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Iron and other transition metals in Patagonian riverborne and windborne materials: geochemical control and transport to the southern South Atlantic Ocean |
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| Authors: | DM Gaiero J-L Probst PJ Depetris L Leleyter |
| Institution: | 1 CIGeS, FCEFyN, Universidad Nacional de Córdoba, Avda. Vélez Sàrsfield 1611, X50166CA Córdoba, Argentina 2 Centre de Géochemie de la Surface (CNRS), 1, rue Blessig, 67084 Strasbourg Cedex, France 3 Laboratoire des Mécanismes de Tranferts en Géologie, UMR CNRS/Université Paul Sabatier n° 5563, 38, rue des 36 Ponts, 31400 Toulouse, France 4 Departamento de Geología, Universidad Nacional del Sur, Bahía Blanca, San Juan 670, 8000 Bahía Blanca, Argentina 5 Equipe de Recherche en Physico-Chimie et Biotechnologies, Université de Caen, Bd. du Marechal Juin, 14032 Caen, Cedex, France |
| Abstract: | 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 yr−1) and coastal erosion (∼40 × 106 T yr−1) with much less coming from the rivers (∼2.0 × 106 T yr−1). 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 m−2 yr−1 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. |
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