Diatom biostratigraphy of tsunami deposits: Examples from the 1998 Papua New Guinea tsunami     

Sue Dawson   《Sedimentary Geology》2007,200(3-4):328-335

Distinctive diatom assemblages may be associated with tsunami sediments and may often contrast with the assemblages found within sediments underlying the tsunami deposit as well as those associated with the modern coastal environment. Sediments associated with the 1998 tsunami that destroyed much of the Sissano lagoon area in northern Papua New Guinea have been investigated. Surface sediments from three transects across the sediment spit near Warapu have been examined for diatom content and preservation. The preservation is variable, and the data show an, often chaotic, assemblage that can be attributed to the tsunami waves incorporating and depositing diatoms from distinctive habitat zones during their runup and subsequent backwash. The diatoms identified within the Warapu sediments indicate an origin from within the inter-tidal and offshore area rather than from the beach–sand spit complex. The sand deposits disclose a high percentage, in excess of 75%, of broken diatom valves, and a predominance of centric (circular) species due to preferential preservation. The study demonstrates that the application of diatom biostratigraphy to modern tsunami deposits can be used in conjunction with other stratigraphical lines of evidence to interpret the source and provenance of historical and palaeo-tsunami deposits.  相似文献   

The representer method for two-phase flow in porous media     

John Baird  Clint Dawson 《Computational Geosciences》2007,11(3):235-248

The representer method is applied to a one-dimensional two-phase flow model in porous media; capillary pressure and gravity are neglected. The Euler–Lagrange equations must be linearized, and one such linearization is presented here. The representer method is applied to the linear system iteratively until convergence, though a rigorous proof of convergence is out of reach. The linearization chosen is easy to calculate but does not converge for certain weights; however, a simple damping restores convergence at the cost of extra iterations. Numerical experiments are performed that illustrate the method, and quick comparison to the ensemble Kalman smoother is made. This research was supported by NSF grant EIA-0121523.  相似文献   

The ocean-coast effect re-examined     

U. Raval  J. T. Weaver  T. W. Dawson 《Geophysical Journal International》1981,67(1):115-123

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Thermal radiation properties of Apollo 14 fines     

Richard C. Birkebak  James P. Dawson 《Earth, Moon, and Planets》1973,6(1-2):93-99

The thermal radiation properties as a function of bulk density, angle of illumination and wavelength are presented for lunar fines from the Apollo 14 mission. The density range covered is from 1095 kg/m³ to 1590 kg/m³ and a wavelength range of 0.36–14.5 μm. The solar albedo and total emittance were calculated from spectral values and are compared to Apollo 11 and 12 values.  相似文献   

The determination of α-amino acids in seawater using a fluorimetric analyser     

Rodger Dawson  Richard Gary Pritchard 《Marine Chemistry》1978,6(1):27-40

A method is described for the detection of free α-amino acids in the picomole range in seawater samples of less than 100 ml volume. The modifications made to a standard amino acid analyser to incorporate a fluorimetric detection system are described in detail, together with the methods for desalting the seawater samples on cation exchange resin and the concentration procedures prior to analysis. A complete analysis of up to 30 amino acids requires around 3 h with a detection limit of around 0.05 μg of an individual acid per litre. Twenty samples of seawater from different depths in the open Baltic have been analysed for their FAA contents together with 3 samples taken from the Kiel Fjord. The total FAA content of the samples ranges from 4.5 to 84 μg/l with a mean of around 25 μg/l. Five samples were hydrolysed prior to analysis in order to estimate the CAA content of the seawater. The values lay in the range 438–805 μg/l.  相似文献   

Godunov Mixed Methods on Triangular Grids for Advection–Dispersion Equations     

A. Mazzia  L. Bergamaschi  C.N. Dawson  M. Putti 《Computational Geosciences》2002,6(2):123-139

A time-splitting approach for advection–dispersion equations is considered. The dispersive and advective fluxes are split into two separate partial differential equations (PDEs), one containing the dispersive term and the other one the advective term. On triangular elements a triangle-based high resolution Finite Volume (FV) scheme for advection is combined with a Mixed Hybrid Finite Element (MHFE) technique to solve dispersion. This approach introduces an error proportional to the time step and the overall scheme is only first order accurate if special care is not taken in the definition of the numerical flux approximation for advection. By incorporating the diffusive effects into the definition of this numerical flux, near second order accuracy (up to a logh factor) can be proved theoretically and validated by numerical experiments in both one- and two-dimensional cases.  相似文献   

Tsunami Deposits   总被引：1，自引：0，他引：1  

A. G. Dawson  S. Shi 《Pure and Applied Geophysics》2000,157(6-8):875-897

—Geological investigations of coastal sediments indicate that prehistoric tsunamis can be identified. Their characterisation has altered our knowledge of the past frequency and magnitude of tsunamis for different areas of the world. Yet there have been relatively few geological studies of modern tsunamis with virtually no direct observations of the processes associated with tsunami sediment transport and deposition. This paper discusses these issues and draws on the results of recent research to summarise our current knowledge on the nature of tsunami deposits.  相似文献   

Cosmic rays from the galactic center     

R. W. Clay  B. R. Dawson  J. Bowen  M. Debes 《Astroparticle Physics》2000,12(4)

We examine the possibility that recent data on cosmic ray anisotropies presented by the AGASA group may lead to the conclusion that our Galactic Center is a major source of the highest energy cosmic rays in our galaxy. We discuss how such a source would contribute to the magnitude and directional properties of the observed flux when measured against a background of extragalactic cosmic rays. We do this using the results of previous propagation calculations and our own more recent calculations which are specifically for a Galactic Center source.We find that the AGASA data can indeed be plausibly interpreted in this way and also that an argument can be made that the Galactic Center has the appropriate physical properties for acceleration to energies of the order of 10¹⁸ eV. We show that data from the SUGAR array are compatible with the AGASA result.  相似文献   

Holocene relative sea‐level changes in Harris,Outer Hebrides,Scotland, UK     

Jason T. Jordan  David E. Smith  Sue Dawson  Alastair G. Dawson 《第四纪科学杂志》2010,25(2):115-134

Evidence for relative sea‐level changes during the middle and late Holocene is examined from two locations on the Atlantic coast of Harris, Outer Hebrides, Scotland, using morphological mapping and survey, stratigraphical, grain size and diatom analysis, and radiocarbon dating. The earliest event identified is a marine flood, which occurred after 7982–8348 cal. a (7370 ± 80 ¹⁴C a) BP, when the sea crossed a threshold lying at ?0.08 m Ordnance Datum Newlyn (OD) (?2.17 m mean high water springs (MHWS)) before withdrawing. This could have been due to a storm or to the Holocene Storegga Slide tsunami. By 6407–6122 cal. a (5500 ± 60 ¹⁴C a) BP, relative sea levels had begun to fall from a sandflat surface with an indicated MHWS level of between 0.08 and ?1.96 m (?2.01 to ?4.05 m). This fall reached between ?0.30 and ?2.35 m (?2.39 to ?4.44 m) after 5841–5050 cal. a (4760 ± 130 ¹⁴C a) BP, but was succeeded by a relative sea‐level rise which reached between 0.54 and ?1.57 m (?1.55 to ?3.66 m) by 5450–4861 cal. a (4500 ± 100 ¹⁴C a) BP. This rise continued, possibly with an interruption, until a second sandflat surface was reached between 2.34 and ?0.26 m (0.25 to ?2.35 m) between 2952–3375 cal. a (3000 ± 80 ¹⁴C a) and 1948–2325 cal. a (2130 ± 70 ¹⁴C a) BP, before present levels were reached. The regressive episode from the earliest sandflat is correlated with the abandonment of the Main Postglacial Shoreline. It is maintained that the fluctuations in relative sea level recorded can be correlated with similar events elsewhere on the periphery of the glacio‐isostatic centre and may therefore reflect secular changes in nearshore sea surface levels. Despite published evidence from trim lines of differential ice sheet loading across the area, no evidence of variations in uplift between the locations concerned could be found. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Changing sea ice conditions and marine transportation activity in Canadian Arctic waters between 1990 and 2012   总被引：2，自引：0，他引：2  

Larissa Pizzolato  Stephen E. L. Howell  Chris Derksen  Jackie Dawson  Luke Copland 《Climatic change》2014,123(2):161-173

Declining sea ice area in the Canadian Arctic has gained significant attention with respect to the prospect of increased shipping activities. To investigate relationships between recent declines in sea ice area with Arctic maritime activity, trend and correlation analysis was performed on sea ice area data for total, first-year ice (FYI), and multi-year ice (MYI), and on a comprehensive shipping dataset of observed vessel transits through the Vessel Traffic Reporting Arctic Canada Traffic Zone (NORDREG zone) from 1990 to 2012. Links to surface air temperature (SAT) and the satellite derived melt season length were also investigated. Between 1990 and 2012, statistically significant increases in vessel traffic were observed within the NORDREG zone on monthly and annual time-scales coincident with declines in sea ice area (FYI, MYI, and total ice) during the shipping season and on a monthly basis. Similarly, the NORDREG zone is experiencing increased shoulder season shipping activity, alongside an increasing melt season length and warming surface air temperatures (SAT). Despite these trends, only weak correlations between the variables were identified, although a step increase in shipping activity is apparent following the former summer sea ice extent minimum in 2007. Other non-environmental factors have also likely contributed to the observed increase in Arctic shipping activity within the Canadian Arctic, such as tourism demand, community re-supply needs, and resource exploration trends.  相似文献