Impact of projected climate change on hydrologic regime of the Upper Paraguay River basin

We present an assessment of climate change impacts on the hydrologic regime of the 600,000 km² Upper Paraguay River basin, located in central South America based on predictions of 20 Atmospheric/Ocean General Circulation Models (AOGCMs). We considered two climate change scenarios from the Intergovernmental Panel on Climate Change (IPCC) and two 30-years time intervals centered at 2030 and 2070. Projected temperature and precipitation anomalies estimated by the AOGCMs for the study site are spatially downscaled. Time series of projected temperature and precipitation were estimated using the delta change approach. These time series were used as input to a detailed coupled hydrologic-hydraulic model aiming to estimate projected streamflow in climate change scenarios at several control points in the basin. Results show that impacts on streamflow are highly dependent on the AOGCM used to obtain the climate predictions. Patterns of temperature increase persist over the entire year for almost all AOGCMs resulting in an increase in the evapotranspiration rate of the hydrological model. The precipitation anomalies show large dispersion, being projected as either an increase or decrease in precipitation rates. Based on these inputs, results from the coupled hydrologic-hydraulic model show nearly one half of projections as increasing river discharge, and other half as decreasing river discharge. If the mean or median of the predictions is considered, no discernible change in river discharge should be expected, despite the dispersion among results of the AOGCMs that reached +/?10 % in the short horizon and +/? 20 % in the long horizon, at several control points.     

Accuracy assessment of the GPS-TEC calibration constants by means of a simulation technique

During the last 2 decades, Global Positioning System (GPS) measurements have become a very important data-source for ionospheric studies. However, it is not a direct and easy task to obtain accurate ionospheric information from these measurements because it is necessary to perform a careful estimation of the calibration constants affecting the GPS observations, the so-called differential code biases (DCBs). In this paper, the most common approximations used in several GPS calibration methods, e.g. the La Plata Ionospheric Model (LPIM), are applied to a set of specially computed synthetic slant Total Electron Content datasets to assess the accuracy of the DCB estimation in a global scale scenario. These synthetic datasets were generated using a modified version of the NeQuick model, and have two important features: they show a realistic temporal and spatial behavior and all a-priori DCBs are set to zero by construction. Then, after the application of the calibration method the deviations from zero of the estimated DCBs are direct indicators of the accuracy of the method. To evaluate the effect of the solar activity radiation level the analysis was performed for years 2001 (high solar activity) and 2006 (low solar activity). To take into account seasonal changes of the ionosphere behavior, the analysis was repeated for three consecutive days close to each equinox and solstice of every year. Then, a data package comprising 24 days from approximately 200 IGS permanent stations was processed. In order to avoid unwanted geomagnetic storms effects, the selected days correspond to periods of quiet geomagnetic conditions. The most important results of this work are: i) the estimated DCBs can be affected by errors around ±8 TECu for high solar activity and ±3 TECu for low solar activity; and ii) DCB errors present a systematic behavior depending on the modip coordinate, that is more evident for the positive modip region.     

Effects of sugar cane monocultures on origin and characteristics of dissolved organic matter in the Manguaba lagoon in northeast Brazil

Brazil has extensive sugar cane monocultures, which significantly alter hydrogeochemical material fluxes. We studied dissolved organic matter (OM) fluxes in the Manguaba lagoon-estuary system, which drains a sugar cane monoculture-dominated hinterland and discharges into the Atlantic coastal ocean. The OM fluxes into the lagoon originate from baseflow, field runoff and sugar cane factory effluents. In the study, dissolved organic carbon (DOC) concentration, δ¹³C DOC and UV absorbance were analysed along a freshwater-seawater salinity gradient that encompasses river (DOC 9-11 mg l⁻¹, δ¹³C −22.2‰ to −25.5‰); lagoon (4-11 mg l⁻¹, −20.5‰ to −24.8‰); estuary (3-9 mg l⁻¹, −22.6‰ to −25.3‰) and coastal waters (1.64 mg l⁻¹, −21‰) with different intra-seasonal runoff conditions. We used the carbon isotope data to quantify the sugar cane derived DOC. Where river water meets brackish lagoon water, substantial loss of DOC occurs during rainy conditions, when suspended sediment from eroded fields in the river is very high. During dry weather, at much lower suspension levels, DOC increases, however, presumably from addition of photolysed resuspended sedimentary OM. In the estuary, mixing of DOC is strictly conservative. Ca. 1/3 of riverine DOM discharged into the lagoon has a sugar cane source. Within the lagoon on avg. 20% of the bulk DOM is comprised of sugar cane DOM, whereas during heavy rainfall the amount increases to 31%, due to intensified drainage flow and soil erosion. In the estuary, 14-26% is of sugar cane origin. The sugar cane-derived component follows the mixing patterns of bulk DOM.     

Source controlled 87Sr/86Sr isotope variability in granitic magmas: The inevitable consequence of mineral-scale isotopic disequilibrium in the protolith

The broad Sr isotopic variability exhibited by granitoid rocks is commonly interpreted to reflect the mixing of magmas from different sources. However, evidence from granites and migmatites indicates that melting and magma extraction from crustal sources can occur sufficiently rapidly that trace-element and isotopic equilibration between liquid and residual phases is commonly not achieved. Additionally, evidence from unmelted high-grade metamorphic rocks indicates that major reactant minerals in the fluid-absent melting process, principally biotite and plagioclase, do not always attain equilibrium during regional metamorphism. When these two circumstances occur in combination, the melt does not inherit its radiogenic isotopic signature from the bulk source in a simple way. In such situations, the isotopic composition of the melt will be dependent on the isotopic compositions of the reactant phases and the stoichiometry of the melting reaction. This study has used information from experimental studies of fluid absent partial melting in metapelites and metagreywackes to investigate the consequences of Sr isotopic disequilibrium between the reactant minerals for magma composition. The study demonstrates that a range of isotopically distinct magmas can arise from progressive melting of a single source that is able to undergo melting through different reactions as temperature increases. When translated to the typically layered sources constituted by sedimentary and volcano-sedimentary rocks, this process will produce magmas characterized by Sr isotope variability that reflects the differences in melting reaction stoichiometry within the different layers, even with no bulk-rock isotopic variability between layers. This study demonstrates that the Sr isotope variability commonly observed within granitic suites, as well as at the grain and sub-grain scale within individual magmatic bodies, can be primary, reflecting differences in composition between magma batches produced from the progressive melting of a single source.     

Magnetostratigraphy and paleomagnetism of early and middle Miocene synorogenic strata: basement partitioning and minor block rotation in Argentine broken foreland

Magnetostratigraphic and paleomagnetic studies on early Andean synorogenic strata (Del Crestón Fm.), in the Famatina Belt (28.7°S, 67.5°W) clarify details of chronology that permit calculation of sedimentation rates within the broken foreland of west Argentina. The Del Crestón Fm represents the first record of broken foreland sedimentation within the southern Central Andean belt and the earliest retroarc volcanic rocks exposed several hundred kilometers from the trench. Twenty-five out of 49 sites collected along the succession presented a primary remanence, as determined through positive fold and reversal tests. Correlation of the local magnetic polarity section with the global polarity time scale indicates that the sedimentation of Del Crestón Fm started at ~16.7 Ma and continued until ~14.5 Ma. The youngest strata are represented by conglomerates bearing abundant Lower Paleozoic granite boulders indicating unroofing of the crystalline basement within the NW Sierras Pampeanas. This result supports the hypothesis of an early broken foreland stage at these latitudes of the Andes, with involvement of the basement in deformation and coeval retroarc volcanism, common attributes of flat-subduction regimes. A mean site paleomagnetic direction of Dec: 6.3°, Inc: ?43.6° (α95: 8.0°, N = 24) confirm our earlier intrepretation that the central part of the Famatina Belt within the Sierras Pampeanas did not undergo large vertical axes rotations since the Middle Miocene.     

The oldest known metriorhynchid crocodylian from the Middle Jurassic of North-eastern Italy: Neptunidraco ammoniticus gen. et sp. nov.

Metriorhynchidae is a clade of marine-adapted crocodilians known from several Middle Jurassic–Early Cretaceous specimens collected predominantly in South America and Europe, but poorly known in the northern margin of Gondwana. The “Portomaggiore crocodile” is the most complete specimen of an Italian metriorhynchid to date: it consists of a partial skeleton that has been provisionally referred to an unnamed species of Late Jurassic Metriorhynchus or Geosaurus. The specimen is preserved in the reddish, nodular limestone of the Rosso Ammonitico Veronese Formation (Bajocian–Tithonian); new data on microfossil associations constrain the age of the metriorhynchid to the late Bajocian–earliest Bathonian. On the basis of cranial synapomorphies, the “Portomaggiore crocodile” falls as the closest sister-taxon of the Late Jurassic–Early Cretaceous geosaurines, and is referred to Neptunidraco ammoniticus gen. et sp. nov. It is unique among Middle Jurassic metriorhynchids in showing an incipient streamlining of the skull, shared with Late Jurassic and Cretaceous taxa. Since Neptunidraco is the oldest known member of Metriorhynchidae, its phylogenetic position supports the hypothesis that the timing of the initial metriorhynchid and geosaurine diversifications should start in the Bajocian.     

Miocene to recent Cariaco basin, offshore Venezuela: Structure, tectonosequences, and basin-forming mechanisms

The Cariaco basin, located ∼40 km off the central part of the coast of Venezuela, is the largest (∼4000 km²) and bathymetrically deepest (1400 m BSL) Neogene fault-bounded basin within the right-lateral strike-slip plate boundary zone that separates the Caribbean and South American plates. Using subsurface geophysical data, we test two previously proposed tectonic models for the age, distribution and nature of east-west-striking, strike-slip faults, and basin-forming mechanism for the two main depocenters of the Cariaco basin. The earliest interpretation for the opening of the twin Cariaco depocenters by Schubert (1982) proposes that both depocenters formed synchronously by extension along transverse (north-south) normal faults at a ∼30-km-wide rhomboidally-shaped pull-apart basin between the right-lateral, east-west-striking, and parallel San Sebastian and El Pilar fault zones. A later model by Ben-Avraham and Zoback (1992) proposes that both depocenters formed synchronously by a process of ”transform-normal parallel extension”, or rifting in a north-south direction orthogonal to the east-west-striking and parallel strike-slip faults.We use more than 4000 km of 2D single- and multi-channel seismic data tied to 11 wells to map 5 tectono-stratigraphic sequences and to produce a series of structural and isopach maps showing how the faults that controlled both Cariaco depocenters evolved from Paleogene to the present. Comparison of fault and isopach maps for dated horizons from Paleogene to late Neogene in age show three main phases in basin development: 1) from middle Miocene to Pliocene, the West Cariaco basin formed as a rhomboidally-shaped pull-apart at a 30-km-wide stepover between the northern branch of the San Sebastian fault and the El Pilar fault zone; 2) during the early Pliocene, a new strike-slip fault transected the West Cariaco basin (southern branch of the San Sebastian fault) and caused extension to cease; and 3) during the early Pliocene to recent, a “lazy-Z” shaped pull-apart formed along the curving connection between the southern branch of the San Sebastian and El Pilar fault zones.     

Realised added value in dynamical downscaling of Australian climate change

Climate Dynamics - Coarse resolution global climate models (GCMs) cannot resolve fine-scale drivers of regional climate, which is the scale where climate adaptation decisions are made. Regional...     

Geological and archaeological evidence of active faulting on the Martana Fault (Umbria–Marche Apennines,Italy) and its geodynamic implications

This paper examines the morphotectonic and structural–geological characteristics of the Quaternary Martana Fault in the Umbria–Marche Apennines fold‐and‐thrust belt. This structure is more than 30 km long and comprises two segments: a N–NNW‐trending longer segment and a 100°N‐trending segment. After developing as a normal fault in Early Pleistocene times, the N–NNW Martana Fault segment experienced a phase of dextral faulting extending from the Early to Middle Pleistocene boundary until around 0.39 Ma, the absolute age of volcanics erupted in correspondence to releasing bends. The establishment of a stress field with a NE–ENE‐trending σ₃ axis and NW–NNW σ₁ axis in Late Pleistocene to Holocene times resulted in a strong component of sinistral faulting along N–NNW‐trending fault segments and almost pure normal faulting on newly formed NW–SE faults. Fresh fault scarps, the interaction of faulting with drainage systems and displacement of alluvial fan apexes provide evidence of the ongoing activity of this fault. The active left‐lateral kinematic along N–NNW‐trending fault segments is also revealed by the 1.8 m horizontal offset of the E–W‐trending Decumanus road, at the Roman town of Carsulae. We interpret the present‐day kinematics of the Martana Fault as consistent with a model connecting surface structures to the inferred north‐northwest trending lithospheric shear zone marking the western boundary of the Adria Plate. Copyright © 2003 John Wiley & Sons, Ltd.