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101.
We report here on cirque infills mapped in the Khibiny Mountains, Kola Peninsula, Russia. Cirque infills are morainic deposits located near the headwalls of valleys and cirques. Their location and shape, often with concave margins towards the valley side, indicate that they were deposited by ice flowing up‐valley, into the mountains, rather than by local glaciers. We suggest that they formed during the last deglaciation, when Khibiny was a nunatak and Fennoscandian ice sheet lobes extended into valleys and cirques of the massif. The formation of cirque infills is probably more related to ice sheet dynamic factors, occurring when the ice margin retreated from the cirques, than to climate‐driven interruption in the ice‐marginal retreat. Glacial conditions similar to those prevalent when the Khibiny cirque infills were formed, occur today in Antarctica where the ice sheets engulf nunatak ranges. In Heimefrontfjella, Antarctica, the formation of supraglacial moraines at the head of cirques are linked to blue‐ice conditions, indicating locally low accumulation rates, a dry continental climate and sublimation dominated ablation. We suggest that these Antarctic moraines are modern analogues of cirque infills on the Kola Peninsula, and possibly, that the cirque infills may be used as palaeoenvironmental indicators. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
102.
Shao-Yi Huang Yue-Gau Chen George S. Burr Manoj K. Jaiswal Yunung Nina Lin Gongming Yin Jingwei Liu Shujun Zhao Zhongquan Cao 《Quaternary Research》2014
We present a reconstructed lithologic column compiled from a series of lacustrine outcrops along a tributary of the Nyang River, a major tributary of the Yarlung-Tsangpo in southeast Tibet. The deposits were preserved between terraces at altitudes of 2950–3100 m asl. The stratigraphic record features at least two sets of coarsening-upward sequences depicting episodic aggradation and progradation of a glacially dammed lake related delta. Recognized facies changes illustrate the evolution cycles of depositional environments from pro-delta, delta front, to delta plain. Radiocarbon and optically stimulated luminescence dates reveal an aging-downward trend in stratigraphic order and provide an approximate timeline for the formation of glacially dammed lakes in late Pleistocene. This result reflects that the Zelunglung Glacier had progressively advanced to block the Yarlung-Tsangpo river and the dam materials had stepwise stacked up to an altitude of 3095 m asl during Marine Oxygen Isotope Stages 4 to 2. 相似文献
103.
Journal of Geographical Systems - Scale effects are pervasive in geospatial modeling and affect the reliability of analysis results. This paper examines the neighborhood scale effects on the... 相似文献
104.
Stark JS Johnstone GJ Palmer AS Snape I Larner BL Riddle MJ 《Marine pollution bulletin》2006,52(12):1595-1610
The water quality of a marine embayment (Brown Bay) was monitored during the remediation of an abandoned waste disposal site at Casey Station, East Antarctica, using a combination of biomonitoring and chemical methods. The Antarctic amphipod Paramoera walkeri, in field mesocosms suspended in the water column, was deployed adjacent to the site and at two reference sites for periods of 14 days, repeated three times during the remediation period (December to February). Diffusive gradients in thin film (DGT) samplers were deployed for the same periods to provide estimates of dissolved metals. No difference in mortality of amphipods was observed between Brown Bay and reference sites. There were significant differences, however, in accumulated metal concentrations between amphipods from Brown Bay and reference sites, with greater concentrations of antimony, copper, cadmium, lead, iron and tin at Brown Bay. The melt water/runoff treatment strategy employed for the remediation was successful in preventing acute toxic effects, but water quality was reduced at Brown Bay, where increased metal bioavailability may have been high enough to induce chronic effects in some biota. DGT samplers were less sensitive than amphipods in detecting differences in metal concentrations between sites, indicating that metals bound to suspended particulates were a potentially significant source of contamination. 相似文献
105.
Palmer AS Snape I Stark JS Johnstone GJ Townsend AT 《Marine pollution bulletin》2006,52(11):1441-1449
Remediation of the Thala Valley waste disposal site near Casey Station, East Antarctica was conducted in the austral summer of 2003/2004. Biomonitoring of the adjacent marine environment was undertaken using the gammaridean amphipod Paramoera walkeri as a sentinel species [Stark, J.S., Johnstone, G.J., Palmer, A.S., Snape, I., Larner, B.L., Riddle, M.J., in press, . Monitoring the remediation of a near shore waste disposal site in Antarctica using the amphipod Paramoera walkeri and diffusive gradients in thin films (DGTs). Marine Pollution Bulletin and references therein]. Determination of uptake of metals and hypothesis testing for differences that could be attributed to contamination required the establishment of baseline metal concentrations in P. walkeri. Baseline metal concentrations from two reference locations in the Windmill Islands are presented here. P. walkeri was a found to be a sensitive bioaccumulating organism that recorded spatial and temporal variability at the reference sites. Measurement of metals in P. walkeri required the development of a simple digestion procedure that used concentrated nitric acid. For the first time, rare earth metals were determined with additional clean procedures required to measure ultra low concentrations using magnetic sector ICP-MS. Certified and in-house reference materials were employed to ensure method reliability. 相似文献
106.
Rainfall thresholds for the initiation of landslides in central and southern Europe 总被引:20,自引:0,他引:20
F. Guzzetti S. Peruccacci M. Rossi C. P. Stark 《Meteorology and Atmospheric Physics》2007,98(3-4):239-267
Summary We review rainfall thresholds for the initiation of landslides world wide and propose new empirical rainfall thresholds for
the Central European Adriatic Danubian South-Eastern Space (CADSES) area, located in central and southern Europe. One-hundred-twenty-four
empirical thresholds linking measurements of the event and the antecedent rainfall conditions to the occurrence of landslides
are considered. We then describe a database of 853 rainfall events that resulted or did not result in landslides in the CADSES
area. Rainfall and landslide information in the database was obtained from the literature; climate information was obtained
from the global climate dataset compiled by the Climate Research Unit of the East Anglia University. We plot the intensity-duration
values in logarithmic coordinates, and we establish that with increased rainfall duration the minimum intensity likely to
trigger slope failures decreases linearly, in the range of durations from 20 minutes to ∼12 days. Based on this observation,
we determine minimum intensity-duration (ID) and normalized-ID thresholds for the initiation of landslides in the CADSES area.
Normalization is performed using two climatic indexes, the mean annual precipitation (MAP) and the rainy-day-normal (RDN).
Threshold curves are inferred from the available data using a Bayesian statistical technique. Analysing the obtained thresholds
we establish that lower average rainfall intensity is required to initiate landslides in an area with a mountain climate,
than in an area characterized by a Mediterranean climate. We further suggest that for rainfall periods exceeding ∼12 days
landslides are triggered by factors not considered by the ID model. The obtained thresholds can be used in operation landslide
warning systems, where more accurate local or regional thresholds are not available. 相似文献
107.
108.
Amphipoda are a diverse and important faunal component of deep‐sea habitats worldwide. However, relatively little is known about species that are associated with cold‐water corals, in particular concerning their genetic diversity, population genetic processes, population differentiation, and potential host specificity. We exemplarily investigate these questions studying three pleustid species—Stenopleustes aff. malmgreni (Boeck, 1871), Stenopleustes aff. nodifera (Sars, 1883) and Neopleustes aff. boecki (Hansen, 1888)—that are associated with cold‐water corals and polychaete assemblages along the Reykjanes Ridge southwest of Iceland. We sequenced mitochondrial COI and performed ddRAD to study thousands of nuclear loci. These species and a pair of morphologically cryptic species within Stenopleustes aff. nodifera were consistently delimited by COI and ddRAD. We conclude that all of our studied species are new to science, raising the number of pleustids reported from cold‐water corals to six. Two species were collected only once, and these species exhibited high levels of inbreeding, suggesting little exchange with other populations, which might be a result of strong host specificity. The other two species were wider distributed, with very low differentiation among populations, even between populations separated by 130 km. These species showed signs of recent population expansions, possibly in relation to changes in the cold‐water coral associated ecosystem (e.g., due to glacial cycles and/or volcanic or geothermal activities). They had lower levels of inbreeding and were each associated with three different host coral species, which might facilitate dispersal and gene flow. Our results show divergent population genetic patterns for the studied pleustid species. These might be attributed to the species’ host specificity and highlight important differences among species with seemingly similar life‐styles. Species diversities appear to be greatly underestimated, limiting our abilities to truly assess the vulnerability of the fauna living in these threatened cold‐water coral habitats. 相似文献
109.
Nina Keul John W. Morse Rik Wanninkhof Dwight K. Gledhill Thomas S. Bianchi 《Aquatic Geochemistry》2010,16(3):337-351
This paper presents the results of two cruises in the Northern Gulf of Mexico in 2008 that investigated local and short-term
factors influencing the carbonate chemistry dynamics and saturation state with respect to aragonite (Ωaragonite) of surface seawater in this region. One cruise covered much of the northern half of the Gulf, and the other focused on
the coastal zone west of the Atchafalaya Bay outlet of the Mississippi River—the region where the hypoxic “dead zone” occurs
on the Louisiana shelf. Offshore waters (>100 m depth) exhibited only small variations in CO2 fugacity (fCO2), total alkalinity (TA) and Ωaragonite. Values were close to those typically observed in subtropical Atlantic Ocean and Caribbean Sea waters of similar salinity.
However, inner shelf waters (<50 m depth) exhibited large variations in fCO2, TA, and Ωaragonite that were not directly related to salinity or distance from the Mississippi River plume. Changes in TA values were not the
result of simple mixing of end-member freshwater and seawater TA concentrations but exhibited a minimum in values near salinity
of 25. This minimum could be the result of microbial recycling across salinity gradients, biological removal of alkalinity
by formation of calcium carbonate or mixing of a third end-member with a low alkalinity such as Terrebonne Bay. All waters
were supersaturated with respect to aragonite. Offshore waters had an average Ωaragonite of 3.86 with a standard deviation of only ±0.06 and inner shelf waters had a range in Ωaragonite values from 3.9 to 9.7 with a median of 4.3. Shelf water Ωaragonite values were elevated relative to the offshore as a consequence of both high TA input from Mississippi River and biological
drawdown of CO2. A dominant factor controlling Ωaragonite distribution in offshore waters with relatively constant temperatures was fCO2, with higher supersaturation occurring in areas with low fCO2. 相似文献
110.
Julia Semprich Nina S. C. Simon Yuri Yu. Podladchikov 《International Journal of Earth Sciences》2010,99(7):1487-1510
Constraints on density as a function of pressure, temperature, and composition are crucial to understand isostatic movements
during geodynamic processes. Here, we provide a systematic series of density diagrams extracted from thermodynamic calculations
for a variety of crustal compositions within a wide P–T range. We quantify systematic density changes in collisional settings for relevant compositional variations and attempt to
simplify the density–composition relationships. Rock densities depend strongly on pressure, temperature, and composition.
Densities at some selected pressure–temperature conditions increase linearly with increasing Al2O3 as well as MgO/FeO contents in pelitic rocks. Al- and Fe-rich pelites yield the highest densities, which is mostly due to
the formation of garnet but also depends on other minerals and changes of reactions. The effect of loading on densities is
investigated, and we show that for deep burial, a meta-pelite rich in Fe and Mg yields much larger density changes than a
dry basalt and that the burial of such a rock with a composition close to typical lower crust may result in significant negative
buoyancy. Metamorphism of hydrous lower crust due to pressurization and heating thus leads to densification of thickened lower
crust, while heating of dry crust leads to a decrease in density. Hence, water-loaded isostatic subsidence due to metamorphism
of water-saturated lower crust is substantial and increases with the thickness and depth of the reacting layer, while dry
compositions show much less or only transient densification and subsidence. The density change due to thermal expansion, an
extensively used concept in geodynamic models, predicts uplift under the same P–T conditions and is an order of magnitude smaller than the density variation calculated from petrologically consistent diagrams. 相似文献