The extent of permafrost in China during the local Last Glacial Maximum (LLGM)

Recent investigations into relict periglacial phenomena in northern and western China and on the Qinghai–Tibet Plateau provide information for delineating the extent of permafrost in China during the Late Pleistocene. Polygonal and wedge‐shaped structures indicate that, during the local Last Glacial Maximum (LLGM, between ～35 and 10.5 ka BP), the southern limit of latitudinal permafrost in northern China advanced southward at least to ～38–40°N in the east and to ～37–39°N in the west. This represents an advance of about 5–10° of latitude beyond present‐day permafrost limits. The lower limits of elevationally controlled permafrost on the Qinghai–Tibet Plateau and its peripheries were about 1000 m lower: this permafrost was largely continuous during the LLGM. This suggests a cooling of between 4 and 10°C, or more. This paper discusses the extent of permafrost during the LLGM and presents maps that have been constructed on the basis of extensive and integrative analysis of all reliable and pertinent data. The results indicate that the extent of LLGM permafrost in China was between ～3.8 and 4.3×10⁶ km². This is 80 to 100% more than that of ～2.15×10⁶ km² in the 1970s, and 120 to ～150% more than that of ～1.75×10⁶ km² today.     

Estimation of Accumulation of Chromium Ion Impurities in the CaSiO3 and MgSiO3 Phases of the Earth’s Lower Mantle at Pressures of 18–25 GPa

Doklady Earth Sciences - Based on the data of atomic modeling, the different schemes of isomorphic incorporation of Cr3+ ions into the crystal structures of CaSiO3 and MgSiO3 were tested in the...     

Transient seawater inflow into seacoast aquifers

The coastal zone of the sea is a boundary domain between seawater and land, making most processes within it to show specific features. Seawater can penetrate into aquifers in the land part of the shore through the underwater part of the sea–shore interface and move over considerable distances from the shoreline, mixing with fresh groundwater. This process is of critical importance for the construction of oil and gas pipelines in permafrost areas.     

Permafrost warming in the Tien Shan Mountains, Central Asia

The general features of alpine permafrost such as spatial distribution, temperatures, ice content, permafrost and active-layer thickness within the Tien Shan Mountains, Central Asia are described. The modern thermal state of permafrost reflects climatic processes during the twentieth century when the average rise in mean annual air temperature was 0.006–0.032 °C/yr for the different parts of the Tien Shan. Geothermal observations during the last 30 yr indicate an increase in permafrost temperatures from 0.3 °C up to 0.6 °C. At the same time, the average active-layer thickness increased by 23% in comparison to the early 1970s. The long-term records of air temperature and snow cover from the Tien Shan's high-mountain weather stations allow reconstruction of the thermal state of permafrost dynamics during the last century. The modeling estimation shows that the altitudinal lower boundary of permafrost distribution has shifted by about 150–200 m upward during the twentieth century. During the same period, the area of permafrost distribution within two river basins in the Northern Tien Shan decreased approximately by 18%. Both geothermal observations and modeling indicate more favorable conditions for permafrost occurrences and preservation in the coarse blocky material, where the ice-rich permafrost could still be stable even when the mean annual air temperatures exceeds 0 °C.     

Radiocarbon chronology of occupation of the site Chicha and Bayesian statistics for the assessment of a discontinuous transition from Late Bronze to Early Iron Age (West Siberia)

The Late Bronze to Iron Age transition in West Siberia involved significant cultural and political changes, which were reflected in the emergence of protourban settlements in the forest-steppe zone. The transition is roughly dated to the turn from the 2nd to the 1st mil. BC, mainly based on archaeological artefacts and on the general sociocultural development. A more precise radiocarbon dating for this transition was problematic mainly because of the general lack of data for West Siberia. This paper analyzes the chronology of the Late Bronze to Iron Age transition at Chicha, a reference site in the region for this period. The assessment of a possible hiatus between the Late Bronze Age and the following transitional period at Chicha is the key issue of our paper, as its presence may have far reaching cultural implications. To increase the precision of the radiocarbon chronology with focus on the possible hiatus, the samples from well-defined stratigraphic contexts were analyzed using Bayesian modeling incorporating stratigraphic information. The performed chronological modeling supports existing archaeological hypothesis of a hiatus at the very end of the 2nd mil. BC, just before the regular emergence of a new protourban settlement at the site of an abandoned Late Bronze settlement. A sensitivity analysis including the simulated hiatus confirms the reliability of the model. A complete population change seems to be plausible. The protourban settlement of Chicha, typical of the Transitional period, did not exist very long. With the emergence of the early nomadic cultures in the South Siberian steppes at the beginning of the 1st mil. BC, it most probably stopped functioning. The cultural development of that time, former believed to be continuous, was deeply interrupted several times.     

Meteorites from meteor showers: A case study of the Taurids

We propose that the Taurid meteor shower may contain bodies able to survive and be recovered as meteorites. We review the expected properties of meteorite‐producing fireballs, and suggest that end heights below 35 km and terminal speeds below 10 km s^?1 are necessary conditions for fireballs expected to produce meteorites. Applying the meteoroid strength index (PE criteria) of Ceplecha and McCrosky (1976) to a suite of 33 photographically recorded Taurid fireballs, we find a large spread in the apparent meteoroid strengths within the stream, including some very strong meteoroids. We also examine in detail the flight behavior of a Taurid fireball (SOMN 101031) and show that it has the potential to be a (small) meteorite‐producing event. Similarly, photographic observations of a bright, potential Taurid fireball recorded in November of 1995 in Spain show that it also had meteorite‐producing characteristics, despite a very high entry velocity (33 km s^?1). Finally, we note that the recent Maribo meteorite fall may have had a very high entry velocity (28 km s^?1), further suggesting that survival of meteorites at Taurid‐like velocities is possible. Application of a numerical entry model also shows plausible survival of meteorites at Taurid‐like velocities, provided the initial meteoroids are fairly strong and large, both of which are characteristics found in the Taurid stream.     

Wind Ionization Structure of the Short-Period Eclipsing LMC Wolf-Rayet Binary BAT99-129: Preliminary Results

BAT99-129 is a rare, short-period eclipsing Wolf-Rayet binary in the Large Magellanic Cloud. We present here medium-resolution NTT/EMMI spectra that allow us to disentangle the spectra of the two components and find the orbital parameters of the binary. We also present VLT/FORS1 spectra of this binary taken during the secondary eclipse, i.e. when the companion star passes in front of the Wolf-Rayet star. With these data we are able to extract, for the first time in absolute units for a WR + O binary, the sizes of the line emitting regions.Based on observations obtained at the La Silla and Paranal Observatories, European Southern Observatory (Chile).