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131.
Marc S. Humphries Claudia R. Benitez-Nelson Michael Bizimis Timothy J. Ralph Zacchary T. Larkin Terence S. McCarthy 《地球表面变化过程与地形》2020,45(8):1705-1716
Dust plays a globally important role in supplying biologically essential elements to landscapes underlain by nutrient-poor substrates. Here we show that dust may play a significant role in sustaining productivity in the vast wetlands of the Okavango Delta in southern Africa, one of the world's richest biodiversity hotspots. Dust accumulates preferentially on tree-covered islands in the seasonal swamps of the Delta, creating pockets of fine-grained, nutrient-rich material within the semi-arid landscape of the Kalahari Desert. Strontium and neodymium isotopes reveal that this dust likely originates predominantly from the Makgadikgadi salt pans, located 300 km away, and contributes 10–80% of the fine-grained material present in Okavango island soils. Surface material sourced from the Makgadikgadi Pans contains relatively high amounts of bioavailable phosphorus and iron, potentially influencing Okavango Delta biological productivity. We propose that long-term ecosystem productivity and nutrient availability in the Okavango may be strongly mediated by regional dust inputs. Understanding the influence of dust deposition on nutrient loads and biogeochemical cycling is thus critical for predicting the response of the Okavango Delta to future changes in climate. We suggest that dust inputs may play a significant role in the supply of nutrients to other large, global wetland systems located in dryland environments. © 2020 John Wiley & Sons, Ltd 相似文献
132.
John D. Monnier Stefan Kraus Michael J. Ireland Fabien Baron Amelia Bayo Jean-Philippe Berger Michelle Creech-Eakman Ruobing Dong Gaspard Duchêne Catherine Espaillat Chris Haniff Sebastian Hönig Andrea Isella Attila Juhasz Lucas Labadie Sylvestre Lacour Stephanie Leifer Antoine Merand Ernest Michael Stefano Minardi Christoph Mordasini David Mozurkewich Johan Olofsson Claudia Paladini Romain Petrov Jörg-Uwe Pott Stephen Ridgway Stephen Rinehart Keivan Stassun Jean Surdej Theo ten Brummelaar Neal Turner Peter Tuthill Kerry Vahala Gerard van Belle Gautam Vasisht Ed Wishnow John Young Zhaohuan Zhu 《Experimental Astronomy》2018,46(3):517-529
The Planet Formation Imager (PFI, www.planetformationimager.org) is a next-generation infrared interferometer array with the primary goal of imaging the active phases of planet formation in nearby star forming regions. PFI will be sensitive to warm dust emission using mid-infrared capabilities made possible by precise fringe tracking in the near-infrared. An L/M band combiner will be especially sensitive to thermal emission from young exoplanets (and their disks) with a high spectral resolution mode to probe the kinematics of CO and H2O gas. In this paper, we give an overview of the main science goals of PFI, define a baseline PFI architecture that can achieve those goals, point at remaining technical challenges, and suggest activities today that will help make the Planet Formation Imager facility a reality. 相似文献
133.
Claudia Spinetti Francesco Mazzarini Ruggero Casacchia Laura Colini Marco Neri Boris Behncke Rosamaria Salvatori Maria Fabrizia Buongiorno Maria Teresa Pareschi 《International Journal of Applied Earth Observation and Geoinformation》2009
Spectral properties of volcanic materials in the optical region (350–2500 nm) of the electromagnetic spectrum are analyzed. The goal is to characterize air-fall deposits, recent lava flows, and old lava flows based on their spectral reflectance properties and on the textural characteristics (grain size) of pyroclastic deposits at an active basaltic volcano. Data were acquired during a spectroradiometric field survey at Mt. Etna (Italy) in summer 2003 and combined with hyperspectral satellite (Hyperion) and airborne LiDAR (Light Detection and Ranging) data. In addition, air-fall deposits produced by the highly explosive 2002–2003 eruption have been sampled and spectrally characterized at different distances from the new vents. The spectral analysis shows that air-fall deposits are characterized by low reflectance values besides variations in grain size. This distinguishes them from other surface materials. Old lava flows show highest reflectance values due to weathering and vegetation cover. The spectral data set derived from the field survey has been compared to corrected satellite hyperspectral data in order to investigate the Hyperion capabilities to differentiate the surface cover using the reflectance properties. This has allowed us to identify the 2002–2003 air-fall deposits in a thematic image just few months after their emplacement. Moreover, the observed differences in the field spectra of volcanic surfaces have been compared with differences in the signal intensity detected by airborne LiDAR survey showing the possibility to include information on the texture of volcanic surfaces at Mt. Etna. The approach presented here may be particularly useful for remote and inaccessible volcanic areas and also represents a potentially powerful tool for the exploration of extraterrestrial volcanic surfaces. 相似文献
134.
Precise geodesy with the Very Long Baseline Array 总被引:2,自引:2,他引:0
Leonid Petrov David Gordon John Gipson Dan MacMillan Chopo Ma Ed Fomalont R. Craig Walker Claudia Carabajal 《Journal of Geodesy》2009,83(9):859-876
We report on a program of geodetic measurements between 1994 and 2007 which used the Very Long Baseline Array (VLBA) and up
to ten globally distributed antennas. One of the goals of this program was to monitor positions of the array at a 1 mm level
of accuracy and to tie the VLBA into the international terrestrial reference frame. We describe the analysis of these data
and report several interesting geophysical results including measured station displacements due to crustal motion, earthquakes,
and antenna tilt. In terms of both formal errors and observed scatter, these sessions are among the very best geodetic very
long baseline interferometry experiments. 相似文献
135.
136.
Driven by the comprehensive modernization of the GLONASS space segment and the increased global availability of GLONASS-capable
ground stations, an updated set of satellite-specific antenna phase center corrections for the current GLONASS-M constellation
is determined by processing 84 weeks of dual-frequency data collected between January 2008 and August 2009 by a worldwide
network of 227 GPS-only and 115 combined GPS/GLONASS tracking stations. The analysis is performed according to a rigorous
combined multi-system processing scheme providing full consistency between the GPS and the GLONASS system. The solution is
aligned to a realization of the International Terrestrial Reference Frame 2005. The estimated antenna parameters are compared
with the model values currently used within the International GNSS Service (IGS). It is shown that the z-offset estimates are on average 7 cm smaller than the corresponding IGS model values and that the block-specific mean value
perfectly agrees with the nominal GLONASS-M z-offset provided by the satellite manufacturer. The existence of azimuth-dependent phase center variations is investigated
and uncertainties in the horizontal offset estimates due to mathematical correlations and yaw-attitude modeling problems during
eclipse seasons are addressed. Finally, it is demonstrated that the orbit quality benefits from the updated GLONASS-M antenna
phase center model and that a consistent set of satellite antenna z-offsets for GPS and GLONASS is imperative to obtain consistent GPS- and GLONASS-derived station heights. 相似文献
137.
138.
The Albian to Santonian Colorado Group in the heavy oil area of Cold Lake, east-central Alberta represents a relatively condensed
section of shale-dominated sedimentation within the Western Interior Sea. These shales form the cap rock to the underlying
Clearwater and Grand Rapids formations that are exploited for bitumen extraction. Two cores covering the entire Colorado Group
provide a unique opportunity for establishment of a stratigraphic reference in an area that has received attention only for
its heavy oil-bearing Mannville Group. Based on sedimentology, geochemistry, micropaleontology, nannofossils, and wireline
log data, the Colorado Group was subdivided into the Joli Fou, Viking, Westgate, Fish Scales, Belle Fourche, Second White
Specks, and Niobrara formations. The Niobrara Formation was subdivided further into the Verger Member, informal Cold Lake
member, and First White Specks Member. Because of this region’s small accommodation space and distance to sources of coarse
clastic sediment, disconformities are indicated lithologically by bioclastic layers and missing biozones. Foraminiferal subzones
revealed two erosional boundaries associated with the Viking Formation. Faunal and floral evidence coupled with wireline log
correlations suggest that the Middle to Upper Turonian Carlile Formation, as described from southeastern Alberta, is missing.
That extends the Middle Turonian to Coniacian unconformity, as recognized in central Saskatchewan, westwards into Alberta. 相似文献
139.
Anomalous Emissions of SO2 During the Recent Eruption of Santa Ana Volcano, El Salvador, Central America 总被引:1,自引:0,他引:1
Rodolfo Olmos José Barrancos Claudia Rivera Francisco Barahona Dina L. López Benancio Henriquez Agustín Hernández Efrain Benitez Pedro A. Hernández Nemesio M. Pérez Bo Galle 《Pure and Applied Geophysics》2007,164(12):2489-2506
Santa Ana volcano in western El Salvador, Central America, had a phreatic eruption at 8:05 am (local time) on October 1, 2005,
101 years after its last eruption. However, during the last one hundred years this volcano has presented periods of quiet
degassing with fumarolic activity and an acidic lake within its crater. This paper presents results of frequent measurements
of SO2 degassing using the MiniDOAS (Differential Optical Absorption Spectroscopy) system and a comparison with the volcanic seismicity
prior to the eruption, during, and after the eruption. Vehicle measurements of SO2 flux were taken every hour during the first nine days of the eruption and daily after that. The period of time reported here
is from August to December, 2005. Three periods of degassing are distinguished: pre-eruptive, eruptive, and post-eruptive
periods. The intense activity at Santa Ana volcano started in July 2005. During the pre-eruptive period up to 4306 and 5154
ton/day of SO2 flux were recorded on October 24 and September 9, 2005, respectively. These values were of the same order of magnitude as
the recorded values just after the October 1st eruption (2925 ton/day at 10:01 am). Hourly measurements of SO2 flux taken during the first nine days after the main eruptive event indicate that explosions are preceded by an increase
in SO2 flux and that this parameter reaches a peak after the explosion took place. This behavior suggests that increasing accumulation
of exsolved magmatic gases occurs within the magmatic chamber before the explosions, increasing the pressure until the point
of explosion. A correlation between SO2 fluxes and RSAM (Real Time Seismic Amplitude Measurements) is observed during the complete sampling period. Periodic fluctuations
in the SO2 and RSAM values during the entire study period are observed. One possible mechanism explaining these fluctuations it that
convective circulation within the magmatic chamber can bring fresh magma periodically to shallow levels, allowing increasing
degasification and then decreasing degasification as the batch of magma lowers its gas content, becomes denser, and sinks
to give space to a new magma pulse. These results illustrate that the measurements of SO2 flux can provide important warning signals for incoming explosive activity in active volcanoes. 相似文献
140.
Steven P. Oncley Thomas Foken Roland Vogt Wim Kohsiek H. A. R. DeBruin Christian Bernhofer Andreas Christen Eva van Gorsel David Grantz Christian Feigenwinter Irene Lehner Claudia Liebethal Heping Liu Matthias Mauder Andrea Pitacco Luis Ribeiro Tamas Weidinger 《Boundary-Layer Meteorology》2007,123(1):1-28
An overview of the Energy Balance Experiment (EBEX-2000) is given. This experiment studied the ability of state-of-the-art
measurements to close the surface energy balance over a surface (a vegetative canopy with large evapotranspiration) where
closure has been difficult to obtain. A flood-irrigated cotton field over uniform terrain was used, though aerial imagery
and direct flux measurements showed that the surface still was inhomogeneous. All major terms of the surface energy balance
were measured at nine sites to characterize the spatial variability across the field. Included in these observations was an
estimate of heat storage in the plant canopy. The resultant imbalance still was 10%, which exceeds the estimated measurement
error. We speculate that horizontal advection in the layer between the canopy top and our flux measurement height may cause
this imbalance, though our estimates of this term using our measurements resulted in values less than what would be required
to balance the budget.
The National Center for Atmospheric Research is supported by the National Science Foundation 相似文献