TY - JOUR
T1 - Stable isotope variations (δ18O and δD) in modern waters across the Andean Plateau
AU - Bershaw, John
AU - Saylor, Joel E.
AU - Garzione, Carmala N.
AU - Leier, Andrew
AU - Sundell, Kurt E.
N1 - Publisher Copyright:
© 2016 Elsevier Ltd
PY - 2016/12/1
Y1 - 2016/12/1
N2 - Environmental parameters that influence the isotopic composition of meteoric water (δ18O and δD) are well characterized up the windward side of mountains, where orographic precipitation results in a predictable relationship between the isotopic composition of precipitation and elevation. The topographic and climatic evolution of the Andean Plateau and surrounding regions has been studied extensively by exploiting this relationship through the use of paleowater proxies. However, interpretation on the plateau itself is challenged by a poor understanding of processes that fractionate isotopes during vapor transport and rainout, and by the relative contribution of unique moisture sources. Here, we present an extensive dataset of modern surface water samples for the northern Andean Plateau and surrounding regions to elucidate patterns and causes of isotope fractionation in this continental environment. These data show a progressive increase in δ18O of stream water west of the Eastern Cordillera (∼1‰/70 km), almost identical to the rate observed across the Tibetan Plateau, attributed to a larger fraction of recycled water in precipitation and/or increased evaporative enrichment downwind. This may lead to underestimates of paleoelevation, particularly for sites deep into the rainshadow of the Eastern Cordilleran crest. That said, elevation is a primary control on the isotopic composition of surface waters across the entire Andean Plateau and its flanks when considering the most negative δ18O values, highlighting the need for sufficiently large datasets to distinguish minimally evaporated samples. There is a general increase in δ18O on the plateau from north to south, concomitant with an increase in aridity and decrease in convective moistening (amount effect). Lastly, stable isotope and seasonal precipitation patterns suggest easterlies provide the vast majority of moisture that falls as precipitation across the Andean Plateau and Western Cordillera, from Peru to northern Bolivia (−13° to −20° latitude), with Pacific-derived moisture contributing a minor amount at low elevations near the coast.
AB - Environmental parameters that influence the isotopic composition of meteoric water (δ18O and δD) are well characterized up the windward side of mountains, where orographic precipitation results in a predictable relationship between the isotopic composition of precipitation and elevation. The topographic and climatic evolution of the Andean Plateau and surrounding regions has been studied extensively by exploiting this relationship through the use of paleowater proxies. However, interpretation on the plateau itself is challenged by a poor understanding of processes that fractionate isotopes during vapor transport and rainout, and by the relative contribution of unique moisture sources. Here, we present an extensive dataset of modern surface water samples for the northern Andean Plateau and surrounding regions to elucidate patterns and causes of isotope fractionation in this continental environment. These data show a progressive increase in δ18O of stream water west of the Eastern Cordillera (∼1‰/70 km), almost identical to the rate observed across the Tibetan Plateau, attributed to a larger fraction of recycled water in precipitation and/or increased evaporative enrichment downwind. This may lead to underestimates of paleoelevation, particularly for sites deep into the rainshadow of the Eastern Cordilleran crest. That said, elevation is a primary control on the isotopic composition of surface waters across the entire Andean Plateau and its flanks when considering the most negative δ18O values, highlighting the need for sufficiently large datasets to distinguish minimally evaporated samples. There is a general increase in δ18O on the plateau from north to south, concomitant with an increase in aridity and decrease in convective moistening (amount effect). Lastly, stable isotope and seasonal precipitation patterns suggest easterlies provide the vast majority of moisture that falls as precipitation across the Andean Plateau and Western Cordillera, from Peru to northern Bolivia (−13° to −20° latitude), with Pacific-derived moisture contributing a minor amount at low elevations near the coast.
KW - Altiplano
KW - Andes
KW - Climate
KW - Meteoric water
KW - Paleoaltimetry
KW - South America
KW - Stable isotope geochemistry
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U2 - 10.1016/j.gca.2016.08.011
DO - 10.1016/j.gca.2016.08.011
M3 - Article
AN - SCOPUS:84989181307
SN - 0016-7037
VL - 194
SP - 310
EP - 324
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
ER -