concentration in oceanic surface waters to levels at
which their growth would not be impacted (o10
À12
mol l
À1 ). During an upwelling event, cyanobacterial
production of the L 1 ligand might not exceed the
newly upwelled Cu
2þ , therefore cyanobacteria
abundance would decline. Actual field evidence is
supporting the speculation that species composition
and seasonal species successions of phytoplankton
are influenced by Cu
2þ concentrations, especially in
high-nutrient–low-chlorophyll areas.
Growth limitation experiments, like those for
copper, have also been performed for iron, zinc, and
manganese. These experiments showed that sufficiently low free ion activities of these nutrient
metals could result in species shifts in phytoplankton
communities. Iron is perhaps the most important
nutrient transition metal to phytoplankton and its
speciation is extremely complex and is not known
with any reliability. Forms of iron that are speculated
to have biological importance are organic Fe(III)
complexes, Fe(III) oxides, and Fe(III)–siderophore
complexes. Unlike Cu
2þ which acts as a toxin, increased free Zn
2þ concentrations in upwelled water
could enhance reproduction of phytoplankton communities. Manganese in sea water, which shows no
evidence of any organic complexation, appears to be
maintained by photochemical reduction processes
and photoinhibition of microbial oxidation of Mn
2þ .
Low manganese concentrations could potentially
limit oceanic productivity if not supplied in sufficient
quantities by atmosphere or horizontal mixing.
Therefore, the distributions of Zn
2þ , Mn
2þ , and
dissolved iron have important consequences for
species composition and species succession of a
phytoplankton community.
Oceanic concentrations of dissolved cadmium may
be outside the range causing cadmium toxicity.
However, in estuarine and riverine areas, anthropogenic sources could supply excessive cadmium inputs, leading to cadmium toxicity in aquatic
phytoplankton. On the other hand, some researchers
have shown that cadmium can promote growth of
zinc-limited oceanic phytoplankton by substituting
for zinc in certain macromolecules, thereby causing
growth at lower than expected free Zn
2þ concentrations. It has been speculated that this biochemical
substitution of cadmium for zinc by phytoplankton
could account for the nutrient-type oceanic distribution of cadmium.
Summary
Major advances in procedural, analytical, and instrumental techniques have advanced our knowledge
of the concentrations, distributions, and speciation
of the transition metals and heavy metals in the
oceans, and therefore our understanding of their
biogeochemical cycling. For most of the transition
metals and heavy metals we have a first-order
understanding of their oceanic distributions, and
now with more data and better sea-going analytical
techniques, basin-wide cross-sections of the distributions of some metals (e.g., aluminum, manganese,
and iron) are becoming available. These basin-wide
distributions allow more interpretation of sources
and fates of these metals. Mediation by light and
microorganisms dominates the biogeochemical cycling of certain metals such as copper, iron, and
manganese. Organic complexation has come into the
forefront of metal speciation research. Not only has
the evidence for the existence of organic complexation been overwhelming, but organic ligands dominate the speciation of copper, zinc, and iron in
oceanic surface waters. Organic complexation of
certain metals in the oceans has important biological
implications (i.e., controlling availability of metals as
nutrients and toxicants) for phytoplankton.
See also
Carbon Cycle. Metal Pollution. Tracers of Ocean
Productivity.
Further Reading
Belli SL and Zirino A (1993) Behavior and calibration of
the copper(II) ion-selective electrode in high chloride
media and marine waters. Analytical Chemistry 65:
2583--2589.
Brand LE, Sunda WG, and Guillard RRL (1986) Reduction
of marine phytoplankton reproduction rates by copper
and cadmium. Journal of Experimental Marine Biology
and Ecology 96: 225--250.
Broecker WS and Peng TH (1982) Tracers in the Sea. New
York: Eldigio Press.
Bruland KW (1983) Trace elements in sea-water. In: Riley
JP and Chester R (eds.) Chemical Oceanography, vol. 8,
pp. 157–220. London: Academic Press.
Bruland KW, Donat JR, and Hutchings DA (1991)
Interactive influences of bioactive trace metals on
biological production in oceanic waters. Limnology and
Oceanography 36: 1555--1577.
Bruno J (1990) The influence of dissolved carbon dioxide
on trace metal speciation in seawater. Marine Chemistry
30: 231--240.
Burton JD and Statham PJ (1988) Trace metals as tracers in
the ocean. Philosophical Transactions of the Royal
Society of London Series A 325: 127--145.
TRANSITION METALS AND HEAVY METAL SPECIATION 79
which their growth would not be impacted (o10
À12
mol l
À1 ). During an upwelling event, cyanobacterial
production of the L 1 ligand might not exceed the
newly upwelled Cu
2þ , therefore cyanobacteria
abundance would decline. Actual field evidence is
supporting the speculation that species composition
and seasonal species successions of phytoplankton
are influenced by Cu
2þ concentrations, especially in
high-nutrient–low-chlorophyll areas.
Growth limitation experiments, like those for
copper, have also been performed for iron, zinc, and
manganese. These experiments showed that sufficiently low free ion activities of these nutrient
metals could result in species shifts in phytoplankton
communities. Iron is perhaps the most important
nutrient transition metal to phytoplankton and its
speciation is extremely complex and is not known
with any reliability. Forms of iron that are speculated
to have biological importance are organic Fe(III)
complexes, Fe(III) oxides, and Fe(III)–siderophore
complexes. Unlike Cu
2þ which acts as a toxin, increased free Zn
2þ concentrations in upwelled water
could enhance reproduction of phytoplankton communities. Manganese in sea water, which shows no
evidence of any organic complexation, appears to be
maintained by photochemical reduction processes
and photoinhibition of microbial oxidation of Mn
2þ .
Low manganese concentrations could potentially
limit oceanic productivity if not supplied in sufficient
quantities by atmosphere or horizontal mixing.
Therefore, the distributions of Zn
2þ , Mn
2þ , and
dissolved iron have important consequences for
species composition and species succession of a
phytoplankton community.
Oceanic concentrations of dissolved cadmium may
be outside the range causing cadmium toxicity.
However, in estuarine and riverine areas, anthropogenic sources could supply excessive cadmium inputs, leading to cadmium toxicity in aquatic
phytoplankton. On the other hand, some researchers
have shown that cadmium can promote growth of
zinc-limited oceanic phytoplankton by substituting
for zinc in certain macromolecules, thereby causing
growth at lower than expected free Zn
2þ concentrations. It has been speculated that this biochemical
substitution of cadmium for zinc by phytoplankton
could account for the nutrient-type oceanic distribution of cadmium.
Summary
Major advances in procedural, analytical, and instrumental techniques have advanced our knowledge
of the concentrations, distributions, and speciation
of the transition metals and heavy metals in the
oceans, and therefore our understanding of their
biogeochemical cycling. For most of the transition
metals and heavy metals we have a first-order
understanding of their oceanic distributions, and
now with more data and better sea-going analytical
techniques, basin-wide cross-sections of the distributions of some metals (e.g., aluminum, manganese,
and iron) are becoming available. These basin-wide
distributions allow more interpretation of sources
and fates of these metals. Mediation by light and
microorganisms dominates the biogeochemical cycling of certain metals such as copper, iron, and
manganese. Organic complexation has come into the
forefront of metal speciation research. Not only has
the evidence for the existence of organic complexation been overwhelming, but organic ligands dominate the speciation of copper, zinc, and iron in
oceanic surface waters. Organic complexation of
certain metals in the oceans has important biological
implications (i.e., controlling availability of metals as
nutrients and toxicants) for phytoplankton.
See also
Carbon Cycle. Metal Pollution. Tracers of Ocean
Productivity.
Further Reading
Belli SL and Zirino A (1993) Behavior and calibration of
the copper(II) ion-selective electrode in high chloride
media and marine waters. Analytical Chemistry 65:
2583--2589.
Brand LE, Sunda WG, and Guillard RRL (1986) Reduction
of marine phytoplankton reproduction rates by copper
and cadmium. Journal of Experimental Marine Biology
and Ecology 96: 225--250.
Broecker WS and Peng TH (1982) Tracers in the Sea. New
York: Eldigio Press.
Bruland KW (1983) Trace elements in sea-water. In: Riley
JP and Chester R (eds.) Chemical Oceanography, vol. 8,
pp. 157–220. London: Academic Press.
Bruland KW, Donat JR, and Hutchings DA (1991)
Interactive influences of bioactive trace metals on
biological production in oceanic waters. Limnology and
Oceanography 36: 1555--1577.
Bruno J (1990) The influence of dissolved carbon dioxide
on trace metal speciation in seawater. Marine Chemistry
30: 231--240.
Burton JD and Statham PJ (1988) Trace metals as tracers in
the ocean. Philosophical Transactions of the Royal
Society of London Series A 325: 127--145.
TRANSITION METALS AND HEAVY METAL SPECIATION 79