Exposure history of the Torino meteorite

Abstract— We determined He, Ne, Ar, ¹⁰Be, ²⁶Al, ³⁶Cl, and ¹⁴C concentrations, as well as cosmic-ray track densities and halogen concentrations in different specimens of the H6 chondrite Torino, in order to constrain its exposure history to cosmic radiation. The Torino meteoroid had a radius of ～20 cm and travelled in interplanetary space for 2.5–10 Ma. Earlier, Torino was part of a larger body. The smallest possible precursor had a radius of 55 cm and a journey through space longer than ～65 Ma. If the first-stage exposure took place in a body with a radius of >3 m or in the parent asteroid, then it lasted nearly 300 Ma. The example of Torino shows that it is easy to underestimate first-stage exposure ages when constructing two-stage histories.     

The Influence of Advection on the Short Term CO 2 -Budget in and Above a Forest Canopy

An experimental micrometeorological set-up was established at the CARBOEURO-FLUX site in Tharandt, Germany, to measure all relevant variables for the calculation of the vertical and horizontal advective fluxes of carbon dioxide. The set-up includes two auxiliary towers to measure horizontal and vertical CO₂ and H₂O gradients through the canopy, and to make ultrasonic wind measurements in the trunk space. In combination with the long-term flux tower an approximately even-sided prism with a typical side-length of 50 m was established. It is shown that under stable (nighttime) conditions the mean advective fluxes have magnitudes on the same order as the daily eddy covariance (EC) flux, which implies that they play a significant, but not yet fully understood, role in the carbon budget equation. The two advective fluxes are opposite and seem to cancel each other at night (at least for these measurements). During the day, vertical advection tends to zero, while horizontal advection is still present implying a flow of CO₂ out of the control volume. From our measurements, a mean daily gain of 2.2 gC m^–2 d^–1 for the horizontal advection and a mean daily loss of 2.5 gC m^–2d^–1 for the vertical advection is calculated for a period of 20 days. However the large scatter of the advective fluxes has to be further investigated. It is not clear yet whether the large variability is natural or due to measurement errors and conceptual deficiencies of the experiment. Similar results are found in the few comparable studies.     

Sea level induced variations in clay mineral composition in the southwestern South China Sea over the past 17,000 yr

Variations in clay mineral composition of sediment cores from the margin and continental slope of the Sunda Shelf (southern South China Sea, SE Asia) covering the past 17,000 yr reflect changing influences of sediment sources together with clay mineral partitioning processes in shallow waters. We identify the deglacial sea level rise as the principal factor driving these changes. During the late glacial, high values of kaolinite are interpreted to reflect a higher contribution of clays from soils that have formed on the exposed Sunda Shelf and in the southern archipelagos of Indonesia. At this time core sites were located in close proximity to the mouths of the Sunda Shelf palaeo-drainage systems on the emerged shelf (“Sundaland”). The progressive landward displacement of the coastline and breakdown of these vast drainage systems during deglaciation led to a decrease in influence of the kaolinite-rich southern sources. When the coastline had retreated closely to its present-day position in mid-Holocene times, the former dominance of southern sources was replaced by a stronger influence of illite-rich sources (e.g. Borneo). The overriding control of sea level changes on the clay mineral distribution patterns precludes a definite climatic interpretation of clay mineral data in terms of climatic/monsoonal changes in such highly dynamic sedimentary environment.     

Morphology and structure of the Galapagos Rise

Geophysical data collected on three U.S. Naval Oceanographic Office cruises to the Galapagos Rise are presented. These data allow definition of the morphology and structure of the Galapagos Rise.A postulated “hot spot” beneath the Galapagos platform is suggested as the cause of: (1) decreased seismicity along the spreading center for a 400 km E—W distance from the islands; (2) distinctive petro-chemistry of tholeiites from the islands and adjacent oceanic crust generated by the Galapagos Rise; (3) high-amplitude magnetic anomalies in a 1,000 km E—W band including and just north of the Galapagos platform; and (4) morphologic shape and the regionally elevated sea floor of the Galapagos Rise as it approaches the insular platform.     

Detection and analysis of coherent structures in urban turbulence

Summary The continuous wavelet transform provides a suitable tool to visualize the vertical structure of turbulence and to detect coherent structures in turbulent time series. This is demonstrated with a simple example of an artificially ramp structured time series. In this study turbulence data, i.e. the fluctuations of the horizontal wind components u′ and v′, the vertical component w′ and temperature T′, sampled with 20.83 Hz and measured simultaneously at three levels (z/h=1.5, 2.1 and 3.2, with z as the sensor height and h the height of the roughness elements) over an urban canopy in the inner city of Basel, Switzerland, are analyzed. The detection of the coherent structures was performed using the Mexican hat wavelet and the zero-crossing method. The analysis for unstable conditions shows that organized structures (ejection-sweep cycles) cover about 45% of the total run time. A conditional average from a total of 116 detected ejection-sweep sequences during 7 hours was calculated over a time window of 100 seconds. This dominating time scale was derived from peak frequencies of the wavelet spectra as well as from the Fourier spectra. It is shown that the normalized amplitudes of fluctuations of temperature and longitudinal wind speed during the events are largest at the lowest measurement level just above the canopy and decrease with increasing distance from the roughness elements. A comparison of related studies over different non-urban surfaces (mainly forests) shows that the shape of conditionally averaged ejection-sweep sequences is very similar for all canopies, however, the dominating time scale in general increases the rougher the surface is and the higher the roughness elements are.     

Morphotectonic evolution of two depressions at the southern border of the Baikal rift system

Detailed study of two dry depressions in the Baikal rift system: the E–W Khoito Ghol-Tunka-Bistraya depression and the SW–NE Gusinoje–Ivolga depression, aims to provide a better understanding of tectonic control on the intershoulder relief evolution after the rift opened. Both depressions are grabens and both feature a suite of 10–20 km-wide basins alternating with more or less massive highs. Field and laboratory analysis shows that this pattern is of recent tectonic origin and that local breaking-up and subsidence followed the general sinking which originally formed the grabens. The subsidence belts seem to have gradually shifted north and northeastwards. Geomorphological analysis reveals that in both depressions the highs are remnants of a former pediment which was broken up. The young basins display numerous relevant hydrographic anomalies of the secondary channels and a general water-logging. They also suggest that the subsidence belts have gradually shifted north-and northeastwards. In the Gusinoje–Ivolga depression evidence was found of a Plio-Pleistocene river course, parallel to the Selenga river, which was later dismantled by the breaking-up. This depression, parallel to the Baikal rift and belonging to the Mesozoic system of grabens in the Caledonian fold belt, seems to have been included into the general system of rifts during the Pliocene tectonic phase. As for the main hydrographic axes, the Selenga river was set on a Palaeogene-age planation surface before the first tectonic phase and kept its original course. The Irkut river flowed in the Khoito Gol–Tunka–Bistraya depression after the first tectonic phase and was not affected by the later breaking-up. In contrast, the secondary drainage network is largely discordant. Despite their different geotectonic contexts, the two depressions show a similar development of relief pattern,which poses the question of the style of rift dynamics after the main Pliocene tectonic phase.