Open AccessNew views on “old” carbon in the Amazon River: Insight from the source of organic carbon eroded from the Peruvian Andes
Author(s) -
Clark K. E.,
Hilton R. G.,
West A. J.,
Malhi Y.,
Gröcke D. R.,
Bryant C. L.,
Ascough P. L.,
Robles Caceres A.,
New M.
Publication year - 2013
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1002/ggge.20122
Subject(s) - tributary , amazon rainforest , biogeochemical cycle , total organic carbon , geology , radiocarbon dating , isotopes of carbon , carbon cycle , sedimentary rock , hydrology (agriculture) , sediment , carbon fibers , particulates , environmental science , earth science , environmental chemistry , geochemistry , ecosystem , ecology , paleontology , geography , chemistry , materials science , cartography , geotechnical engineering , composite number , composite material , biology
Mountain rivers play a key role in the delivery of particulate organic carbon (POC) to large river systems and the ocean. Due to the extent of its drainage area and runoff, the Amazon River is one of Earth's most important biogeochemical systems. However, the source of POC eroded from the humid region of the Eastern Andes and the input of fossil POC from sedimentary rocks (POC fossil ) remains poorly constrained. Here we collected suspended sediments from the Kosñipata River during flood events to better characterize Andean POC, measuring the nitrogen to organic carbon ratio (N/C), stable carbon isotopes (δ 13 C org ) and radiocarbon (Δ 14 C org ). Δ 14 C org values ranged from −711‰ to −15‰, and significant linear trends between Δ 14 C org, N/C and δ 13 C org suggested that this reflects the mixing of POC fossil with very young organic matter (Δ 14 C org ~ 50‰) from the terrestrial biosphere (POC non‐fossil ). Using N/C and Δ 14 C org in an end‐member mixing analysis, we quantify the fraction of POC fossil (to within 0.1) and find that it contributes a constant proportion of the suspended sediment mass (0.37 ± 0.03%) and up to 80% of total POC. In contrast, the relative contribution of POC non‐fossil was variable, being most important during the rising limb and peak discharges of flood events. The new data shed light on published measurements of “old” POC (low Δ 14 C org ) in Andean‐fed tributaries of the Amazon River, with their Δ 14 C org and δ 13 C org values consistent with variable addition of POC fossil . The findings suggest a greater persistence of Andean POC in the lowland Amazon than previously recognized.