Stochastic Simulation of Nonstationary Rainfall Fields, Accounting for Seasonality and Atmospheric Circulation Pattern Evolution

A model for generating daily spatial correlated rainfall fields suitable for evaluating the impacts of climate change on water resources is presented. The model, termed Stochastic Rainfall Generating Process, is designed to incorporate two major nonstationarities: changes in the frequencies of different precipitation generating mechanisms (frontal and convective), and spatial nonstationarities caused by interactions of mesoscale atmospheric patterns with topography (orographic effects). These nonstationarities are approximated as discrete sets of the time-stationary Stochastic Rainfall Generating Process, each of which represents the different spatial patterns of rainfall (including its variation with topography) associated with different atmospheric circulation patterns and times of the year (seasons). Each discrete Stochastic Rainfall Generating Process generates daily correlated rainfall fields as the product of two random fields. First, the amount of rainfall is generated by a transformed Gaussian process applying sequential Gaussian simulation. Second, the delimitation of rain and no-rain areas (intermittence process) is defined by a binary random function simulated by sequential indicator simulations. To explore its applicability, the model is tested in the Upper Guadiana Basin in Spain. The result suggests that the model provides accurate reproduction of the major spatiotemporal features of rainfall needed for hydrological modeling and water resource evaluations. The results were significantly improved by incorporating spatial drift related to orographic precipitation into the model.     

Sipunculus nudus Linnaeus, 1766 (Sipuncula): cosmopolitan or a group of pseudo‐cryptic species? An integrated molecular and morphological approach

Sipunculan taxonomy relies on a limited set of external morphological and internal anatomical characters. In addition, this marine group is characterized by an unusual large number of putatively cosmopolitan species. However, this ‘cosmopolitan’ status could be an artifact of their conserved morphology and the small number of unambiguous taxonomic characters available for delimiting species. Species delimitation can therefore be aided by molecular techniques. We investigated the case of the widespread and common species Sipunculus nudus Linnaeus, 1766 to determine its systematic validity. We analysed the morphology of multiple specimens of S. nudus collected from 11 localities around the world and undertook phylogenetic analyses using molecular sequence data from four genes (28S rRNA, 16S rRNA, histone H3 and cytochrome c oxidase subunit I). High levels of genetic differentiation are present between distantly related populations of the putative species S. nudus. Five distinct lineages were identified by phylogenetic analyses, three of which – the best‐represented populations – can be distinguished morphologically. Our phylogenetic and morphological analyses thus do not favor the cosmopolitan status of S. nudus, suggesting instead that it constitutes a complex of morphologically similar but distinguishable species.     

Aeolian/fluvial interactions and high-resolution sequence stratigraphy of a non-marine lowstand wedge: the Avilé Member of the Agrio Formation (Lower Cretaceous), central Neuquén Basin, Argentina

Abstract Accumulation within the unconformity‐based Hauterivian Avilé Sandstone of the Neuquén Basin, Argentina, was characterized by a close interaction between fluvial and aeolian processes developed after a major relative sea‐level drop that almost completely desiccated the entire basin and juxtaposed these non‐marine deposits on shallow‐ and deep‐marine facies. Aeolian deposits within the Avilé Member include dune (A1) and sand sheet (A2) units that characterize the lower part of the unit. Fluvial deposits comprise distal flood units (F1) interbedded with aeolian dune deposits in the middle part of the succession, and low‐ (F2) and high‐sinuosity (F3) channels associated with floodplain deposits (F4) towards the top. The internal characteristics of the aeolian system indicate that its accumulation was strongly controlled by water‐table dynamics, with the development of multiple horizontal deflation super surfaces that truncate dune deposits and form the basal boundary of flood deposits and sand sheet units. A long‐term wetting‐upward trend is recorded throughout the entire unit, with an increase in fluvial activity towards the top and the development of a more permanent fluvial system overlying a major erosion surface interpreted as a sequence boundary. The upward increase in water‐table influence might be related to relative sea‐level rise, which controlled the position of the water table and allowed the accumulation of tabular aeolian units bounded by horizontal deflation surfaces. This high‐frequency, eustatically driven process acted together with a long‐term climatic change towards wetter conditions.     

The Upper Jurassic (Kimmeridgian) fluvial–aeolian systems of the southern Neuquén Basin, Argentina

The Kimmeridgian Quebrada del Sapo Formation in the southernmost Neuquén Basin in Argentina represents a succession up to 40 m thick of coarse- to fine-grained fluvial deposits overlain by aeolian deposits. These fluvial–aeolian deposits reflect a significant palaeogeographic change in the basin and are related to a major, tectonically enhanced, relative sea-level fall. The fluvial section is dominated by braided-channel, fine-grained ephemeral, and sheetflood deposits. Aeolian facies are dominated by dune deposits, with minor sandsheet and interdune units. Changes in the nature of both fluvial and aeolian sedimentation within the studied area suggest a regional variability of accommodation/sediment supply conditions. The regional changes of the aeolian succession likely reflect different relative positions within a major erg. In the upwind margin of the erg, a shallow water table promoted water-lain sedimentation in interdune areas, whereas in the central parts of the erg, dry sediment accumulation took place above the regional water-table level. The vertical transition observed in the Quebrada del Sapo Formation, from fluvial to aeolian deposits, may be the result of a local climatic change to drier conditions due to the development of a climatic barrier imposed by growth of a magmatic arc to the west. Alternatively, the vertical transition could be related to a lowering of the water table associated with the compartmentalization of the basin during a period of low sea level.     

Parameters of Higuchi’s method to characterize primary waves in some seismograms from the Mexican subduction zone

Higuchi’s method is a procedure that, if applied appropriately, can determine in a reliable way the fractal dimension D of time series; this fractal dimension permits to characterize the degree of correlation of the series. However, when analyzing some time series with Higuchi’s method, there are oscillations at the right-hand side of the graph, which can cause a mistaken determination of the fractal dimension. In this work, an appropriate explanation is given to this type of behaviour. Using the seismogram as a time series and the properties of the P and S waves, it is possible to use the properties of Higuchi’s method to previously detect the arrival of the earthquake shacking stage, some seconds in advance, approximately 30–35 s in the case of Mexico City. Thus, we propose the Higuchi’s method to characterize and detect the P waves in order to estimate the strength of the forthcoming S waves.     

Stock Evaluation of Three Littoral Echinoid Species on the Catalan Coast North-Western Mediterranean

Abstract. We estimated the abundances of the three common littoral echinoid species Paracentrotus lividus, Arbacia lixula and Sphaerechinus granularis in a littoral zone between 0 and 10m depth on the Catalan shores NE Spain. Densities of each species were estimated from a total number of 11 571× 1 m² sampling units deployed at 152 sites along the 13 zones into which the coast was divided. The surface area available in each of these zones was estimated at the scale of the sampling unit 1 m² taking into account the fractal dimension of the shore. The stocks individuals > 2cm test diameter of these species for the whole Catalan shore ≅ 300 km, straight-line distance were estimated to be about 279.1 × 10⁶ individuals for P. lividus , 28.9 × 10⁶ individuals for A. lixula and 10.9 × 10⁶ individuals for S. granularis. These sea-urchins are key species in the regulation of algal communities and some of them P. lividus. S. granularis are of commercial interest. This information will provide a tool for the future monitoring and management of this resource, which now faces diverse pressures of human origin.     

Contrasting beach-ridge systems in different types of coastal settings

Beach-ridge systems are geomorphological features common in every type of coast and have been widely interpreted as geo-archives of past sea-level, climatic, or tectonic changes. These relict morphological elements are well-known by their facies, architecture, stratigraphy, and evolution. However, the coastal context where beach ridges are formed has never been evaluated. Coastal beach-ridge systems were classified into four main types corresponding to deltaic strandplains, non-deltaic strandplains, spits, and barrier islands. Our study consisted of three scales of analysis: (1) the entire beach-ridge system; (2) beach-ridge sets; and (3) individual beach ridges. Several beach-ridge systems having formed in different types of coastal settings are compared by their present characteristics. Geomorphic data generated from processing and interpreting satellite images combined with previous studies are used to quantify multi-scale attributes of beach-ridge systems. These attributes include the area, length, width, number of sets, number of ridges per set, set rotation, ridge spacing, and ridge elevation. Our findings demonstrate that significant differences define beach-ridge systems including deltaic strandplains, large non-deltaic strandplains, small non-deltaic strandplains, large spits (cuspate forelands), small spits (flying spits, bay-mouth spits and tombolos) and barrier islands. A more comprehensive characterization of the factors controlling beach-ridge variability will improve our ability to recognize the sedimentary record of ancient of these systems. The proposed basic platform can be used to isolated different beach-ridge types and systems to facilitate future process and morphodynamic studies.