Projecting future drought in Mediterranean forests: bias correction of climate models matters!

Global and regional climate models (GCM and RCM) are generally biased and cannot be used as forcing variables in ecological impact models without some form of prior bias correction. In this study, we investigated the influence of the bias correction method on drought projections in Mediterranean forests in southern France for the end of the twenty-first century (2071–2100). We used a water balance model with two different atmospheric climate forcings built from the same RCM simulations but using two different correction methods (quantile mapping or anomaly method). Drought, defined here as periods when vegetation functioning is affected by water deficit, was described in terms of intensity, duration and timing. Our results showed that the choice of the bias correction method had little effects on temperature and global radiation projections. However, although both methods led to similar predictions of precipitation amount, they induced strong differences in their temporal distribution, especially during summer. These differences were amplified when the climatic data were used to force the water balance model. On average, the choice of bias correction leads to 45 % uncertainty in the predicted anomalies in drought intensity along with discrepancies in the spatial pattern of the predicted changes and changes in the year-to-year variability in drought characteristics. We conclude that the choice of a bias correction method might have a significant impact on the projections of forest response to climate change.     

The Australia telescope 20 GHz survey: hardware, observing strategy, and scanning survey catalog

The Australia Telescope 20 GHz (AT20G) survey is a large area (2?? sr), sensitive (40 mJy), high frequency (20 GHz) survey of the southern sky. The survey was conducted in two parts: an initial fast scanning survey, and a series of more accurate follow-up observations. The follow-up survey catalog has been presented by Murphy et al. (MNRAS 402:2403, 2010). In this paper we discuss the hardware setup and scanning survey strategy as well as the production of the scanning survey catalog.     

Nickel abundance in stony cosmic spherules: Constraining precursor material and formation mechanisms

Abstract– We report bulk and olivine compositions in 66 stony cosmic spherules (Na₂O < 0.76 wt%), 200–800 μm in size, from the Transantarctic Mountains, Antarctica. In porphyritic cosmic spherules, relict olivines that survived atmospheric entry heating are always Ni‐poor and similar in composition to the olivines in carbonaceous or unequilibrated ordinary chondrites (18 spherules), and equilibrated ordinary chondrites (one spherule). This is consistent with selective survival of high temperature, Mg‐rich olivines during atmospheric entry. Olivines that crystallized from the melts produced during atmospheric entry have NiO contents that increase with increasing NiO in the bulk spherule, and that range from values similar to those observed in chondritic olivines (NiO generally <0.5 wt%) to values characteristic of olivines in meteoritic ablation spheres (NiO > 2 wt%). Thus, NiO content in olivine cannot be used alone to distinguish meteoritic ablation spheres from cosmic spherules, and the volatile element contents have to be considered. We propose that the variation in NiO contents in cosmic spherules and their olivines is the result of variable content of Fe, Ni metal in the precursor. NiO contents in olivines and in cosmic spherules can thus be used to discuss their parent body. Ni‐poor spherules can be derived from C‐rich and/or metal‐poor precursors, either related to CM, CI, CR chondrites or to chondritic fragments dominated by silicates, regardless of the parent body. Ni‐rich spherules (NiO > 0.7 wt%) that represent 55% of the 47 barred‐olivine spherules we studied, were derived from the melting of C‐poor, metal‐rich precursors, compatible with ordinary chondrite or CO, CV, CK carbonaceous chondrite parentages.     

Gebel Kamil: The iron meteorite that formed the Kamil crater (Egypt)

Abstract– The 45 m in diameter Kamil impact crater was formed <5000 yr ago in the eastern Sahara, close to the southern border of modern Egypt. The original features of this structure, including thousands of fragments of the meteorite impactor, are extremely well preserved. With the exception of a single 83 kg regmaglypted individual, all specimens of Gebel Kamil (the iron meteorite that formed the Kamil crater) are explosion fragments weighing from <1 g to 34 kg. Gebel Kamil is an ungrouped Ni‐rich (about 20 wt% Ni) ataxite characterized by high Ge and Ga contents (approximately 120 μg g^?1 and approximately 50 μg g^?1, respectively) and by a very fine‐grained duplex plessite metal matrix. Accessory mineral phases in Gebel Kamil are schreibersite, troilite, daubréelite, and native copper. Meteorite fragments are cross‐cut by curvilinear shear bands formed during the explosive terrestrial impact. A systematic search around the crater revealed that meteorite fragments have a highly asymmetric distribution, with greater concentrations in the southeast sector and a broad maximum in meteorite concentration in the 125–160° N sector at about 200 m from the crater rim. The total mass of shrapnel specimens >10 g, inferred from the density map compiled in this study is 3400 kg. Field data indicate that the iron bolide approached the Earth’s crust from the northwest (305–340° N), travelling along a moderately oblique trajectory. Upon hypervelocity impact, the projectile was disrupted into thousands of fragments. Shattering was accompanied by some melting of the projectile and of the quartz‐arenite target rocks, which also suffered shock metamorphism.     

Ocean expansion: The role of detachment faults

Detachment faulting at slow spreading ocean ridge axes is recognized as a major surface creation mechanism, yet the structural relationships of these faults with feeder-dykes of on-axis volcanoes remained unresolved. This summary study shows that surface creation leading to ocean widening is exclusively controlled by detachment faults, shallow tracers of tectonic stresses induced by the westward drift of plates. Volcanoes are fed by feeder-dykes following on-axis rotational detachment faults. Once formed volcanoes are dragged along the detachment whose footwall is made of mantle material sometimes hosting gabbro sills. Due to the faster drift of the uppermost lithospheric layer, the feeder-dykes are then intersected by active deeper low-angle detachments, become inactive and are replaced by new ones on-axis. Rooted vertically on either side of the plate boundary, the detachment flexing is all the earlier and more progressive as the faults are far from the axis, positioning gabbro as sills at shallow level within a deformed mantle interspersed with cataclasite horizons. Correlations between shallow and deep lithospheric processes are then clarified.