Interpreting the Ca isotope record of marine biogenic carbonates     

Neil G. Sime  Edward T. Tipper  Albert Galy 《Geochimica et cosmochimica acta》2007,71(16):3979-3989

An 18 million year record of the Ca isotopic composition (δ^44/42Ca) of planktonic foraminiferans from ODP site 925, in the Atlantic, on the Ceara Rise, provides the opportunity for critical analysis of Ca isotope-based reconstructions of the Ca cycle. δ^44/42Ca in this record averages +0.37 ± 0.05 (1σ SD) and ranges from +0.21‰ to +0.52‰. The record is a good match to previously published Neogene Ca isotope records based on foraminiferans, but is not similar to the record based on bulk carbonates, which has values that are as much as 0.25‰ lower. Bulk carbonate and planktonic foraminiferans from core tops differ slightly in their δ^44/42Ca (i.e., by 0.06 ± 0.06‰ (n = 5)), while the difference between bulk carbonate and foraminiferan values further back in time is markedly larger, leaving open the question of the cause of the difference. Modeling the global Ca cycle from downcore variations in δ^44/42Ca by assuming fixed values for the isotopic composition of weathering inputs (δ^44/42Ca_w) and for isotope fractionation associated with the production of carbonate sediments (Δ_sed) results in unrealistically large variations in the total mass of Ca²⁺ in the oceans over the Neogene. Alternatively, variations of ±0.05‰ in the Ca isotope composition of weathering inputs or in the extent of fractionation of Ca isotopes during calcareous sediment formation could entirely account for variations in the Ca isotopic composition of marine carbonates. Ca isotope fractionation during continental weathering, such as has been recently observed, could easily result in variations in δ^44/42Ca_w of a few tenths of permil. Likewise a difference in the fractionation factors associated with aragonite versus calcite formation could drive shifts in Δ_sed of tenths of permil with shifts in the relative output of calcite and aragonite from the ocean. Until better constraints on variations in δ^44/42Ca_w and Δ_sed have been established, modeling the Ca²⁺ content of seawater from Ca isotope curves should be approached cautiously.  相似文献   

The Dark Matter Problem     

Albert Bosma 《Celestial Mechanics and Dynamical Astronomy》1998,72(1-2):69-90

In these notes I will briefly summarize our knowledge about the dark matter problem, and emphasize the corresponding dynamical aspects. This covers a wide area of research, so I have been selective, and have concentrated on the subject of dark matter in nearby galaxies, in particular spirals. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Crustal thickening and crustal extension as controls on the evolution of the drainage network of the central Swiss Alps between 30  Ma and the present: constraints from the stratigraphy of the North Alpine Foreland Basin and the structural evolution of the Alps     

Fritz Schlunegger  Rudy Slingerl  & Albert Matter 《Basin Research》1998,10(2):197-212

The combined information about sedimentary petrography from the North Alpine Foreland Basin and structural geology from the Alps allows a qualitative reconstruction of the drainage network of the central Swiss Alps between 30 Ma and the present. This study suggests that crustal thickening and crustal thinning significantly controlled the location of the drainage divide. It also reveals the possible controls of crustal thickening/thinning on the change of the orientation of the drainage network from across-strike between 30 and 14 Ma to along-strike thereafter. Initial crustal thickening in the rear of the wedge is considered to have formed the drainage divide between north and south at 30 Ma. Because the location of crustal thickening shifted from east to west between ≈30–20 Ma, the catchment areas of the eastern dispersal systems reached further south than those of the western Alpine palaeorivers for the same time slice. Similarly, the same crustal dynamics appear to have controlled two phases of denudation that are reflected in the Molasse Basin by petrographic trends. Uplift in the rear of the wedge caused the Alpine palaeorivers to expand further southward. This is reflected in the foreland basin by increasing admixture of detritus from structurally higher units. However, tectonic quiescence in the rear of the wedge allowed the Alpine palaeorivers to cut down into the Alpine edifice, resulting in an increase of detritus from structurally lower units. Whereas uplift in the rear of the wedge was responsible for initiation of the Alpine drainage systems, underplating of the external massifs some 50 km further north is thought to have caused along-strike deviation of the major Alpine palaeorivers. Besides crustal thickening, extension in the rear of the wedge appears to have significantly controlled the evolution of the drainage network of the western Swiss Alps. Slip along the Simplon detachment fault exposed the core of the Lepontine dome, and caused a 50-km-northward shift of the drainage divide.  相似文献   

Lead and copper in the waters of Raritan and Lower New York Bays     

Ruth Waldhauer  Albert Matte  Robert E Tucker 《Marine pollution bulletin》1978,9(2):38-42

A survey of waters adjacent to this heavily urbanized and industrialized region showed concentrations of copper, 65 μg l.^?1 to be the highest reported to date for estuarine waters, and lead up to 13.9 μg l.^?1 Correlations between distributions of dissolved and total metal concentration in the water column, hydrography, and metal in the sediment were related to benthic studies in this area. Laboratory studies are cited which show the potential for adverse effects on marine animals at these metal concentrations.  相似文献   

Environmental changes during the past 2000 years in north-central Wisconsin: Analysis of pollen,charcoal, and seeds from varved lake sediments     

Albert M. Swain 《Quaternary Research》1978,10(1):55-68

A 2000-year accumulation of varved sediments from Hell's Kitchen Lake in north-central Wisconsin was analyzed for pollen, charcoal, and seeds. The varves provided an accurate time scale for the study. The pollen record indicates changes on two different time scales. Short-term changes lasting several decades appear to be superimposed on long-term changes lasting several centuries. The short-term changes are related to individual fires, and the long-term changes result from increases or decreases in the frequency of these perturbations. From 2000 to 1150 years ago the average interval between fires was about 100 years, and from 1150 to 120 years ago the interval increased to about 140 years. Evidence from pollen, seeds, and charcoal at Hell's Kitchen Lake suggests that at least two “moist” intervals occurred during the past 2000 years, one between 2000 and 1700 years ago and the other between 600 and 100 years ago. A third but minor “moist” period occurred about 1150 to 850 years ago. A pollen and seed diagram shows that these intervals are characterized by increased percentages of white pine pollen, hemlock pollen, and yellow birch seeds, and by decreased levels of charcoal. The “dry” interval of 1700 to 1150 years ago is characterized by increased percentages of paper birch seeds, oak pollen, and aspen pollen, along with high levels of charcoal. The times of climatic change indicated at Hell's Kitchen Lake are nearly synchronous with those based on studies of tree rings, soils, glacial activity, and other pollen studies from various regions of North America, but the direction of these inferred changes is not always the same. This result suggests that the long-wave pattern of the general circulation has been variable during the past 2000 years.  相似文献   

Paleobotany of Wisconsinan interstadials, eastern Great Lakes region, North America     

Albert A. Berti   《Quaternary Research》1975,5(4):591-619

This study concerns the pollen and plant macrofossils from Mid-Wisconsinan Interstadial sites within the Wisconsinan ice margin in eastern North America. The time period covered is from about 55,000 years BP to 22,500 years BP, an interval much longer than the postglacial. Sediments examined are principally those of large lakes deposited in the Erie and Ontario basins during intervals of ice retreat.The Port Talbot I Interval (from about 55,000 to 50,000 years BP) in the Erie basin is characterized by pollen assemblages alternating from Pinus-dominated zones to ones with abundant Pinus, Quercus, and nonarboreal pollen. These assemblages are interpreted as indicating relatively warm and dry conditions. Mean July temperatures fluctuated between 15 and 21°C.During the succeeding Port Talbot II Interval and Plum Point Interstadial, in both the Erie and Ontario basins, pollen assemblages are characterized by dominant Pinus and Picea. Characteristic macrofossils include needles of the boreal Picea and Larix and leaves of species with a more northerly distribution, such as Dryas integrifolia, Betula glandulosa var. glandulosa, Vaccinium uliginosum var. alpinum, and Salix herbacea. These fossil assemblages are interpreted as indicating cooler and moister conditions in a forest-tundra environment. Mean July temperatures fluctuated between 10 and 15°C during the Port Talbot II Interval and Plum Point Interstadial.  相似文献   

Experimental confirmation of the lack of carbon isotope exchange between methane and carbon oxides at high temperatures     

William M. Sackett  H.Moses Chung 《Geochimica et cosmochimica acta》1979,43(2):273-276

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Parametric studies of physical conditions in the Earth's upper mantle     

Dae H. Chung 《Tectonophysics》1980,64(3-4)

Seismic body-wave and surface-wave data indicate the existence of a substantial lowvelocity, low-Q zone in the upper mantle beneath western North America. Conditions in this zone are distinctively different from those that are typical of the upper mantle in shield regions. The present study, using Walsh's model for partially melted rock, suggests a common mechanism for low-velocity and low-Q zones. This parametric study also indicates that the pronounced low-velocity, low-Q zone and anomalous travel-time delays of both P and S waves in the Basin and Range Province are consistent with the combined effects of high temperature, chemical composition, phase changes, and partial melting. The observed low P_n velocity in this region is consistent with high temperature, chemical composition, and the presence of a partially molten layer within the upper mantle, but the observed teleseismic delay times result principally from the thickness of the lowvelocity zone. The teleseismic delay-time variations are therefore related to the seismic Q distribution in the asthenosphere. Conditions a few kilometers beneath the Moho boundary influence the P_n velocity; however, the observed correlation among the teleseismic signal amplitudes, travel-time delays, and the upper mantle Q indicates that the P_n velocity is a better indicator of upper mantle Q than suggested by the P_n path alone. This knowledge of the upper mantle seems to account for the anomalous effects of the Basin and Range Province and other regions of similar tectonic nature on observations of teleseismic events. This will provide a practical technique for comparing seismic observations made in unstable tectonic regions with observations made in shield areas.  相似文献   

A²²⁶Ra section across the East Pacific Rise     

Y. Chung 《Earth and Planetary Science Letters》1980,49(2):319-328

Four vertical Ra profiles have been measured across the East Pacific Rise (EPR) from Callao to Tahiti. These profiles show that Ra in the deep water (below 2 km depth) increases toward the EPR. However, this increase does not necessarily indicate a Ra source on the EPR. The increase from Tahiti toward the EPR reflects the general trend of the Pacific Ra distribution. The decrease from the EPR eastward to the Peru Basin is probably due to the continental effect with higher sedimentation rates.The hydrography, especially potential temperature and oxygen, indicates significant differences below about 3 km depth between the east and west flanks of the EPR indicating the effect of the cold bottom water to the west of the EPR. The benthic front is identified at 3.9 km depth at the westernmost station near Tahiti. Silicate and salinity data are by no means unique and reflect a complicated local circulation and mixing pattern with a minor intrusion of the Antarctic Bottom Water from the south into the Peru Basin.The θ-Ra and Ra-Si relationships both indicate an enrichment of Ra in the deep water below 2 km depth probably due to input from the underlying sediments. Above 2 km depth, Ra covaries almost linearly with θ as well as Si, mimicking a stable conservative property. This suggests that the radiodecay rate is nearly balanced by the input rate within the water column between 1 and 2 km depth in which θ is linearly correlated withS.Simple vertical model calculations show that the in-situ production of Ra by particulate dissolution in the deep water is negligible within a reasonable range of upwelling rates from 2 to 12 m/yr. Thus the Ra profiles show a net decay effect and so the θ-Ra relations are not linear in the deep water. In fact, the composite θ-Ra plots show a break at 25 dpm/100 kg (at 2 km depth) rather than a smooth curve, while theθ-S plots are essentially linear. A maximum Ra production rate of about 8 × 10^?3 (dpm/100 kg) yr^?1 is obtained from all the profiles with minimum upwelling rates between 0.7 and 3.5 m/yr.  相似文献   

Sedimentation in Lake Biel,an eutrophic,hard-water lake in northwestern Switzerland   总被引：1，自引：0，他引：1  

Dr. Richard F. Wright  Prof. Albert Matter  Marc Schweingruber  Ulrich Siegenthaler 《Aquatic Sciences - Research Across Boundaries》1980,42(2):101-126

A 2-year study of sedimentation in Lake Biel reveals that three major factors can account for the spatial and temporal patterns of tripton sedimentation. Allochthonous inputs of particulate matter mostly derived from the Aare river during spring snowmelt and other high-water periods, provide about 50% of the carbonate and 50% of the siliceous matter collected in sediment traps. Phytoplankton activity in this eutrophic, hard-water lake accounts for the rest of the carbonate and siliceous matter, the latter being mostly diatom frustules. Sedimentation rates are thus highest during periods of maximum river flooding, maximum phytoplankton activity and following the breakdown of the thermocline, at which time trapped particles settle out. Resuspension of sediment is important in at least one basin. Resolution of carbonate appears to be minor.  相似文献