Variability of the chemical index of alteration (CIA) in the Paraná River suspended load

Variability of the chemical index of alteration (CIA) in the Paraná River suspended loa

A uniform isotopic and chemical signature of dust exported from Patagonia: Rock sources and occurrence in southern environments

Patagonia is considered to be the most important source of dust from South America that is deposited in surrounding areas, and we present here a systematic Sr and Nd isotopic study of sediment currently being exported. Eolian and suspended riverine sediments from Patagonia have a homogeneous chemical and isotopic composition that results from the mixing of by-products from explosive Andean volcanism, derived from the extensive Jurassic silicic Province of Chon Aike and pyroclastic materials from the basic to intermediate southern Andean Quaternary arc, which are easily denudated and dispersed. The main Andean uplift and the glaciations that began in the Late Tertiary account for the extensive distribution of these sediments in the extra-Andean region. The present geochemical signature of Patagonian sediments was produced during the Pleistocene, along with the onset of the southern Andean explosive arc volcanism. Previously published compositions of sediments from other southern South American source regions, assumed to be representative of Patagonia, are distinct from our data. Considering the alleged importance of Patagonia as a dust source for different depositional environments in southern latitudes, it is surprising to verify that the chemical and isotopic signatures of Patagonian-sourced sediments are different from those of sediments from the Southern Ocean, the Pampean Region or the Antarctic ice. Sediments from these areas have a crustal-like geochemical signature reflecting a mixed origin with sediment from other southern South American sources, whereas Patagonian sediments likely represent the basic to intermediate end-member composition

Riverine transfer of heavy metals from Patagonia to the southwestern Atlantic Ocean

The occurrence and geochemical behaviour of Fe, Mn, Pb, Cu, Ni, Cr, Zn and Co are studied in riverine detrital materials transported by Patagonian rivers. Their riverine inputs have been estimated and the nature of these inputs to the Atlantic Ocean is discussed. Most of the metals are transported to the ocean via the suspended load; there is evidence that Fe oxides and organic matter are important phases controlling their distribution in the detrital non-residual fraction. Most heavy metal concentrations found in bed sediments, in suspended matter, and in the dissolved load of Patagonian rivers were comparable to those reported for non-polluted rivers. There is indication that human activity is altering riverine metal inputs to the ocean. In the northern basins – and indicatinganthropogenic effects – heavy metals distribution in the suspended load is very different from that found in bed sediments. The use of pesticides in the Negro River valley seems correlated with increased riverine input of Cu, mostly bound to the suspended load. The Deseado and Chico Rivers exhibit increased specific yield of metals as a consequence of extended erosion within their respective basins. The Santa Cruz is the drainage basin least affected by human activity and its metal-exporting capacity should be taken as an example of a relatively unaffected large hydrological system. In contrast, coal mining modifies the transport pattern of heavy metals in the Gallegos River, inasmuch as they are exported to the coastal zone mainly as dissolved load

The signature of river- and wind-borne materials exported from Patagonia to the southern latitudes: a view from REEs and implications for paleoclimatic interpretations

Riverine and wind-borne materials transferred from Patagonia to the SW Atlantic exhibit a homogeneous rare earth element (REE) signature. They match well with the REE composition of Recent tephra from the Hudson volcano,and hence this implies a dominance of material supplied by this source and other similar Andean volcanoes. Due to the trapping effect of proglacial and reservoir lakes,the larger Patagonian rivers deliver to the ocean a suspended load with a slightly modified Andean signature,that shows a REE composition depleted in heavy REEs. In this paper we redefine Patagonia as a source of sediments,which is in contrast with other sources located in southern South America. Quaternary sediments deposited in the northern and,to a lesser extent, in the southern Scotia Sea, and most of the dust in ice cores of east Antarctica have REE compositions very similar to the loess from Buenos Aires Province and to Patagonian eolian dust. However,we rule out Buenos Aires province as a Holocene major source of sediments. Similarly to Buenos Aires loess (a proximal facies),it is likely that the REE compositions of most sediment cores of the Scotia Sea and Antarctica reflect a distal transport of dust with an admixed composition from two main sources: a major contribution from Patagonia,and a minor proportion from source areas containing sediments with a clear upper crustal signature (e.g.,western Argentina) or from Bolivia’s Altiplano. Evidence indicates that only during the Last Glacial Maximum,Patagonian materials were the predominant sediment source to the southern latitudes

Iron and other transition metals in Patagonian riverborne and windborne materials: Geochemical control and transport to the southern South Atlantic Ocean

The bulk of particulate transition metals transported by Patagonian rivers shows an upper crustal composition. Riverine particulate 0.5 N HCl leachable trace metal concentrations are mainly controlled by Fe-oxides. Complexation of Fe by dissolved organic carbon (DOC) appears to be an important determinant of the phases transporting trace metals in Patagonian rivers. In contrast, aeolian trace elements have a combined crustal and anthropogenic origin. Aeolian materials have Fe, Mn, and Al contents similar to that found in regional topsoils. However, seasonal concentrations of some metals (e.g., Co, Pb, Cu, and Zn) are much higher than expected from normal crustal weathering and are likely pollutant derived. We estimate that Patagonian sediments are supplied to the South Atlantic shelf in approximately equivalent amounts from the atmosphere (30 106 T yr1) and coastal erosion (40 106 T yr1) with much less coming from the rivers (2.0 106 T yr1). Low trace metal riverine fluxes are linked to the low suspended particulate load of Patagonian rivers, inasmuch most of it is retained in pro-glacial lakes as well as in downstream reservoirs. Based on our estimation of aeolian dust fluxes at the Patagonian coastline, the high nutrient-low chlorophyll sub Antarctic South Atlantic could receive 1.0 to 4.0 mg m2 yr1 of leachable (0.5 N HCl) Fe. Past and present volcanic activity in the southern Andes—through the ejection of tephra—must be highlighted as another important source of Fe to the South Atlantic Ocean. Based on the 1991 Hudson volcano eruption, it appears that volcanic events can contribute several thousand-fold the mass of “leachable” Fe to the ocean as is introduced by annual Patagonian dust fallout

d13C tracing of dissolved inorganic carbon sources in Patagonian rivers (Argentina)

The main Patagonian rivers (Colorado, Negro, Chubut, Deseado, Coyle, Chico, Santa Cruz and Gallegos) were sampled between September 1995 and November 1998 to determine their chemical and isotopic compositions, the origins of the suspended and dissolved river loads and their inputs to the South Atlantic Ocean. This paper focuses on the dissolved inorganic carbon (DIC) transport and its υ13C isotopic signature. The υ13CDIC values vary between 12Ð8 and 1Ð8‰ and allow one to distinguish two river groups: (i) the Colorado, Negro, Chubut and Santa Cruz, which display the highest values and the lowest seasonal variations; (ii) the Deseado, Coyle, Chico and Gallegos, which show the lowest values and the highest seasonal variations. For the first group, υ13CDIC is mainly controlled by important exchanges between the river waters and atmospheric CO2, due to the presence of lakes and dams. For the second group, υ13CDIC also appears to be controlled by the oxidation of organic carbon, showing a negative relationship between υ13CDIC and the dissolved organic carbon. These biogeochemical processes interfere with the contribution of carbonate and silicate weathering to the riverine DIC and do not allow use of υ13CDIC alone to distinguish these contributions. The annual DIC flux exported by Patagonian Rivers to the South Atlantic Ocean averages 621 ð 109 g. of C, i.e. a specific yield of 2Ð7 g m2 year1. The mean υ13CDIC can be estimated to 4Ð9‰, which is high compared with other rivers of the world

Geochemistry in Argentina: from pioneers to the present

Argentine geochemistry evolved during the nineteenth century hand in hand with other sciences. The Scotsman John J. Kyle was the first chemist to arrive in Argentina in 1862, contributing during his lifetime reports that expanded the geochemical knowledge of local natural resources. After visiting the USA and Europe (1868), Argentina’s President Sarmiento requested Hermann Burmeister (a prestigious biologist) to engage European scientists to foster the teaching and research of Natural Sciences (sensulato) in Argentina. The first to arrive, in August 1871 at the National Academy of Sciences and the university in Cordoba, was Max Siewert, a chemist from the German Martin Luther University. Siewert set up a state-of-the-art laboratory and analyzed, as Kyle had a few years before, a range of materials from waters and minerals to natural salts and biological materials. Some years later, Adolf Doring replaced Siewert. In the twentieth century, Gustavo Fester is the personality to highlight as a chemist/geochemist because he accomplished a vast task as teacher and researcher at the Universidad Nacional del Litoral and other institutions. During the 1950s and 1960s Argentine Geochemistry experienced slow but sustained growth, promoted by competent university professors such as Felix Gonzalez Bonorino, Jose Catoggio, Mario Teruggi and Carlos Gordillo. The first Geochemistry curriculum was initiated in 1958 at the Universidad Nacional de La Plata as a result of the bold initiative of Catoggio and Teruggi. Nowadays, Geochemistry is solidly established in Earth Sciences curricula and Argentine geochemical papers are found in all the international journals of the specialty.Facultad de Ciencias Naturales y MuseoCentro de Investigaciones Geológica

Hidroquímica de ríos de montaña (Sierras de Córdoba, Argentina): elementos mayoritarios disueltos.

Las Sierras Pampeanas de Córdoba constituyen un sitio importante para el estudio de sistemas hídricos por su importancia socio-económico-cultural. Allí se originan redes de drenajes muy importantes que proveen agua potable a la población del este y del oeste de las sierras. Litológicamente el área de estudio está representada por granitoides del Batolito de Achala (cuenca alta y media), y por gneises y sedimentos modernos aguas abajo. El clima es semiárido con precipitaciones medias anuales de ~750 mm. La clasificación geoquímica de los ríos y arroyos estudiados indica que, en general, son aguas diluidas y bicarbonatadas-mixtas a sódico-potásicas, con algunos ejemplos sin especie iónica dominante. El origen de los solutos está controlado por dos factores principales: las precipitaciones y la incipiente meteorización. La señal química de las precipitaciones prevalece en las cabeceras de los ríos, lo cual es notorio al analizar las señales de iones tales como Ca2+ y Cl-. El resto de los iones evidencian un aumento en las concentraciones en arroyos y vertientes de altura. La variación estacional de las precipitaciones ejerce un control principalmente sobre los elementos mayoritarios, cuyas concentraciones se diluyen en épocas húmedas y se incrementan durante el período seco, bajo condiciones de caudal de base. La dinámica de los iones mayoritarios se basa en los procesos geoquímicos que controlan el transporte de los mismos. Espacialmente se verifica un aumento en sus concentraciones (en especial del Ca2+) aguas abajo al igual que en el resto de los parámetros físico-químicos provenientes de la meteorización congruente e incongruente de los minerales presentes en el área de estudio. El modelo geoquímico propuesto (PHREEQC) para estos sistemas en particular evidencia que los principales procesos que explican la evolución química del agua en esta cuenca son la disolución y/o hidrólisis de minerales primarios presentes en las rocas aflorantes, tales como muscovita, oligoclasa, calcita, biotita y yeso y la formación de minerales secundarios tales como illita y caolinita. Para que se produzca esta meteorización química se consumen 4.10-3 moles de CO2 por litro de agua. Debido a la homogeneidad litológica y climática de las zonas serranas de la región de las Sierras Pampeanas, los resultados de este trabajo pueden ser extrapolados a la mayoría de los sistemas hídricos de la región, además de contribuir al conocimiento de la geoquímica de elementos mayoritarios en sistemas hídricos de alta montaña de otras regiones graníticas en el mundo