This study is a ge
ochemical investigati
on
of the Andean and F
oreland basins
of the Amaz
on River at high spatial and time res
oluti
on, carried
out within the framew
ork
of the HYBAM research pr
ogram (Hydr
o-ge
odynamics
of the Amaz
on Basin). M
onthly sampling was carried
out at 27 gauging stati
ons l
ocated in the upper tributaries
of the Amaz
on Basin (fr
om n
orth t
o s
outh: the Nap
o, Mara
xf1;
on, Ucayali, Madre de Di
os-Beni and Mam
ore Rivers). The aim
of this paper is t
o estimate the present-day chemical weathering rate (CWR), as well as the flux
of CO
2 c
onsumpti
on fr
om t
otal and silicate weathering in the Andes and F
oreland Amaz
on basins, and t
o discuss their distributi
on as a functi
on
of ge
om
orphic and structural parameters. Based
on the f
orward meth
od, the Nap
o and
other Ecuad
orian basins present high silicate weathering rates in c
omparis
on with the
other basins. We c
onfirm that the Mara
xf1;
on and Ucayali Rivers c
ontr
ol the Amaz
on hydr
ochemistry due t
o the presence
of salt r
ocks and carb
onates in these basins. The Madre de Di
os, Beni and Mam
ore basins d
o n
ot c
ontribute much t
o the Amaz
on diss
olved l
oad. This n
orth t
o s
outh CWR gradient can be explained by the c
ombinati
on
of decreasing weatherable lith
ol
ogy surface and decreasing run
off rates fr
om the n
orth t
o the s
outh. The f
oreland part
of the basins (
or M
ountain–L
owland transiti
on) acc
ounts f
or nearly the same pr
op
orti
on
of the Amaz
on silicate chemical weathering and carb
onate chemical weathering fluxes as the Andean part. This result dem
onstrates the imp
ortance
of the sediment accumulati
on areas in the Amaz
on Basin weathering budget and can be explained by the
occurrence
of a higher temperature, the dep
ositi
on
of fresh sediments fr
om Andean er
osi
on and a higher sediment residence time than in the upper part
of the basin.
With a total CO2 consumption rate of 744.103 moles km−² year− 1 and a silicate CO2 consumption rate of 300.103 moles km−² year− 1, the Upper Amazon River (Andes + Foreland part) is the most intense part of the Amazon Basin in terms of atmospheric CO2 consumption by weathering processes. It is an important CO2 sink by weathering processes but accounts for only somewhat more than half of the CO2 consumption by silicate weathering of the Amazon Basin. This result points out the importance of the Lowland part of the basin in the inorganic C silicate budget. The Upper Amazon accounts for 2–4 % of the world's silicate CO2 consumption, which is the same proportion as for the southern and southern-east Himalaya and Tibetan plateau.