The Amazon River is the largest river in the world. It discharges about one fifth of global freshwater runoff, resulting in a freshwater plume rich in nutrients and trace elements entering the Atlantic Ocean.
Until now, it was assumed that the suspended solids partially dissolve in the water plume of the estuary and thus represent an important source of trace metals, but the latest results refute this theory. Isotopes of the elements neodymium (Nd) and hafnium (Hf) were examined. These can serve as tracers or origin, i.e. their analysis can be used to determine where water masses come from. Each river has its own isotopic signature that represents the source rock in the hinterland.
“A previous study had found an increase in the dissolved concentration and variability of neodymium isotopes in the Amazon estuary and concluded that these are dissolved from particles carried by the river on its way to the open ocean,” says the study’s first author Antao Xu.
He is a Ph.D. student in the Chemical Paleoceanography group headed by Professor Dr. Martin Frank at GEOMAR Helmholtz Centre for Ocean Research Kiel, who was co-chief scientist of the METEOR expedition M147 (official GEOTRACES process study GApr11) in the Amazon estuary (chief scientist was Prof. Dr. Andrea Koschinsky, Constructor University Bremen).
“We have now disproved this conclusion,” says Martin Frank. “We can show that the changes in isotope composition are a result of the admixture of freshwater from the nearby Pará River.”
2023-07-31 10:48:03
Original from phys.org rnrn