The impact of glaciation, river-discharge and sea-level change on Late Quaternary environments in the southwestern Kara Sea     

Leonid Polyak  Mikhail Levitan  Valery Gataullin  Tatiana Khusid  Valery Mikhailov  Valentina Mukhina 《International Journal of Earth Sciences》2000,89(3):550-562

Sedimentary records from the southwestern Kara Sea were investigated to better understand the extent of the last glaciation on the Eurasian Arctic shelf, sea-level change, and history of the Ob' and Yenisey river discharge. Sediment-core and seismic-reflection data indicate that the Quaternary depositional sequence in the southwestern Kara Sea consists of glacial, glaciomarine, and marine sedimentary units. Glaciogenic sediments in the deep Novaya Zemlya Trough are presumably related to the Last Glacial Maximum (LGM), whereas further east they may represent an earlier glaciation. Thus, it is inferred that the southeastern margin of the LGM Barents-Kara ice sheet was contained in the southwestern Kara Sea east of the Novaya Zemlya Trough. Changes in mineralogical, foraminiferal, and stable-isotopic composition of sediment cores indicate that riverine discharge strongly influenced sedimentary and biotic environments in the study area during the Late Weichselian and early Holocene until ca. 9 ka, consistent with lowered sea levels. Subsequent proxy records reflect minor changes in the Holocene hydrographic regime, generally characterized by reduced riverine inputs.  相似文献   

Observations on New Approaches for the Determination of Platinum-Group Elements, Gold and Silver in Different Geochemical Samples from Siberia and the Far East   总被引：1，自引：0，他引：1  

Valentina G. Tsimbalist  Gennady N. Anoshin  Valentin N. Mitkin  Ljudmila I. Razvorotneva  Nadezhda P. Golovanova 《Geostandards and Geoanalytical Research》2000,24(2):171-182

Some recent experiments on the determination of Au and the platinum-group elements (PGE) in geochemical samples are reviewed. Emphasis is given to the determination of ultra-low levels of PGE concentrations in resistant matrices, including chromites, molybdenites and ultrabasic ores. The problems and features of PGE determination in samples of various chemical composition are considered. For each sample type studied, a series of sample preparation techniques are proposed. These techniques included acid digestion, fusion with sodium peroxide, cold sintering with an oxidizing mixture of Na₂O₂+ Na₂CO₃ and also oxidizing fluorination with bromine trifluoride. A new approach for preparing geochemical material prior to digestion, based on mechano-chemical activation with simultaneous hyperfine grinding, is proposed and studied. The instrumental determination of PGE contents was carried out directly by AAS from extracted organic phases. It was found that a combination of digestion processes was required to achieve geochemical background levels of Au and PGE concentrations with the following detection limits: Pd, Rh - 1 ng g⁻¹, Pt, Ru - 10 ng g⁻¹, Au - 0.2 ng g⁻¹, Ag - 0.1 ng g^−1. The uncertainty in PGE and Au determination in geochemical samples is dependent on metal concentration, and also on their distribution in samples. The total analytical uncertainty of the proposed method is between 15-30%.  相似文献   

The distribution of trace metals in Florida Bay sediments   总被引：1，自引：0，他引：1  

Caccia VG  Millero FJ  Palanques A 《Marine pollution bulletin》2003,46(11):1420-1433

The distribution of trace metals based on surface sediments collected at 40 stations across Florida Bay was done in June, November and February 2000-2001. Concentrations of Sc, V, Ba, Cd, Cr, Co, Cu, Pb, Mn, Ni, Zn, Al and Mg were determined by ICP-MS, and the total Fe was determined by spectrophotometry. Organic carbon (OC), nitrogen (N), and calcium carbonate (CaCO3) were also measured. Eleven of 13 metals showed a similar distribution pattern for the various months studied. Maximum concentrations of metals were lower than those found in most estuarine systems and were concentrated in the north-central and western zones of the Bay. The Mn and Fe concentrations, unlike the other metals, gradually decreased from north (Everglades) to south (Florida Keys). Some metals (Ni, Zn, Cu, Cr, Pb and Ba) associated with petroleum use showed high concentrations at stations near the Tavernier marina. Florida Bay sediments are predominately CaCO3 (65.9-92.5%). The greatest value for OC (5.5%) and the lowest value of CaCO3 (65.9%) were found in the western zone. Trace metal distribution patterns are similar to the OC and N in the sediments. There was a strong correlation between most metals (V>Cu>Ni>Cr>Al>Co>Ba>Zn>Pb>Mg) and the percentage of OC. The maximum C/N values (9-12) were observed at the stations with the highest OC, where dense colonies of seagrass are found and most of the metals are concentrated. All metals except Mg, Mn and Co showed a strong correlation with Al and the fine fraction of the sediments (aluminosilicates) associated with continental input and river runoff.  相似文献   

Effects of climate, invasive species and anthropogenic impacts on the growth of the seagrass Posidonia oceanica (L.) Delile in Liguria (NW Mediterranean Sea)     

Peirano A  Damasso V  Montefalcone M  Morri C  Bianchi CN 《Marine pollution bulletin》2005,50(8):817-822

Eight shallow water Posidonia oceanica meadows were sampled in June 1999 along 300 km of the Ligurian coast and were compared through shoot density and lepidochronology. The growth of the seagrass was examined in the light of climate fluctuations and local stresses, colonisation by alien, invasive alga Caulerpa taxifolia, and effects of the oil spill from the tanker "Haven", and other anthropogenic impacts. Both shoot density and lepidochronology pointed to a generalised state of regression of all the meadows. The analysis of long-term growth curves of the rhizomes showed a positive trend parallel to the increase of air temperature. Two main groups of meadows were individuated on the basis of growth curve similarity. The first included four meadows, namely Ventimiglia, Imperia, Noli and Prelo, that were characterised by average values of rhizome growth of 8-9.1 mmyear(-1) and shoot density greater than 200 shootsm(-2). Although the Imperia meadow was the only one where the alien invasive alga C. taxifolia was found, it did not show differences for rhizome growth in comparison to the other meadows. The second group was formed by meadows that had suffered past anthropogenic impacts: Arenzano and Monterosso al Mare. They showed higher rhizome growth rates (9.4-10.6 mmyear(-1)) and shoot densities between 200 and 100 shootsm(-2). At Arenzano, where "Haven" oil was stranded in April 1991, no rhizome older than 8 years was found, thus confirming the shoot mortality induced by the oil spill event. The two last meadows exhibited growth curves very different from all the others: Portovenere, is a shallow meadow where P. oceanica merely survives in an extremely degraded situation with highest rhizome growth rate (12 mmyear(-1)), the other, Riva Trigoso, is the only meadow implanted on rock and had the lowest growth rates (7.1 mm year(-1)).  相似文献   

Women as individuals and members of minority groups: how to reconcile human rights and the values of cultural pluralism     

Valentina Capurri 《GeoJournal》2006,65(4):329-337

The paper represents an attempt to understand how, in a democratic and pluralistic state, it is possible to reconcile the values of individual freedom with those granted to minority groups. In this perspective, the paper argues that, without questioning the importance of differentiated cultural rights that allow cultural minorities to be on an equal footing with the mainstream society, women’s rights cannot be ignored. Instead, rights for women are not exclusive of any particular culture or society, being indeed one of the human rights common to all groups of people, those rights which attest to the existence of a bond among individuals as members of the human community.  相似文献   

Linking two centuries of tree growth and glacier dynamics with climate changes in Kamchatka     

Jiri Dolezal  Jan Altman  Valentina P. Vetrova  Toshihiko Hara 《Climatic change》2014,124(1-2):207-220

Glaciers around the world retreated as the climate warmed substantially. For the majority of alpine and arctic areas, however, the lack of meteorological data over a long period makes it difficult to build long-term climate and glacial fluctuation relationships, emphasizing the importance of natural proxy archives. Here we use the 230-year record of stem radial growth of birch trees (Betula ermanii) from the treeline forests above the receding glaciers in eastern maritime Kamchatka to analyse temporal variations of climate as well as glacial advance and retreat. Glaciers in Kamchatka Peninsula represent the southern limit of glaciation in far eastern Eurasia, which makes them prone to global warming. Using instrumental climate data (1930–1996) from local meteorological stations, we find that the July temperature had most prominent positive impact on birch growth. On the contrary, smaller ring increments are associated with the positive summer and net annual ice mass balance of Koryto Glacier. The prevailing trend of higher summer temperatures and lower snowfall over the past 70 years has enhanced tree growth while causing the glacier’s surface to lower by about 35 m and its front to retreat by about 490 m. Assuming these same relationships between climate, tree growth, and glacier mass balance also existed in the past, we use tree rings as a proxy record of climatically induced temporary halts in the glacier’s retreat over the past two centuries, which in total was over 1,000 m. Both direct observations and tree ring proxies indicate several prolonged warm periods (1990s, 1960s, 1930–1940s, 1880–1900s) interspersed with cooler periods (1984–1985, 1970–1976, 1953–1957, 1912–1926, 1855–1875, 1830–1845, 1805–1820 and 1770–1780) when the glacier re-advanced, creating several consecutive terminal moraine ridges. We conclude that birch tree-rings are suitable for assessing tree growth/climate/glacial relationships over a longer timescale in maritime Kamchatka.  相似文献   

A snapshot of the Late Jurassic Western Tethys seafloor composition and morphology provided by the geochemistry of pelitic sediments (Corsica,Central Alps and Northern Apennines)     

L. Bracciali  L. Pandolfi  S. Rocchi 《Basin Research》2014,26(3):461-485

The chemical composition of fine‐grained siliciclastic sediments is a powerful tool in provenance studies, either as a complement to other whole rock/single grain methods, or as a stand‐alone method when other techniques are not applicable, and particularly in those cases where the coarser sediment fractions are not available or the regional‐scale geologic framework is lost due major successive tectonic events. A comprehensive geochemical investigation of pelites from the post‐rift deposits of the Ligurian‐Piedmont ocean (sampled in tectonic units of the Alpine‐Apennine orogen: Balagne Nappe, Corsica; Tuscan Nappe and Internal Ligurian units, Northern Apennines; Err‐Platta units, Central Alps) has identified for the first time a major mafic‐ultramafic input immediately following rifting. Key trace element ratios (e.g. La_N/Yb_N < 10; avg. Eu/Eu* = 0.73 ± 0.06, 1SD; Th/(Cr + Ni + V) < 0.03) show that the pelitic siliciclastic layers intercalated in the Radiolarite Formation (the first post‐rift deposits) are systematically enriched in a mafic‐ultramafic source component compared with the younger post rift sediments (Calpionella Limestone and Palombini Shale). Such a peculiar chemical fingerprint is interpreted as the result of erosion and distribution across the whole basin (even to continental domains) of intraoceanic ophiolitic debris by turbidity and bottom currents sweeping the sea floor at the time of deposition of the Radiolarite Formation. Exhumed mantle and gabbroic‐basaltic rocks exposed at the morphologically articulated seafloor of the slow‐spreading Ligurian‐Piedmont ocean were available to erosion during the whole time‐span of the deposition of the Radiolarite Formation, whilst they became progressivey subordinate as a source as the basin floor was progressively covered by the siliciclastic input from the developing passive continental margins.  相似文献