We investigate if the commonly neglected riverine detrital carbonate
fluxes might balance several chemical mass balances of the global ocean.
Particulate inorganic carbon (PIC) concentrations in riverine suspended
sediments, i.e., carbon contained by these detrital carbonate minerals,
was quantified at the basin and global scale. Our approach is based on
globally representative datasets of riverine suspended sediment
composition, catchment properties and a two-step regression procedure.
The present day global riverine PIC flux is estimated at 3.1 ± 0.3 Tmol
C/y (13% of total inorganic carbon export and 4 % of total carbon
export), with a flux-weighted mean concentration of 0.26 ± 0.03 wt%.
The flux prior to damming was 4.1 ± 0.5 Tmol C/y. PIC fluxes are
concentrated in limestone-rich, rather dry and mountainous catchments of
large rivers in Arabia, South East Asia and Europe with 2.2 Tmol C/y
(67.6 %) discharged between 15 °N and 45 °N. Greenlandic and Antarctic
meltwater discharge and ice-rafting additionally contribute 0.8 ± 0.3
Tmol C/y. This amount of detrital carbonate minerals annually discharged
into the ocean implies a significant contribution of calcium
(~ 4.75 Tmol Ca/y) and alkalinity fluxes
(~ 10 Tmol(eq)/y) to marine mass balances and moderate
inputs of strontium (~ 5 Gmol Sr/y), based on
undisturbed riverine and cryospheric inputs and a dolomite/calcite ratio
of 0.1. Magnesium fluxes (~ 0.25 Tmol Mg/y), mostly
hosted by less-soluble dolomite, are rather negligible. These
unaccounted fluxes help elucidating respective marine mass balances and
potentially alter conclusions based on these budgets.