Abstract:Despite the absence of tectonic activity, cratonic environments are characterized by strongly variable, and in places significant, rock weathering rates. This is shown here through an exploration of the weathering rates in two inter-tropical river basins from the Atlantic Central Africa: the Ogooué and Mbei River basins, Gabon. We analyzed the elemental and strontium isotope composition of 24 water samples collected throughout these basins. Based on the determination of the major element sources we estimate th… Show more
“…These previous estimates were based on either river end‐member concentrations from the Zaire River (Edmond et al., 1978; Paytan & Kastner, 1996) or a series of unnamed rivers in North America (Livingstone, 1963; Wolgemuth & Broecker, 1970). We reassessed this input vector by compiling available dBa concentrations at the mouths of several rivers at salinity <0.5 (Cao et al., 2016, 2020; Carroll et al., 1993; Charbonnier et al., 2020; Edmond et al., 1978; Guay & Falkner, 1998; Hsieh & Henderson, 2017; Joung & Shiller, 2014; Moore, 1997; Moquet et al., 2021; Shiller, 2003, 2005a, 2005b) (Table 3). Together these rivers account for ∼40% of the global freshwater discharge to the ocean (Dürr et al., 2011), and their drainage basins account for 31% of total global exorheic area (Dürr et al., 2011).…”
Processes controlling dissolved barium (dBa) were investigated along the GEOTRACES GA03 North Atlantic and GP16 Eastern Tropical Pacific transects, which traversed similar physical and biogeochemical provinces. Dissolved Ba concentrations are lowest in surface waters (∼35–50 nmol kg−1) and increase to 70–80 and 140–150 nmol kg−1 in deep waters of the Atlantic and Pacific transects, respectively. Using water mass mixing models, we estimate conservative mixing that accounts for most of dBa variability in both transects. To examine nonconservative processes, particulate excess Ba (pBaxs) formation and dissolution rates were tracked by normalizing particulate excess 230Th activities. Th‐normalized pBaxs fluxes, with barite as the likely phase, have subsurface maxima in the top 1,000 m (∼100–200 μmol m−2 year−1 average) in both basins. Barite precipitation depletes dBa within oxygen minimum zones from concentrations predicted by water mass mixing, whereas inputs from continental margins, particle dissolution in the water column, and benthic diffusive flux raise dBa above predications. Average pBaxs burial efficiencies along GA03 and GP16 are ∼37% and 17%–100%, respectively, and do not seem to be predicated on barite saturation indices in the overlying water column. Using published values, we reevaluate the global freshwater dBa river input as 6.6 ± 3.9 Gmol year−1. Estuarine mixing processes may add another 3–13 Gmol year−1. Dissolved Ba inputs from broad shallow continental margins, previously unaccounted for in global marine summaries, are substantial (∼17 Gmol year−1), exceeding terrestrial freshwater inputs. Revising river and shelf dBa inputs may help bring the marine Ba isotope budget more into balance.
“…These previous estimates were based on either river end‐member concentrations from the Zaire River (Edmond et al., 1978; Paytan & Kastner, 1996) or a series of unnamed rivers in North America (Livingstone, 1963; Wolgemuth & Broecker, 1970). We reassessed this input vector by compiling available dBa concentrations at the mouths of several rivers at salinity <0.5 (Cao et al., 2016, 2020; Carroll et al., 1993; Charbonnier et al., 2020; Edmond et al., 1978; Guay & Falkner, 1998; Hsieh & Henderson, 2017; Joung & Shiller, 2014; Moore, 1997; Moquet et al., 2021; Shiller, 2003, 2005a, 2005b) (Table 3). Together these rivers account for ∼40% of the global freshwater discharge to the ocean (Dürr et al., 2011), and their drainage basins account for 31% of total global exorheic area (Dürr et al., 2011).…”
Processes controlling dissolved barium (dBa) were investigated along the GEOTRACES GA03 North Atlantic and GP16 Eastern Tropical Pacific transects, which traversed similar physical and biogeochemical provinces. Dissolved Ba concentrations are lowest in surface waters (∼35–50 nmol kg−1) and increase to 70–80 and 140–150 nmol kg−1 in deep waters of the Atlantic and Pacific transects, respectively. Using water mass mixing models, we estimate conservative mixing that accounts for most of dBa variability in both transects. To examine nonconservative processes, particulate excess Ba (pBaxs) formation and dissolution rates were tracked by normalizing particulate excess 230Th activities. Th‐normalized pBaxs fluxes, with barite as the likely phase, have subsurface maxima in the top 1,000 m (∼100–200 μmol m−2 year−1 average) in both basins. Barite precipitation depletes dBa within oxygen minimum zones from concentrations predicted by water mass mixing, whereas inputs from continental margins, particle dissolution in the water column, and benthic diffusive flux raise dBa above predications. Average pBaxs burial efficiencies along GA03 and GP16 are ∼37% and 17%–100%, respectively, and do not seem to be predicated on barite saturation indices in the overlying water column. Using published values, we reevaluate the global freshwater dBa river input as 6.6 ± 3.9 Gmol year−1. Estuarine mixing processes may add another 3–13 Gmol year−1. Dissolved Ba inputs from broad shallow continental margins, previously unaccounted for in global marine summaries, are substantial (∼17 Gmol year−1), exceeding terrestrial freshwater inputs. Revising river and shelf dBa inputs may help bring the marine Ba isotope budget more into balance.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.