New views on “old” carbon in the Amazon River: Insight from the source of organic carbon eroded from the Peruvian Andes
Article first published online: 31 MAY 2013
©2013. American Geophysical Union. All Rights Reserved.
Geochemistry, Geophysics, Geosystems
Volume 14, Issue 5, pages 1644–1659, May 2013
How to Cite
2013), New views on “old” carbon in the Amazon River: Insight from the source of organic carbon eroded from the Peruvian Andes, Geochem. Geophys. Geosyst., 14, 1644–1659, doi:10.1002/ggge.20122., , , , , , , , and (
- Issue published online: 27 JUN 2013
- Article first published online: 31 MAY 2013
- Accepted manuscript online: 21 MAR 2013 10:26AM EST
- Manuscript Accepted: 17 MAR 2013
- Manuscript Revised: 14 MAR 2013
- Manuscript Received: 24 DEC 2012
- National Environmental Research Council (NERC). Grant Number: 1516.0910
- organic carbon;
 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 (δ13Corg) and radiocarbon (Δ14Corg). Δ14Corg values ranged from −711‰ to −15‰, and significant linear trends between Δ14Corg, N/C and δ13Corg suggested that this reflects the mixing of POCfossil with very young organic matter (Δ14Corg ~ 50‰) from the terrestrial biosphere (POCnon-fossil). Using N/C and Δ14Corg 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 Δ14Corg) in Andean-fed tributaries of the Amazon River, with their Δ14Corg and δ13Corg values consistent with variable addition of POCfossil. The findings suggest a greater persistence of Andean POC in the lowland Amazon than previously recognized.