Also included in Table 1 is an estimate of the
average oceanic residence times for these elements. A
shorter residence time indicates a more rapid removal from the oceans. Another way to estimate the
relative reactivity of elements with crustal sources is
to compare their sea water concentrations with their
abundance in the Earth’s crust. This is presented in
Table 2 (with a normalization to aluminum) and is
shown graphically in Figure 1. If variations in the
composition of continental materials and differences
in the solubility of the elements from these materials
are not too great, then to a first approximation the
removal rate should be inversely related to the degree
of enrichment in seawater. Relative to aluminum,
iron is the only element considered here that is not
enriched in the oceans. Titanium and thorium are
very slightly enriched; indium, barium and yttrium
are greatly enriched (by 2–3 orders of magnitude),
and tantalum, niobium, gallium, scandium, zirconium, and hafnium show intermediate enrichment.
The degree of enrichment does not correlate well
with estimates of the residence times of these elements. These discrepancies will be discussed in the
following sections.
Table 1 Summary of the hydroxide speciation, concentrations, and residence times for the refractory elements in the oceans
Table 2 The average abundance of the refractory elements in the Earth’s crust, and their degree of enrichment, relative to
aluminum, in the oceans
REFRACTORY METALS 53
average oceanic residence times for these elements. A
shorter residence time indicates a more rapid removal from the oceans. Another way to estimate the
relative reactivity of elements with crustal sources is
to compare their sea water concentrations with their
abundance in the Earth’s crust. This is presented in
Table 2 (with a normalization to aluminum) and is
shown graphically in Figure 1. If variations in the
composition of continental materials and differences
in the solubility of the elements from these materials
are not too great, then to a first approximation the
removal rate should be inversely related to the degree
of enrichment in seawater. Relative to aluminum,
iron is the only element considered here that is not
enriched in the oceans. Titanium and thorium are
very slightly enriched; indium, barium and yttrium
are greatly enriched (by 2–3 orders of magnitude),
and tantalum, niobium, gallium, scandium, zirconium, and hafnium show intermediate enrichment.
The degree of enrichment does not correlate well
with estimates of the residence times of these elements. These discrepancies will be discussed in the
following sections.
Table 1 Summary of the hydroxide speciation, concentrations, and residence times for the refractory elements in the oceans
Table 2 The average abundance of the refractory elements in the Earth’s crust, and their degree of enrichment, relative to
aluminum, in the oceans
REFRACTORY METALS 53