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