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1.
In their 2007 report, IPCC working group 1 refers to an increased heterogeneity of climate during medieval times about 1000 years ago. This conclusion would be of relevance, as it implies a contrast in the spatial signature and forcing of current warmth to that during the Medieval Warm Period. Our analysis of the data displayed in the IPCC report, however, shows no indication of an increased spread between long-term proxy records. We emphasize the relevance of sample replication issues, and argue that an estimation of long-term spatial homogeneity changes is premature based on the smattering of data currently available. 相似文献
2.
Kerstin S. Treydte David C. Frank Gerhard Helle Jan Esper 《Geochimica et cosmochimica acta》2009,73(16):4635-7303
We present one millennium-long (1171-year), and three 100 year long annually resolved δ13C tree-ring chronologies from ecologically varying Juniperus stands in the Karakorum Mountains (northern Pakistan), and evaluate their response to climatic and atmospheric CO2 changes. All δ13C records show a gradual decrease since the beginning of the 19th century, which is commonly associated with a depletion of atmospheric δ13C due to fossil fuel burning. Climate calibration of high-frequency δ13C variations indicates a pronounced summer temperature signal for all sites. The low-frequency component of the same records, however, deviates from long-term temperature trends, even after correction for changes in anthropogenic CO2. We hypothesize that these high-elevation trees show a response to both climate and elevated atmospheric CO2 concentration and the latter might explain the offset with target temperature data. We applied several corrections to tree-ring δ13C records, considering a range of potential CO2 discrimination changes over the past 150 years and calculated the goodness of fit with the target via calibration/verification tests (R2, residual trend, and Durbin-Watson statistics). These tests revealed that at our sites, carbon isotope fixation on longer timescales is affected by increasing atmospheric CO2 concentrations at a discrimination rate of about 0.012‰/ppmv. Although this statistically derived value may be site related, our findings have implications for the interpretation of any long-term trends in climate reconstructions using tree-ring δ13C, as we demonstrate with our millennium-long δ13C Karakorum record. While we find indications for warmth during the Medieval Warm Period (higher than today’s mean summer temperature), we also show that the low-frequency temperature pattern critically depends on the correction applied. Patterns of long-term climate variation, including the Medieval Warm Period, the Little Ice Age, and 20th century warmth are most similar to existing evidence when a strong influence of increased atmospheric CO2 on plant physiology is assumed. 相似文献
3.
Considered in the work are data characterizing stratotypes of regional and local stratigraphic subdivisions, which are distinguished in the Neopleistocene-Holocene sedimentary succession of the Caspian region. The succession is composed of sediments deposited by the Caspian transgressions and intervening continental sediments of the late Quaternary. Except for stratotypes of the Tyurkyany Horizon and Gyurgyany Formation, which are established in borehole sections, the other ones represent the well-stratified natural sections accessible for examination of their subdivisions distinguished based on biostratigraphic criteria. Mollusks of the genus Didacna Eichwald and fossil assemblages of large mammals are used to substantiate stratigraphy of marine and terrestrial deposits, respectively. 相似文献
4.
Between 2001 and 2005, a large debris rock slide occurred on the western slope of the Cordillera de Santa Cruz in the southeast
Andean corner of the Province of San Juan (31°40′ S–70°16′ W). The landslide material accumulated in a downstream gorge as
a natural dam of the Santa Cruz river, forming a large-volume lake. In November 2005, probably as a result of the increasing
pressure of the water volume, this natural dam breached off with a violent and unexpected flash flood. In addition to life-threatening
instances lived by some people downstream, this flood caused great economic loss to main localities of the Department of Calingasta,
as well as considerable damage to one of the most relevant projects of the Province, the Caracoles Hydropower Project dam
on the San Juan river. Considering the high costs of any physical remediation for a natural dam located in this high, remote,
and inaccessible mountain area with no reliable road access, the main protective measures left to be pondered are the installation
of a flash-flood early-warning system connected to downstream localities, along with a program of hydrological monitoring
at the dam-forming area and annual satellital monitoring to verify the evolution of accumulated mass movements. 相似文献
5.
6.
María Yanina Esper Angillieri 《Environmental Geology》2008,55(1):107-111
This work analyzes various morphometric characteristics of the Colangüil river basin in order to evaluate flash flood hazards.
Such high-water events pose a risk to the similarly named small village located at the basin’s foot area. For this purpose,
the basin is divided into seven sub-basins and some basic measurements (surface, perimeter, basin length, river beds, elevations
and slope of the main river bed, and of a number of minor river beds) are calculated. These measurements permit to predict
approximately the behavior of the basin in the presence of a series of theoretical rainstorms that may generate unusual runoff
volumes that make up such flash floods. 相似文献
7.
Long-term summer temperature variations in the Pyrenees 总被引：4，自引：0，他引：4
Two hundred and sixty one newly measured tree-ring width and density series from living and dry-dead conifers from two timberline
sites in the Spanish Pyrenees were compiled. Application of the regional curve standardization method for tree-ring detrending
allowed the preservation of inter-annual to multi-centennial scale variability. The new density record correlates at 0.53
(0.68 in the higher frequency domain) with May–September maximum temperatures over the 1944–2005 period. Reconstructed warmth
in the fourteenth to fifteenth and twentieth century is separated by a prolonged cooling from ∼1450 to 1850. Six of the ten
warmest decades fall into the twentieth century, whereas the remaining four are reconstructed for the 1360–1440 interval.
Comparison with novel density-based summer temperature reconstructions from the Swiss Alps and northern Sweden indicates decadal
to longer-term similarity between the Pyrenees and Alps, but disagreement with northern Sweden. Spatial field correlations
with instrumental data support the regional differentiation of the proxy records. While twentieth century warmth is evident
in the Alps and Pyrenees, recent temperatures in Scandinavia are relatively cold in comparison to earlier warmth centered
around medieval times, ∼1450, and the late eighteenth century. While coldest summers in the Alps and Pyrenees were in-phase
with the Maunder and Dalton solar minima, lowest temperatures in Scandinavia occurred later at the onset of the twentieth
century. However, fairly cold summers at the end of the fifteenth century, between ∼1600–1700, and ∼1820 were synchronized
over Europe, and larger areas of the Northern Hemisphere. 相似文献
8.
9.
The dissolution of prismatic and rhombohedral quartz surfaces by KOH/H2O solutions was investigated by atomic force microscopy. Rates of dissolution of different classes of surface features (e.g., steps, voids, and dislocation etch pits) were measured. The prismatic surface etched almost two orders of magnitude faster than the rhombohedral surface, mostly due to the difference in the number and the rate of dissolution of extended defects, such as dislocations. Because of the presence of imperfect twin boundaries, defect densities on the prismatic surface were estimated at 50-100 μm−2, whereas the rhombohedral surface possessed only ∼0.5-1.0 μm−2, mostly in the form of crystal voids. Crystal voids etched almost one order of magnitude faster on the prismatic surface than on the rhombohedral surface due to differences in the number and the density of steps formed by voids on the different surfaces. In the absence of extended defects, both surfaces underwent step-wise dissolution at similar rates. Average rates of step retreat were comparable on both surfaces (∼3-5 nm/h on the prismatic surface and ∼5-10 nm/h on the rhombohedral surface). Prolonged dissolution left the prismatic surface reshaped to a hill-and-valley morphology, whereas the rhombohedral surface dissolved to form coalescing arrays of oval-shaped etch pits. 相似文献
10.
A 1052-year tree-ring proxy for Alpine summer temperatures 总被引：6，自引：0，他引：6
Ulf Büntgen Jan Esper David C. Frank Kurt Nicolussi Martin Schmidhalter 《Climate Dynamics》2005,25(2-3):141-153
A June–August Alpine temperature proxy series is developed back to AD 951 using 1,527 ring-width measurements from living trees and relict wood. The reconstruction is composed of larch data from
four Alpine valleys in Switzerland and pine data from the western Austrian Alps. These regions are situated in high elevation
Alpine environments where a spatially homogenous summer temperature signal exists. In an attempt to capture the full frequency
range of summer temperatures over the past millennium, from inter-annual to multi-centennial scales, the regional curve standardization
technique is applied to the ring width measurements. Correlations of 0.65 and 0.86 after decadal smoothing, with high elevation
meteorological stations since 1864 indicate an optimal response of the RCS chronology to June–August mean temperatures. The
proxy record reveals warm conditions from before AD 1000 into the thirteenth century, followed by a prolonged cool period, reaching minimum values in the 1820s, and a warming
trend into the twentieth century. This latter trend and the higher frequency variations compare well with the actual high
elevation temperature record. The new central Alpine proxy suggests that summer temperatures during the last decade are unprecedented
over the past millennium. It also reveals significant similarities at inter-decadal to multi-centennial frequencies with large-scale
temperature reconstructions, however, deviating during certain periods from H.H. Lamb‘s European/North Atlantic temperature
history. 相似文献