Rise in seawater sulphate concentration associated with the Paleoproterozoic positive carbon isotope excursion: evidence from sulphate evaporites in the ∼2.2–2.1 Gyr shallow‐marine Lucknow Formation,South Africa     

S. Schröder  A. Bekker  N. J. Beukes  H. Strauss  H. S. Van Niekerk 《地学学报》2008,20(2):108-117

Abstract Past oceanic sulphate concentration is important for understanding how the oceans’ redox state responded to atmospheric oxygen levels. The absence of extensive marine sulphate evaporites before ～1.2 Gyr probably reflects low seawater sulphate and/or higher carbonate concentrations. Sulphate evaporites formed locally during the 2.22–2.06 Gyr Lomagundi positive δ¹³C excursion. However, the ～2.2–2.1 Gyr Lucknow Formation, South Africa, provides the first direct evidence for seawater sulphate precipitation on a carbonate platform with open ocean access and limited terrestrial input. These marginal marine deposits contain evidence for evaporite molds, pseudomorphs after selenite gypsum, and solid inclusions of Ca‐sulphate in quartz. Carbon and sulphur isotope data match the global record and indicate a marine source of the evaporitic brines. The apparent precipitation of gypsum before halite requires ≥2.5 mm L^?1 sulphate concentration, higher than current estimates for the Paleoproterozoic. During the Lomagundi event, which postdates the 2.32 Gyr initial rise in atmospheric oxygen, seawater sulphate concentration rose from Archean values of ≤200 μm L^?1, but dropped subsequently because of higher pyrite burial rates and a lower oceanic redox state.  相似文献   

Gold mineralisations in the SW Iberian Pyrite Belt     

G. K. Strauss  J. S. Beck 《Mineralium Deposita》1990,25(4):237-245

The occurrence and distribution of gold in the massive sulfide orebodies of the upper Palaeozoic volcano-sedimentary environment of the SW Iberian Pyrite Belt have long been assumed to be quite uniform. Recent investigations in several working mines indicate that the gold content of the ores varies between ore types, and is controlled by physico-chemical and time factors during deposition. Above-average gold grades occur in the following ore types: lead-zinc-rich ores, situated laterally and on top of the massive sulfide lenses; copper-rich siliceous basal ore facies; footwall stringer sulfides; and gangue-rich massive sulfides (siliceous, carbonate-rich, baryte bearing, or carbonaceous matrix). Exploration possibilities therefore are promising in foot- and hanging-wall environments within an orebody, as well as in disseminated and stringer ores in its footwall.  相似文献   

On the regional climatic impact of contrails: microphysical and radiative properties of contrails and natural cirrus clouds     

B. Strauss  R. Meerkoetter  B. Wissinger  P. Wendling  M. Hess 《Annales Geophysicae》1997,15(11):1457-1467

The impact of contrail-induced cirrus clouds on regional climate is estimated for mean atmospheric conditions of southern Germany in the months of July and October. This is done by use of a regionalized one-dimensional radiative convective model (RCM). The influence of an increased ice cloud cover is studied by comparing RCM results representing climatological values with a modified case. In order to study the sensitivity of this effect on the radiative characteristics of the ice cloud, two types of additional ice clouds were modelled: cirrus and contrails, the latter cloud type containing a higher number of smaller and less of the larger cloud particles. Ice cloud parameters are calculated on the basis of a particle size distribution which covers the range from 2 to 2000 m, taking into consideration recent measurements which show a remarkable amount of particles smaller than 20 m. It turns out that a 10% increase in ice cloud cover leads to a surface temperature increase in the order of 1K, ranging from 1.1 to 1.2K in July and from 0.8 to 0.9K in October depending on the radiative characteristics of the air-traffic-induced ice clouds. Modelling the current contrail cloud cover which is near 0.5% over Europe yields a surface temperature increase in the order of 0.05 K.  相似文献   

Near-shore swell estimation from a global wind-wave model: Spectral process,linear, and artificial neural network models     

Matthew Browne  Bruno Castelle  Darrell Strauss  Rodger Tomlinson  Michael Blumenstein  Chris Lane 《Coastal Engineering》2007

Estimation of swell conditions in coastal regions is important for a variety of public, government, and research applications. Driving a model of the near-shore wave transformation from an offshore global swell model such as NOAA WaveWatch3 is an economical means to arrive at swell size estimates at particular locations of interest. Recently, some work (e.g. Browne et al. [Browne, M., Strauss, D., Castelle, B., Blumenstein, M., Tomlinson, R., 2006. Local swell estimation and prediction from a global wind-wave model. IEEE Geoscience and Remote Sensing Letters 3 (4), 462–466.]) has examined an artificial neural network (ANN) based, empirical approach to wave estimation. Here, we provide a comprehensive evaluation of two data driven approaches to estimating waves near-shore (linear and ANN), and also contrast these with a more traditional spectral wave simulation model (SWAN). Performance was assessed on data gathered from a total of 17 near-shore locations, with heterogenous geography and bathymetry, around the continent of Australia over a 7 month period. It was found that the ANNs out-performed SWAN and the non-linear architecture consistently out-performed the linear method. Variability in performance and differential performance with regard to geographical location could largely be explained in terms of the underlying complexity of the local wave transformation.  相似文献   

Potential of time‐lapse photography for identifying saturation area dynamics on agricultural hillslopes          下载免费PDF全文

Rasmiaditya Silasari  Juraj Parajka  Camillo Ressl  Peter Strauss  Günter Blöschl 《水文研究》2017,31(21):3610-3627

Mapping saturation areas during rainfall events is important for understanding the dynamics of overland flow. In this study, we evaluate the potential of high temporal resolution time‐lapse photography for mapping the dynamics of saturation areas (i.e., areas where water is visually ponding on the surface) on the hillslope scale during natural rainfall. We take 1 image per minute over a 100 × 15 m² depression area on an agricultural field in the Hydrological Open Air Laboratory, Austria. The images are georectified and classified by an automated procedure, using grey intensity as a threshold to identify saturation area. The optimum threshold T is obtained by comparing saturation areas from the automated analysis with the manual analysis of 149 images. T is found to be highly correlated with an image brightness characteristic defined as the greyscale image histogram mode M (Pearson correlation r = 0.91). We estimate T as T = M + C where C is a calibration parameter assumed to be constant during each event. The automated procedure estimates the total saturation area close to the manual analysis with mean normalized root mean square error of 9% and 21% if C is calibrated for each event and taken constant for all events, respectively. The spatial patterns of saturation are estimated with a geometric mean accuracy index of 94% as compared to the manual analysis of the same photos. The patterns are tested against field observations for one date as a preliminary demonstration, which yields a root mean square error of the shortest distance between the measured boundary points and the automatically classified boundary as 23 cm. The usefulness of the patterns is illustrated by exploring run‐off generation processes of an example event. Overall, the proposed classification method based on grey intensity is found to process images with highly varying brightnesses well. It is more efficient than the manual tracing for a large number of images, which allows the exploration of surface flow processes at high temporal resolution.  相似文献   

Gravitational tidal waves in Titan's upper atmosphere     

Darrell F. Strobel 《Icarus》2006,182(1):251-258

Tidal waves driven by Titan's orbital eccentricity through the time-dependent component of Saturn's gravitational potential attain nonlinear, saturation amplitudes (|T^′|>10 K, , and ) in the upper atmosphere (?500 km) due to the approximate exponential growth as the inverse square root of pressure. The gravitational tides, with vertical wavelengths of ∼100-150 km above 500 km altitude, carry energy fluxes sufficient in magnitude to affect the energy balance of the upper atmosphere with heating rates in the altitude range of 500-900 km.  相似文献   

How sensitive are estimates of carbon fixation in agricultural models to input data?     

Markus Tum  Franziska Strauss  Ian McCallum  Kurt Günther  Erwin Schmid 《Carbon balance and management》2012,7(1):1-13

Background

Accurate, high-resolution mapping of aboveground carbon density (ACD, Mg C ha^-1) could provide insight into human and environmental controls over ecosystem state and functioning, and could support conservation and climate policy development. However, mapping ACD has proven challenging, particularly in spatially complex regions harboring a mosaic of land use activities, or in remote montane areas that are difficult to access and poorly understood ecologically. Using a combination of field measurements, airborne Light Detection and Ranging (LiDAR) and satellite data, we present the first large-scale, high-resolution estimates of aboveground carbon stocks in Madagascar.

Results

We found that elevation and the fraction of photosynthetic vegetation (PV) cover, analyzed throughout forests of widely varying structure and condition, account for 27-67% of the spatial variation in ACD. This finding facilitated spatial extrapolation of LiDAR-based carbon estimates to a total of 2,372,680 ha using satellite data. Remote, humid sub-montane forests harbored the highest carbon densities, while ACD was suppressed in dry spiny forests and in montane humid ecosystems, as well as in most lowland areas with heightened human activity. Independent of human activity, aboveground carbon stocks were subject to strong physiographic controls expressed through variation in tropical forest canopy structure measured using airborne LiDAR.

Conclusions

High-resolution mapping of carbon stocks is possible in remote regions, with or without human activity, and thus carbon monitoring can be brought to highly endangered Malagasy forests as a climate-change mitigation and biological conservation strategy.  相似文献   

Molecular hydrogen in Titan’s atmosphere: Implications of the measured tropospheric and thermospheric mole fractions     

Darrell F. Strobel 《Icarus》2010,208(2):878-886

The third most abundant species in Titan’s atmosphere is molecular hydrogen with a tropospheric/lower stratospheric mole fraction of 0.001 derived from Voyager and Cassini infrared measurements. The globally averaged thermospheric H₂ mole fraction profile from the Cassini Ion Neutral Mass Spectrometer (INMS) measurements implies a small positive gradient in the H₂ mixing ratio from the tropopause region to the lower thermosphere (∼950-1000 km), which drives a downward H₂ flux into Titan’s surface comparable to the H₂ escape flux out of the atmosphere (∼2 × 10¹⁰ cm⁻² s⁻¹ referenced to the surface) and requires larger photochemical production rates of H₂ than obtained by previous photochemical models. From detailed model calculations based on known photochemistry with eddy, molecular, and thermal diffusion, the tropospheric and thermospheric H₂ mole fractions are incompatible by a factor of ∼2. The measurements imply that the downward H₂ surface flux is in substantial excess of the speculative threshold value for methanogenic life consumption of H₂ (McKay, C.P., Smith, H.D. [2005], Icarus 178, 274-276. doi:10.1016/j.icarus.2005.05.018), but without the extreme reduction in the surface H₂ mixing ratio.  相似文献   

Seed bank dynamics in a Great Basin salt playa     

Bilquees Gul  Darrell J. Weber 《Journal of Arid Environments》2001,49(4):785

Salt playa are common in the Great Basin area with halophytes as the dominant flora. The relationship between the seed bank flora and existing vegetation was studied. The seed bank flora showed a high degree of similarity with that of perennial and annual halophytic vegetation. Both above and below ground components of the community are dominated by halophyte species like Allenrolfea occidentalis, Holosteum umbellatum, Salicornia rubra and Salicornia utahensis. Seasonal variation in the seed bank was also studied for the 1995–1996 and 1996–1997 growing seasons. The seeds of A. occidentalis persist in the soil of the upper zone in large densities. Salicornia utahensis was much higher in the upper zone throughout the study period. Most species demonstrated the persistent nature of the seed banks with their numbers increasing after seed dispersal and decreasing in subsequent months. The variation illustrates the transient nature of the seed bank. We concluded that A. occidentalis is more dependent on a large seed bank for maintaining its population than the two annual halophytes. The significance of the seed bank and their variation due to environmental conditions for perennial and annual species of the Great Basin salt playa community is discussed.  相似文献   

Comparison of three types of laser optical disdrometers under natural rainfall conditions     

Lisbeth Lolk Johannsen  Nives Zambon  Peter Strauss  Tomas Dostal  Martin Neumann  David Zumr 《水文科学杂志》2020,65(4):524-535

ABSTRACT

Optical disdrometers can be used to estimate rainfall erosivity; however, the relative accuracy of different disdrometers is unclear. This study compared three types of optical laser-based disdrometers to quantify differences in measured rainfall characteristics and to develop correction factors for kinetic energy (KE). Two identical PWS100 (Campbell Scientific), one Laser Precipitation Monitor (Thies Clima) and a first-generation Parsivel (OTT) were collocated with a weighing rain gauge (OTT Pluvio²) at a site in Austria. All disdrometers underestimated total rainfall compared to the rain gauge with relative biases from 2% to 29%. Differences in drop size distribution and velocity resulted in different KE estimates. By applying a linear regression to the KE–intensity relationship of each disdrometer, a correction factor for KE between the disdrometers was developed. This factor ranged from 1.15 to 1.36 and allowed comparison of KE between different disdrometer types despite differences in measured drop size and velocity.  相似文献