Hydrochemical appraisal of ice‐ and rock‐glacier meltwater in the hyperarid Agua Negra drainage basin, Andes of Argentina

Abstract

Abstract:The Agua Negra drainage system (30°12 0 S, 69°50 0 W), in the Argentine Andes holds several ice-and rock-glaciers, which are distributed from 4200 up to 6300 m a.s.l. The geochemical study of meltwaters reveals that ice-glaciers deliver a HCO 3 -Ca 2C solution and rock-glaciers a SO 4 2 -HCO 3 -Ca 2C solution. The site is presumably strongly influenced by sublimation and dry deposition. The main processes supplying solutes to meltwater are sulphide oxidation (i.e. abundant hydrothermal manifestations), and hydrolysis and dissolution of carbonates and silicates. Marine aerosols are the main source of NaCl. The fine-grained products of glacial comminution play a significant role in the control of dissolved minor and trace elements: transition metals (e.g. Mn, Zr, Cu, and Co) appear to be selectively removed from solution, whereas some LIL (large ion lithophile) elements, such as Sr, Cs, and major cations, are more concentrated in the lowermost reach. Daily concentration variation of dissolved rare earth elements (REE) tends to increase with discharge. Through PHREEQC inverse modelling, it is shown that gypsum dissolution (i.e. sulphide oxidation) is the most important geochemical mechanism delivering solutes to the Agua Negra drainage system, particularly in rock-glaciers. At the lowermost reach, the chemical signature appears to change depending on the relative significance of different meltwater sources: silicate weathering seems to be more important when meltwater has a longer residence time, and calcite and gypsum dissolution is more conspicuous in recently melted waters. A comparison with a non-glacierized semiarid drainage of comparable size shows that the glacierized basin has a higher specific denudation, but it is mostly accounted for by relatively soluble phases (i.e. gypsum and calcite). Meltwater chemistry in glacierized arid areas appears strongly influenced by sublimation/evaporation, in contrast with its humid counterparts.

Ice content and interannual water storage changes of an active rock glacier in the dry Andes of Argentina

“…Discharge measurements confirmed that meltwater from areas affected by permafrost conditions and seasonally frozen ground account for an important share of ~20% discharge, which increases up to 30% after snow melt during the ablation season (Schrott, 1994;Schrott, 1996). Hydrochemical analysis of melt water indicates significant internal recycling by sublimation and 120 evaporation and delayed meltwater throughputs from rock glaciers (Lecomte et al, 2008). Geophysical investigations on the El Paso rock glacier suggest that the active layer traps and conducts water and interacts with the permafrost table during summer thaw, while ice-rich permafrost is an important water reservoir releasing water mainly during droughts (Croce and Milana, 2002).…”

“…The hydrologic importance of water storage capacities in rock glaciers compared to glaciers (Croce and Milana, 2002;Milana and Maturano, 1999) as well as river discharge (Schrott, 1996) and chemistry during summer months due to the melt of frozen ground (Lecomte et al, 2008) has been previously investigated in the Upper Agua Negra catchment in the dry Andes of Argentina. The present study of the talus rock glacier 'Dos Lenguas' builds upon this earlier research and presents 90 results of high-resolution surface detections and extensive hydro-geophysical subsurface measurements in the data-scarce region of the dry Andes.…”

Lithological and hydrological controls on water composition: evaporite dissolution and glacial weathering in the south central Andes of Argentina (33°–34°S)

“…Despite its high TDS concentration, Tunuyán River Na + /Ca 2+ ratios (~0.76) are low for waters exposed to intense evaporation. Moreover, the waters of adjacent basins under equal climatic conditions but in volcanic lithology are diluted (Lecomte et al ., ). The usual represented end‐member for evaporitic rocks influencing the river chemistry is high in salt rock content and therefore is expected to show high Na + /Ca 2+ values (Ollivier et al ., ).…”

“…Lecomte et al . () studied the hyperarid Agua Negra Stream basin (~30 ° S, ~4000 m asl), located at 160 km from the ocean. These authors found Na + /Ca 2+ ratios ~2.40 in snow samples and estimated that all Cl − and part of Na + transported by that stream originate from marine aerosols.…”

“…Lecomte et al . () analysed snow samples obtained in the 2002–2003 water year, which had higher precipitations than the historical average (166%). Hoke et al .…”