New views on "old" carbon in the Amazon River: Insight from the source of organic carbon eroded from the Peruvian Andes. (31st May 2013)

• Record Type: Journal Article
• Authors: 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.
• Is Part Of: Geochemistry, geophysics, geosystems. Volume 14:Number 5(2013)
• Page Start: 1644
• Page End: 1659
• Publication Date: 2013-05-31
• Subjects: organic carbon -- erosion -- Andes -- Amazon -- radiocarbon; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 550.5
• DOI: 10.1002/ggge.20122
• Languages: English
• ISSNs: 1525-2027

Abstract

Abstract: [1] 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 (POCfossil ) 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 Corg ) and radiocarbon (Δ 14 Corg ). Δ 14 Corg values ranged from −711‰ to −15‰, and significant linear trends between Δ 14 Corg, N/C and δ 13 Corg suggested that this reflects the mixing of POCfossil with very young organic matter (Δ 14 Corg ~ 50‰) from the terrestrial biosphere (POCnon‐fossil ). Using N/C and Δ 14 Corg in an end‐member mixing analysis, we quantify the fraction of POCfossil (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 POCnon‐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 Corg ) in Andean‐fed tributaries of the Amazon River, with their Δ 14 Corg and δ 13 Corg values consistent with variable addition of POCfossil . The findings suggest a greater persistence of Andean POC in the lowland Amazon than previously recognized. Key Points: Enrichment of soil and vegetation content at peak floods in Andean Rivers Fossil particulate organic carbon a significant presence in Andean river POC