A high-resolution Holocene record on the Southern Brazilian shelf: Paleoenvironmental implications

A high-resolution, multi-proxy record has been used to determine the environmental changes during the Holocene on the southern Brazilian shelf. Present oceanographic conditions reveal wind and freshwater input as the determinants of short-term productivity changes in the study area. Magnetic susceptibility and grain-size variations, together with proxies of productivity (organic carbon, carbon accumulation rate, Ba, Sr, and Ca content, Ba/Al, Ba/Ti, and Al/Ti ratios) were analyzed and compared with proxies of redox condition (V/Ti ratio), terrigenous input (Fe/Ca and Ti/Ca ratios), as well as other Element/Ti ratios, to evaluate the paleoceanographic and paleoclimatic changes over the period.The core covers a time interval of about 7650 years, with sedimentation rates varying from 0.025 to 0.250 cm a⁻¹, which represent time intervals of between 8 and 80 a per sample. There is a clear change in the sedimentation rate at about 2800 B.P.All grain-size and elemental results indicate the occurrence of conspicuous changes between 5200 and 5000 cal. B.P., as well as between 3000 and 2800 cal. B.P. A comparison of the results with the palynological information available from the adjacent continental areas suggests that the sedimentary changes in this last interval may be correlated with the onset of modern climatic conditions in South America, and especially, with the onset of the Plata Plume Water, a water mass that carries cold, less saline waters towards the north. However, minor changes are observed at ca. 1500 B.P. and are correlated with an increase in the atmospheric humidity. Furthermore, a time-series analysis undertaken using several proxies indicated the occurrence of Sub-Milankovitch cycles, which may be compared with those reported worldwide.     

Seasonal and inter-annual zooplankton dynamics in temporary pools with different hydroperiods

The results of a research carried out in 2001 on nine temporary mountain pools (Northern Apennines, Italy) underlined a major role of hydroperiod in shaping zooplankton communities of temporary habitats. In 2002, the same pools were studied to assess inter-annual differences in zooplankton seasonal patterns. Data on precipitations (both snow and rainfalls) were collected to evaluate the influence of precipitation regimes on hydroperiod and concurrently on hydrochemical features and zooplankton dynamics.Mean annual snow and rainfall abundances were highly similar in both years but precipitation patterns were different. Moreover, different air temperatures were measured in the 2 years of study. These factors influenced water persistence and dry and wet cycles in the pools: in 2001, three pools dried out in summer and remained dry until autumn rainfalls (type A pools), in five pools (type B pools) the summer dry period was interrupted by re-filling due to storms in July and only in one pool water did remain for the entire research period (C1). In 2002, type A and B pools underwent only one dry phase (June–July) while C1 showed a hydroperiod similar to the one that occurred in the previous year. Overall, type A and B pools can be classified as ‘seasonal’ and C1 as ‘near-permanent or permanent’.Principal component analysis and paired t-tests did not show significant differences between years in the hydrochemical features of the pools. However, the seasonal pools showed a wide range of variation in their hydrochemical parameters while water features of the permanent pool presented less variability.Within the pools, divergences in the number and in the type of zooplankton taxa between the 2 years were limited. Rotifer and copepod density of the seasonal pools were comparable over years and only cladocerans exhibited distinct density dynamics. Cladoceran appeared to be associated with ionic content and influenced by the occurrence of ice-melting and by the wet phase length of the pools.On the contrary, the permanent pool showed diverse zooplankton seasonal patterns in 2001 compared to 2002. Over years, different pH values were measured; pH and conductivity varied with changing water volume, which in turn explained a significant amount of the observed variation in zooplankton densities in 2002.     

Sonoran Desert productivity and the effect of trap size on litterfall estimates in dryland vegetation

We describe the temporal and spatial litterfall and test the accuracy of different litter collection devices in a Sonoran Desert community. Two low-lying PVC litter trap designs were tested and compared against a standard IBP trap. The test traps collected significantly more plant litter than the IBP traps, which failed to capture most of the litter of ephemerals and low shrubs. The largest differences between the traps appeared after the pulses of growth of ephemeral plants. Data collection for a period of almost 2 years showed an annual total litterfall of 3·43 Mg ha⁻¹for the test traps and 2·77 Mg ha⁻¹for the IBP traps. These values are well above the average for deserts and fit better into the lower range of tropical dry forests. The test PVC traps are inexpensive, economical in collecting and sorting effort, and less prone to vandalism. Also, they can be laid in higher numbers than IBP traps, thus providing a better representation of the highly heterogeneous desert environment.     

A GIS-based approach for gully erosion susceptibility modelling: a test in Sicily, Italy

The aim of this study is to analyze the susceptibility conditions to gully erosion phenomena in the Magazzolo River basin and to test a method that allows for driving the factors selection. The study area is one of the largest (225 km²) watershed of southern Sicily and it is mostly characterized by gentle slopes carved into clayey and evaporitic sediments, except for the northern sector where carbonatic rocks give rise to steep slopes. In order to obtain a quantitative evaluation of gully erosion susceptibility, statistical relationships between the spatial distributions of gullies affecting the area and a set of twelve environmental variables were analyzed. Stereoscopic analysis of aerial photographs dated 2000, and field surveys carried out in 2006, allowed us to map about a thousand landforms produced by linear water erosion processes, classifiable as ephemeral and permanent gullies. The linear density of the gullies, computed on each of the factors classes, was assumed as the function expressing the susceptibility level of the latter. A 40-m digital elevation model (DEM) prepared from 1:10,000-scale topographic maps was used to compute the values of nine topographic attributes (primary: slope, aspect, plan curvature, profile curvature, general curvature, tangential curvature; secondary: stream power index; topographic wetness index; LS-USLE factor); from available thematic maps and field checks three other physical attributes (lithology, soil texture, land use) were derived. For each of these variables, a 40-m grid layer was generated, reclassifying the topographic variables according to their standard deviation values. In order to evaluate the controlling role of the selected predictive variables, one-variable susceptibility models, based on the spatial relationships between each single factor and gullies, were produced and submitted to a validation procedure. The latter was carried out by evaluating the predictive performance of models trained on one half of the landform archive and tested on the other. Large differences of accuracy were verified by computing geometric indexes of the validation curves (prediction and success rate curves; ROC curves) drawn for each one-variable model; in particular, soil texture, general curvature and aspect demonstrated a weak or a null influence on the spatial distribution of gullies within the studied area, while, on the contrary, tangential curvature, stream power index and plan curvature showed high predictive skills. Hence, predictive models were produced on a multi-variable basis, by variously combining the one-variable models. The validation of the multi-variables models, which generally indicated quite satisfactory results, were used as a sensitivity analysis tool to evaluate differences in the prediction results produced by changing the set of combined physical attributes. The sensitivity analysis pointed out that by increasing the number of combined environmental variables, an improvement of the susceptibility assessment is produced; this is true with the exception of adding to the multi-variables models a variable, as slope aspect, not correlated to the target variable. The addition of this attribute produces effects on the validation curves that are not distinguishable from noise and, as a consequence, the slope aspect was excluded from the final multi-variables model used to draw the gully erosion susceptibility map of the Magazzolo River basin. In conclusion, the research showed that the validation of one-variable models can be used as a tool for selecting factors to be combined to prepare the best performing multi-variables gully erosion susceptibility model.     

Neutron star surface emission: Beyond the dipole model

Recent Chandra and XMM-Newton observations of a number of X-ray “dim” pulsating neutron stars revealed quite unexpected features in the emission from these sources. Their soft thermal spectrum, believed to originate directly from the star surface, shows evidence for a phase-varying absorption line at some hundred eVs. The pulse modulation is relatively large (pulsed fractions in the range ～8–35% in amplitude), the pulse shape is often non-sinusoidal, and the hard X-ray color appears to be anti-correlated in phase with the total emission. Moreover, the prototype of this class, RX J0720.4-3125, has been found to undergo rather sensible changes both in its spectral and timing properties over a timescale of a few years. By modeling the light curves of two sources, RBS 1223 and RX J0720.4-3125, it has been found evidence for two hot regions located at a slightly non antipodal direction. All these new findings are difficult to reconcile with the standard picture of a cooling neutron star endowed with a purely dipolar magnetic field. Here we present more realistic models of surface emission, where the effects of different neutron star thermal and magnetic surface distributions are accounted for. We show how a star-centered field made of a dipolar and a quadrupolar component can influence the properties of the observed light curves and we present results that account self-consistently for toroidal and poloidal crustal field configurations.     

New estimations of precipitation and surface sublimation in East Antarctica from snow accumulation measurements

Surface mass balance (SMB) distribution and its temporal and spatial variability is an essential input parameter in mass balance studies. Different methods were used, compared and integrated (stake farms, ice cores, snow radar, surface morphology, remote sensing) at eight sites along a transect from Terra Nova Bay (TNB) to Dome C (DC) (East Antarctica), to provide detailed information on the SMB. Spatial variability measurements show that the measured maximum snow accumulation (SA) in a 15 km area is well correlated to firn temperature. Wind-driven sublimation processes, controlled by the surface slope in the wind direction, have a huge impact (up to 85% of snow precipitation) on SMB and are significant in terms of past, present and future SMB evaluations. The snow redistribution process is local and has a strong impact on the annual variability of accumulation. The spatial variability of SMB at the kilometre scale is one order of magnitude higher than its temporal variability (20–30%) at the centennial time scale. This high spatial variability is due to wind-driven sublimation. Compared with our SMB calculations, previous compilations generally over-estimate SMB, up to 65% in some areas.     

Development of agroclimatic zoning model to delimit the potential growing areas for macaw palm (Acrocomia aculeata)

Theoretical and Applied Climatology - The growing biodiesel production requires the use of new technologies and alternative feedstocks to maintain the growing demand of this biofuel. The macaw...     

Chronology of ‘dry fogs’ in Italy, 1374–1891

Summary A chronology and some comments about the occurrence of dry fogs i.e. clouds of volcanic aerosols trapped in the planetary boundary layer (PBL) are reported. The dry fogs have severely affected the biosphere, and they also had local climatic effects affecting the terrestrial albedo. In the most severe cases the fog persisted for months and obscured the sun, in the lesser ones a mist persisted for a few days and the sun was seen as weak and the moon with a red halo. The volcanic aerosols were trapped in the PBL in the warm season, when the atmosphere is particularly stable over the relatively cold Mediterranean waters and the Azores Anticyclone causes the absence of winds.     

Age and geotectonic setting of Late Neoproterozoic juvenile mafic gneisses and associated paragneisses from the Ribeira belt (SE Brazil) based on geochemistry and Sm–Nd data — Implications on Gondwana assembly

Mafic gneisses and associated paragneisses from the Cabo Frio Tectonic Domain in the southeastern part of the Ribeira Belt, along the coast of Rio de Janeiro State in southeast Brazil, were subjected to a geochemical and Sm–Nd isotope study. Four lithotypes are distinguished: aluminous paragneisses (mainly sillimanite–kyanite–garnet–biotite gneiss), calcsilicate lenses, quartzo–feldspathic metasedimentary gneisses and mafic–ultramafic lenses. The whole-rock major and trace, including rare earth element distributions in the mafic–ultramafic intercalations indicate that derivation from subalkaline basalt/gabbro of tholeiitic affinity with E-MORB signature from a non-subduction environment. These mafic rocks have positive ε_Nd(t) and T_DM of 1.1 Ga. The metasedimentary rocks have negative ε_Nd(t) and T_DM of 1.7 Ga. A Sm–Nd whole rock isochron of mafic rocks yielded an age of 604 ± 38 Ma for the crystallization. This matches with the age of some detrital zircon grains from the paragneisses. The depositional basin, named Buzios–Palmital, was active at least until 620 Ma (age of the youngest detrital zircon) and was subsequently deformed and metamorphosed at ca. 525 Ma (age of metamorphic zircons) during the Buzios Orogeny. It is interpreted as a back arc basin with relation to the 630 Ma magmatic arc of the Oriental Terrane in the Ribeira Belt to the NW. However, after 600 Ma, the Buzios–Palmital basin changed to an active margin setting because the arc collided with the continental margin and the subduction shifted to the back arc environment. By 610 Ma, most of the Brasiliano belts registered collisional events related to multiple convergent blocks. The stress fields and paleocontinent shapes would have allowed the occurrence of extensional areas with not only sedimentary deposition but also ocean floor spreading. Its remnants are preserved in this Brazilian coastal region as an ancient suture, reworked intensively during the Mesozoic rifting events. The reconnaissance of Late Neoproterozoic basins in the Brasiliano–Pan-African belts is of major importance to partially unravel the final amalgamation events of SW Gondwana. Considering that the Buzios–Palmital basin rock units are mostly covered by the marginal Atlantic basins, it is possible that other evidence could be preserved in the coastal regions of SW-Africa and SE-South America.