Lateglacial varve chronology and biostratigraphy of lakes Holzmaar and Meerfelder Maar, Germany     

ACHIM BRAUER  THOMAS LITT  JÖRG F. W. NEGENDANK  BERND ZOLITSCHKA 《Boreas: An International Journal of Quaternary Research》2001,30(1):83-88

In this paper we briefly compare previously published data on four lateglacial sediment profiles from lakes Holzmaar and Meerfelder Maar in the Eifel region. Two of these profiles (one from each lake) are varvedated, whereas the other two pollen profiles are on depth scales. In general, the palynological signal in all profiles compares well, proving the regional validity of the individual data sets. There are some discrepancies between Holzmaar and Meerfelder Maar, however, mainly concerning varve dating of major lateglacial features, and these are explained after detailed correlation using a combination of varve dating and palynological signals. The result is a consistent varve-dated biostratigraphy for the Lateglacial in the Eifel region. Moreover, it is demonstrated that a combination of varve chronology and high resolution palynostratigraphy in several lake profiles enables even gaps of a few decades up to a few centuries to be detected, thus providing a valuable tool for precise regional palaeoenvironmental study. This multi-core study on two lakes from the same region demonstrates the likelihood of undetected errors in single-core studies on non-varved sediments.  相似文献   

Kinematics and parameters of the gas in the vicinity of TW Hya     

S. A. Lamzin  A. S. Kravtsova  M. M. Romanova  C. Batalha 《Astronomy Letters》2004,30(6):413-427

The following conclusions about the kinematics and parameters of the gas in the vicinity of TW Hya have been drawn from an analysis of optical and ultraviolet line profiles and intensities. The accreting matter rises in the magnetosphere to a distance z>R_* above the disk plane and falls to the star near its equator almost perpendicular to its plane. The matter outflows from a disk region with an outer radius of ≤0.5 AU. The [OI], [SII], and H2 lines originate in the disk atmosphere outside the outflow region, where the turbulent gas velocity is close to the local speed of sound. In the formation region of the forbidden lines, T?8500 K and N_e?5×10⁶ cm^?3, and the hydrogen is almost neutral: x_e<0.03. The absorption features observed in the blue wings of some of the ultraviolet lines originate in the part of the wind that moves almost perpendicular to the disk plane, i.e., in the jet of TW Hya. The V _z gas velocity component in the jet decreases with increasing distance from the jet axis from 200 to 30 km s^?1. The matter outflowing from the inner disk boundary, moves perpendicular to the disk plane in the formation region of blue absorption line components, at a distance of ～0.5 AU from the axis of symmetry of the disk. This region of the wind is collimated into the jet at a distance of <3 AU from the disk plane. The gas temperature in the formation region of absorption components is ?2×10⁴ K, and the gas density is <3×10⁶ cm^?3. This region of the jet is on the order of several AU away from the disk plane, while free recombination in the jet begins even farther from the disk. The mass-loss rate for TW Hya is \(\dot M_w < 7 \times 10^{ - 10} M_ \odot yr^{ - 1}\), which is a factor of 3lower than the mean accretion rate. The relative abundance of silicon and aluminum in the jet gas is at least an order of magnitude lower than its standard value.  相似文献   

The diatom flora in the Fram Strait. A comparison with the Pleistocene/Holocene boundary flora in the Norwegian Sea     

BJØRG STABELL 《Polar research》1987,5(3):321-322

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Analysis of Changes in the Aral Sea Coastal Zone in 1975–1999     

Kravtsova  V. I. 《Water Resources》2001,28(6):596-603

Changes in the Aral Sea coastline and coastal zone over different time intervals during the period of the sea level drop are studied with the use of space photographs obtained from the orbital station Salyut-4 and satellites of the Resurs-O system. Interannual variations in the above characteristics are analyzed for 1975–1989, 1989–1993, 1993–1996, 1997, 1998, and 1999. Seasonal variations in the water area and coastal landscapes are studied with the help of photographic images of the sea made in different seasons, mainly in 1998.  相似文献