Taphonomic phenomenon of ancient hair from Glacial Beringia: perspectives for palaeoecological reconstructions

An accumulation of mammoth hair, discovered in the Bol'shaya Chukochya River valley (northeast Yakutia, Russia), was found to contain remains of terrestrial and aquatic organisms, including plants, insects, crustaceans, birds and mammals. Radiocarbon dating indicated that this post‐mortem taphocoenosis represented multiple time periods. The mammoth hair was dated to older than 45 ka BP, the plants were dated to 12 750±50 a BP (which corresponds to a shift in the environmental conditions and landscapes during the formation of thermokarst in northeastern Russia) and the bird feathers were dated to 4115±40 a BP. A scenario of the formation of this fossil assemblage is proposed, covering the MIS 3‐1 time range. The hair also yielded various Arctic branchiopod crustaceans, which inhabit shallow temporary water bodies and therefore are important for reconstruction of palaeoenvironments. The cladoceran subgenus Daphnia (Ctenodaphnia), currently absent from the Asian part of Beringia, is reported from this region for the first time. The study demonstrates that the discovered permafrost‐preserved hair is a unique repository of Ice Age organisms.     

Cenozoic stratigraphy of the northern Sakhalin shelf

The analysis of diatom, palynofloral, and benthic foraminiferal assemblages made it possible to substantiate the age of Cenozoic sections recovered by wells on the northern and northeastern Sakhalin shelf. Biostratigraphic materials, lithological properties of stratigraphic units, and standard logs served as the basis for developing the first stratigraphic correlation scale of Cenozoic sequences on the Sakhalin shelf.     

Considerations concerning the non-rigid Earth nutation theory

This paper presents the reflections of the Working Group of which the tasks were to examine the non-rigid Earth nutation theory. To this aim, six different levels have been identified: Level 1 concerns the input model (giving profiles of the Earth's density and theological properties) for the calculation of the Earth's transfer function of Level 2; Level 2 concerns the integration inside the Earth in order to obtain the Earth's transfer function for the nutations at different frequencies; Level 3 concerns the rigid Earth nutations; Level 4 examines the convolution (products in the frequency domain) between the Earth's nutation transfer function obtained in Level 2, and the rigid Earth nutation (obtained in Level 3). This is for an Earth without ocean and atmosphere; Level 5 concerns the effects of the atmosphere and the oceans on the precession, obliquity rate, and nutations; Level 6 concerns the comparison with the VLBI observations, of the theoretical results obtained in Level 4, corrected for the effects obtained in Level 5.Each level is discussed at the state of the art of the developments.     

Atmospheric trajectory and orbit of the Omolon meteorite

Abstract— The Omolon meteorite fell on 1981 May 15 at 17:10 U.T. to a point with the coordinates φ = 64°01′08″ N, λ = 161°48′30″ E. This is the fifth pallasite that was observed at the moment of its fall and the largest of the pallasites known worldwide (250 kg). The history of the observation, search, and finding of the meteorite is briefly described. From the size of the meteorite and the funnel that it produced, the velocity of its encounter with the ground is estimated by aerodynamic formulas to be 220 m/s. An attempt at estimating the meteorite's initial velocity and mass from its terminal values (which yielded the mass range of 390–490 kg that corresponds to the velocity range of 12–15 km/s) was successful for the mass but unsuccessful for the velocity and the incidence angle, because the problem was ill posed. The position of the radiant is determined from the available observations to be α = 176.4°, δ = +24.1° (Leo). The radiant was situated at an elongation of 29° from the antapex, which means that this was an overtaking meteorite and its entry velocity did not exceed 16 km/s. Three variants of the calculation of the orbital elements—for an entry velocity of 12, 14, and 16 km/s—are presented. In all the three cases, the meteoroid's orbit is close to the orbits of Apollo asteroids and to the orbits of iron meteoroids observed as fireballs with bright iron lines in their spectra. The Omolon meteorite was probably a fragment of an Apollo M-type asteroid. This study is the first attempt at calculating the orbit of a pallasite.     

A Pulsar Time Scale

Astronomy Reports - A pulsar time scale is considered, including possibilities for its realization and possible applications to fundamental problems in astronomy and physics.     

Physical origins for variations in the apparent positions of quasars

The physical origins of the apparent motion of radio sources in the ICRF are considered. The sources can be divided into four groups, according to the characteristics of their motion. Here, we consider the model for the motion of the first group of sources—those displaying uniform linear motion. Since the apparent speeds of the radio sources are close to, and sometimes exceeding, the speed of light, it is natural to suppose that these sources are relativistic jets or plasma clouds moving with speeds close to the speed of light. Uniform linear motion can be explained by a model invoking precession of the jet. We consider the physical characteristics of a number of selected sources of the ICRF in the proposed model.     

Microarcsecond instability of the celestial reference frame

The fluctuation of the angular positions of reference extragalactic radio and optical sources under the influence of the irregular gravitational field of visible Galactic stars is considered. It is shown that these angular fluctuations range from a few up to hundreds of microarcseconds. This leads to a small rotation of the celestial reference frame. The non-diagonal coefficients of the rotation matrix are of the order of a microarcsecond. The temporal variation of these coefficients due to the proper motion of the foreground stars is of the order of one microsecond per 20 years. The celestial reference frame can therefore be considered inertial and homogeneous only to microarcsecond accuracy. Astrometric catalogues with microarcsecond accuracy will be unstable, and must be re-established every 20 years.     

Disproportion among Cladocera (Crustacea) skeletal components in lake sediment taphocoenoses and significance with respect to two methods of sub-fossil enumeration

Journal of Paleolimnology - Analysis of Cladocera (Crustacea: Branchiopoda) subfossil remains in lake sediments features prominently in paleolimnological studies. It is well known, however, that...     

Principles for selecting a list of reference radio sources for a celestial coordinate system

Time series of the coordinates of radio sources defining the celestial coordinate frame are analyzed. Methods for selecting such sources so as to enhance the stability of the frame are considered. Some of these sources, including so-called “defining” sources, demonstrate significant proper motions. Since the stability of the celestial coordinate frame is determined by an absence of global rotation relative to the defining sources (no net rotation), variation in their coordinates will lead to a rotation of the axes of the celestial coordinate frame. The parameters of this rotation are calculated for two physical models for the motions of extragalactic radio sources. The motions displayed by the first group of sources are linear and uniform. Since the apparent speeds of radio sources are often close to, and sometimes exceed, the speed of light, it is supposed that such radio sources have relativistic jets or plasma clouds that move with speeds roughly equal to the speed of light. The observed uniform, linear motion can then be explained by precession of the jet. The second group of sources display non-linear motions, interpreted as a manifestation of the acceleration of matter by the jet. It is assumed that a cloud of particles that moves into the path of the jet is accelerated to relativistic speeds by the jet. A list of sources that should form a very stable coordinate system for several decades into the future is composed based on these two models.