How “African” was the early human dispersal out of Africa?

In this paper we review a number of scenarios which have been proposed to explain the first hominin “out of Africa” at the base of the Pleistocene. These are the brain expansion scenario, the cultural exclusion scenario, the migratory wave scenario and the common African home scenario. These scenarios are checked against the current evidence provided by the Georgian site of Dmanisi, which contains the oldest Eurasian hominins. Therefore, it is concluded that none of these scenarios fits with the existing evidence, and that the only real African influence in Dmanisi is restricted to early Homo itself. In order to explain the presence of early Homo at Dmanisi, it is concluded that the expansion out of Africa should have happened before the actual datum of Dmanisi, most probably linked to the spread of Mode 1 tools in Africa.     

Short-term effects of gamma ray bursts on oceanic photosynthesis

We continue our previous work on the potential short-term influence of a gamma ray bursts on Earth’s biosphere, focusing on the only important short-term effect on life: the ultraviolet flash which occurs as a result of the retransmission of the γ radiation through the atmosphere. Thus, in this work we calculate the ultraviolet irradiances penetrating the first hundred meters of the water column, for Jerlov’s ocean water types I, II and III. Then we estimate the UV flash potential for photosynthesis inhibition in the whole photic zone, showing that it can be important in the first tens of meters of the water column.     

Regional provenance from southwestern Colombia fore‐arc and intra‐arc basins: implications for Middle to Late Miocene orogeny in the Northern Andes

Andean orogenic processes controlled the spatial and temporal distribution of the magmatic and sedimentary record. This contribution integrates new U/Pb zircon ages, heavy mineral analyses and biostratigraphic constraints from the Neogene sedimentary record of the fore‐arc and intra‐arc basins and volcano‐plutonic rocks of southwestern Colombia, to reconstruct these orogenic processes. The results reveal continuous arc magmatism since the Late Oligocene, with a major post‐Middle Miocene magmatic peak and exhumation. When integrated with other geological constraints, the tectonic evolution of the margin includes Eocene‐Oligocene oblique convergence with limited magmatic activity, followed by the initiation of a Late Oligocene‐Early Miocene arc that migrated to the east in the Middle Miocene, when it experienced a major increase in magmatic activity, crustal deformation, exhumation and thickening. This orogenic evolution is related to the shallowing of the slab dip due to the subduction of the Neogene Nazca Plate.     

与地形相关的街道网络分析及其对快速增长型城市的意义(英文)

In addition to socio-economic factors, major landforms may affect the city structure and urban form. Here we show that landforms have significant effects on the city shape and street patterns of the fast-growing Iranian cities of Dezful(a river) and Khorramabad(mountains and valleys), but no clear effects on the cities of Yazd and Nain. Also, where the street orientation is peaked, the Gibbs/Shannon entropy(a measure of dispersion or spread) is low, but increases as the distribution becomes more uniform because of landform constraints. The streets in the old inner parts of all the cities are, on average, shorter and denser(more streets per unit area) than the streets of the newer outer parts. The entropies of the outer parts are also greater than those of the inner parts, implying that the street-length distribution gradually becomes more dispersed or spread as the city expands. All these cities have been fast growing in the past decades, with the newer outer parts expanding rapidly. As shown here, the rapidly formed outer parts(with greater dispersion in street patterns) have significantly different textures from those of the older inner parts, indicating different functionality and growth processes. These quantitative methods for street-network analysis can be used worldwide, particularly for analysing the effects of landforms on city shape and texture.     

Validation of IPCC AR4 models over the Iberian Peninsula

This paper reports analysis of the ability of 24 coupled global climate models that were used in the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change to simulate the current monthly seasonal cycle of sea level pressure, surface air temperature and precipitation over the Iberian Peninsula in the last two decades of the twentieth century. The period investigated runs from 1979 to 1998. In order to assess the performance of the models, averaged seasonal cycles and probability density functions (PDFs) calculated from model simulations are compared with the corresponding seasonal cycles, whilst PDFs are also obtained using the data from the ERA40 reanalysis and the Global Precipitation Climatology Project. We found that simulated PDFs generally provided a better fit to actual PDFs than seasonal cycles do. This conclusion indicates that when evaluating model performance, the climate variability as measured by means of PDFs is not the only climatic element that should be tested. Regarding the comparison based on the seasonal cycle, results also show that the root mean square skill score is more useful than the r skill score. To rank the AR4 models, sea level pressure, surface air temperature and precipitation variables were selected and a group of five AR4 models were identified as the models which best reproduce current climate in the area: MIROC3.2-HIRES, MPI-ECHAM5, GFDL-CM2.1, BCCR-BCM2.0 and UKMO-HADGEM1. The rank obtained should not be understood in a hierarchical manner because there is a certain degree of internal variability in the model ensembles. Finally, it should be noted that these results are in good agreement with other classifications found in the scientific literature.     

Classifying wave forecasts with model-based Geostatistics and the Aitchison distribution

This paper proposes a non-parametric method of classification of maps (i.e., variable fields such as wave energy maps for the Western Mediterranean Sea) into a set of D typical regimes (calm, E-, SW- or N/NW-wind dominated storms, the 4 synoptic situations more often occurring in this region). Each map in the training set is described by its values at P measurement points and one of these regime classes. A map is thus identified as a labelled point in a P-dimensional feature space, and the problem is to find a discrimination rule that may be used for attaching a classification probability to future unlabelled maps. The discriminant model proposed assumes that some log-contrasts of these classification probabilities form a Gaussian random field on the feature space. Then, available data (labelled maps of the training set) are linked to these latent probabilities through a multinomial model. This model is quite common in model-based Geostatistics and the Gaussian process classification literature. Inference is here approximated numerically using likelihood based techniques. The multinomial likelihood of labelled features is combined in a Bayesian updating with the Gaussian random field, playing the role of prior distribution. The posterior corresponds to an Aitchison distribution. Its maximum posterior estimates are obtained in two steps, exploiting several properties of this family. The first step is to obtain the mode of this distribution for labelled features, by solving a mildly non-linear system of equations. The second step is to propagate these estimates to unlabelled features, with simple kriging of log-contrasts. These inference steps can be extended via Markov-chain Monte Carlo (MCMC) sampling to a hierarchical Bayesian problem. This MCMC sampling can be improved by further exploiting the Aitchison distribution properties, though this is only outlined here. Results for the application case study suggest that E- and N/NW-dominated storms can be successfully discriminated from calm situations, but not so easily distinguished from each other.     

Spatio-temporal patterns of the interaction between groundwater and surface water in plains

The study of the dynamics of anthropic disturbances that have an effect on the hydrological systems in plains requires integral simulation tools for their diagnosis. The objective of this article is, first, to analyse and reproduce the spatio-temporal interactions between groundwater (GW) and surface water, net recharge, GW level, surface run-off, and evapotranspiration in the upper creek basin of Del Azul, which is located in the centre of the province of Buenos Aires, Argentina, and second, to obtain insights to apply the methodology to other similar situations. For this purpose, a model coupling the semidistributed hydrological model (Soil and Water Assessment Tool [SWAT]) and the hydrogeological model (MODFLOW) has been used. A simulation was carried out for a period of 13 years (2003–2015) on a daily scale. The application of the SWAT–MODFLOW coupling gave good results based on the adjustment between the calculated flows and levels, reaching a Nash–Sutcliffe of 0.6 and R²0.6 at the Seminario hydrometric station located at the watershed outlet point. According to the annual average balance, out of the total rainfall, evapotranspiration accounts for 85%, recharge accounts for 10.2%, and surface run-off accounts for 4.8%. Annual and monthly trends of the stream–aquifer interaction were determined, obtaining on average an annual GW discharge of 34 mm and an annual average recharge of the stream to the aquifer of 1.4 mm. Monthly GW discharges are higher in winter–spring (July to December with an average of 3.3 mm) and lower in summer–autumn (January to June with an average of 2.8 mm). The monthly average recharge of the stream towards the aquifer varies from 0.02 to 0.36 mm and is higher in March, May, and August, when water excess is produced in the basin. Through the analysis of coupled modelling, it is possible to analyse and reproduce the spatio-temporal transitions of flow existing between the stream, the hyporheic zone, and the aquifer.     

New unspiked K–Ar ages of Quaternary sub-glacial and sub-aerial volcanic activity in Iceland

Indisputable geochronology of Icelandic volcanism may contribute to improving the use of volcanic proxies for paleoenvironmental studies. Accurate and reliable ages may also provide some useful constraints in studying the possible relationship between volcanism and deglaciation in Iceland. Given the difficulty of dating accurately young and low potassic volcanic samples from Iceland, the relationship between deglaciation and increasing levels of volcanism has been shown only for the last deglaciation. The purpose of this study is to evaluate the potential of the unspiked K–Ar dating method for dating Quaternary Icelandic volcanic rocks, because we consider that reliable K–Ar ages of interglacial and sub-glacial volcanic products may generate useful data sets for paleoclimatic reconstructions, so enabling the link between glaciation and volcanic activity to be better established. Given the ages and precisions obtained, this study demonstrates that the unspiked K–Ar method is a promising tool for reconstructing the recent volcanic activity in Iceland during glacial and interglacial intervals.     

Multi-day rainfall trends over the Iberian Peninsula

In order to analyze the effects of the duration of precipitation events, trends in extreme rainfall over the Iberian Peninsula (IP) for multi-day extreme precipitation events (1 to 7?days) were evaluated from records of 52 observatories regularly distributed over Iberia with no missing data for the common period 1958–2004. Two approaches were used: first, the nonparametric Mann–Kendall test together with the Sen method, and second, a parametric test based on the statistical theory of extreme values, involving time-dependent parameters to account for possible temporal changes in the frequency distribution. It was found that, in winter, there were significant negative trends for a great part of the Iberian Peninsula, but significant positive trends for the southeast over areas that shrank as the number of days considered for the precipitation event increased. Spring also showed negative trends for a great part of the IP but with a major area of positive trend over the northeast that remained unchanged when considering the maxima of from 1 to 7?days of rainfall. Autumn showed a bipolar spatial pattern, with the west being positive and the east negative.     

Emplacement and arrest of sheets and dykes in central volcanoes

Sheet intrusions are of two main types: local inclined (cone) sheets and regional dykes. In Iceland, the inclined sheets form dense swarms of (mostly) basaltic, 0.5–1 m thick sheets, dipping either at 20–50° or at 75–90° towards the central volcano to which they belong. The regional dykes are (mostly) basaltic, 4–6 m thick, subvertical, subparallel and form swarms, less dense than those of the sheets but tens of kilometres long, in the parts of the volcanic systems that are outside the central volcanoes. In both types of swarms, the intrusion intensity decreases with altitude in the lava pile. Theoretical models generally indicate very high crack-tip stresses for propagating dykes and sheets. Nevertheless, most of these intrusions become arrested at various crustal depths and never reach the surface to supply magma to volcanic eruptions. Two principal mechanisms are proposed to explain arrest of dykes and sheets. One is the generation of stress barriers, that is, layers with local stresses unfavourable for the intrusion propagation. The other is mechanical anisotropy whereby sheet intrusions become arrested at discontinuities. Stress barriers may develop in several ways. First, analytical solutions for a homogeneous and isotropic crust show that the intensity of the tensile stress associated with a pressured magma chamber falls off rapidly with distance from the chamber. Thus, while dyke and sheet injection in the vicinity of a chamber may be favoured, dyke and sheet arrest is encouraged in layers (stress barriers) at a certain distance from the chamber. Second, boundary-element models for magma chambers in a mechanically layered crust indicate abrupt changes in tensile stresses between layers of contrasting Young’s moduli (stiffnesses). Thus, where soft pyroclastic layers alternate with stiff lava flows, as in many volcanoes, sheet and dyke arrest is encouraged. Abrupt changes in stiffness between layers are commonly associated with weak and partly open contacts and other discontinuities. It follows that stress barriers and discontinuities commonly operate together as mechanisms of dyke and sheet arrest in central volcanoes.