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341.
Seanpaul La Selle Bruce M. Richmond Bruce E. Jaffe Alan R. Nelson Frances R. Griswold Maria E. M. Arcos Catherine Chagué James M. Bishop Piero Bellanova Haunani H. Kane Brent D. Lunghino Guy Gelfenbaum 《Sedimentology》2020,67(3):1249-1273
Over the past 200 years of written records, the Hawaiian Islands have experienced tens of tsunamis generated by earthquakes in the subduction zones of the Pacific ‘Ring of Fire’ (for example, Alaska–Aleutian, Kuril–Kamchatka, Chile and Japan). Mapping and dating anomalous beds of sand and silt deposited by tsunamis in low-lying areas along Pacific coasts, even those distant from subduction zones, is critical for assessing tsunami hazard throughout the Pacific basin. This study searched for evidence of tsunami inundation using stratigraphic and sedimentological analyses of potential tsunami deposits beneath present and former Hawaiian wetlands, coastal lagoons, and river floodplains. Coastal wetland sites on the islands of Hawai΄i, Maui, O΄ahu and Kaua΄i were selected based on historical tsunami runup, numerical inundation modelling, proximity to sandy source sediments, degree of historical wetland disturbance, and breadth of prior geological and archaeological investigations. Sand beds containing marine calcareous sediment within peaty and/or muddy wetland deposits on the north and north-eastern shores of Kaua΄i, O΄ahu and Hawai΄i were interpreted as tsunami deposits. At some sites, deposits of the 1946 and 1957 Aleutian tsunamis are analogues for deeper, older probable tsunami deposits. Radiocarbon-based age models date sand beds from three sites to ca 700 to 500 cal yr bp , which overlaps ages for tsunami deposits in the eastern Aleutian Islands that record a local subduction zone earthquake. The overlapping modelled ages for tsunami deposits at the study sites support a plausible correlation with an eastern Aleutian earthquake source for a large prehistoric tsunami in the Hawaiian Islands. 相似文献
342.
Palynological studies undertaken in the mountainous regions of the northwest of the Iberian Peninsula are few in number and have been concerned largely with the second half of the Holocene. New pollen data from two Galician sierras, the Courel and Queixa Sierras, provide a 10000‐yr record of vegetation and climate change. In the Courel Sierra before 9750 yr BP, Laguna Lucenza (1420 m a.s.l.) reflects a period of open landscape covered by Poaceae and heliophilous plants, which may be correlated with the Younger Dryas. The onset of the Holocene is characterised by the expansion of oak woodland, prior to 9300 yr BP, following a short phase of birch along with the gradual decline of pine. The oak values reach a peak at 8350 ± 80 yr BP. Towards 8800 yr BP Corylus begins to expand, followed by Alnus (7500 yr BP) and Ulmus. During this period, the Fraga pollen assemblage (Queixa Sierra, 1360 m a.s.l.) indicates Betula woodland surrounding the site, masking the regional predominance of oak. After 5000 yr BP there is a gradual decrease in arboreal pollen values in both Sierras. Castanea appears in Laguna Lucenza (Courel Sierra) at 4075 ± 75 yr BP. There is widespread deforestation during the last 4000 yr. During this period the presence of large quantities of microcharcoal particles points to the occurrence of fire. The reduction in forest is associated with the arrival of cultivation at 4000 yr BP at low altitudes in the Queixa Sierra. At higher altitudes the first agricultural activity is dated at later than 2000 yr BP. This coincides with the first record of cereal cultivation at high altitude in the Courel Sierra. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
343.
Riccardo Camattari Marco Romagnoni Andrea Mazzolari Gianfranco Paternò Vincenzo Guidi Thomas Buslaps 《Experimental Astronomy》2018,46(2):309-321
In this paper we report progresses in the realization of self-standing bent crystals, which are suitable as optical elements for Laue lenses, i.e. for optic to focus hard X-rays in the 100–1000 keV energy range. The curvature of the crystals is a key factor to enhance diffraction efficiency and energy bandpass for such an optic. In particular, two bent crystals featuring a thickness of 5 mm, made of Si and Ge respectively, were produced at the Sensor and Semiconductor Laboratory in Ferrara, Italy. The crystals were bent through the application of a carbon fibre composite. This proved to be a relatively low cost method for crystal bending, suitable for mass production. The manufactured samples were characterised via optical interferometry, and showed a fairly uniform curvature. Finally, the samples were tested exploiting hard X-ray diffraction at the ID11 facility of the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. A careful analysis of the experimental data highlighted that the samples feature large energy bandpass, wide geometrical acceptance for incoming hard X-rays, and high diffraction efficiency. We therefore conclude that such self-standing crystals are good candidates as Laue lens components for astrophysics applications. 相似文献
344.
Jonathan Deborde Pierre Anschutz Frédéric Guérin Dominique Poirier Danielle Marty Guy Boucher Gérard Thouzeau Mathieu Canton Gwenaël Abril 《Estuarine, Coastal and Shelf Science》2010
The Arcachon lagoon is a 156 km2 temperate mesotidal lagoon dominated by tidal flats (66% of the surface area). The methane (CH4) sources, sinks and fluxes were estimated from water and pore water concentrations, from chamber flux measurements at the sediment–air (low tide), sediment–water and water–air (high tide) interfaces, and from potential oxidation and production rate measurements in sediments. CH4 concentrations in waters were maximal (500–1000 nmol l−1) in river waters and in tidal creeks at low tide, and minimal in the lagoon at high tide (<50 nmol l−1). The major CH4 sources are continental waters and the tidal pumping of sediment pore waters at low tide. Methanogenesis occurred in the tidal flat sediments, in which pore water concentrations were relatively high (2.5–8.0 μmol l−1). Nevertheless, the sediment was a minor CH4 source for the water column and the atmosphere because of a high degree of anaerobic and aerobic CH4 oxidation in sediments. Atmospheric CH4 fluxes at high and low tide were low compared to freshwater wetlands. Temperate tidal lagoons appear to be very minor contributor of CH4 to global atmosphere and to open ocean. 相似文献
345.
Growth modelling indicates hurricanes and severe storms are linked to low coral recruitment in the Caribbean 总被引:2,自引:2,他引:0
Crabbe MJ Martinez E Garcia C Chub J Castro L Guy J 《Marine environmental research》2008,65(4):364-368
This study set out to test the hypothesis that hurricanes and tropical storms limit the recruitment and subsequent survival of massive non-branching corals on the barrier reef off the coast of Belize in the Gulf of Honduras. Overall, the surface areas of 523 individual coral specimens were measured, and recruitment dates were then modelled. There was no significant difference in coral cover or coral biodiversity between any of the sites studied (p > 0.1). There were significant differences in non-branching coral recruitment in years when hurricanes impacted the area (p < 0.05) compared with years when no hurricanes impacted the area. There were significantly more non-branching massive corals recruited in non-hurricane years (mean 7.7) than in hurricane years (mean 3.8; p = 0.011). When years with tropical storms are added to the years with hurricanes, there was significantly lower coral recruitment (mean 4.7) relative to non-storm or hurricane years (mean 7.4; p = 0.019). These results show that hurricanes and severe storms limited the recruitment and survival of massive non-branching corals of the Mesoamerican barrier reef and on patch reefs near the Belize coast in the Caribbean, and suggests that marine park managers may need to assist coral recruitment in years where there are hurricanes or severe storms. 相似文献
346.
347.
Pierre ROCHETTE Jérôme GATTACCECA Michèle BOUROT‐DENISE Guy CONSOLMAGNO Luigi FOLCO Tomas KOHOUT Lauri PESONEN Leonardo SAGNOTTI 《Meteoritics & planetary science》2009,44(3):405-427
Abstract— A database of magnetic susceptibility measurements of stony achondrites (acapulcoite‐lodranite clan, winonaites, ureilites, angrites, aubrites, brachinites, howardite‐eucrite‐diogenite (HED) clan, and Martian meteorites, except lunar meteorites) is presented and compared to our previous work on chondrites. This database provides an exhaustive study of the amount of iron‐nickel magnetic phases (essentially metal and more rarely pyrrhotite and titanomagnetite) in these meteorites. Except for ureilites, achondrites appear much more heterogeneous than chondrites in metal content, both at the meteorite scale and at the parent body scale. We propose a model to explain the lack of or inefficient metal segregation in a low gravity context. The relationship between grain density and magnetic susceptibility is discussed. Saturation remanence appears quite weak in most metal‐bearing achondrites (HED and aubrites) compared to Martian meteorites. Ureilites are a notable exception and can carry a strong remanence, similar to most chondrites. 相似文献
348.
According to historical reports, the north-eastern coastal sector of the volcanic Pantelleria Island (Sicily Channel, Italy) was uplifted up to 1.0 m a.s.l. in the year preceding the October 1891 offshore eruptive event. To better understand the nature and timing of coastal uplift, a detailed survey of morphological and biological indicators of raised palaeo-shorelines has been carried out along the island coastline. This survey identified raised palaeo-shoreline levels at three elevation ranges: 2.5–4.2 m a.s.l. (highest), 1.5–2.7 m a.s.l. (intermediate) and 0.4–1.0 m a.s.l. (lowest). Radiocarbon dating on samples of corals and vermetids placed tight temporal constraints on the uplifting of the raised shorelines. In general, they indicate that the north-eastern sector of the island, centred on the area of Cala del Gadir, has undergone major uplifting, tilting the island towards the southwest from 900 years ago. Applying accurate corrections for sea-level variations, the total amount of volcano-tectonic uplift can be estimated. Uplift rates up to 5 mm/a suggest that the vertical deformation was caused by inflation processes related to magmatic intrusion along feeding fissures. 相似文献
349.
High-resolution δ18O and δ13C records obtained from seven cores were drilled from ledges of the reef builder gastropod Dendropomapetreaum and used to reconstruct variations in the Levantine basin sea surface temperature, hydrology and productivity during the past 500 years. The δ18O of the aragonite shell of living D. petreaum indicate that skeletal deposition occurs under isotopic equilibrium and faithfully record the temperature and surface water δ18O during summer and autumn. The mean down core δ18O record clearly captures global and local climatic events, such as the Little Ice Age (LIA) and the recent warming of surface waters in the Eastern Mediterranean. Comparison to the Western Mediterranean vermetid δ18O record reveals changes in the freshwater/evaporation budgets of the two basins during cold and warm periods. The Eastern basin had lower surface temperatures and excess evaporation during the LIA and experienced a relatively larger warming and/or a decrease in freshwater/evaporation during the past 70 years. The D. petraeum δ13C is strongly related to δ13C of dissolved inorganic carbon and to the primary productivity of the surface water. The mean down core δ13C record exhibits enrichment during the LIA maximum and a strong depletion trend during the last century. The LIA δ13C enrichment is attributed to an increase in primary production and high nutrient levels which resulted from increased vertical mixing and upwelling. The last century δ13C depletion is mostly related to the increased anthropogenic emissions of 13C depleted carbon dioxide and to a certain decrease in primary production. The data indicate that D. petraeum isotopic signatures are unique proxies for last 500 years high-resolution reconstruction of paleo-oceanographic environments in the Mediterranean and potentially in the sub-tropical Atlantic regions. 相似文献
350.
Pascal Sailhac Maksim Bano Mickael Behaegel Jean-François Girard Ester Falgàs Para Juanjo Ledo Guy Marquis Pierre-Daniel Matthey José Ortega-Ramírez 《Comptes Rendus Geoscience》2009,341(10-11):818-830
We consider a series of hydrogeophysical techniques that provide a multiscale investigation of the water content in the vadose zone and of the perched aquifer at the experimental site of “La Soutte” in the Vosges Mountains (France). It is located in a catchment area where several springs and streams occur along fractured volcanic and weathered plutonic rocks. The site is the object of a long-term study that uses both continuous and repeated measurements to monitor hydrogeological processes. The main results from AMT and DC resistivity techniques allow the determination of a high-resolution 3D resistivity model over a large range of depths (from 100 to 103 m). We discuss their use and propose a hydrogeological model (porosity, water conductivity and water content). We also use MRS and GPR for a detailed investigation of the shallow part of the catchment that consists of soil and weathered rocks of highly varying thickness (0 to 15 m). MRS is used to map the thickness and total water volume content by unit surface of the saturated weathered zone. It also yields estimates of the vadose zone thickness through the depth to the top of the saturated zone. Moreover, we show results from GPR CMP measurements that yield estimates of the water content and porosity in the shallowest layer (0–30 cm) by simple interpretation of the ground direct wave. 相似文献