Assessing the Validity of Seismo-Acoustic Predictor Equations for Obtaining Seabed and Sub-Surface Sediment Physical Properties     

Arne Schnack-Friedrichsen  Angela M. Davis  Jim D. Bennell  Dei G. Huws 《Marine Georesources & Geotechnology》2001,19(4):221-243

The interdependence between the seismo-acoustic properties of a marine sediment and its geotechnical/physical parameters has been known for many years, and it has been postulated that this should allow the extraction of geotechnical information from seismic data. Though in the literature many correlations have been published for the surficial layer, there is a lack of information for greater sediment depths. In this article, a desktop study on a synthetic seafloor model illustrates how the application of published near-surface prediction equations to subsurface sediments (up to several tens of meters burial depth) can lead to spurious predictions. To test this further, acoustic and geotechnical properties were measured on a number of sediment core samples, some of which were subjected to loading in acoustically-equipped consolidation cells (oedometers) to simulate greater burial depth conditions. For low effective pressures (representing small burial depths extending to around 10 meters subsurface), the general applicability of established relationships was confirmed: the prediction of porosity, bulk density, and mean grain size from acoustic velocity and impedance appears generally possible for the investigated sedimentary environments. As effective pressure increases through, the observed relationships deviate more and more from the established ones for the near-surface area. For the samples tested in this study, in some instances increasing pressure even resulted in decreasing velocities. There are several possible explanations for this abnormal behavior, including the presence of gas, overconsolidation, or bimodal grain size distribution. The results indicate that an appropriate depth correction must be introduced into the published prediction equations in order to obtain reliable estimates of physical sediment properties for greater subsurface depths.  相似文献   

The measurement of marine geothermal heat flow by a multipenetration probe with digital acoustic telemetry and insitu thermal conductivity     

R. D. Hyndman  E. E. Davis  J. A. Wright 《Marine Geophysical Researches》1979,4(2):181-205

The design and use of a marine heat probe with capability for measuring thermal conductivity insitu with high accuracy, and providing digital acoustic transmission of data to the ship, is described. The instrument employs the violin bow strength member and parallel sensor string configuration suggested by C. R. B. Lister. Several hundred measurements have been made in the deep ocean on multipenetration or pogostick profiles using a 3 m probe and in deep inlets of western Canada using a 7 m probe. The insitu thermal conductivity technique using a calibrated heat pulse has been studied in detail through laboratory calibration of the probe in materials of known conductivity, through numerical models, and through comparison of insitu measurements with needle probe measurements on sediment cores taken from the same sites. The insitu technique permits a conductivity accuracy of better than ±5% with a recording time of 7 minutes following 7 minutes in the bottom to establish the geothermal gradient. The pulse heating is also more energy efficient than the conventional continuous heating technique.Contribution from the Earth Physics Branch No. 807.  相似文献   

Geologic development and morphodynamics of Egmont Key, Florida     

Jennifer K. Stott  Richard A. Davis  Jr.   《Marine Geology》2003,200(1-4):61-76

Egmont Key is a small, elongate island located on the huge ebb-tidal delta at the mouth of Tampa Bay, FL, USA. The multiple sets of intersecting beach/dune ridges that comprise the low-lying island indicate several periods of growth spaced between periods of erosion. The island has experienced considerable expansion and erosion during recorded history. The oldest of these ridges represents accumulation that took place about 1000 years before the present. Over the past century of well-documented change, there has been a general reduction in the area of the island as the result of extended periods of erosion punctuated by short accretion periods. The net change during this period has been a loss of approximately 40% of the area of the island. A 1-year, time-series monitoring of the Egmont shoreline during 1996–1997 showed sediment loss of 26 500 m³, while the annual average over the period of 1877–1996 was only 3360 m³. A single storm is responsible for most of this loss leading to the conclusion that the island is storm-dominated. Inferences from time intervals during which hurricanes took place support this conclusion. This island provides a major contrast in its coastal location, development and stratigraphy as compared to typical barrier islands. There is no underlying sediment deposited in shallow, paralic environments. The development of the island was lateral rather than having a vertical component through time, partly because of its relatively young age but also because of its position on a thick, ebb-tidal delta sand body.  相似文献   

Nutrient Dynamics in Vegetated and Unvegetated Areas of a Southern Everglades Mangrove Creek     

S. E. Davis  III  D. L. Childers  J. W. Day  Jr  D. T. Rudnick  F. H. Sklar 《Estuarine, Coastal and Shelf Science》2001,52(6):753

Flow-through flumes were used to quantify net areal fluxes of nutrients in the fringe mangrove zone of lower Taylor River in the southern Everglades National Park. We also quantified net areal fluxes along the open water portion of the channel to determine the relative importance of either zone (vegetated vs. unvegetated) in the regulation of nutrient exchange in this system. Taylor River's hydrology is driven mainly by precipitation and wind, as there is little influence of tide. Therefore, quarterly samplings of the vegetated and unvegetated flumes were slated to include typical wet season and dry season periods, as well as between seasons, over a duration of two years. Concentrations of dissolved and total organic carbon (DOC and TOC) were highest during the wet season and similar to one another throughout the study, reflecting the low particulate loads in this creek. Dissolved inorganic nitrogen (nitrate+nitrite+ammonium) was 10–15% of the total nitrogen (TN) content, with NO−x and NH+4 showing similar concentration ranges over the 2-year study. Soluble reactive phosphorus (SRP) was usually <0·05μM, while total phosphorus (TP) was typically an order of magnitude higher. Net areal fluxes were calculated from nutrient concentration change over the length of the flumes. Most flux occurred in the vegetated zone. Dissolved inorganic nitrogen and DOC were usually taken up from the water column; however, we saw no seasonal pattern for any constituent over the course of this study. Total nutrients (TOC, TN, and TP) showed little net exchange and, like SRP, had fluxes that shifted irregularly throughout the study. Despite the lack of a clear seasonal pattern, there was a great deal of consistency between vegetated flumes, especially for NO−x and NH+4, and fluxes in the vegetated flumes were generally in the same direction (import, export, or no net flux) during a given sampling. These findings suggest that the fringe mangrove zone is of considerable importance in regulating nutrient dynamics in lower Taylor River. Furthermore, the influence of this zone may at times extend into northeast Florida Bay, as the bay is the primary recipient of water and nutrients during the wet season.  相似文献   

Salt marsh geomorphology: Physical and ecological effects on landform   总被引：1，自引：0，他引：1  

Raymond Torres  Sergio Fagherazzi  Danika vanProosdij  Charles Hopkinson   《Estuarine, Coastal and Shelf Science》2006,69(3-4):309

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Morphodynamics of the barrier-inlet system, west-central Florida     

Richard A. Davis  Jr.  Patrick Barnard 《Marine Geology》2003,200(1-4):77-101

The barrier-inlet system along the Gulf Coast of peninsular Florida has one of the most diverse morphologies of any barrier system in the world. The delicate balance between tidal- and wave-generated processes on this low-energy coast permits only slight changes in either of these processes to result in significant and rapidly developing morphologic responses. Some of these responses are the result of natural phenomena such as hurricanes opening tidal inlets, closure of inlets due to longshore transport of sediment, and changes in the availability of sediment. Tidal prism is the primary factor in controlling inlet morphology and is greatly influenced by anthropogenic activities in the backbarrier area. Human activity has also modified the coast in many ways over the past several decades, beginning with the construction of the first causeways in the 1920s. The various modifications by development have resulted in important morphodynamic changes in the barrier-inlet system. These include hardening the coast on the beach and at inlets, dredging and filling in backbarrier environments, and construction of fill-type causeways connecting the islands to the mainland. Construction of seawalls and jetties has inhibited normal coastal processes. Examples include the downdrift erosion at Blind Pass and Big Sarasota Pass. Construction of fill-type causeways between the barriers and the mainland has created artificial tidal divides that reduce the tidal prism at some inlets, thereby resulting in instability or closure such as Blind Pass and Dunedin Pass. This is further exacerbated by dredge and fill construction that reduces tidal prism by reducing the area of open water in the backbarrier. Dredging of the Intracoastal Waterway also results in a negative impact on selected inlets by channeling tidal flux away from some inlets. Impacts of these changes inhibit the barrier/inlet environments from responding to open coast processes.  相似文献   

Seasonal trends in the abundance, composition and bioavailability of particulate and dissolved organic matter in the Chukchi/Beaufort Seas and western Canada Basin     

Jenny Davis  Ronald Benner 《Deep Sea Research Part II: Topical Studies in Oceanography》2005,52(24-26):3396

The objectives of this study were to investigate the seasonality, abundance, sources and bioreactivity of organic matter in the water column of the western Arctic Ocean. The concentrations of particulate and dissolved amino acids and amino sugars, as well as bulk properties of particulate and dissolved organic matter (DOM), were measured in shelf, slope and basin waters collected during the spring and summer of 2002. Particulate organic matter concentrations in shelf waters increased by a factor of 10 between spring and summer. Dissolved organic carbon (DOC) and nitrogen (DON) concentrations exhibited only minor seasonal variations, whereas dissolved amino acid concentrations doubled between spring and summer, and dissolved amino sugars increased by 31% in shelf waters of the Chukchi and Beaufort Seas. Concentrations of DOC did not exhibit a significant seasonal change in surface waters of the Canada Basin, but dissolved amino acid concentrations increased by 45% between spring and summer. No significant seasonal differences were detected in the concentration or composition of DOM in waters below 100 m in depth. Concentrations of particulate and dissolved amino acids and amino sugars were strongly correlated with chlorophyll-a, indicating a plankton source of freshly produced organic matter. The amino acid and amino sugar compositions of freshly produced DOM indicated that a large portion of this material is bioavailable. While freshly produced DOM was found to be relatively bioreactive, preformed DOM in the Arctic appears to be less bioreactive but similar in degradation state to average DOM in the Atlantic and Pacific. These data demonstrate substantial summer production of POM and DOM on the Chukchi and Beaufort shelves that is available for utilization in shelf waters and export to the Canada Basin.  相似文献   

Report of the committee on the nomenclature of faults     

H. F. Reid  W. M. Davis  A. C. Lawson  F. L. Ransome 《International Journal of Earth Sciences》1914,5(4):299-301

Ohne Zusammenfassung

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Report of the committee on the nomenclature of faults

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Excursion to Keston,Kent, and Fairchildes,Surrey: Saturday,April 30th, 1927     

A.G. Davis 《Proceedings of the Geologists' Association. Geologists' Association》1929,40(1):103-104

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On the fish fauna of the Yorkshire Coal Field     

James W. Davis 《Proceedings of the Geologists' Association. Geologists' Association》1880,6(8):359-370

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