Astrometry from space: GAIA and planet detection

The proposed baseline GAIA mission will be able to detect the astrometric signature of Jupiter-size planets around of the order of a million stars, using either global or narrow-angle astrometry. If the mission can realize the higher astrometric accuracy that photon statistics allows for bright stars, lower-mass planets (from Earth size to ten times larger) can be found around ten to a few hundred stars.     

Detrital record of Mesozoic shortening in the Yanshan belt, NE China: testing structural interpretations with basin analysis

The Yanshan fold‐thrust belt is an exposed portion of a major Mesozoic orogenic system that lies north of Beijing in northeast China. Structures and strata within the Yanshan record a complex history of thrust faulting characterized by multiple deformational events. Initially, Triassic thrusting led to the erosion of a thick sequence of Proterozoic and Palaeozoic sedimentary strata from northern reaches of the thrust belt; Triassic–Lower Jurassic strata that record this episode are deposited in a thin belt south of this zone of erosion. This was followed by postulated Late Jurassic emplacement of a major allochthon (the Chengde thrust plate), which is thought to have overridden structures and strata associated with the Triassic event and is cut by two younger thrusts (the Gubeikou and Chengde County thrusts). The Chengde allochthon is now expressed as a major east–west trending, thrust‐bounded synform (the Chengde synform), which has been interpreted as a folded klippe 20 km wide underlain by a single, north‐vergent thrust fault. Two sedimentary basins, defined on the basis of provenance, geochronology and palaeodispersal trends, developed within the Yanshan belt during Late Jurassic–Early Cretaceous time and are closely associated with the Chengde thrust and allied structures. Shouwangfen basin developed in the footwall of the Gubeikou thrust and records syntectonic unroofing of the hanging wall of that fault. Chengde basin developed in part atop Proterozoic strata interpreted as the upper plate of the Chengde allochthon and records unroofing of the adjacent Chengde County thrust. Both the Chengde County thrust and the Gubeikou thrust are younger than emplacement of the postulated Chengde allochthon, and structurally underlie it, yet neither Shouwangfen basin nor Chengde basin contain a detrital record of the erosion of this overlying structure. In addition, facies, palaeodispersal patterns and geochronology of Upper Jurassic strata that are cut by the Chengde thrust suggest only limited (ca. 5 km) displacement along this fault. We suggest that the units forming the Chengde synform are autochthonous, and that the synform is bounded by two limited‐displacement faults of opposing north and south vergence, rather than a single large north‐directed thrust. This conclusion implies that the Yanshan belt experienced far less Late Jurassic shortening than was previously thought, and has major implications for the Mesozoic evolution of the region. Specifically, we argue that the bulk of shortening and uplift in the Yanshan belt was accomplished during Triassic–Early Jurassic time, and that Late Jurassic structures modified and locally ponded sediments from a well‐developed southward drainage system developed atop this older orogen. Although Upper Jurassic strata are widespread throughout the Yanshan belt, it is clear that these strata developed within several discrete intermontane basins that are not correlable across the belt as a single entity. Thus, the Yanshan has no obvious associated foreland basin, and determining where the Mesozoic erosional products of this orogen ultimately lie is one of the more intriguing unresolved questions surrounding the palaeogeography of North China.     

Circulation and currents in the southwestern East/Japan Sea: Overview and review

A review is made of circulation and currents in the southwestern East/Japan Sea (the Ulleung Basin), and the Korea/Tsushima Strait which is a unique conduit for surface inflow into the Ulleung Basin. The review particularly concentrates on describing some preliminary results from recent extensive measurements made after 1996. Mean flow patterns are different in the upstream and downstream regions of the Korea/Tsushima Strait. A high velocity core occurs in the mid-section in the upstream region, and splits into two cores hugging the coasts of Korea and Japan, the downstream region, after passing around Tsushima Island located in the middle of the strait. Four-year mean transport into the East/Japan Sea through the Korea/Tsushima Strait based on submarine cable data calibrated by direct observations is 2.4 Sv (1 Sv = 10⁶ m³ s⁻¹). A wide range of variability occurs for the subtidal transport variation from subinertial (2–10 days) to interannual scales. While the subinertial variability is shown to arise from the atmospheric pressure disturbances, the longer period variation has been poorly understood.Mean upper circulation of the Ulleung Basin is characterized by the northward flowing East Korean Warm Current along the east coast of Korea and its meander eastward after the separation from the coast, the Offshore Branch along the coast of Japan, and the anticyclonic Ulleung Warm Eddy that forms from a meander of the East Korean Warm Current. Continuous acoustic travel-time measurements between June 1999 and June 2001 suggest five quasi-stable upper circulation patterns that persist for about 3–5 months with transitions between successive patterns occurring in a few months or days. Disappearance of the East Korean Warm Current is triggered by merging the Dok Cold Eddy, originating from the pinching-off of the meander trough, with the coastal cold water carried Southward by the North Korean Cold Current. The Ulleung Warm Eddy persisted for about 20 months in the middle of the Ulleung Basin with changes in its position and spatial scale associated with strengthening and weakening of the transport through the Korea/Tsushima Strait. The variability of upper circulation is partly related to the transport variation through the Korea/Tsushima Strait. Movements of the coastal cold water and the instability of the polar front also appear to be important factors affecting the variability.Deep circulation in the Ulleung Basin is primarily cyclonic and commonly consists of one or more cyclonic cells, and an anticyclonic cell centered near Ulleung Island. The cyclonic circulation is conjectured to be driven by a net inflow through the Ulleung Interplain Gap, which serves as a conduit for the exchange of deep waters between the Japan Basin in the northern East Sea and the Ulleung Basin. Deep currents are characterized by a short correlation scale and the predominance of mesoscale variability with periods of 20–40 days. Seasonality of deep currents is indistinct, and the coupling of upper and deep circulation has not been clarified yet.     

Post-collisional tectonics of the Turkish-Iranian plateau and a comparison with Tibet

The Turkish-Iranian Plateau (Fig. 1) is a high region with an average elevation of about 1.5 km. During the late Miocene the last piece of oceanic lithosphere between the Eurasian and Arabian continents was eliminated at the Bitlis/Zagros suture zone. Continued convergence across the collision site resulted in the shortening of the plateau across strike by thickening and by sideways motion of parts of it. Predominantly calcalkaline volcanism is present on the highest portions of the area, despite the absence of a descending slab of lithosphere. Surface geology and volcanism of the Turkish-Iranian Plateau resemble greatly those of the Tibetan Plateau, and both are underlain by a zone of seismic attenuation. From a comparison of these features and their tectonic setting we argue that the two plateaux are homologous structures, albeit at different stages of their evolution. Both areas appear to be tectonically alive and actively shortening. Available evidence lends little support to the hypothesis of large-scale underthrusting of continental lithosphere and of plastic-rigid indentation where such high plateaux, located directly in front of the “rigid indenter”, are considered to be tectonically “dead”. Their peculiar features are best explained in terms of shortening and thickening the continental crust whereby its lower levels are partially melted to give rise to calc-alkaline surface volcanism. Minor associated alkaline volcanism may be due to local longitudinal cracking of the crust to provide access to mantle.     

Synthetic Seismograms and Wide-angle Seismic Attributes from the Gaussian Beam and Reflectivity Methods for Models with Interfaces and Velocity Gradients

— The effects of interfaces and velocity gradients on wide-angle seismic attributes are investigated using synthetic seismograms. The seismic attributes considered include envelope amplitude, pulse instantaneous frequency, and arrival time of selected phases. For models with interfaces and homogeneous layers, head waves can propagate which have lower amplitudes, as well as frequency content, compared to the direct arrivals. For media with interfaces and velocity gradients, higher amplitude diving waves and interference waves can also occur. The Gaussian beam and reflectivity methods are used to compute synthetic seismograms for simple models with interfaces and gradients. From the results of these methods, seismic attributes are obtained and compared. It was found that both methods were able to simulate wide-angle seismic attributes for the simple models considered. The advantage of using the Gaussian beam method for seismic modeling and inversion is that it is fast and also asymptotically valid for laterally varying media.     

Contesting ‘Local’ Commemoration of the Second World War: the case of the Changi Chapel and Museum in Singapore

This paper concerns the performance of national war memory at the Changi Chapel and Museum, a site honouring the many prisoners interned in Japanese-Occupied Singapore—especially at Changi—during the Second World War. In the light of the global nature of ‘the Changi story’, and the predominantly transnational nature of its present in situ memorialisation, we first examine how the Singapore state has sought to ‘localise’ the site to make it equally appealing to Singaporeans, as a place where a sense of their ‘shared history’ may be invoked. We then explore the Singaporeans' views about the site and its reconfiguration as a national icon, arguing how the state's task of ‘localising’ the site has been a vexed process due to myriad factors such as ethnic and religious plurality, and the already foreign-centric bias of prevailing knowledge about Changi. Following that, we show how this performance of national memory is also inflected by Australia's national remembrance of the same event. More broadly, we highlight the contested process of ‘localising’ such war memoryscapes as national iconography, suggesting how it may be more fruitful to conceive them as ‘international memoryscapes’, or places to which all individuals can relate regardless of race or national affiliations.     

Effect of relative humidity on the angular distribution of scattered light intensity for rural and urban aerosols

The change in atmospheric relative humidity affects the physical and optical properties of aerosol particles. It would be interesting to study the effect of an increase in relative humidity on the angular scattering of light by aerosols (by incorporating the changes due to it as the complex refractive index and the parameters of the size distribution function). In the present paper we have computed the angular scattering function for rural and urban aerosols, for light of wavelength 0.55 μn. The results obtained for these two models, representative of different environments, are interesting and show some discriminating features.     

Distribution and source of tar on the Pacific Ocean

Petroleum residues, or tar lumps, are concentrated in the northwestern portion of the Pacific Ocean, particularly in the Kuroshio current system. The source of the tar appears to be tank washings from tankers on the very large Middle East to Japan route. Tar pollutants apparently are discharged by tankers south of Japan, become entrained in the Kuroshio current, and create a plume of contamination which extends downstream for 7000 km across the Pacific.     

Late Quaternary glaciation and equilibrium-line altitudes of the Mayan Ice Cap, Guatemala, Central America

The Sierra los Cuchumatanes (3837 m), Guatemala, supported a plateau ice cap and valley glaciers around Montaña San Juan (3784 m) that totaled ∼ 43 km² in area during the last local glacial maximum. Former ice limits are defined by sharp-crested lateral and terminal moraines that extend to elevations of ∼ 3450 m along the ice cap margin, and to ca. 3000-3300 m for the valley glaciers. Equilibrium-line altitudes (ELAs) estimated using the area-altitude balance ratio method for the maximum late Quaternary glaciation reached as low as 3470 m for the valley glaciers and 3670 m for the Mayan Ice Cap. Relative to the modern altitude of the 0°C isotherm of ∼ 4840 m, we determined ELA depressions of 1110-1436 m. If interpreted in terms of a depression of the freezing level during maximal glaciation along the modern lapse rate of − 5.3°C km^− 1, this ΔELA indicates tropical highland cooling of ∼ 5.9 to 7.6 ± 1.2°C. Our data support greater glacial highland cooling than at sea level, implying a high tropical sensitivity to global climate changes. The large magnitude of ELA depression in Guatemala may have been partially forced by enhanced wetness associated with southward excursions of the boreal winter polar air mass.