Atmospheric forcing of fine-sand transport on a low-energy inner shelf: south-central Louisiana,USA     

David A. Pepper  Gregory W. Stone 《Geo-Marine Letters》2002,22(1):33-41

Hydrodynamic and sediment transport measurements from instrumentation deployed during a 54-day winter period at two sites on the Louisiana inner shelf are presented. Strong extratropical storms, with wind speeds of 7.8 to 15.1 m s^-1, were the dominant forcing mechanism during the study. These typically caused mean oscillatory flows and shear velocities about 33% higher than fair weather (averaging 12.3 and 3.2 cm s^-1 at the landward site, and 11.4 and 2.7 cm s^-1 at the seaward site, respectively). These responses were coupled with mean near-bottom currents more than twice as strong as during fair weather (10.3 and 7.5 cm s^-1 at the landward and seaward sites, respectively). These flowed in approximately the same direction as the veering wind, causing a net offshore transport of fine sand. Weak storms were responsible for little sediment transport whereas during fair weather, onshore sand transport of approximately 25-75% of the storm values appears to have occurred. This contradicts previous predictions of negligible fair-weather sediment movement on this inner shelf.  相似文献   

The importance of extratropical and tropical cyclones on the short-term evolution of barrier islands along the northern Gulf of Mexico, USA     

Gregory W. Stone  Baozhu Liu  David A. Pepper  Ping Wang 《Marine Geology》2004,210(1-4):63-78

Data are presented indicating the complexity and highly variable response of beaches to cold front passages along the northern Gulf of Mexico, in addition to the impacts of tropical cyclones and winter storms. Within the past decade, an increase in the frequency of tropical storms and hurricanes impacting the northern Gulf has dramatically altered the long-term equilibrium of a large portion of this coast. A time series of net sediment flux for subaerial and nearshore environments has been established for a section of this coast in Florida, and to a lesser extent, Mississippi. The data incorporate the morphological signature of six tropical storms/hurricanes and more than 200 frontal passages.

Data indicate that (1) barrier islands can conserve mass during catastrophic hurricanes (e.g., Hurricane Opal, a strong category 4 hurricane near landfall); (2) less severe hurricanes and tropical storms can promote rapid dune aggradation and can contribute sediment to the entire barrier system; (3) cold fronts play a critical role in the poststorm adjustment of the barrier by deflating the subaerial portion of the overwash terrace and eroding its marginal lobe along the bayside beach through locally generated, high frequency, steep waves; and (4) barrier systems along the northern Gulf do not necessarily enter an immediate poststorm recovery phase, although nested in sediment-rich nearshore environments. While high wave energy conditions associated with cold fronts play an integral role in the evolution and maintenance of barriers along the northern Gulf, these events are more effective in reworking sediment after the occurrence of extreme events such as hurricanes. This relationship is even more apparent during the clustering of tropical cyclones.

It is anticipated that these findings will have important implications for the longer term evolution of barrier systems in midlatitude, microtidal settings where the clustering of storms is apparent, and winter storms are significant in intensity and frequency along the coast.  相似文献   

Cosmogenic-nuclide ages for New England coastal moraines, Martha's Vineyard and Cape Cod, Massachusetts, USA     

Greg Balco  John O.H. Stone  Stephen C. Porter  Marc W. Caffee   《Quaternary Science Reviews》2002,21(20-22)

Cosmogenic-nuclide exposure ages for 13 glacially transported boulders atop the Martha's Vineyard moraine, MA, USA, indicate that the southeastern margin of the Laurentide ice sheet reached its maximum extent during the last glaciation 23,200±500 yr ago. Another 10 age determinations from the younger Buzzards Bay moraine near Woods Hole, MA, indicate that this moraine complex was formed 18,800±400 yr ago. These ages correlate approximately with the terminations of cooling cycles recorded in Greenland ice cores and coeval ice-rafting events, suggesting that the marginal position of this sector of the ice sheet was tightly coupled to North Atlantic climate during the last glacial maximum.  相似文献   

Hydrologic and geomorphic processes in the Colville River delta, Alaska     

H. Jesse Walker  Paul F. Hudson 《Geomorphology》2003,56(3-4):291

The Colville basin drains the North Slope of Alaska and is one of several large Arctic river systems located within permafrost. The timing and style of fluvial processes in the earth's permafrost regions differ from those occurring in midlatitude settings. Moreover, in comparison to temperate-zone systems, rivers located entirely within permafrost perform most of their work during relatively short periods of time. This paper examines river ice hydrology and the resulting geomorphic processes that occur within the Colville delta, Alaska. Fluvial processes and landform development within the Colville delta occur after the flood-pulse is initiated by the breakup of river ice. During this 4-month period, the geomorphic processes are largely influenced by the movement of ice. The flood-pulse and accompanying river ice influences erosional and depositional processes and results in unique styles of sediment transport, deposition, and riverbank erosion.  相似文献   

Uncertainty Analysis of Climate Change and Policy Response   总被引：1，自引：3，他引：1  

Mort Webster  Chris Forest  John Reilly  Mustafa Babiker  David Kicklighter  Monika Mayer  Ronald Prinn  Marcus Sarofim  Andrei Sokolov  Peter Stone  Chien Wang 《Climatic change》2003,61(3):295-320

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Using Hydrogeochemical Methods To Evaluate Complex Quaternary Subsurface Stratigraphy Block Island,Rhode Island,USA     

Anne I. Veeger  Byron D. Stone 《Hydrogeology Journal》1996,4(4):69-82

One of the major problems in hydrogeologic investigations of glaciated regions is the determination of complex stratigraphic relationships in the subsurface where insufficient information is available from drilling and geophysical records. In this paper, chemical characteristics of groundwater were used to identify stratigraphic changes in glacial deposits that were previously inferred on Block Island, Rhode Island, USA, an emergent remnant of the late Wisconsinan terminal moraine, located approximately 16 km south of the Rhode Island mainland. Two chemically distinct water types are recognized on the island: 1) high-iron, characterized by dissolved silica levels in excess of 20 mg/L, bicarbonate greater than 30 mg/L and dissolved iron ranging from 1-20 mg/L; and 2) low-iron, characterized by dissolved silica levels below 16 mg/L, bicarbonate less than 30 mg/L, and less than 0.3 mg/L dissolved iron. The spatial distribution of iron-bearing minerals and organic matter and the resulting redox conditions are believed to control the occurrence of high-iron groundwater. The high-iron waters occur almost exclusively in the eastern half of the island and appear to coincidence with the presence of allochthonous blocks of Cretaceous-age coastal-plain sediments that were incorporated into Pleistocene-age deposits derived from the Narragansett Bay-Buzzard's Bay lobe of the Late Wisconsinan Laurentide ice sheet. The low-iron waters occur in the western half of the island, where the occurrence of these Cretaceous-age blocks is rare and the sediments are attributed to a sublobe of the Hudson-Champlain lobe of the Late Wisconsinan ice-sheet. RÉSUMÉ: L'un des principaux problèmes dans les études hydrogeologiques des régions qui ont été englacées est la définition des relations stratigraphiques complexes sous la surface, lá où les informations fournies par les forages et par la géophysique sont insuffisantes. Dans l'exemple traité, les caractéristiques chimiques de l'eau souterraine sont utilisées pour identifier les variations stratigraphiques dans les dépôts glaciaires qui avaient auparavant été supposées, sur l'île de Block (Rhode Island), restes émergeant d'une moraine terminale du Wisconsinien récent, situé à environ 16 km au sud de Rhode Island. Deux types d'eau chimiquement distincts ont été reconnus dans l'île: 1) à fortes teneurs en fer, caractérisées par des concentrations en silice supérieures à 20 mg/L, en bicarbonates supérieures à 30 mg/L et en fer comprises entre 1 et 20 mg/L; et 2) à faibles teneurs en fer, marquées par des concentrations en silice inférieures à 16 mg/L, en bicarbonate inférieures à 30 mg/L et en fer dissous inférieures à 0.3 mg/L. La distribution spatiale des minéraux riches en fer et de la matière organique et les conditions redox résultantes contrôlent probablement la présence de fer dans les eaux souterraines à fortes concentrations. Les eaux à fortes teneurs en fer sont connues presque exclusivement dans la moitié orientale de l'île et semblent coïncider avec la présence de blocs allochtones provenant des sédiments côtiers crétacés, introduits dans les formations pléistocènes liées au lobe glaciaire des baies de Narragansett et du Busard de la calotte glaciaire laurentide du Wisconsinien récent. Les eaux à faibles teneurs en fer apparaissent dans la moitié occidentale de l'île, là où ces blocs de Crétacé sont rares et où les sédiments sont attrbués à une digitation du lobe de l'Hudson-Champlain de la calotte glaciaire du Wisconsinien récent. RESUMEN: Uno de los mayores problemas en la investigación hidrogeológica en regiones glaciares es la determinación de las complejas relaciones estratigráficas en el subsuelo, donde la información procedente de registros de perforaciones y de geofísica no es suficiente. En este artículo, se han usado las características químicas del agua subterránea para identificar unos cambios estratigráficos que se habían predicho previamente en unos depósitos glaciares en Block Island, Rhode Island (Estados Unidos), un remanente emergente de la morrena terminal del Winsconsiniense tardío, situada unos 16 km al sur de la Rhode Island continental. En la isla se encuentran dos tipos de agua distintos: 1) de alto contenido en hierro, caracterizada por niveles de sílice disuelto superando los 20 mg/L, bicarbonatos por encima de 30 mg/L y hierro disuelto oscilando entre 1-20 mg/L; y 2) de bajo contenido en hierro, caracterizada por niveles de sílice disuelto inferiores a 16 mg/L, bicarbonatos por debajo de 30 mg/L y menos de 0.3 mg/L de hierro disuelto. La distribución espacial de los minerales ricos en hierro y de la materia orgánica, así como las condiciones redox resultantes se supone que condicionan la presencia de aguas de alto contenido en hierro. Estas aguas aparecen casi exclusivamente en la mitad oriental de la isla y parecen coincidir con la presencia de bloques alóctonos de sedimentos costeros, de edad cretácica, que se incorporaron a los depósitos de edad pleistocena procedentes del lóbulo de la Bahía de Narragansett-Bahía de Buzzard, correspondiente a la capa glaciar del Winsconsiniense-Lauréntido tardío. Las aguas de bajo contenido en hierro aparecen en la mitad occidental de la isla, donde la presencia de estos sedimentos de edad cretácica es rara y los sedimentos se suponen procedentes de un sublóbulo del lóbulo de Hudson-Camplain, correspondiente a la capa glaciar del Winsconsiniense tardío.  相似文献   

Evaluating the influence of landform, surficial geology, and land use on streams using hydrologic simulation modeling   总被引：1，自引：0，他引：1  

Jesse D. Schomberg  George Host  Lucinda B. Johnson  Carl Richards 《Aquatic Sciences - Research Across Boundaries》2005,67(4):528-540

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Early Permian climate change in the Falkland Islands     

Phil Stone  Kate Horan 《Geology Today》2016,32(3):107-114

An Early Permian glacial diamictite forms a distinctive unit within the Falkland Islands sedimentary succession and two aspects of its significance have recently been serendipitously enhanced. Fossil discoveries in exotic limestone clasts bear on palaeogeography, whilst a series of mineral‐exploration borehole cores have allowed a detailed study of the sedimentary record of deglaciation that followed deposition of the diamictite. Statistical analysis of reflectance and XRF core‐scanning data has identified likely Milankovitch periodicities and enabled tentative time‐scale modelling. The ‘icehouse to greenhouse’ transition appears to have spanned approximately 1.2 million years, with waning cycles of re‐advance superimposed on overall glacial retreat. The new results play into a long‐debated geological paradox: although the Falkland Islands are now proximal to the South Atlantic coastline of South America, their geology bears an uncanny resemblance to that of the Cape Fold Belt and Karoo Basin in South Africa. This puzzled the geological pioneers, but became readily explicable when first continental drift and then plate tectonics were invoked to reconstruct the break‐up of the Gondwana supercontinent—although the details remain controversial. One of the key stratigraphical correlation levels throughout the major fragments of southern Gondwana—South Africa, South America, Antarctica and Australia—is the glacigenic deposit left behind by the extensive, Late Carboniferous to Early Permian regional glaciation; in the Falkland Islands it is designated the Fitzroy Tillite Formation.  相似文献   

The influence of weather extremes on the spatial correlation of corn yields     

Jesse B. Tack  Matthew T. Holt 《Climatic change》2016,134(1-2):299-309

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Identification of Uranyl Minerals Using Oxygen K‐Edge X‐Ray Absorption Spectroscopy          下载免费PDF全文

Jesse D. Ward  Mark Bowden  C. Tom Resch  Steven Smith  Bruce K. McNamara  Edgar C. Buck  Gregory C. Eiden  Andrew M. Duffin 《Geostandards and Geoanalytical Research》2016,40(1):135-148

Although most of the world's uranium exists as pitchblende or uraninite, this mineral can be weathered to a great variety of secondary uranium minerals, most containing the uranyl cation. Anthropogenic uranium compounds can also react in the environment, leading to spatial–chemical alterations that could be useful for nuclear forensics analyses. Soft X‐ray absorption spectroscopy (XAS) has the advantages of being non‐destructive, element‐specific and sensitive to electronic and physical structure. The soft X‐ray probe can also be focused to a spot size on the order of tens of nanometres, providing chemical information with high spatial resolution. However, before XAS can be applied at high spatial resolution, it is necessary to find spectroscopic signatures for a variety of uranium compounds in the soft X‐ray spectral region. To that end, we collected the near edge X‐ray absorption fine structure (NEXAFS) spectra of a variety of common uranyl‐bearing minerals, including uranyl carbonates, oxyhydroxides, phosphates and silicates. We find that uranyl compounds can be distinguished by class (carbonate, oxyhydroxide, phosphate or silicate) based on their oxygen K‐edge absorption spectra. This work establishes a database of reference spectra for future spatially resolved analyses. We proceed to show scanning X‐ray transmission microscopy (STXM) data from a schoepite particle in the presence of an unknown contaminant.  相似文献