Inferring Glacier Mass Balance Using Radarsat: Results From Peyto Glacier, Canada     

Michael Demuth  & Alain Pietroniro 《Geografiska Annaler: Series A, Physical Geography》1999,81(4):521-540

The capability of RADARSAT synthetic aperture radar (SAR) for the purpose of snow-line/accumulation area mapping for a temperate alpine glacier is examined. In agreement with other orbital C-band SAR studies, RADARSAT can discriminate between firn and bare ice facies. Limited observations are reported with respect to the electromagnetic variability of the ice facies in the ablation area, but they are inconclusive. Operational considerations are discussed with respect to reconciling the uncertainties of late-summer weather and their possible impact on the dielectric and scattering properties of the glacier surface. Vagaries associated with other glacier settings, mass balance states and their associated facies configurations are discussed including the difficulty of using the transient snow-line to define the equilibrium line and the lower extent of the accumulation area for glaciers where superimposed ice may form.
The radar remote-sensing reconnaissance of equilibrium line altitude (ELA) and accumulation area ratio (AAR) for estimating glacier mass balance requires serious consideration in those instances where traditional ground measurements used in the direct glaciological method are absent. However, with respect to the ELA, such estimates can vary depending on the accuracy of the reference digital elevation information. Moreover, for many glacier configurations, where mass balance variations due to altitude are influenced or in some cases completely masked by local balance variations, defining the ELA may be an irreconcilable problem. Using the AAR may be more robust in this regard. It is further determined that the total error inherent in the reconnaissance method would have serious implications for the confident estimation of mass balance normals and climate-related trends if the method were to be utilized over the longer term.  相似文献   

The pattern speed of the bar in NGC 4596     

Joris Gerssen  Konrad Kuijken  Michael R. Merrifield 《Monthly notices of the Royal Astronomical Society》1999,306(4):926-930

The pattern speed is a defining parameter of any barred galaxy. A large number of model-dependent techniques have therefore been developed to derive the pattern speed. However, the only model-independent technique for measuring this quantity – the Tremaine–Weinberg method – has hitherto been applied to just one case, the SB0 galaxy NGC 936. In this paper, we apply the technique to a second system, the SBa galaxy NGC 4596. The resulting estimate for the pattern speed is Ω_p=52±13 km s⁻¹ kpc⁻¹. This result is corroborated by a spectrum obtained along the major axis of the bar in this system. The corotation radius associated with this pattern speed lies just beyond the end of the bar indicating a fast bar. Combining the bar major-axis spectra with data obtained from a Hubble Space Telescope WFPC2 image, we also find strong evidence for a nuclear disc.  相似文献   

Subsource characterization: Obsidian utilization of subsources of the Coso volcanic field,Coso Junction,California, USA     

Jonathon E. Ericson  Michael D. Glascock 《Geoarchaeology》2004,19(8):779-805

Six chemical subsource groups were identified in the analysis of 84 obsidian samples collected from subsource locations at Coso volcanic field, California. In prehistoric times, Coso provided obsidian for artifacts found from San Francisco Bay to San Diego to Death Valley to the eastern Mojave Desert. Subsource groups were defined by instrumental neutron activation analysis (INAA) of 29 elements followed by cluster analysis, principal component analysis, and bivariate plotting. The new data are compared to previously published INAA and X‐ray fluorescence data. Characterization of 55 obsidian artifacts from archaeological sites located approximately 100 miles from Coso suggests preferential usage of specific subsources as a function of the directionality of travel. The results are consistent with a bimodal (resident and itinerant) model of procurement. This research illustrates the importance of accurate sourcing of obsidian artifacts when attempting to define subsource usage. © 2004 Wiley Periodicals, Inc.  相似文献   

Enhancements for Passive Vapor Extraction: The Hanford Study   总被引：3，自引：0，他引：3  

Michael G. Ellerd  Joel W. Massmann  Daniel P. Schwaegler  Virginia J. Rohay 《Ground water》1999,37(3):427-437

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西藏措勤地区中生代的构造变形     

陈正乐  王小凤  An Yin  Michael Murphy  Soren B.Durr 《地质通报》1999,18(2)

：１∶１０万野外地质填图发现,在措勤地区北侧的白垩系中发育了一系列逆冲推覆构造和褶皱构造,且有侵入岩体分布,又被未变形的火山凝灰岩不整合覆盖。根据侵入岩的钾长石和角闪石及其不整合的火山凝灰岩中蚀变斜长石的ＡｒＡｒ法同位素年龄、沉积物质的组成和沉积地层的空间展布等特征,笔者推测这些逆冲断层和褶皱构造均发育于晚白垩世,并早于第三纪。  相似文献   

THE PELAGOS PROJECT     

Efstathios Balopoulos  Michael Collins 《Progress in Oceanography》1999,44(4):540

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Water fluxes through the Cretan Arc Straits, Eastern Mediterranean Sea: March 1994 to June 1995     

Harilaos Kontoyiannis  Alexander Theocharis  Efstathios Balopoulos  Soterios Kioroglou  Vassilios Papadopoulos  Michael Collins  Antonios F. Velegrakis  Athanasia Iona 《Progress in Oceanography》1999,44(4):58

Five research cruises were undertaken incorporating ADCP sections along the Cretan Arc Straits and CTD surveys covering the entire area of the Straits and the Cretan Sea. In addition, six moorings (with 15 current meters) were deployed within the Straits, which monitored flows in the surface (50 m), intermediate (250 m), and deep (50 m from the bottom) layers. The ADCP, CM, and CTD datasets enable the derivation of water transports through the Cretan Arc Straits to be assessed. Flow structure through the Cretan Arc Straits is not the typical flow regime with a surface inflow and deep outflow, instead there is a persistent deep outflow of Cretan Deep Water (CDW) (σ_θ>29.2) with an annual mean of ˜0.6 Sv, through the Antikithira and Kassos Straits at depths below 400 m and 500 m, respectively. CDW outflowing transports are higher (˜0.8 Sv) in April–June, and lower (˜0.3 Sv) in October–December. Within the upper water layer (0–˜400 m), the transport and the water exchanges through the Straits are controlled by local circulation features, which weaken substantially below 200 m. The Asia Minor Current (AMC) influences the Rhodes and the Karpathos Straits, resulting in a net inflow of water. In contrast, the Mirtoan/West Cretan Cyclone influences the Antikithira and Kithira Straits, where there is a net outflow. In the Kassos Strait, there is a complex interaction between the East Cretan Cyclone, the Ierapetra Anticyclone and the westward extension of the Rhodes Gyre, which results in a variable flow regime. There is a net inflow in autumn and early winter, and a switch to a net outflow in early spring and summer. The total inflow and outflow, throughout all of the Straits, ranged from ˜2 to ˜3.5 Sv, with higher values in autumn and early winter and lower in summer. The AMC carries ˜2 Sv of inflow through the Rhodes and Karpathos Straits, and this accounts for 60–80% of the total inflow. About 10–15% of the total outflow is of CDW, and a further 45–70% occurs through the upper 400 m of the Kithira and Antikithira Straits. The Kassos Strait exhibits a net inflow of ˜0.7 Sv in autumn and early winter, with a net outflow of ˜0.5 Sv in early spring and summer.  相似文献   

Sources and history of heavy metal contamination and sediment deposition in Tivoli South Bay, Hudson River, New York   总被引：1，自引：0，他引：1  

Gaboury Benoit  Edward X. Wang  William C. Nieder  Michael Levandowsky  Vincent T. Breslin 《Estuaries and Coasts》1999,22(2):167-178

Persistent inorganic constitutents preserved in sediments of aquatic ecosystems record temporal variability of biogeochemical functioning and anthropogenic impacts.²¹⁰Pb and¹³⁷Cs dating techniques were used to study the past variations of heavy metals (Pb, Cu, and Zn) and accumulation rates of sediments for Tivoli South Bay, in the Hudson River National Estuarine Research Reserve ecosystem. South Bay, a tidal freshwater embayment of the Hudson, may play an important role in the sediment dynamics of this important river. The measured sedimentation rate range of 0.59 to 2.92 cm yr⁻¹ suggests that rapid accumulation occurred during the time period represented by the length of the cores (approximately the past 50 yr). Direct measurements of sediment exchange with the Hudson River reveal high variability in the sediment flux from one tidal cycle to the next. Net exchange does not seem to be adequate to explain sediment accumulation rates in the bay as measured by²¹⁰Pb and¹³⁷Cs. The difference may be supplied from upland streams or the Hudson River during storm events. Concentrations of the metals Pb, Cu and Zn were found to be well correlated with each other within individual cores at five of six sites tested. This suggests a common proximate source for the three metals at a specific site. The evidence is consistent with mixing in some environmental compartment before delivery to the bay. While metals self-correlate within individual cores, absolute concentrations, depth distribution patterns, and ratios of the metals to each other vary among the cores collected at different locations within the bay. Organic matter, Fe content, and particle size distribution of sediments do not account for the intercore variations in metal concentration. It is likely that cores collected from different sites may have derived metals from different sources, such as watershed streams and tidal exchange with the Hudson River.  相似文献   

Dispersion and recruitment of crab larvae in the Chesapeake Bay plume: Physical and biological controls     

Michael R. Roman  William C. Boicourt 《Estuaries and Coasts》1999,22(3):563-574

As part of the Microbial Exchanges and Coupling in Coastal Atlantic Systems (MECCAS) Project, crab larvae were collected in the shelf waters off Chesapeake Bay in June and August 1985 and April 1986. We conducted hydrographic (temperature, salinity, nutrients) and biological (chlorophyll, copepods) mapping in conjunction with Eulerian and Lagrangian time studies of the vertical distribution of crab larvae in the Chesapeake Bay plume. These abundance estimates are used with current meter records and drifter trajectories to infer mechanisms of larval crab dispersion to the shelf waters and recruitment back into Chesapeake Bay. The highest numbers of crab larvae were usually associated with the Chesapeake Bay plume, suggesting that it was the dominant source of crab larvae to shelf waters. Patches of crab larvae also were found in the higher salinity shelf waters, and possibly were remnants of previous plume discharge events. The distribution of crab larvae in the shelf waters changed on 1–2 d time scales as a consequence of both variations in the discharge rate of the Chesapeake Bay plume and local wind-driven currents. Downwelling-favorable winds (NW) intensified the coastal jet and confined the plume and crab larvae along the coast. In April during a downwelling event (when northwesterly winds predominated), crab zoeae were transported southward along the coast at speeds that at times exceeded 168 km d⁻¹. During June and August the upwelling-favorable winds (S, SW) opposed the anticyclonic turn of the plume and, via Ekman circulation, forced the plume and crab larvae to spread seaward. Plume velocities during these conditions generally were less than 48 km d⁻¹. The recruitment of crab larvae to Chesapeake Bay is facilitated in late summer by the dominance of southerly winds, which can reverse the southward flow of shelf waters. Periodic downwelling-favorable winds can result in surface waters and crab larvae moving toward the entrance of Chesapeake Bay. Approximately 27% of the larval crabs spend at least part of the day in bottom waters, which have a residual drift toward the bay mouth. There appears to be a variety of physical transport mechanisms that can enhance the recruitment of crab larvae into Chesapeake Bay.  相似文献   

Does the common reed,Phragmites australis, affect essential fish habitat?     

Michael P. Weinstein  John H. Balletto 《Estuaries and Coasts》1999,22(3):793-802

Since the early 1900sPhragmites australis has been replacing other vegetation in Atlantic and gulf coast marshes at a rate of about 1% to 6% of the marsh surface per year. Vast areas of coastal marsh are now characterized by dense monotypic stands of this species. By virtue of its ability to build up the marsh surface,P. australis affects the landscape, hydrology, and hydroperiod of the marsh as well as drainage density, and other geomorphic features. Smoothed microtopography results in more difficult access to the marsh by nekton, and possibly reduced exchange of organic materials between the marsh and adjacent estuary. The pattern of replacement byP. australis results in fragmentation of existing stands ofSpartina alterniflora and other extant macrophytes, thereby altering landscape ecology and the ability of the marsh to support biodiversity and the production of marsh fauna.  相似文献