The age of the Roter Kamm impact crater,Namibia: Constraints from 40Ar-39Ar,K-Ar,Rb-Sr,fission track,and 10Be-26Al studies     

Christian Koeberl  Jack B. Hartung  Michael J. Kunk  Jeffrey Klein  Jun-Ichi Matsuda  Keisuke Nagao  Wolf Uwe Reimold  Dieter Storzer 《Meteoritics & planetary science》1993,28(2):204-212

Abstract The well-preserved 2.5 km diameter Roter Kamm impact crater is located in the Namib desert in Namibia. The impact has occurred in Precambrian granitic and granodioritic orthogneisses of the 1200–900 Ma old Namaqualand Metamorphic Complex which were partly covered by Gariep metasediments; the granites are invaded by quartz veins and quartz-feldspar-pegmatites. Previous geological field evidence suggested a crater age of about 5–10 Ma. In order to constrain this age, we selected a set of basement rocks (granites, granodiorites) exposed at the crater rim and studied the Rb-Sr, K-Ar, ⁴⁰Ar-³⁹Ar, and ¹⁰Be-²⁶Al isotopic systems as well as apatite fission track ages of these samples. The Rb-Sr isotopic systematics confirm the derivation of these samples from the Namaqualand basement (age about 1.29 Ga), which underwent Damaran orogenesis at about 650 Ma. No basement rocks with Rb-Sr ages younger than about 410 Ma were identified. The K-Ar ages of pseudotachylite and melt breccia samples show that these samples are dominated by incompletely degassed fragments of basement rocks, with some retaining their original metamorphic ages of about 470 Ma. The apatite fission track ages range from 20–28 Ma, which may be interpreted as an extension of the 25 Ma Burdigalian peneplanation event, or as incomplete resetting of the apatite fission tracks during the impact event. The ¹⁰Be and ²⁶Al exposure age of a quartz sample isolated from a quartz-pegmatite was found to be 150 ka; it is likely that the exposure of the sample began after material covering it had been removed by erosion 150 ka ago. Two glassy fractions extracted from a rim granite were dated by ⁴⁰Ar-³⁹Ar analysis. One sample gives practically a plateau age of 3.7 ± 0.3 Ma, while the other gives a minimum age of 3.6 Ma. The best available age estimate for the Roter Kamm crater is therefore 3.7 ± 0.3 Ma.  相似文献   

Key natural analogue input required to build a safety case for direct disposal of spent nuclear fuel in Japan     

Ian G. McKinley  Hideki Kawamura  Susie M. L. Hardie  Elizaveta Klein  Tara M. Beattie 《Swiss Journal of Geoscience》2015,108(1):147-154

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Specification of monthly mean anomalies of surface air temperature in Canada and Alaska     

William H. Klein 《大气与海洋》2013,51(2):155-176

Abstract

Anomalies of monthly mean surface temperature observed at 55 stations in Canada and 13 in Alaska from 1951 through 1980 are related to concurrent anomalies of monthly mean 700‐mb height at a network of 107 grid points in North America and the surrounding oceans. The data are screened by a stepwise forward selection procedure to yield multiple regression equations for specifying the monthly mean temperature anomaly at each city and for each month from the field of simultaneous 700‐mb heights plus the previous month's local temperature anomaly. On the average, the specification equations explain 70% of the temperature variance and select as predictors approxiamtely 2 heights to the west of the reference station, 1.5 heights in the vicinity, 1 height to the east, and 0.5 previous temperatures.

Most of this paper describes various properties of the specification equations and related atmospheric characteristics on a regional, seasonal and month‐to‐month basis. Five statistical features are mapped for the months of January, April, July and October, and marked regional differences are noted. The above features are then averaged for the entire region and graphed month by month; the annual cycle of other properties is also described. Systematic spatial and temporal variations in the characteristics of temperature variability, persistence, correlation with height, and specification equations are illustrated.  相似文献   

Solar Energetic Particles and Associated EIT Disturbances in Solar Cycle 23     

R. Miteva  K.-L. Klein  I. Kienreich  M. Temmer  A. Veronig  O. E. Malandraki 《Solar physics》2014,289(7):2601-2631

We explore the link between solar energetic particles (SEPs) observed at 1 AU and large-scale disturbances propagating in the solar corona, named after the Extreme ultraviolet Imaging Telescope (EIT) as EIT waves, which trace the lateral expansion of a coronal mass ejection (CME). A comprehensive search for SOHO/EIT waves was carried out for 179 SEP events during Solar Cycle 23 (1997?–?2006). 87 % of the SEP events were found to be accompanied by EIT waves. In order to test if the EIT waves play a role in the SEP acceleration, we compared their extrapolated arrival time at the footpoint of the Parker spiral with the particle onset in the 26 eastern SEP events that had no direct magnetic connection to the Earth. We find that the onset of proton events was generally consistent with this scenario. However, in a number of cases the first near-relativistic electrons were detected too early. Furthermore, the electrons had in general only weakly anisotropic pitch-angle distributions. This poses a problem for the idea that the SEPs were accelerated by the EIT wave or in any other spatially confined region in the low corona. The presence of weak electron anisotropies in SEP events from the eastern hemisphere suggests that transport processes in interplanetary space, including cross-field diffusion, play a role in giving the SEPs access to a broad range of helio-longitudes.  相似文献   

Long-term variations in the microwave brightness temperature of the Uranus atmosphere     

M.J. Klein 《Icarus》2006,184(1):170-180

We present a self-consistent, 36-year record of the disk-averaged radio brightness of Uranus at wavelengths near 3.5 cm. It covers nearly half a uranian year, and includes both equatorial and polar viewing geometries (corresponding to equinox and solstice, respectively). We find large (greater than 30 K) changes over this time span. In agreement with analyses made of more limited microwave data sets, our observations suggest the changes are not caused by geometric effects alone, and that temporal variations may exist in the deep uranian troposphere down to pressures of tens of bars. Our data also support an earlier suggestion that a rapid, planetary-scale change may have occurred in late 1993 and early 1994. The seasonal record presented here will be useful for constraining dynamical models of the deep atmosphere, and for interpreting observations made during Uranus' 2007 equinox passage. As part of a multi-wavelength observing campaign for this event, the Goldstone-Apple Valley Radio Telescope (GAVRT) project will continue to make frequent, single-dish observations near 3.5 cm.  相似文献   

Constraints on the composition of the Venus atmosphere from microwave measurements near 1.35 cm wavelength     

Michael A. Janssen  Michael J. Klein 《Icarus》1981,46(1):58-69

The determination of the brightness temperature of Venus near 1.35 cm wavelength is reviewed. The observed brightness temperature is compared with models for the microwave emission based on the physical and chemical structure of the atmosphere as obtained from spacecraft. Upper limits are set on the concentrations of microwave-absorbing minor constituents. In particular, upper limits are determined for SO₂ (180 ppm) and H₂O (0.3%) for a mixing-ratio profile that is uniformly mixed up to the cloud bottom at 50 km and is rapidly depleted ($\text{scale height}\text{? 1}\text{km}\text{)}$ at higher altitudes. The total optical depth of the cloud region at or above 50 km is <0.17 at 1.35 cm wavelength. The SO₂ upper limit is only in marginal agreement with the spacecraft results, and it may be that the latter have been overestimated, or that the distribution of SO₂ is more complex than given by the uniform mixing model.  相似文献   

Venus I. Carbon monoxide distribution and molecular-line searches     

W.J. Wilson  M.J. Klein  R.K. Kahar  S. Gulkis  E.T. Olsen  P.T.P. Ho 《Icarus》1981,45(3):624-637

An observational program to study variations of the vertical distribution of CO in the Venus atmosphere is presented. Measurements of the J = 0 → 1 absorption line at 2.6 mm wavelength are reported for two phase angles in 1977, one near eastern elongation (Feb.) and the other near inferior conjunction (Apr.). The two spectra are significantly different, with the April absorption line being narrower and deeper. The results of numerical inversion calculations show that the CO mixing ratio increases a factor of ～ 100 between 78 and 100 km and that the CO abundance above ～ 100 km is greatest on the night-side hemisphere. These conclusions are in qualitative agreement with theoretical models. In addition to the CO observations, a search for other molecules was made to provide further information on the composition of the Venus middle atmosphere. The J = 0 → 1 transition of ¹³CO was detected and upper limits were derived for nine other molecules.  相似文献   

Land cover change over the last three centuries due to human activities: The availability of new global data sets   总被引：15，自引：0，他引：15  

Kees?Klein GoldewijkEmail author  Navin?Ramankutty 《GeoJournal》2004,61(4):335-344

Land use and land cover change is an important driver of global change (Turner et al., 1993). It is recognized that land use change has important consequences for global and regional climates, the global biogeochemical cycles such as carbon, nitrogen, and water, biodiversity, etc. Nevertheless, there have been relatively few comprehensive studies of global, long-term historical changes in land cover due to land use. In this paper, we review the development of global scale data sets of land use and land cover change. Furthermore, we assess the differences between two recently developed global data sets of historical land cover change due to land use. Based on historical statistical inventories (e.g. census data, tax records, land surveys, historical geography estimates, etc) and applying different spatial analysis techniques, changes in agricultural land cover (croplands, pastures) were reconstructed for the last 300 years. The two data sets indicate that cropland areas expanded from 3–4 million km² in 1700 to 15–18 million km² in 1990 (mostly at the expense of forests), while grazing land area expanded from 5 million km² in 1700 to 31 million km² in 1990 (mostly at the expense of natural grasslands). The data sets disagree most over Latin America and Oceania, and agree best over North America. Major differences in the two data sets can be explained by the use of a fractional versus Boolean approach, different modelling assumptions, and inventory data sets.  相似文献   

The fast Ice Nucleus chamber FINCH   总被引：2，自引：0，他引：2  

U. Bundke  B. Nillius  R. Jaenicke  T. Wetter  H. Klein  H. Bingemer 《Atmospheric Research》2008,90(2-4):180-ICNAA07

We present first results of our new developed Ice Nucleus (IN) counter FINCH from the sixth Cloud and Aerosol Characterization Experiment (CLACE 6) campaign at Jungfraujoch station, 3571 m asl. Measurements were made at the total and the ICE CVI inlet. Laboratory measurements of ice onset temperatures by FINCH are compared to those of the static diffusion chamber FRIDGE (FRankfurt Ice Deposition Freezing Experiment). Within the errors of both new instruments the results compare well to published data.  相似文献   

Fe-Ni-Co-O-S Phase Relations in Peridotite-Seawater Interactions   总被引：4，自引：0，他引：4  

Klein  Frieder; Bach  Wolfgang 《Journal of Petrology》2009,50(1):37-59

Serpentinization of abyssal peridotites is known to produceextremely reducing conditions as a result of dihydrogen (H₂,aq)release upon oxidation of ferrous iron in primary phases toferric iron in secondary minerals by H₂O. We have compiled andevaluated thermodynamic data for Fe–Ni–Co–O–Sphases and computed phase relations in fO₂,g–fS₂,g andaH₂,aq–aH₂S,aq diagrams for temperatures between 150 and400°C at 50 MPa. We use the relations and compositions ofFe–Ni–Co–O–S phases to trace changesin oxygen and sulfur fugacities during progressive serpentinizationand steatitization of peridotites from the Mid-Atlantic Ridgein the 15°20'N Fracture Zone area (Ocean Drilling ProgramLeg 209). Petrographic observations suggest a systematic changefrom awaruite–magnetite–pentlandite and heazlewoodite–magnetite–pentlanditeassemblages forming in the early stages of serpentinizationto millerite–pyrite–polydymite-dominated assemblagesin steatized rocks. Awaruite is observed in all brucite-bearingpartly serpentinized rocks. Apparently, buffering of silicaactivities to low values by the presence of brucite facilitatesthe formation of large amounts of hydrogen, which leads to theformation of awaruite. Associated with the prominent desulfurizationof pentlandite, sulfide is removed from the rock during theinitial stage of serpentinization. In contrast, steatitizationindicates increased silica activities and that high-sulfur-fugacitysulfides, such as polydymite and pyrite–vaesite solidsolution, form as the reducing capacity of the peridotite isexhausted and H₂ activities drop. Under these conditions, sulfideswill not desulfurize but precipitate and the sulfur contentof the rock increases. The co-evolution of fO₂,g–fS₂,gin the system follows an isopotential of H₂S,aq, indicatingthat H₂S in vent fluids is buffered. In contrast, H₂ in ventfluids is not buffered by Fe–Ni–Co–O–Sphases, which merely monitor the evolution of H₂ activitiesin the fluids in the course of progressive rock alteration.The co-occurrence of pentlandite–awaruite–magnetiteindicates H₂,aq activities in the interacting fluids near thestability limit of water. The presence of a hydrogen gas phasewould add to the catalyzing capacity of awaruite and would facilitatethe abiotic formation of organic compounds. KEY WORDS: serpentinization; ODP Expedition 209; sulfide; oxygen fugacity; sulfur fugacity; hydrothermal system; metasomatism; Mid-Atlantic Ridge  相似文献