Temporal variability and annual budget of inorganic dissolved matter in Andean Pacific Rivers located along a climate gradient from northern Ecuador to southern Peru

Contrasted Chemical Weathering Rates in Cratonic Basins: The Ogooué and Mbei Rivers, Western Central Africa

“…The highest values obtained for the Southern Ogooué basins (F spe TZ + sil = 3.9 +2.3 −2.4 to 12.1 +4.4 −5.3 t km −2 yr −1 ) are on the order of those measured in the Kaveri Basin (India), a region particularly active in terms of silicate weathering (Gurumurthy et al, 2012;Pattanaik et al, 2013). Interestingly, by comparison with the silicate weathering rates measured in orogenic areas, these values are in the lower range of those recorded in the Andes (F spe TZ + sil = 9-104 t km −2 yr −1 ; Moquet et al, 2011Moquet et al, , 2018, in the New Zealand Alps (F spe TZ + sil = 2-187 t km −2 yr −1 ; Moore et al, 2013) but are commensurate to, or higher than those recorded in the Himalayas (mean F spe TZ + sil = 5.78 t km −2 yr −1 , West et al, 2002), in the European Alps (F spe TZ + sil = 0.03-11 t km −2 yr −1 , Donnini et al, 2016) Moquet et al, 2016; note that these values were updated for the period 2003-2019 from the HYBAM observatory database. These TZ + sil rates correspond to the cation fluxes corrected from the atmospheric inputs, according to the method performed in the present study.…”

“…At the Lambaréné station, the Ogooué River discharge variation follows the rainfall regime of the basin (Mahe et al, 1990). Overall, the seasonal variability in discharge (SV as quantified by the ratio between maximum and minimum monthly discharge; SV = 3.7; Figure 3) is relatively low by comparison with other intertropical rivers experiencing a monsoonal regime (e.g., Pacific Peruvian rivers: SV = 6-21; Moquet et al, 2018; Nethravati River: SV = 600-1,100; Gurumurthy et al, 2012). The elevation of the Ogooué basin, as considered in the present study, extends from 914 m.a.s.l (Lolo River sub-basin upstream) to 20 m.a.s.l.…”

“…The main characteristic of this region amongst the sub-basins of the Ogooué Basin is the relatively steeper slopes than the Northern sub-basins and the main Ogooué channel (mean slopes = 1.5-2% for the Southern sub-basins; Table 1). It is widely acknowledged that in tectonically active areas mountain uplift triggers mechanical erosion, which in turns favors the exposure of "fresh" mineral surfaces to water and reactive gases, providing a potential explanation for the high weathering rates recorded in orogenic regions (Larsen et al, 2014) such as the Himalayas (Raymo and Ruddiman, 1992;France-Lanord et al, 2003), the Andes (Stallard, 1985;Moquet et al, 2011Moquet et al, , 2014Moquet et al, , 2018Carretier et al, 2018), or the Australian Alps (Hagedorn and Cartwright, 2009). The Ogooué Basin drains a tectonically inactive area, such that mountain uplift cannot be invoked as a control on weathering rates via increased erosion.…”

Control of seasonal and inter-annual rainfall distribution on the Strontium-Neodymium isotopic compositions of suspended particulate matter and implications for tracing ENSO events in the Pacific coast (Tumbes basin, Peru)

“…It drains the western slope of the Andes (between longitude -3.47 and -4.25 decimal degree) over an area of 4.8 10 3 km² including ~70% in the Andean mountains above 500 m.a.s.l. (meter above sea level; Moquet et al, 2018). It originates in the Andes (~ 3800 m.a.s.l.)…”

“…Interestingly Eastern slope mineralogical contrast. Higher illite and chlorite content in the Pacific slope of the Andes can be related to the stronger physical erosion recorded over this area (Armijos et al, 2013;Morera et al, 2017) while high contents of smectite and kaolinite in Amazonian slope can be attributed to the higher weathering intensity measured in the eastern slope of the Andes (Moquet et al, 2011(Moquet et al, , 2014(Moquet et al, , 2018. In the Tumbes basin, geochemical tracers need to be used to track SPM sources variability.…”