A 30000 year record of physical and optical properties of microparticles from an East Antarctic ice core and implications for paleoclimate reconstruction models     

A. Royer  M. De Angelis  J. R. Petit 《Climatic change》1983,5(4):381-412

Ice samples from the 905 m deep Dome C core (East Antarctica) were studied in terms of insoluble microparticle contents. Various techniques were used: right angle light scattering, nephelometer (multiangle light scattering), Coulter counter and microscope analyses, in order to make a thorough study of the physical and optical properties of microparticles and their variations over the last 30000 years. Because of the possible effect of atmospheric turbidity on the earth-atmosphere radiation balance, optical parameters of climatic importance were estimated for insoluble microparticles. The detailed profile of total microparticle mass concentrations shows a drastic (factor of 17 ± 13) difference between high Last Glacial Maximum (LGM) and low Holocene concentrations. The optical scattering properties of 18000 BP continental dust do not indicate a significant difference with respect to Holocene dust in terms of particle size distribution and complex refractive index. The number to log radius size distribution of microparticles for the entire 30 000 yr period can be fitted by a log-normal distribution with two parameters (modal radius 0.25 ± 0.08 μm; geometric standard deviation 2.2. ± 0.2). However, for the smallest particles a better adjustment between experimental and theoretical scattering diagrams is obtained by adding to the observed size distribution another log-normal distribution (modal radius = 0.025 μm, σ _g = 2). The complex refractive index is 1.53 to 1.56 for the real part and 0.005 ± 0.005 for the imaginary part at the wavelength used (λ= 546 nm). During the LGM stage, over the whole of Antarctica, the change in the total optical depth due to the drastic change in the insoluble aerosol loading is small because insoluble impurities are not the dominant aerosol component. It may have produced a slight warming of the snow surface (≈ 2 K). In the dust source regions, the optical depth would have been a maximum of 2 to 4 times the present value. The possible warming of the atmosphere in these regions is estimated at 3 K per day and should therefore be taken into account in paleoclimate reconstruction models.  相似文献   

Projecting future drought in Mediterranean forests: bias correction of climate models matters!   总被引：1，自引：0，他引：1  

Julien Ruffault  Nicolas K Martin-StPaul  Carole Duffet  Fabien Goge  Florent Mouillot 《Theoretical and Applied Climatology》2014,117(1-2):113-122

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.  相似文献   

Ocean expansion: The role of detachment faults     

Françoise Chalot-Prat  Rémi Magott  Carole Berthod 《地学学报》2023,35(1):15-22

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.  相似文献