Marked isotopic variability within and between the Amazon River and marine dissolved black carbon pools.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 31488815.
- Also identified by DOI 10.1038/s41467-019-11543-9 and PMC identifier 6728373.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Riverine dissolved organic carbon (DOC) contains charcoal byproducts, termed black carbon (BC). To determine the significance of BC as a sink of atmospheric CO<sub>2</sub> and reconcile budgets, the sources and fate of this large, slow-cycling and elusive carbon pool must be constrained. The Amazon River is a significant part of global BC cycling because it exports an order of magnitude more DOC, and thus dissolved BC (DBC), than any other river. We report spatially resolved DBC quantity and radiocarbon (Δ<sup>14</sup>C) measurements, paired with molecular-level characterization of dissolved organic matter from the Amazon River and tributaries during low discharge. The proportion of BC-like polycyclic aromatic structures decreases downstream, but marked spatial variability in abundance and Δ<sup>14</sup>C values of DBC molecular markers imply dynamic sources and cycling in a manner that is incongruent with bulk DOC. We estimate a flux from the Amazon River of 1.9-2.7 Tg DBC yr<sup>-1</sup> that is composed of predominately young DBC, suggesting that loss processes of modern DBC are important.