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Source area and seasonal 87 Sr/ 86 Sr variations in rivers of the Amazon basin
Author(s) -
Santos Roberto V.,
Sondag Francis,
Cochonneau Gérard,
Lagane Cristelle,
Brunet Pierre,
Hattingh Karina,
Chaves Jeane G. S.
Publication year - 2014
Publication title -
hydrological processes
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.222
H-Index - 161
eISSN - 1099-1085
pISSN - 0885-6087
DOI - 10.1002/hyp.10131
Subject(s) - geology , precambrian , drainage basin , amazon rainforest , structural basin , phanerozoic , sediment , isotope , geochemistry , hydrology (agriculture) , isotopes of strontium , provenance , geomorphology , cenozoic , geography , ecology , geotechnical engineering , biology , physics , cartography , quantum mechanics
We report the results of a detailed study of dissolved Sr isotopes in the Solimões and Beni‐Madeira Rivers of the Amazon basin. This study developed data collected over 8 years indicating large spatial and temporal variations in dissolved Sr isotopes among the rivers of the Amazon basin. The large 87 Sr/ 86 Sr variations were found to be correlated with the geology of the source areas of the suspended sediments. The Beni‐Madeira River displays a high average 87 Sr/ 86 Sr ratio and large 87 Sr/ 86 Sr fluctuations during the hydrological cycle. This large average value and fluctuations were related to the presence of Precambrian rocks and Ordovician sediments in the source area of the suspended sediment of the river. In contrast, the Solimões River displays a narrow range of Sr isotope ratio variations and an average value close to 0.709. This river drains mostly Phanerozoic rocks of northern Peru and Ecuador that are characterized by low Sr isotope ratios. The isotopic fluctuations in the Beni‐Madeira River were observed to propagate downstream at least as far as Óbidos. This signal is characterized by an inverse relationship between the concentration of elemental Sr and its isotopic ratios. We further demonstrate that the Sr isotopic composition and content in the Beni‐Madeira River is controlled by suspended sediments derived from the Andes. Despite draining areas underlain by Precambrian rocks and having high 87 Sr/ 86 Sr ratios, such rivers as the Negro and Tapajós play a minor role in the total Sr budget of the Amazon basin. Copyright © 2013 John Wiley & Sons, Ltd.