Late Holocene temperature fluctuations on the Tibetan Plateau

Proxy data of palaeoclimate, like ice cores, tree rings and lake sediments, document aspects of climate changes on the Tibetan Plateau during the last 2000 years. The results show that the Tibetan Plateau experienced climatic episodes such as the warm intervals during AD 800–1100 and 1150–1400, the “Little Ice Age” between AD 1400 and 1900, and an earlier cold period between the 4th and 6th centuries. In addition, temperatures varied from region to region across the plateau. A warm period from AD 800 to 1100 in the northeastern Tibetan Plateau was contemporaneous with cooling in the southern Tibetan Plateau, which experienced warming between AD 1150 and 1400. Large-scale trends in the temperature history from the northeastern Tibetan Plateau resemble those in eastern China more than the trends from the southern Plateau. The most notable similarities between the temperature variations of the Tibetan Plateau and eastern China are cold phases during AD 1100–1150, 1500–1550, 1650–1700 and 1800–1850.     

On the basic structure of oceanic gravity currents

Results from numerical simulations of idealised, 2.5-dimensional Boussinesq, gravity currents on an inclined plane in a rotating frame are used to determine the qualitative and quantitative characteristics of such currents. The current is initially geostrophically adjusted. The Richardson number is varied between different experiments. The results demonstrate that the gravity current has a two-part structure consisting of: (1) the vein, the thick part that is governed by geostrophic dynamics with an Ekman layer at its bottom, and (2) a thin friction layer at the downslope side of the vein, the thin part of the gravity current. Water from the vein detrains into the friction layer via the bottom Ekman layer. A self consistent picture of the dynamics of a gravity current is obtained and some of the large-scale characteristics of a gravity current can be analytically calculated, for small Reynolds number flow, using linear Ekman layer theory. The evolution of the gravity current is shown to be governed by bottom friction. A minimal model for the vein dynamics, based on the heat equation, is derived and compares very well to the solutions of the 2.5-dimensional Boussinesq simulations. The heat equation is linear for a linear (Rayleigh) friction law and non-linear for a quadratic drag law. I demonstrate that the thickness of a gravity current cannot be modelled by a local parameterisation when bottom friction is relevant. The difference between the vein and the gravity current is of paramount importance as simplified (streamtube) models should model the dynamics of the vein rather than the dynamics of the total gravity current. In basin-wide numerical models of the ocean dynamics the friction layer has to be resolved to correctly represent gravity currents and, thus, the ocean dynamics.     

Astrodynamical Space Test of Relativity using Optical Devices I (ASTROD I)—a class-M fundamental physics mission proposal for cosmic vision 2015–2025: 2010 Update

ASTROD I is a planned interplanetary space mission with multiple goals. The primary aims are: to test General Relativity with an improvement in sensitivity of over 3 orders of magnitude, improving our understanding of gravity and aiding the development of a new quantum gravity theory; to measure key solar system parameters with increased accuracy, advancing solar physics and our knowledge of the solar system; and to measure the time rate of change of the gravitational constant with an order of magnitude improvement and the anomalous Pioneer acceleration, thereby probing dark matter and dark energy gravitationally. It is envisaged as the first in a series of ASTROD missions. ASTROD I will consist of one spacecraft carrying a telescope, four lasers, two event timers and a clock. Two-way, two-wavelength laser pulse ranging will be used between the spacecraft in a solar orbit and deep space laser stations on Earth, to achieve the ASTROD I goals.For this mission, accurate pulse timing with an ultra-stable clock, and a drag-free spacecraft with reliable inertial sensor are required. T2L2 has demonstrated the required accurate pulse timing; rubidium clock on board Galileo has mostly demonstrated the required clock stability; the accelerometer on board GOCE has paved the way for achieving the reliable inertial sensor; the demonstration of LISA Pathfinder will provide an excellent platform for the implementation of the ASTROD I drag-free spacecraft. These European activities comprise the pillars for building up the mission and make the technologies needed ready. A second mission, ASTROD or ASTROD-GW (depending on the results of ASTROD I), is envisaged as a three-spacecraft mission which, in the case of ASTROD, would test General Relativity to one part per billion, enable detection of solar g-modes, measure the solar Lense-Thirring effect to 10 parts per million, and probe gravitational waves at frequencies below the LISA bandwidth, or in the case of ASTROD-GW, would be dedicated to probe gravitational waves at frequencies below the LISA bandwidth to 100?nHz and to detect solar g-mode oscillations. In the third phase (Super-ASTROD), larger orbits could be implemented to map the outer solar system and to probe primordial gravitational-waves at frequencies below the ASTROD bandwidth. This paper on ASTROD I is based on our 2010 proposal submitted for the ESA call for class-M mission proposals, and is a sequel and an update to our previous paper (Appouchaux et al., Exp Astron 23:491?C527, 2009; designated as Paper I) which was based on our last proposal submitted for the 2007 ESA call. In this paper, we present our orbit selection with one Venus swing-by together with orbit simulation. In Paper I, our orbit choice is with two Venus swing-bys. The present choice takes shorter time (about 250?days) to reach the opposite side of the Sun. We also present a preliminary design of the optical bench, and elaborate on the solar physics goals with the radiation monitor payload. We discuss telescope size, trade-offs of drag-free sensitivities, thermal issues and present an outlook.     

Reconstruction of floral changes during deposition of the Miocene Embalut coal from Kutai Basin,Mahakam Delta,East Kalimantan,Indonesia by use of aromatic hydrocarbon composition and stable carbon isotope ratios of organic matter

The distribution of aromatic hydrocarbons and stable carbon isotope ratios of organic matter in a series of nine Miocene Embalut coal samples obtained from nine coal seams of Kutai Basin, East Kalimantan, Indonesia were studied. The rank of the Embalut coals ranged from lignites to low rank sub-bituminous coals (0.36–0.50% Rr), based on measurements of huminite reflectance. The aromatic hydrocarbon fractions of all coal samples were dominated by cadalene in the lower boiling point range and picene derivatives in the higher boiling point range of the gas chromatograms. Cadalene can be attributed to the contribution of Dipterocarpaceae and various hydrated picenes to the contribution of additional angiosperms to the coal forming vegetation. The picenes originate from alpha- and beta-amyrin. However, in some coal samples minor amounts of simonellite and retene were also detected which argues for an additional contribution of gymnosperms (conifers) to coal forming vegetation preferentially in the Middle Miocene and at the beginning of the Late Miocene. The results of stable carbon isotope ratios (δ¹³C) in most of the coal samples are consistent with their origin from angiosperms (δ¹³C between ?27.0‰ and ?28.0‰). During the Miocene the climate of Mahakam Delta was not uniformly moist and cooler than the present day climate. This would have been favourable for the growth of conifers, especially in the montane forests. The contribution of conifers to the Embalut coals might be a result of the cool Middle/Late Miocene climate during peat accumulation in the Kutai Basin.     

Isotopic evidence (He,B, C) for deep fluid and mud mobilization from mud volcanoes in the Caucasus continental collision zone

The Caucasian orogenic wedge formed as a consequence of the closure of the Tethyan Ocean, and numerous fields of active mud volcanoes pepper the area adjacent to the Black and Caspian Seas. Stable isotope ratios of boron, helium, and carbon have been measured for gas, fluid and sediment samples from active mud volcanoes of Taman Peninsula and Georgia to estimate the sources and mobilization depths of the fluid phase and mud. Boron concentrations in mud volcano fluids were found to be 5–35× higher than seawater. Fluid isotope ratios vary between ¹¹B=22 and 39, while isotope ratios of the smectite- and illite-rich extruded mud are considerably depleted in heavy ¹¹B (¹¹B=–8 to +7). B contents of these muds are ~8× higher than modern marine sediments. This suggests that liquefaction prior to mud volcanism was accompanied by both B enrichment and isotope fractionation, most likely at an intermediate depth mud reservoir at 2–4 km.The hydrocarbon-generating source beds to the mud volcanoes are located at 7 to >10 km depth in the folded Maikop Formation and are of proposed Oligocene–Miocene age. The most likely mechanism is re-hydration of these shales by both hydrocarbons and a geochemically mature fluid from greater depth within the orogenic wedge. Such a deep fluid source is supported by our results from gas analyses, which imply an admixture of minor amounts (less than 1%vol) of ³He (Georgia), thermogenic ¹³C in methane as well as "ultraheavy" ¹³C in CO₂ (both Taman and Georgia). The overall results attest active local flow of geochemically different fluids along deep-seated faults penetrating the two study areas in the Caucasian orogenic wedge, with the waters as well as the gases coming from below the Maikop Formation.     

Sedimentary Phosphate Fractions Related to Calcite Precipitation in an Eutrophic Hardwater Lake (Lake Alserio, Northern Italy)

P-fractional composition has been studied in a 64-cm long sediment core collected in an eutrophic hardwater lake (Lake Alserio, northern Italy) in an attempt to identify the main mechanisms (chemical or biologic) controlling CaCO₃ precipitation in the water column. The results of the sedimentary phosphate fractionation showed that the most important P fraction was an organic fraction extracted with hot NaOH: org-P_alkali (26% of P_sed). A digestion of the supernatant of the P-fraction bound to CaCO₃ allowed the detection of a large pool of org-P (19% of P_sed). Although the nature of this fraction is unclear, we suggest that it may be involved in the biologically mediated precipitation of CaCO₃. The high CaCO₃ concentration in the entire vertical sediment profile, as well as the presence of inorg- and org-P bound to Ca in both laminated and non-laminated zones, suggest that the CaCO₃ precipitation is not a recent process but is a process that has been occurring in the lake for some time. Accordingly, the change from a homogeneous sediment to a laminated sequence might be caused by the eutrophication process of Lake Alserio occurring since the 1960s, which has allowed the preservation of the varved sediment as a consequence of the drastic reduction in bioturbation.     

Evidence for a warm-humid climate in arid northwestern China during 40–30 ka BP

Former shorelines and sedimentary records from several lake basins in northwestern China (Xinjiang, Qinghai) give evidence for warm and humid climatic conditions during 40–30 ka BP. Further indications of this favorable climate period are derived from palaeosols from the Ili loess and from cemented calcareous layers on the terraces of the Keriya River at the southern margin of the Tarim Basin and in the Badain Jaran Desert in Inner Mongolia. At that time, annual mean temperature in the Qaidam Basin was 2 °C higher and in the western part of Inner Mongolia even 2–3 °C higher than today. Precipitation in most parts of northwestern China was between 60–300 mm greater than today. These changes were probably a consequence of an increase in ocean surface temperature and evaporation resulting from a higher radiation input at middle and low latitudes caused by changes in the Earth's precessional cycle. As a result of these orbital changes, it is suggested that the intensified westerly circulation was responsible for increased moisture over northwestern China.     

Chronology and depositional processes of the laminated sediment record from Lac d'Annecy, French Alps

A high resolution sediment record spanning the entire time since the ice retreat after the Last Glacial Maximum has been recovered from Lac d'Annecy. The main focus of this study is to develop a reliable chronology of the record and to evaluate the environmental variability during the period of Late Würmian ice retreat. Most of the record is laminated. These laminations are of different structure, composition, and thickness. On the basis of varve stratigraphy five sedimentation units were identified which correspond to particular stages in the deglaciation of the region. Except for one each facies type has been related to an annual cycle of deposition. Varve counting in combination with radiocarbon dating provides the time control of the record and dates the base of lacustrine deposits to 16,600 varve yrs BP. The beginning of the Late Glacial is marked by a shift from clastic to endogenic carbonate varves caused by the climatic warming. Clastic varves have been further subdivided into a succession of complex and standard varve types. These variations of clastic varve formation are triggered by the ice retreat and related hydrological variations in the watershed of the lake. Sedimentological, mineralogical and isotopic data help identify different sediment sources of the sub-layers. Proximal sediments originate from local carbonaceous bedrock whereas distal sediments have characteristics of the molassic complex of the outer Alps. The alternation of proximal and distal sediments in the varve sequence reflects the deglaciation of the Annecy area with a changing influence of local and regional glaciers. The melting of the Alpine ice sheet is the driving force for regional environmental changes which in turn control the sediment transport and deposition processes in Lac d'Annecy.     

Statistical characteristics of instantaneous dense gas clouds released in an atmospheric boundary-layer wind tunnel

Wind tunnel experiments were performed to examine the behavior of suddenly released volumes of dense gas in a turbulent shear layer. Instantaneous concentrations were measured with hot-wire katherometers. Multiple replications of each cloud volume, density, and velocity combination produced statistics for plume arrival time, arrival of maximum concentration time, plume departure time, and maximum concentrations. Probability distributions and standard deviations of each plume property permit prediction of hazard risks.