Impacts of post‐glacial rebound on landslide spatial distribution at a regional scale in northern Iceland (Skagafjörður)

In de‐glaciated areas, para‐glaciation (i.e. the conditioning of landscapes by prior glaciation) has often been considered a major predisposing factor in landslide occurrence; its consequences have been particularly well identified at a fine scale (especially on bedrock jointing). Hitherto, the relative impacts of para‐glaciation on hillslope dynamics at a regional scale had nevertheless not been quantified statistically. We examine Skagafjörður area (northern Iceland) where landslides are widespread (at least 108 were mapped in an area of c. 3000 km²). We compare the role of para‐glaciation (debuttressing, influence of post‐glacial rebound) with that of classic factors (topography, lithology, etc.) in landslide occurrence and location, using a spatial analysis based on a chi‐square test. On the one hand, the results highlight that landslides are over‐represented in areas where post‐glacial rebound was at its maximum, with a stronger concentration of landslides in the northern part of the fjord. On the other hand, the distribution of landslides did not show any clear relationship with the pattern of glacial debuttressing. Tschuprow coefficient highlights that the influence of post‐glacial rebound on landslide location is higher than the combined influence of slope gradient, curvature or geological structure. This result is supported by our initial evidence for the timing of landslides in the area: most landslides occurred during the first half of the Holocene, and a period of hillslope instability was initiated when the post‐glacial uplift was at its maximum. Finally, the mechanisms that link post‐glacial rebound and landsliding as well as the geomorphic impacts of landslides, are discussed. Copyright © 2013 John Wiley & Sons, Ltd.     

T2L2 - Time transfer by Laser link: a new optical time transfer generation

The T2L2 experiment allows the synchronisation of remote clocks on Earth, and the monitoring of a satellite clock with an accuracy in the 50 ps range. It is based on the propagation of light pulses in space which is better controlled than the radio waves propagation. Some new optical timer and the definition of a new time origin allow direct accurate time transfer without external calibration. The time equations and the uncertainty budget are presented so as to justify the announced performance. This optical time transfer associated to an ultra-stable clock in space has many scientific application as the study of some aspects of the gravitation.     

Formation and evolution of lateritic profiles in the middle Amazon basin: Insights from radiation-induced defects in kaolinite

The content of radiation-induced defects (RIDs) in kaolinite samples originating from lateritic soils and continental detritic sediments of the middle Amazon Basin (Brazil) is investigated using electron paramagnetic resonance. The paleodose registered by kaolinites ranges from 80 to 900 kGy. Present-day dose rates of radiation, determined from the whole-rock U and Th content, range between 4000 and 40,000 mGy/ka. In most samples, U and Th concentrations are correlated, suggesting that U has not been remobilized by lateritization. This observation is consistent with the fact that ∼80% of the total U content is incorporated in resistant minerals, such as zircon and Ti oxides. The heterogeneous distribution of U, observed by induced fission tracks mapping, makes it possible to neglect the α-radiation contribution of the U decay chains in the dose-rate calculation. The interpretation of the measured content of RIDs in kaolinite is then performed using the calculated present-day dose rate and assuming equilibrium in the radioactive decay chains. For the sedimentary samples, the amount of RIDs is broadly correlated to the dose rate and provides apparent absolute ages older than 20 Ma. The RID contents in kaolinites from the lateritic soils provide apparent ages ranging from 10 to 6 Ma. The high RID content of these lateritic kaolinites shows that their chemical, isotopic, and crystallographic properties are not representative of present-day weathering conditions. Models assuming the “dynamical equilibrium” of kaolinites with local physical-chemical conditions prevailing in lateritic soils are thus questionable. Alternatively, our findings bring strong support for the use of the isotopic composition of kaolinites to decipher continental paleo-climates.     

Small-scale, nature-based tourism as a pro-poor development intervention: Two examples in Kwazulu-Natal, South Africa

Tourism is widely acknowledged as a key economic sector that has the potential to contribute to national and local development and, more specifically, serve as a mechanism to promote poverty alleviation and pro-poor development within a particular locality. In countries of the global South, nature-based tourism initiatives can make a meaningful impact on the livelihoods of the poor, in particular the subsistence based rural poor. Taking two examples in KwaZulu-Natal Province, South Africa, where small-scale tourism initiatives were developed recently in response to existing natural attractions in the context of coping with local economic crises, this paper broadly assesses the modest benefits to date, as well as drawbacks, in improving conditions of life.     

Contribution of interstitial OH groups to the incorporation of water in forsterite

Water incorporation in forsterite samples synthesized under low to medium silica-activity conditions mostly occurs via a substitutional mechanism in which a Si vacancy is compensated by four protons. Corresponding IR absorption spectra display a cluster of narrow and weakly anharmonic OH-stretching bands at wavenumbers above 3,500 cm^?1. However, this diagnostic spectrum is often superimposed to one broader absorption band, rarely two, displaying pronounced temperature-dependent properties and tentatively assigned to H atoms in interstitial position (Ingrin et al. in Phys Chem Miner 40:499–510, 2013). Here, we investigate the structural and vibrational properties of selected interstitial H-bearing defects in forsterite using a first-principles modeling approach. We show that the broad bands discussed by Ingrin et al. (Phys Chem Miner 40:499–510, 2013) are most likely related to interstitial OH groups in the vacant octahedral sites alternating with the M2 sites along the c axis of the forsterite structure. The corresponding OH defects lead to the formation of fivefold coordinated Si species. Their peculiar thermal properties stem from the vibrational phase relaxation due to the anharmonic coupling of the high-energy local OH-stretching mode with a low-energy vibrational mode. This “exchange mode” corresponds to the hindered longitudinal translation of the OH group. These results suggest that at high pressure, hydrogen incorporation in forsterite is dominated by coexisting interstitial OH groups and (4H)_Si defects.     

Extraterrestrial water in micrometeorites and cosmic spherules from Antarctica: An ion microprobe study

Abstract— The D/H ratios and water contents were measured by ion microprobe analysis in 52 individual Antarctic micrometeorites (AMMs) and 10 Antarctic cosmic spherules (ACSs) containing nuggets of iron hydroxide (COPS phase). In AMMs, δD values vary from ?366 to +249%‰ and water contents lie between 0.4-3.7 wt%. The COPS nuggets in cosmic spherules have high water contents (2 to 8 wt%) and exhibit δD values from ?144 to +167%‰, which is indicative of an extraterrestrial origin of their constituent water. The silicate portion of ACSs also contain extraterrestrial H equivalent to ～0.l to 1.2 wt% water. Deuterium-exchange experiments were performed with isotopically spiked water. These experiments demonstrate that water in mineral phases of AMMs and ACSs is indigenous and does not result from contamination during residence in Antarctic ice. The frequency distribution of D/H ratios in AMMs allows us to further narrow the relationship between AMMs and carbonaceous chondrites to CM and CI chondrites but contrasts with that of stratospheric interplanetary dust particles (IDPs) of similar sizes (from ?10 to 50 μm). The relatively narrow range of D/H ratios measured in AMMs as well as in ACSs (which are more resistant and thus less susceptible to collection biases) suggests that D-rich IDP-like particles are very rare in our AMMs collections. This indicates that these D-rich grains might constitute a minor fraction of the micrometeorite flux in the interplanetary medium and that possible collection biases in Antarctica would not be responsible for their strong depletion in the AMMs collections.     

Influence of Continental Sources on Oceanic Air Composition at the Eastern Edge of the North Atlantic Ocean, TOR 1992–1995

The atmospheric concentrations of O3, NMHCs, PAN and NOx were measured at the TOR station in Porspoder (Brittany, France) from 1992 to 1995. The results from April 1992 to December 1994 are reported here. In order to study the behaviour of trace gases in the air masses coming from the Atlantic Ocean, the origin of these air masses was characterised by the analysis of the five-day back-trajectories reaching 950 mbar at Porspoder. Three kinds of oceanic air masses are considered, depending on their origin: North Atlantic northern and southern latitudes and North American continent. It appears that the oceanic high-latitude troposphere was strongly influenced by continental emissions, which in turn impacted the median latitude troposphere during polar outflow events. A greater accumulation of anthropogenic compounds in the Arctic sector was calculated and may be at the origin of the high oxidant levels measured in spring in this same sector. The influence of north American emissions on the European coast was also studied and seems to reach a maximum in spring. Long-range transport of long- lived species was observed throughout the year, but evidence for winter transport of more reactive species, such as ethene, is also shown. Meteorological parameters and local photochemistry appear to play an important role in the distribution of the pollutants over the North Atlantic Ocean throughout the year. Further investigations are needed to give more complete information about the origin, formation and destruction of the secondary pollutants.