Gulf of Mexico (Thompson, 1987).Biodegradation varies in severity with depth and reservoir zone, but is frequently overprinted by remigration of light end hydrocarbons. Anaerobic biodegradation by sulfate-reducing bacteria is probably the cause of light to moderate alteration in intermediate depth Pliocene sands which are hydraulically connected to the salt dome (with dissolution of anhydrite from the salt dome providing the sulfate). Widespread late pyrite formation in reservoir sandstones is inferred to represent the ultimate sink for reduced sulfur from sulfate reduction during oil biodegradation. Co-produced water compositions suggest no oxygenated freshwater infusion.  相似文献   

Decametric radio measurement of Jupiter's rotation period     

J. May  T.D. Carr  M.D. Desch 《Icarus》1979,40(1):87-93

A total of 26 measurements of Jupiter's 12-year average rotation period were made at frequencies of 18, 20, and 22.2 MHz at observatories in Florida and Chile. An improved method was employed in which histograms of occurrence probability vs central meridian longitude obtained at the same frequency and observatory during apparitions about 12 years (one Jovian year) apart were cross correlated. The longitude shift giving maximum cross correlation was used to correct the initially assumed rotation period value. The mean of the measurements is 9 hr 55 min 29.689 sec, with a standard deviation of the mean of 0.005 sec. This is about 0.02 sec, or 4 standard deviations, less than the System III (1965) value. The measurements indicate that the rotation period was not changing (linearly) at a rate in excess of 0.03 sec/yr. If the synoptic monitoring program is continued through the next maximum of the jovicentric declination of the Earth (D_E), we will probably be able to detect a rate of change in rotation period as small as 0.002 sec/yr. This accuracy might be sufficient to reveal a secular drift in Jupiter's magnetic field.  相似文献   

Computer simulation of the low-molecular-weight inorganic species distribution of antimony(III) and antimony(V) in natural waters     

Montserrat Filella  Peter M. May 《Geochimica et cosmochimica acta》2003,67(21):4013-4031

Computer speciation models of antimony in aqueous, multicomponent solutions of environmental and biological interest have been developed. Antimony is an element of increasing environmental significance but one whose chemical speciation has not previously been modelled in any comprehensive way. The available thermodynamic data have been critically evaluated and entered into a thermodynamic database. The JESS suite of computer programs has been used to develop the thermodynamically-consistent mass balance equations used for modelling purposes. The calculated speciation distributions successfully account for some but not all key known properties of antimony in natural waters. It is believed that the main difference is most likely due to kinetic factors.  相似文献   

Cogitating on GIS. Response to David O'Sullivan and Matthew Wilson     

May Yuan 《Singapore journal of tropical geography》2021,42(1):40-44

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The variation of air density at 240 and 280 km from April to November 1967     

B.R. May 《Planetary and Space Science》1972

Changes in the orbital periods of two satellites, 1962-βτ6 (Injun 3 rocket) and 1965-11D (Cosmos 54 rocket), have been used to deduce the air density at heights of 240 and 280 km during April–November 1967. At both heights the generally low density observed in July and the higher density in April and October were almost certainly part of a semi-annual variation similar to that observed at other heights in the thermosphere. The ratio of the maximum (October) to minimum (July) density was about 1·8 at 240 km and 2·2 at 280 km. Superimposed upon this variation were short-lived increases in density associated with magnetic storms, the largest being of 65 per cent at 280 km on 25 May, and a periodic variation with an amplitude of up to 25 per cent from the monthly mean density, related to the 10·7 cm solar radiation flux. A diurnal variation of density was also detected with a maximum density at 14 hr and a maximum to minimum ratio of 1·7 at 280 km.  相似文献   

Combined inequality in wealth and risk leads to disaster in the climate change game     

Maxwell N. Burton-Chellew  Robert M. May  Stuart A. West 《Climatic change》2013,120(4):815-830

It is generally agreed that the risk of catastrophic climate change can only be reduced if agents cooperate to reduce greenhouse gas emissions over the course of the 21st Century. Previous economic experiments have suggested that sufficient cooperation can often be achieved providing individuals are adequately and convincingly informed of the consequences of their actions and the stakes involved. However, this previous work, has not allowed for the fact that in the real world agents vary in both: (1) their resources to mitigate climate change, and (2) the consequences that they face from climate change. We develop and expand the protocol of previous economic experiments to investigate the introduction of such combined asymmetries. We find that when inequality in resources is combined with a greater relative risk for poorer members, cooperation collapses, with tragic consequences. This is because the rich invest proportionally less into preventing climate change when they are less at risk. We also find, through the use of a post-game questionnaire, that those individuals who were more skeptical about climate change in the real world cooperated less in our games. Insofar as such experiments can be trusted as a guide to either people’s everyday behaviour or the interactions of nation states, these results suggest that voluntary cooperation to avoid climate catastrophe in the real world is likely to be hard to achieve.  相似文献   

On Rotation of an Isolated Globule     

A. L. Gyulbudaghian  J. May 《Astrophysics》2004,47(3):352-360

During CO observations of new Southern objects with the 15-m SEST mm telescope (Cerro La Silla, Chile) we have found that the globule connected with the object CLN127-128 rotates with an angular velocity 4.3 · 10^-14 s^-1, which corresponds to the velocity of extremely fast rotating globules. The object CLN127-128 is a chain of three stars; two of them are connected with bright nebulae, and the third is a suspected Herbig Ae/Be star. All three stars are bright in near IR, which is specific for the existence of circumstellar shells (or disks) around them. The specific angular momentum of the globule confirms that it is in virial equilibrium. Besides the finding of a rotating globule, CO observations suggest the presence of a blue-shifted outflow from CLN127-128 with a velocity of -1.1 km/s (in the system connected with the globule).  相似文献   

Paleoseismology of the 2016 MW 6.1 Petermann earthquake source: Implications for intraplate earthquake behaviour and the geomorphic longevity of bedrock fault scarps in a low strain-rate cratonic region     

Tamarah Rosellen King  Mark Quigley  Dan Clark  Albert Zondervan  Jan-Hendrik May  Abaz Alimanovic 《地球表面变化过程与地形》2021,46(7):1238-1256

The 20 May 2016 M_W 6.1 Petermann earthquake in central Australia generated a 21 km surface rupture with 0.1 to 1 m vertical displacements across a low-relief landscape. No paleo-scarps or potentially analogous topographic features are evident in pre-earthquake Worldview-1 and Worldview-2 satellite data. Two excavations across the surface rupture expose near-surface fault geometry and mixed aeolian-sheetwash sediment faulted only in the 2016 earthquake. A 10.6 ± 0.4 ka optically stimulated luminescence (OSL) age of sheetwash sediment provides a minimum estimate for the period of quiescence prior to 2016 rupture. Seven cosmogenic beryllium-10 (¹⁰Be) bedrock erosion rates are derived for samples < 5 km distance from the surface rupture on the hanging-wall and foot-wall, and three from samples 19 to 50 km from the surface rupture. No distinction is found between fault proximal rates (1.3 ± 0.1 to 2.6 ± 0.2 m Myr⁻¹) and distal samples (1.4 ± 0.1 to 2.3 ± 0.2 m Myr⁻¹). The thickness of rock fragments (2–5 cm) coseismically displaced in the Petermann earthquake perturbs the steady-state bedrock erosion rate by only 1 to 3%, less than the erosion rate uncertainty estimated for each sample (7–12%). Using ¹⁰Be erosion rates and scarp height measurements we estimate approximately 0.5 to 1 Myr of differential erosion is required to return to pre-earthquake topography. By inference any pre-2016 fault-related topography likely required a similar time for removal. We conclude that the Petermann earthquake was the first on this fault in the last ca. 0.5–1 Myr. Extrapolating single nuclide erosion rates across this timescale introduces large uncertainties, and we cannot resolve whether 2016 represents the first ever surface rupture on this fault, or a > 1 Myr interseismic period. Either option reinforces the importance of including distributed earthquake sources in fault displacement and seismic hazard analyses.  相似文献   

Modeling fresh water lens damage and recovery on atolls after storm-wave washover   总被引：1，自引：0，他引：1  

Chui TF  Terry JP 《Ground water》2012,50(3):412-420

The principal natural source of fresh water on scattered coral atolls throughout the tropical Pacific Ocean is thin unconfined groundwater lenses within islet substrates. Although there are many threats to the viability of atoll fresh water lenses, salinization caused by large storm waves washing over individual atoll islets is poorly understood. In this study, a mathematical modeling approach is used to examine the immediate responses, longer-term behavior, and subsequent (partial) recovery of a Pacific atoll fresh water lens after saline damage caused by cyclone-generated wave washover under different scenarios. Important findings include: (1) the saline plume formed by a washover event mostly migrates downward first through the top coral sand and gravel substrate, but then exits the aquifer to the ocean laterally through the more permeable basement limestone; (2) a lower water table position before the washover event, rather than a longer duration of storm washover, causes more severe damage to the fresh water lens; (3) relatively fresher water can possibly be found as a preserved horizon in the deeper part of an aquifer after disturbance, especially if the fresh water lens extends into the limestone under normal conditions; (4) post-cyclone accumulation of sea water in the central depression (swamp) of an atoll islet prolongs the later stage of fresh water lens recovery.  相似文献