浮游有孔虫壳体Mg/Ca值--SST的替代性指标   总被引：5，自引：0，他引：5  

陈萍方念乔  胡超涌丁旋 《地球科学》2004,29(6):697-702

通过对东北印度洋区MD77181和MD81349两支岩心中Globigerinoides sacculifer壳体极为精细的清洗和溶样后,由ICP—MS测试获得了近260ka以来Mg／Ca值．结果表明Mg／Ca值与δ^18O值变化趋势较为吻合,随温度的增加而升高,浮游有孔虫G．sacculifer壳体Mg／Ca值是海洋表层水温(SST)良好的替代性指标．运用函数式Mg／Ca=0．4717exp(0．0825*SST)计算表明,包括印度洋在内的中、低纬地区,LGM时期的SST与全新世的温差大于最初CLIMAP推测的2℃,很可能达到4℃．  相似文献   

Relationships between sediment contamination and toxicity in San Francisco Bay     

B. Thompson  B. Anderson  J. Hunt  K. Taberski  B. Phillips 《Marine environmental research》1999,48(4-5)

Sediment contamination and toxicity were monitored at 14 sites in San Francisco Bay between 1991 and 1996. Sediment contamination patterns were different in the major reaches of the Bay, and at each site. Several contaminants were consistently above concentrations previously associated with toxicity at most sites. Bulk sediment bioassays using the amphipod Eohaustorius estuarius and sediment elutriate bioassays using larval bivalves (Mytilus spp., Crassostrea gigas) also indicated different patterns of sediment toxicity in space and time. Sediments were most toxic to the amphipods at Redwood Creek (90% of the tests), and were toxic in at least half the tests conducted at five other sites. Sediment elutriates severely reduced normal bivalve larval development at the San Joaquin and Sacramento Rivers in all samples, but toxicity occurred in less than a third of the tests in the Central and South Bays. Toxicity could not be statistically related to seasonal freshwater flow or rainfall in the Bay, but seasonal variation in contaminant concentrations and toxicity was observed. Amphipod toxicity was inversely and significantly related to the mean effects range-median quotient, suggesting that cumulative concentrations of several contaminants were related to toxicity. Further analysis identified suites of specific contaminants at each site that were variably related to amphipod toxicity at each site. Chlordanes, cadmium, and silver were significantly related to amphipod survival in the North Bay. Seasonal patterns in low, and high molecular weight polycyclic aromatic hydrocarbons (PAHs) were related to toxicity at Alameda, and metals and PAHs were related to toxicity at Castro Cove. Larval bivalve toxicity was associated with metals in bulk sediments, but elutriate chemistry was not measured, and relationships with toxicity could not be examined. Hypotheses about effective concentrations of several individual contaminants and mixtures of contaminants were posed.  相似文献   

Comet Hale—Bopp Shells Expansion: A CCD Study     

Manzini  Federico  Crippa  Roberto  Oldani  Virgino  Guaita  Cesare 《Earth, Moon, and Planets》1999,87(2):73-85

Using a CCD camera attached to the 0.335 m and 0.20 m reflectors of S.A.S. Observatory (Novara, Italy), we followed the linear jets and shells of comet Hale–Bopp between May 1996 and May 1997. In addition to confirming the model of Sekanina and Bohenhardt (1997), the study of the linear jets provided indications concerning the orientation of the comet's axis of rotation over time. The study of the shells revealed that the speed at which they move away from the nucleus was not constant. A periodic variation of the shell expansion velocity may not be excluded : if so, a possible precessional effect on the axis of rotation of the comet's nucleus could explain this behavior. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

介形类壳体中Sr/Ca及Mg/Ca比值的ICP-AES测定   总被引：1，自引：0，他引：1  

朱育新  吉磊  王苏民 《湖泊科学》1996,8(2):179-183

沉积物中介形类壳体的Ｓｒ／Ｃａ和Ｍｇ／Ｃａ比值可用于湖泊古盐度和古温度的重建。本文从双通道顺序扫描式ＩＣＰ－ＡＥＳ的特点出发,对μｇ级介形类样品中的低含量元素Ｓｒ和Ｍｇ选择最灵敏谱线和最佳通道,对各项条件进行最优化。Ｓｒ和Ｍｇ的检测限分别为１．１μｇ／Ｌ和１．４μｇ／Ｌ。本文以此法准确测定了介形类样品中Ｓｒ／Ｃａ比值和Ｍｇ／Ｃａ比值,回收率实验结果令人满意。  相似文献   

Rayleigh wave dispersion equation for a layered spherical earth with exponential function solutions in each shell     

Swarn Arora  S. N. Bhattacharya  M. L. Gogna 《Pure and Applied Geophysics》1996,147(3):515-536

We consider the second-order differential equations ofP-SV motion in an isotropic elastic medium with spherical coordinates. We assume that in the medium Lamé's parameters , r ^p and compressional and shear-wave velocities , r, wherer is radial distance. With this regular heterogeneity both the radial functions appearing in displacement components satisfy a fourth-order differential equation which provides solutions in terms of exponential functions. We then consider a layered spherical earth in which each layer has heterogeneity as specified above. The dispersion equation of the Rayleigh wave is obtained using the Thomson-Haskel method. Due to exponential function solutions in each layer, the dispersion equation has similar simplicity, as in a flat-layered earth. The dispersion equation is further simplified, whenp=–2. We obtain numerical results which agree with results obtained by other methods.  相似文献   

Infrared appearance of dynamical models for circumstellar dust shells around long-period variables     

J. M. Winters  A. J. Fleischer  E. Sedlmayr  A. Gauger 《Astrophysics and Space Science》1995,224(1-2):329-332

Synthetic brightness profiles resulting from consistent dynamical models for circumstellar dust shells around long-period variables are presented and discussed with respect to a corresponding observation of IRC +10216.  相似文献   

Sodium and strontium in mollusc shells: preservation,palaeosalinity and palaeotemperature of the Middle Pleistocene of eastern England     

Genevive Findlater  Adam SheltonTimothy Rolin  Julian Andrews 《Proceedings of the Geologists' Association. Geologists' Association》2014

This paper revisits the utility of sodium (Na) content in aragonite and calcite mollusc shells as an indicator of palaeosalinity. The data come mainly from a related suite of Middle Pleistocene marine and freshwater fossils that have been subject to broadly similar diagenetic histories. Environmental salinity is re-affirmed as the primary factor in determining the sodium content of modern and ancient mollusc shells: values <2000 ppm Na are generally indicative of non-marine environments while values >2000 Na ppm are typically from marine shells. There is a positive relationship between Na (salinity) and Sr which is a helpful discriminator of palaeosalinity in the fossil data set. The Na and Sr data give confidence that the fossil shells have not suffered pervasive diagenetic alteration and that the marine fossils lived in fully marine conditions. Oxygen isotope values in the best-preserved, fully marine fossil shells, suggest Middle Pleistocene ‘eastern England’ seawater temperatures were broadly similar to those of the modern North Sea.  相似文献   

Recognizing cryptic environmental changes by using paleoecology and taphonomy of Pleistocene bivalve assemblages in the Oga Peninsula,northern Japan     

Tomoki Chiba  Masaaki Shirai  Shin'ichi Sato 《Quaternary Research》2014

Multivariate analyses applied to Pleistocene bivalve assemblages from the Oga Peninsula (northern Japan) discriminate three distinct assemblages. The assemblages and their taphonomy were used to recognize environmental settings and changes. The Astarte–Cyclocardia–Glycymeris assemblage indicates shelf environment (below the storm wave base) where gravels and shells are transported from shallower settings. Supply of the exotic coarse sediment probably enabled epifaunal bivalves to inhabit the sea floor. The Glycymeris assemblage is characterized by dominance of G. yessoensis and represents current-swept shoreface environment (above the storm wave base). The Moerella assemblage is characterized by bivalves inhabiting bay to open-marine conditions and diverse deposit-feeders, indicating a moderately land-locked environment, such as an open bay or a bay mouth. Fine-grained substrata rich in organic matters in the bay were probably suitable for the deposit-feeders. Ordination also shows the assemblages along two environmental gradients, a bathymetrical one and the other related to open-marine and bay conditions. The environmental changes are explained mainly by glacio-eustatic sea-level changes and alternation of coastal geomorphology caused by local crustal movements. This study also suggests that fossil assemblages can be a powerful tool to reconstruct environments and depositional dynamics even in intensely bioturbated sedimentary facies.  相似文献   

Unusual infrared fading of CH Cygni in 2006     

O. G. Taranova  V. I. Shenavrin 《Astronomy Letters》2007,33(8):531-535

Infrared observations of the unique symbiotic system CH Cyg in 2003–2006 are presented. Analysis of the observations has shown that a fairly dense dust structure (a cloud or a shell) appeared on the line of sight in August–November 2006. The dust grains in the new shell are similar in optical properties to graphite ones and their sizes are mostly within the range 0.14–0.16 μm. The dust shell is optically thick and its optical depth at 2.2 μm is τ(2.2) ≈ 0.97. The dust shell mass is M _d(06) ≈ 8 × 10⁻⁶ M _⊙ and the rate of matter flow into the shell has reached ∼2 × 10⁻⁵ M _⊙ yr⁻¹. Original Russian Text ? O.G. Taranova, V.I. Shenavrin, 2007, published in Pis’ma v Astronomicheskiĭ Zhurnal, 2007, Vol. 33, No. 8, pp. 598–603.  相似文献   

Possible evidence for on-going volcanism on Mars as suggested by thin, elliptical sheets of low-albedo particulate material around pits and fissures close to Cerberus Fossae     

Gerald Patrick Roberts  Ian A. Crawford  David Peacock  Joyce Vetterlein  Elisabeth Parfitt  Louise Bishop 《Earth, Moon, and Planets》2007,100(1-2):1-16

High quality CCD images obtained at two different observatories in North Italy allowed the identification of four morphological structures near the nuclear region of the comet Ikeya-Zhang (I-Z): haloes, jets, shells and spirals. The interpretation of the nature of these structures has been attempted by means of a comparison of different up-to-date image processing techniques, which led to a single common estimate of the rotation period (p=1.48±0.20 days).  相似文献