Download Variation in concentration of solutes in the oceans V: Scavenged

Railsback's Some Fundamentals of Mineralogy and Geochemistry
Variation in concentration of solutes in the oceans V: Scavenged ions
0
Concentration
nanomolar units
Concentrations of highly charged cations (Al3+,
Fe3+, Ni3+, etc.) are small in the surface water
because these cations are relatively insoluble and
instead form oxides or hydroxides.
0
1
Scavenged
cations
3+
(Al , Fe3+, etc.)
(Donat and Bruland 1995
in Salbu & Steinne's
Trace Elements in Natural Waters)
2
Depth
(km)
3
1 nm
Concentrations of highly charged cations are even
smaller in deeper waters because those ions are
"scavenged" (absorbed) by sinking particles. Most
particles have negative surface charge, and highly
charged cations are electrostatically attracted to
those particles and adsorbed onto them.
Near the seafloor, H+ ions of sediment pore
waters more acidic than seawater may displace
cations from the surfaces of particles, allowing
release of cations back into the bottom water.
4
1Å
Sinking three-nanometer particle
with negative surface charge
Cations with large charge
Concentrations of these cations in
deep waters of the Pacific are even
Atlantic
5
smaller than those in the Atlantic
Pacific
because Pacific deep water is
Concentrations of these cations in deep waters of the older and has had more time to
be cleansed by scavenging
Atlantic are small, but not as small as those in the
particles.
Pacific because Atlantic deep water is younger and
hasn't been cleansed as long by scavenging particles.
Atlantic
Greenland
D
W
A
Northern & eastern
Pacific
B
N
Pacific
W
A
Mid-Atlantic Ridge
A
Antarctica
East Pacific Rise
Americas
LBR OceanSolutes18 5/2008