Trace Metals in Seawater

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Lecture 3 Trace Metals in Seawater
What are trace elements? Why are they
important? Principal of Oceanographic
Consistency. Profiles shapes as clues for
controlling processes.
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A first look at spatial variation
What are the different types of elements?
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Trace elements in seawater Definition Those
elements that do not contribute to salinity All
elements less than 1 mg kg-1. Why are they
important? 1. many are micronutrients (e.g. Fe,
Cu) speciation is important 2. others are
toxic (e.g. Cu, Hg) 3. some are tracers for
redox conditions (Mn, Fe, Cr, I, Re, Mo, V, U) 4.
some are enriched in economic deposits such as
manganese nodules (e.g. Cu, Co, Ni, Cd) 5. some
have man made sources and are tracers of
pollution (e.g. Pb, Pu, Ag) Difficult to
collect samples for without contamination and
difficult to analyze.
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Shapes of Profiles clues for controls Conservati
ve - Cesium (Cs) Molybdenum (Mo) - under oxic
conditions Nutrient Like Biological control
Shallow (soft parts) and Deep (hard parts)
Regeneration Zinc Cadmium Nickel
Copper Barium Surface Enrichment Atm input,
River/Coastal inputs Lead Manganese Mid-depth
Maximum Hydrothermal inputs, Oxygen
minimum Manganese Iron Near Bottom Enrichment
sediment source North Sea Metals (Cd, Cu,
Mn) Deep Depletion - scavenging Lead-210 Aluminu
m Manganese
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Nutrient Like Profiles
Superposition of vertical biological flux on
horizontal circulation
Results in low surface water and high deep water
concentrations. Results in higher concentrations
in the older deep Pacific than the younger deep
Atlantic
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Example Comparison of vertical profiles of
nutrients from the Atlantic and
Pacific
PO4
Si
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Nutrient Like Examples Cd, Zn, Cu, Ni
But what about Mn, Pb ??
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Ba Nutrient Like- Deep Regeneration- Hard Parts
Ba and Si strongly correlated. But Why??
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Cd Nutrient Like- Shallow Regeneration- Soft
Parts
Cd and PO4 strongly correlated. But Why??
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Modern Data
Use the Cd-PO4 correlation as a tool to determine
paleo PO4 concentrations.
Paleo Reconstruction
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Al Atmospheric Input and Scavenging
Al profiles Mediterranean to Atlantic to Pacific
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Mid-depth Maximum (200 1000m)
Mn
Depth (km)
Depth (km)
Total
Dissolved
Oxygen Minimum Zone - ETNP
Murray et al (1981)
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MOR Hydrothermal System Mid-Depth Maximum and
Scavenging
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Mid-Depth Maximum (2000m)
Fe and Mn Hydrothermal plume from the Juan de
Fuca Ridge
T anomaly
particles
Mn
Fe
Coale et al (1991) Nature, 352, 325
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Pb
Atmospheric input Pb in Greenland snow
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Atmospheric Input Anthropogenic
Origin Pb Surface Maximum
Flegal and Patterson, 1983
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Pb Ocean Profiles
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Sediment Source High Trace Metal
Concentrations on the Continental Shelf
S
PO4
Si
Cd
Cu
Mn
Kremling (1983) Nature 303, 225
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Ocean Periodic Table (from Ken Johnson,
MBARI) http//www.mbari.org/chemsensor/pteo.htm
Then click on any element of interest for example
profiles.
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Metal Limitation and Toxicity Cu Role of Free
Metal Ion
Cu Speciation and Plankton Growth
pCu - log Cu2 Cutotal Cu2
inorganic complexes organic complexes
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Cu Speciation Ocean Distributions
Total Copper Strong Organic Ligands
Free Cu2 Total Cu
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• Oceanographic consistency
• Acceptance of data must satisfy two criteria
• Vertical profiles should be smooth, not spiky.
• Ocean mixing produces smooth profiles
• 2. Correlations should exist with other elements
  that
• share the same controlling mechanisms.

First Example Cu in surface waters south of
New Zealand (Boyle and Edmond, 1975, Nature,
253, 107)
PO4
NO3
Si
-
SST
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Mn Multiple Controls
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Vertical profile of PCu
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Classification of elements
Conservative (or bio-unlimited)
Bio-limiting (and biointermediate)
Scavenged
Some have a style of their own (e.g. O, Ar, Bi,
Hg)
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