Field tests of seasat bathymetric detections     

B. Keating  N. Z. Cherkis  P. W. Fell  D. Handschmacher  R. N. Hey  A. Lazarewicz  D. F. Naar  R. K. Perry  D. Sandwell  D. C. Schwank  P. Vogt  B. Zondek 《Marine Geophysical Researches》1984,7(1-2):69-71

Knowledge of the locations and sizes of seamounts is of great importance in applications such as inertial navigation and ocean mining. The quality and density of bathymetry data in the equatorial regions and the southern hemisphere are, unifortunately, highly variable. Our present knowledge of bathymetry, and in particular of seamount locations and characteristics, is based upon ship surveys, which are both time-consuming and expensive. It is likely that a significant number of uncharted seamounts exist throughout the oceans, and remote-sensing techniques may be the most effective means of locating them.  相似文献   

Sea-floor terrains of Håkon Mosby Mud Volcano as surveyed by deep-tow video and still photography     

A. Milkov  P. Vogt  G. Cherkashev  G. Ginsburg  N. Chernova  A. Andriashev 《Geo-Marine Letters》1999,19(1-2):38-47

A survey of the submarine Håkon Mosby mud volcano (HMMV) area by photo and video cameras permits the classification and mapping of sea-floor terrains. Approximate concentric zoning is seen in the distribution of the terrains, which correlates well with morphostructural elements of the mud volcano. A relatively limited biological community, dominated by tubeworms (Pogonophora and Polychaeta) and demersal fish, exists on the HMMV. Photo and video images show no evidence for gas bubbles in the water column, although methane is present in the mud volcano sediments. White patches, which comprise over 75% of the sea floor in some areas, are interpreted to be bacterial mats and/or gas hydrates.  相似文献   

Exact general relativistic discs and the advance of perihelion     

D. Vogt  P. S. Letelier 《Monthly notices of the Royal Astronomical Society》2008,384(2):834-842

  相似文献   

Analytical potential–density pairs from complex-shifted Kuzmin–Toomre discs     

D. Vogt  P. S. Letelier 《Monthly notices of the Royal Astronomical Society》2009,398(3):1563-1572

The complex-shift method is applied to the Kuzmin–Toomre family of discs to generate a family of non-axisymmetric flat distributions of matter. These are then superposed to construct non-axisymmetric flat rings. We also consider triaxial potential–density pairs obtained from these non-axisymmetric flat systems by means of suitable transformations. The use of the imaginary part of complex-shifted potential–density pairs is also discussed.  相似文献   

Fractionation,distribution and transport of mercury in rivers and tributaries around Wanshan Hg mining district,Guizhou Province,Southwestern China: Part 2 – Methylmercury     

Hua Zhang  Xinbin Feng  Thorjørn Larssen  Lihai Shang  Rolf D. Vogt  Yan Lin  Ping Li  Hui Zhang 《Applied Geochemistry》2010

Water samples were collected during normal flow (2007) and during a drought period (2008) from five rivers and tributaries draining the Wanshan Hg mining district, Guizhou, China. Unfiltered methylmercury (MeHg) as well as particulate and dissolved fractions of MeHg (P-MeHg, D-MeHg) were measured to assess the spatial and temporal variation of MeHg contamination in the local river system. Most locations (about 80%) displayed higher MeHg concentrations during drought period than during normal discharge conditions. Concentrations of MeHg during the drought period ranged from <0.035 to 11 ng L⁻¹ (geometric mean: 0.43), while during normal flow the concentrations ranged from <0.035 to only 3.4 ng L⁻¹ (geometric mean: 0.21). Concentrations of MeHg were positively correlated with total Hg (THg) concentrations (R² = 0.20–0.58, P < 0.001) and inversely related to distance from the calcines, during both sampling periods (R² = 0.34 and 0.23, P < 0.001, for low and normal flow, respectively) indicating that calcines may be important sources of MeHg to the downstream environment. Approximately 39% of MeHg was bound to particulates and the rest was transported in the dissolved phase along stretches of the entire river, which was different from THg, as this was mainly transported bound to particulates (commonly more than 80%).  相似文献   

Deciphering signals of late Holocene fluvial and aeolian supply from a shelf sediment depocentre off Senegal (north‐west Africa)     

Jean Nizou  Till J.J. Hanebuth  Christoph Vogt 《第四纪科学杂志》2011,26(4):411-421

High‐resolution climatic records of the late Holocene along the north‐west African continental margin are scarce. Here we combine sediment grain size, elemental distribution and mineral assemblage data to trace dust and riverine sources at a shallow‐marine sediment depocentre in the vicinity of the Senegal River mouth. The aim is to understand how these terrigenous components reflect climate variability during the late Holocene. Major element contents were measured and mineral identification was performed on three sub‐fractions of our sediment core: (i) fluvial material < 2 µm, (ii) aeolian material of 18–63 µm and (iii) a sub‐fraction of dual‐origin material of 2–18 µm. Results show that more than 80% of the total Al and Fe terrigenous bulk content is present in the fluviogenic fraction. In contrast, Ti, K and Si cannot be considered as proxies for one specific source off Senegal. The Al/Ca ratio, recording the continental river runoff, reveals two dry periods from 3010 to 2750 cal a BP and from 1900 to 1000 cal a BP, and two main humid periods from 2750 to 1900 cal a BP and from 1000 to 700 cal a BP. The match between (i) intervals of low river runoff inferred by low Al/Ca values, (ii) reduced river discharge inferred by integrated palynological data from offshore Senegal and (iii) periods of enhanced dune reactivation in Mali confirms this interpretation. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Using 87Sr/86Sr, δ18O and δ2H isotopes along with major chemical composition to assess groundwater salinization in lower Shire valley,Malawi     

Maurice Monjerezi  Rolf D. Vogt  Per Aagaard  Asfaw Gebretsadik Gebru  John D.K. Saka 《Applied Geochemistry》2011,26(12):2201-2214

Groundwater resources in some parts of the lower section of Shire River valley, Malawi, are not useable for rural domestic water supply due to high salinity. In this study, a combined assessment of isotopic (⁸⁷Sr/⁸⁶Sr, δ¹⁸O and δ²H) and major ion composition was conducted in order to identify the hydro-geochemical evolution of the groundwater and thereby the causes of salinity. Three major end-members (representing fresh- and saline groundwater, and evaporated recharge) were identified based on major ion and isotopic composition. The saline groundwater is inferred to result from dissolution of evaporitic salts (halite) and the fresh groundwater shows influence of silicate weathering. Conservative mixing models show that brackish groundwater samples result from a three component mixture comprising the identified end-members. Hence their salinity is interpreted to result from mixing of fresh groundwater with evaporated recharge and saline groundwater. On the other hand, the groundwater with low TDS, found at some distance from areas of high salinity, is influenced by mixing of evaporated recharge and fresh groundwater only. Close to the Shire marshes, where there is shallow groundwater, composition of stable isotopes of water indicates that evaporation may also be an important factor.  相似文献   

Ground-truthing 11- to 12-kHz side-scan sonar imagery in the Norwegia–Greenland Sea: Part I: Pockmarks on the Vestnesa Ridge and Storegga slide margin     

P. R. Vogt  J. Gardner  K. Crane  E. Sundvor  F. Bowles  G. Cherkashev 《Geo-Marine Letters》1999,19(1-2):97-110

 Numerous small (50- to 300-m-diameter) strong-backscatter objects were imaged on the 1200- to 1350-m deep crest of Vestnesa Ridge (Fram Strait) and along the 900- to 1000-m deep northeast margin of the Storegga slide valley. Ground-truthing identified most of these objects as 2- to 10-m-deep pockmarks, developed within soft, acoustically stratified silty clays (typical wet bulk density: 1400–1600 kg m^-3; sound speed: 1480– 1505 m s^-1; porosity, 65–75%; shear strength: 5–10 kPa; water content: 80–120%; and thermal conductivity: 0.8–0.9 W m^-1 deg C^-1 in the top 3 m). Gas wipeouts, enhanced reflectors, and reflector discontinuities indicate recent or ongoing activity, but the absence of local heat flow anomalies suggests that any upward fluid flows are modest and/or local.  相似文献   

Location of the Africa-Australia-India Triple Junction and Motion Between the Australian and Indian Plates: Results From an Aeromagnetic Investigation of the Central Indian and Carlsberg Ridges     

Charles Demets  Richard G. Gordon  Peter Vogt 《Geophysical Journal International》1994,119(3):893-930

  相似文献   

Rhyodacites,andesites, ferro-basalts and ocean tholeiites from the galapagos spreading center     

Gary R. Byerly  William G. Melson  Peter R. Vogt 《Earth and Planetary Science Letters》1976,30(2):215-221

Volcanic rocks, dredged from depths greater than 1000 m on the Galapagos spreading center, show extreme chemical diversity, including rhyodacites, andesite, ferro-basalts, and low-K oceanic tholeiite. All samples have fresh glassy margins. The ferro-basalts contain up to 18.5% total iron as FeO and up to 3.75% TiO₂, while the oceanic tholeiites are as low as 0.02% K₂O. The ferro-basalts correlate with the previously proposed zone of high magnetic anomaly amplitudes which flank the Galapagos hot spot, and are consistent with a genesis by shallow fractional crystallization.  相似文献