Hydrogeological and hydrochemical features of an area polluted by heavy metals in central Nicaragua

Geophysical and hydrochemical surveys were used to investigate the hydrogeological conditions in one of the Río Sucio microbasins, in central Nicaragua. Zones of vertical structures (i.e. fractures and quartz veins) and weathering were mapped using Continuous Vertical Electrical Soundings (CVES), as such zones are of major importance for groundwater transport. Water from the springs was analysed to determine concentrations of major ions and heavy metals. Low ion concentrations and ¹⁸O analyses indicate that the springs occur close to their recharge areas and there is a relatively rapid groundwater circulation. Mercury (Hg) content in the springs was low, while comparatively high amounts of lead (Pb) were found. The results presented here demonstrate the important function of weathering and tectonics in the occurrence of groundwater systems in the basin. Hg and Pb found in the springs’ water reveal the existence of an increase in pollution sources disseminating in the area. More than 100 years of using mercury in the gold-mining industry and releasing wastes into rivers has affected water quality and ecosystems. Further investigations are needed in this area to determine the groundwater vulnerability to this pollution as this resource may be needed in the future.The online version of the original article can be found at     

Temperature variability in central Mexico and its possible association to solar activity

Minimum extreme temperature variability from five meteorological stations in the central part of Mexico covering a period from 1920 to 1990 is examined. We found a correlation coefficient (r=0.65) between these temperature records and geomagnetic activity. Furthermore, by performing spectral analysis peaks were obtained with similar periodicities to those found in the sunspot number, the magnetic solar cycle, cosmic ray fluxes and geomagnetic activity; all of these phenomena are modulated by solar activity. Signals with periodicities comparable to those observed in El Niño and the Quasi-Biennial Oscillation were also identified. We conclude that the solar signal is probably present in the minimum extreme temperature record of the central part of Mexico.     

Quaternary intraplate deformation in the southeastern Sierras Pampeanas, Argentina

Neogene strain from the subducting Nazca plate is widely distributed in theAndean foreland as a result of flat-lying subduction beneath central westernArgentina (28^°–33^°S latitude). This fact is indicated byuplifted basement blocks bounded by reverse faults as far as 600 kms eastof the Chilean trench axis. Some deformation in the southern Sierras deCórdoba (southeastern Sierras Pampeanas) indicates significantdisplacements during Quaternary and even late Holocene time. Thisregion has low to moderate seismicity characterized by earthquakemagnitudes 6.7 with no associated noticeable surface ruptures.This paper presents information recently gathered on the most conspicuousregional structures of the area (El Molino, Sierra Chica and Las Lagunasfaults). The last movement along the El Molino fault thrust basement rocksover organic-rich (0.8–1.3 ka) sediment and fault relationships suggestprevious Quaternary displacements. Along the Sierra Chica fault,Precambrian basement has been thrust a minimum of 13.5 m overPleistocene conglomerates, and faulting also affects latePleistocene-Holocene fluvial sediments. The Las Lagunas fault has beenregarded as the source of the 1934 Ms 5.5 and 6.0 earthquakes, whichheavily damaged the nearby village of Sampacho. The faulted surface isburied under Holocene loess, but its trace is expressed as a 24-km-longrectilinear scarp, despite continuous modification due to land use.Although we lack detailed information on probable rupture lengths duringlarge Sierras Pampeanas thrust earthquakes, some preliminary considerationsare made for the regional seismic hazard of these structures. The geologicevidence described here identifies these faults as possible sources of strongearthquakes in the future.     

Unravelling the widening of the earliest Andean northern orogen: Maastrichtian to early Eocene intra‐basinal deformation in the northern Eastern Cordillera of Colombia

The onset of deformation in the northern Andes is overprinted by subsequent stages of basin deformation, complicating the examination of competing models illustrating potential location of earliest synorogenic basins and uplifts. To establish the width of the earliest northern Andean orogen, we carried out field mapping, palynological dating, sedimentary, stratigraphic and provenance analyses in Campanian to lower Eocene units exposed in the northern Eastern Cordillera of Colombia (Cocuy region) and compare the results with coeval succession in adjacent basins. The onset of deformation is recorded in earliest Maastrichtian time, as terrigenous detritus arrived into the basin marking the end of chemical precipitation and the onset of clastic deposition produced by the uplift of a western source area dominated by shaly Cretaceous rocks. Disconformable contacts within the upper Maastrichtian to middle Palaeocene succession document increasing supply of quartzose sandy detritus from Cretaceous quartzose rocks exposed in eastern source areas. The continued unroofing of both source areas produced a rapid shift in depositional environments from shallow marine in Maastrichtian to fluvial‐lacustrine systems during the Palaeocene‐early Eocene. Supply of immature Jurassic sandstones from nearby western uplifts, together with localized plutonic and volcanic Cretaceous rocks, caused a shift in Palaeocene sandstones composition from quartzarenites to litharenites. Supply of detrital sandy fragments, unstable heavy minerals and Cretaceous to Ordovician detrital zircons, were derived from nearby uplifted blocks and from SW fluvial systems within the synorogenic basin, instead of distal basement rocks. The presence of volcanic rock fragments and 51–59 Ma volcanic zircons constrain magmatism within the basin. The Maastrichtian–Palaeocene sequence studied here documents crustal deformation that correlates with coeval deformation farther south in Ecuador and Peru. Slab flattening of the subducting Caribbean plate produced a wider orogen (>400 km) with a continental magmatic arc and intra‐basinal deformation and magmatism.     

Initializing a Mesoscale Boundary-Layer Model with Radiosonde Observations

A mesoscale boundary-layer model is used to simulate low-level regional wind fields over the La Plata River of South America, a region characterized by a strong daily cycle of land–river surface-temperature contrast and low-level circulations of sea–land breeze type. The initial and boundary conditions are defined from a limited number of local observations and the upper boundary condition is taken from the only radiosonde observations available in the region. The study considers 14 different upper boundary conditions defined from the radiosonde data at standard levels, significant levels, level of the inversion base and interpolated levels at fixed heights, all of them within the first 1500 m. The period of analysis is 1994–2008 during which eight daily observations from 13 weather stations of the region are used to validate the 24-h surface-wind forecast. The model errors are defined as the root-mean-square of relative error in wind-direction frequency distribution and mean wind speed per wind sector. Wind-direction errors are greater than wind-speed errors and show significant dispersion among the different upper boundary conditions, not present in wind speed, revealing a sensitivity to the initialization method. The wind-direction errors show a well-defined daily cycle, not evident in wind speed, with the minimum at noon and the maximum at dusk, but no systematic deterioration with time. The errors grow with the height of the upper boundary condition level, in particular wind direction, and double the errors obtained when the upper boundary condition is defined from the lower levels. The conclusion is that defining the model upper boundary condition from radiosonde data closer to the ground minimizes the low-level wind-field errors throughout the region.     

A reassessment of the soil sink for atmospheric carbon tetrachloride based upon static flux chamber measurements

Static flux chamber measurements of CCl₄ uptake by soils in boreal, subtropical and tropical forests have been used to reassess the sink strength for this ozone depleting chemical. Happell and Roche (Geophys. Res. Lett. 30(2), 1088–1091, 2003) used flux estimates from soil concentration gradients to calculate a partial CCl₄ atmospheric lifetime (τ_soil) of 90 years. More recently, it is has been assumed that a better estimate of τ_soil is 195 years (Montzka et al. 2011). In the work here, the rate of CCl₄ uptake was calculated from 453 flux chamber measurements using an exponential fit to the chamber CCl₄ concentration change with time. This analysis indicated that the flux rate estimate in Happell and Roche (Geophys. Res. Lett. 30(2) 1088–1091, 2003) was overestimated by 2.75, yielding a new estimate of τ_soil for CCl₄ of 245 years. Significant correlations of CCl₄ uptake to temperature, soil moisture, or time of year were not observed. This work provides additional evidence that CCl₄ uptake by soils is a common process and needs to be considered when developing an atmospheric budget for this compound.     

Paleoshoreline reconstruction: A proposed method to approach submerged prehistoric landscapes of Espiritu Santo Island,Baja California Sur,Mexico

When the first Americans inhabited the area now known as Isla Espiritu Santo, around 12.5 and 6 ka, the sea level continuously rose. This resulted in the loss of the coastal territory and the retreat of the human population further inland. Part of the archaeological evidence of this period currently lies over the seafloor and under the seabed. Therefore, reconstructing paleoshorelines is a necessary first step toward submerged precontact archaeology and a broad understanding of the spatial context in which those human populations interacted and how the landscapes changed. Isla Espiritu Santo is of prehistoric importance as it contains numerous Paleocoastal tradition sites as early as ~12,400 Cal B.P. This research aims to reconstruct the changing shoreline positions as sea levels rose around Isla Espiritu Santo between 12.5 and 6.5 ka. We apply numerical modeling to map digital elevation models at 1 ka intervals by estimating the changes in the morphology of the seafloor according to the deposition rates and global sea-level curve. The results show the evolution of coastal morphology and paleoshoreline's position. Three primary geoforms are proposed: (1) coastal plains, (2) tombolo, and (3) a coastal lagoon–island barrier system. This also offers insights into the physical aspect of submerged prehistoric landscapes and the possible resource exploitation options of early societies. In this research, the reconstruction of submerged landscapes seeks to contribute to the long-term goal of locating submerged precontact sites.