Climate proxies from Sr/Ca of coccolith calcite: calibrations from continuous culture of Emiliania huxleyi     

Heather M Stoll  Yair RosenthalPaul Falkowski 《Geochimica et cosmochimica acta》2002,66(6):927-936

Continuous culture of the coccolithophorid Emiliania huxleyi reveals that coccolith Sr/Ca ratios depend on temperature and growth rate. At a constant temperature of 18°C, coccolith Sr/Ca ratios increased nearly 15% as growth rate increased from 0.1 to 1.5 divisions per day and calcification rate increased from 1.5 to 50 pg calcite per cell per day. When temperature increased from 7 to 26°C, Sr/Ca ratios increased by more than 25% (i.e., 1%/1°C), although the range in growth and calcification rates was the same as for experiments at constant temperature. The temperature dependence of Sr/Ca ratios in coccoliths is consistent with that observed in planktonic foraminifera and abiogenic calcites, suggesting that it is controlled by thermodynamic processes. However, the positive correlation of coccolith Sr/Ca with temperature contrasts with field studies in the equatorial Pacific, where Sr/Ca ratios are highest at the locus of maximum upwelling and productivity despite depressed temperatures. This paradox may reflect different calcification rate effects between E. huxleyi and the other species dominating assemblages in the equatorial Pacific sediments, which may be resolved by new techniques for separation of monospecific coccolith samples from sediments. Models of crystal growth indicate that kinetic effects on Sr partitioning in calcite due to surface enrichment could explain the Sr/Ca variations observed in constant temperature experiments but not the larger amplitude calcification rate effects observed in equatorial Pacific sediments. Despite the dual influence of temperature and growth rate on coccolith Sr/Ca, coccolith Sr/Ca correlates with “b,” the slope of the dependence of carbon isotope fractionation in biomarkers (ε_p) on CO₂(aq) at a range of growth rates and temperatures. Consequently, using coccolith Sr/Ca in combination with alkenone ε_p may improve paleo-CO₂ determinations.  相似文献   

A study of the diurnal variation in the thermosphere as derived by satellite drag     

L.G. Jacchia  I.G. Campbell  J.W. Slowey 《Planetary and Space Science》1973,21(11):1825-1834

An analysis was performed on 29,574 densities derived from the drag of 10 satellites to determine simultaneously the parameters of the solar-activity effect in the thermosphere on the one hand, and the amplitude and shape of the diurnal-variation curve on the other. This paper reports on the study of the diurnal variation only.Although a considerable amount of smoothing is inherent in the drag method, it seemed useful to see whether we could detect any change in the shape of the diurnal-variation curve with height, latitude and solar activity. None was detected: the curve remains remarkably stable, symmetric, with a maximum at 14 hr 20 min L.S.T. and a minimum at 2 hr 20 min L.S.T. A systematic variation of the temperature range with height is observed when static models are used to derive it.  相似文献   

Transformations of mercury, iron, and sulfur during the reductive dissolution of iron oxyhydroxide by sulfide   总被引：1，自引：0，他引：1  

Aaron J. Slowey  Gordon E. Brown Jr. 《Geochimica et cosmochimica acta》2007,71(4):877-894

Methylmercury can accumulate in fish to concentrations unhealthy for humans and other predatory mammals. Most sources of mercury (Hg) emit inorganic species to the environment. Therefore, ecological harm occurs when inorganic Hg is converted to methylmercury. Sulfate- and iron-reducing bacteria (SRB and FeRB) methylate Hg, but the effects of processes involving oxidized and reduced forms of sulfur and iron on the reactivity of Hg, including the propensity of inorganic Hg to be methylated, are poorly understood. Under abiotic conditions, using a laboratory flow reactor, bisulfide (HS⁻) was added at 40 to 250 μM h⁻¹ to 5 g L⁻¹ goethite (α-FeOOH) suspensions to which Hg(II) was adsorbed (30-100 nmol m⁻²) at pH 7.5. Dissolved Hg initially decreased from 10³ or 10⁴ nM (depending on initial conditions) to 10⁻¹ nM, during which the concentration of Hg(II) adsorbed to goethite decreased by 80% and metacinnabar (β-HgS_(s)) formed, based on identification using Hg L_III-edge extended X-ray absorption fine structure (EXAFS) spectroscopic analysis. The apparent coordination of oxygens surrounding Hg(II), measured with EXAFS spectroscopy, increased during one flow experiment, suggesting desorption of monodentate-bound Hg(II) while bidentate-bound Hg(II) persisted on the goethite surface. Further sulfidation increased dissolved Hg concentrations by one to two orders of magnitude (0.5 to 10 nM or 30 nM), suggesting that byproducts of bisulfide oxidation and Fe(III) reduction, primarily polysulfide and potentially Fe(II), enhanced the dissolution of β-HgS_(s) and/or desorption of Hg(II). Rapid accumulation of Fe(II) in the solid phase (up to 40 μmol g⁻¹) coincided with faster elevation of dissolved Hg concentrations. Fe(II) served as a proxy for elemental sulfur [S(0)], as S(0) was the dominant bisulfide oxidation product coupled to Fe(III) reduction, based on sulfur K-edge X-ray absorption near edge structure (XANES) spectroscopy. In one experiment, dissolved Hg concentrations tracked those of all sulfide species [S(-II)]. These results suggest that S(-II) reacted with S(0) to form polysulfide, which then caused the dissolution of β-HgS_(s). A secondary Fe-bearing phase resembling poorly formed green rust was observed in sulfidized solids with scanning electron microscopy, although there was no clear evidence that either surface-bound or mineralized Fe(II) strongly affected Hg speciation. Examination of interrelated processes involving S(-II) and Fe(III) revealed new modes of Hg solubilization previously not considered in Hg reactivity models.  相似文献   

Runoff and erosion processes and rates in the Zin valley badlands,northern Negev,Israel     

A. Yair  H. Lavee  R. B. Bryan  E. Adar 《地球表面变化过程与地形》1980,5(3):205-225

Badland areas are usually regarded as impermeable zones which generate high runoff and are very vulnerable to sheetwash and rainsplash. To test those considerations sprinkling experiments using two rainfall simulators were carried out on slopes of varying aspect in the northern Negev (Israel). For one unit 1·5 m² plots were used with rainfall of natural characteristics at 36 mm/hr intensity and 43–48 minute duration, runoff being recorded and water/sediment samples taken every 5 minutes. The second unit was used on 30–50 m² plots but rainfall energy production was below that of natural rainfall. Results show that due to the high stability and strong flocculation of clay-rich aggregates rainsplash is ineffective in surface sealing so that infiltration capacities remain high despite intense, prolonged rainfall. Aspect differences are reflected in variation of surface properties despite homogenous bed-rock, which cause marked differences in hydrological response. North-facing slopes respond more quickly, more frequently and produce more runoff than south-facing slopes. Non-uniform runoff generation is also seen within plots of one aspect reflecting subtle variations in surface properties. Comparison of rainfall intensity and duration used during the experiments with those prevailing under natural conditions shows that under present day conditions surface flow in the Zin valley badlands must be extremely infrequent and denudation rates very low.  相似文献   

Holocene rockfalls in the southern Negev Desert,Israel and their relation to Dead Sea fault earthquakes     

Yair Rinat  Ari Matmon  Maurice Arnold  Georges Aumaître  Didier Bourlès  Karim Keddadouche  Naomi Porat  Efrat Morin  Robert C. Finkel 《Quaternary Research》2014

Rockfall ages in tectonically active regions provide information regarding frequency and magnitude of earthquakes. In the hyper-arid environment of the Dead Sea fault (DSF), southern Israel, rockfalls are most probably triggered by earthquakes. We dated rockfalls along the western margin of the DSF using terrestrial cosmogenic nuclides (TCN). At each rockfall site, samples were collected from simultaneously exposed conjugate boulders and cliff surfaces. Such conjugate samples initially had identical pre-fall (“inherited”) TCN concentrations. After boulder detachment, these surfaces were dosed by different production rates due to differences in post-fall shielding and geometry. However, in our study area, pre-rockfall inheritance and post-rockfall production rates of TCN cannot be evaluated. Therefore, we developed a numerical approach and demonstrated a way to overcome the above-mentioned problems. This approach can be applied in other settings where rockfalls cannot be dated by simple exposure dating. Results suggest rockfall ages between 3.6 ± 0.8 and 4.7 ± 0.7 ka. OSL ages of sediment accumulated behind the boulders range between 0.6 ± 0.1 and 3.4 ± 1.4 ka and support the TCN results. Our ages agree with dated earthquakes determined in paleoseismic studies along the entire length of the DSF and support the observation of intensive earthquake activity around 4–5 ka.  相似文献   

Systematic winds at heights between 350 and 675 km from analysis of the orbits of four balloon satellites     

Jack W. Slowey 《Planetary and Space Science》1975,23(5):879-886

Six values of the rate of rotation of the Earth's upper atmosphere have been obtained by analysis of the orbital inclinations of four balloon satellites in the intervals just before the final decay of their orbits. The effective heights of these results range from about 350 to about 675 km. The values themselves range from 0·8 to 1·4 times the Earth's rotation and correspond to zonal wind speeds between 100 m/sec westward and 200 m/sec eastward. All the results correspond to fairly specific local times and are consistent with a diurnal wind pattern in low latitudes having a strong eastward maximum near local midnight and a lesser westward maximum near 10:00 LT. They argue against the contention of a sharp decrease in the rate with respect to that of the Earth, which is supposed to begin at about 360 km. The factors involved in the determination of these values and the method used are discussed in considerable detail.  相似文献   

Hydropedology of a mildly‐arid loess covered area,southern Israel          下载免费PDF全文

Aaron Yair  Naftali Goldshleger  Yossi Shachar 《地球表面变化过程与地形》2017,42(5):781-788

Extensive loess covered areas characterize the mildly arid areas of western Israel, where average annual rainfall is 280 mm. Hydrological data point to a peculiar hydrological behavior of the ephemeral streams. The frequency of sporadic flash floods is very high. However, even in extreme rain events peak discharges are extremely low. Hydrographs are usually characterized by very steep rising and falling limbs, representative of saturated areas, extending over a limited part of the watershed. Following this observation we advanced the hypothesis that storm channel runoff originated in the channel itself, with negligible contribution from the adjoining hillslopes. The study was based on two complementary approaches. The hydrological approach was based on the detailed analysis of rainfall–runoff relationships in a small watershed (11 km²) and on the analysis of the hydrological characteristics of the drainage network. The second approach was based on the toposequence concept. Several boreholes were dug along a hillslope 400 m long. Chemical data obtained show no significant difference in the downslope direction. Similar results were also obtained for the particle size distribution and soil moisture content. Data obtained perfectly fit the concept of ‘Partial Area Contribution’ as it presents an extreme case of hydrological discontinuity at the hillslope–channel interface. The lack of pedological trends in the downslope direction is an additional indication of the limited connectivity between the hillslopes and the adjoining channel. The limited connectivity is attributed to the prevalence of low rain intensities in the study area. The present study is also relevant to our understanding of pedological processes in dryland areas. The high frequency of intermittent low intensity rainstorms limits runoff generation and flow distances, and casts doubt on the general application of the toposequence approach. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Crustal Structure of Israel: Constraints From Teleseismic and Gravity Data   总被引：1，自引：0，他引：1  

Abraham Hofstetter  Lea Feldman  Yair Rotstein 《Geophysical Journal International》1991,104(2):371-379

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Runoff generation in a sandy area—the nizzana sands,Western Negev,Israel     

A. Yair 《地球表面变化过程与地形》1990,15(7):597-609

This paper presents the results of sprinkling experiments conducted over the lower part of vegetated and crusted linear dunes as well as over flat playa surfaces that appear in the interdune corridors. Data obtained show that these two surface units respond quickly to rainstorms. Runoff generation can be expected for any storm exceeding 2-3 mm and runoff coefficients are high. When the topsoil algal crust, 1 to 2 mm thick, is removed from the surface of the dune, infiltration increases drastically and eliminates any possibility of runoff generation under present-day rainfall conditions. This data may be of great help in the understanding of the geomorphology and sedimentary sequence of the corridors separting linear dunes.  相似文献   

Can severe rain events over the Mediterranean region be detected through simple numerical indices?   总被引：1，自引：0，他引：1  

B. Ziv  N. Harats  E. Morin  Y. Yair  U. Dayan 《Natural Hazards》2016,83(2):1197-1212

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