A test of the cosmogenic 10Be(meteoric)/9Be proxy for simultaneously determining basin‐wide erosion rates, denudation rates, and the degree of weathering in the Amazon basin

Content Provider	Semantic Scholar
Author	Wittmann, Hella Blanckenburg, Friedhelm Von Dannhaus, N. Bouchez, Julien Gaillardet, Jérôme Guyot, Jean-Loup Maurice, Laurence Roig, Henrique Filizola, Naziano Christl, Marcus
Copyright Year	2015
Abstract	We present an extensive investigation of a new erosion and weathering proxy derived from the 10Be(meteoric)/9Be(stable) ratio in the Amazon River basin. This new proxy combines a radioactive atmospheric flux tracer, meteoric cosmogenic 10Be, with 9Be, a trace metal released by weathering. Results show that meteoric 10Be concentrations ([10Be]) and 10Be/9Be ratios increase by >30% from the Andes to the lowlands. We can calculate floodplain transfer times of 2–30 kyr from this increase. Intriguingly however, the riverine exported flux of meteoric 10Be shows a deficit with respect to the atmospheric depositional 10Be flux. Most likely, the actual area from which the 10Be flux is being delivered into the mainstream is smaller than the basin-wide one. Despite this imbalance, denudation rates calculated from 10Be/9Be ratios from bed load, suspended sediment, and water samples from Amazon Rivers agree within a factor of 2 with published in situ 10Be denudation rates. Erosion rates calculated from meteoric [10Be], measured from depth-integrated suspended sediment samples, agree with denudation rates, suggesting that grain size-induced variations in [10Be] are minimized when using such sampling material instead of bed load. In addition, the agreement between erosion and denudation rates implies minor chemical weathering intensity in most Amazon tributaries. Indeed, the Be-specific weathering intensity, calculated from mobilized 9Be comprising reactive and dissolved fractions that are released during weathering, is constant at approximately 40% of the total denudation from the Andes across the lowlands to the Amazon mouth. Therefore, weathering in the Amazon floodplain is not detected.
Starting Page	2498
Ending Page	2528
Page Count	31
File Format	PDF HTM / HTML
DOI	10.1002/2015JF003581
Alternate Webpage(s)	https://escidoc.gfz-potsdam.de/ir/item/escidoc:1370930/components/component/escidoc:1423012/content
Alternate Webpage(s)	https://doi.org/10.1002/2015JF003581
Volume Number	120
Language	English
Access Restriction	Open
Content Type	Text
Resource Type	Article