Lecture 3 Trace Metals in Seawater
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Transcript of Lecture 3 Trace Metals in Seawater
Lecture 3Trace Elements in Seawater
What are trace elements?Why are they important?Principal of Oceanographic Consistency.Profiles shapes as clues for controlling processes.
A first look at spatial variation
What are the different “types” of elements?
Trace elements in seawaterDefinition: Those elements that do not contribute to salinityAll elements less than 1 mg kg-1 (<1 ppm)
Why are they important?1. many are micronutrients (e.g. Fe, Cu) – speciation is important2. 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.
Oceanographic consistencyAcceptance of data must satisfy two criteria:
1. Vertical profiles should be smooth, not spiky. Ocean mixing produces smooth profiles2. 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)
SST-
Si
PO4
NO3
Shapes of Profiles – clues for controlsConservative - Cesium (Cs); Molybdenum (Mo) - under oxic conditionsNutrient Like – Biological control Shallow (soft parts) and Deep (hard parts) Regeneration
Zinc (Zn) Cadmium (Cd) Nickel (Ni) Copper (Cu)
Barium (Ba)Surface Enrichment – Atm input, River/Coastal inputs
Lead (Pb)Manganese (Mn)
Mid-depth Maximum – Hydrothermal inputs, Oxygen minimumManganese (Mn)Iron (Fe)
Near Bottom Enrichment – sediment sourceNorth Sea Metals (Cd, Cu, Mn)
Deep Depletion - scavengingLead-210Aluminum (Al)Manganese (Mn)Copper (Cu)
Superposition of vertical biological flux on horizontal circulation
Results in low surface water and highdeep water concentrations.
Results in higher concentrations inthe older deep Pacific than the younger deep Atlantic
Nutrient Like Profiles
Example: Comparison of vertical profiles of nutrients from the Atlantic and Pacific
PO4 Si
Notice differences in shape
Nutrient Like ExamplesCd, Zn, Cu, Ni
But what aboutMn, Pb ??
Ba and Si strongly correlated.
Q. But Why??
Ba
Nutrient Like-Deep Regeneration-Hard Parts
Cd and PO4 stronglycorrelated.
Q. But Why??
Cd
Nutrient Like-Shallow Regeneration-Soft Parts
Use the Cd-PO4 correlationas a tool to determine paleoPO4 concentrations.
Modern Data
Paleo Reconstruction using Cd in the shellsof benthic foraminifera
Al profilesMediterranean toAtlantic to Pacific
Al
Atmospheric InputandScavenging
Depth (km
)
Depth (km
)
Mid-depth Maximum (~200 – 1000m)
Mn
Murray et al (1981)
Dissolved
Total
Oxygen Minimum Zone - ETNP
MOR Hydrothermal System – Mid-Depth Maximum and Scavenging
Fe and Mn
Hydrothermal plume from the Juan de Fuca Ridge
Fe Mn
T anomalyparticles
Coale et al (1991) Nature, 352, 325
Mid-Depth Maximum (~2000m)
Saito et al (2013) Nature Geosciences
Atmospheric input
Pb in Greenland snow
Pb
Atmospheric InputAnthropogenic Origin
Pb
Surface Maximum
Flegal and Patterson, 1983
Pb – Ocean Profiles
Pb Profiles at Bermudain North Atlantic
How have profiles of Pb changed with time?
Boyle et al 2014Oceanography Magazine
Echegoyen-Sanz and Boyle (unpublished). (Boyle and Jenkins, in preparation),
Pb profiles in South Pacific
Extend the record for Pb Back in time using corals.
Kelly et al (2009) EPSL283, 93
Surface coral from North Rock and seawater from Station S, BATS and BTM. Inferred Pb concentrations (in pmol kg− 1) from surface coral proxy records and DP values.
PbSW = (Pb/Ca)coral* CaSW
DP
Another Anthropogenic Example – Mercury (total)Lamborg et al (2014) Nature, 512, 65
NA
SA NEPacDee
p wate
r with
no co
ntamina
tion
We estimate the total amount of anthropogenic mercury present in the global ocean to be 290 ± 80 million moles, with almost two-thirds residing in water shallower than a thousand metres.
Sediment Source
High Trace Metal Concentrationson the Continental Shelf
Kremling (1983) Nature 303, 225
Cd
Cu
Mn
Si
PO4
S
Ocean Periodic Table (from Ken Johnson, MBARI)
http://www.mbari.org/chemsensor/pteo.htm
Then click on any element of interest for example profiles.
GEOTRACES
http://www.geotraces.org/
Latest literature from GEOTRACES
http://www.geotraces.org/science/science-highlight/science-highlights-archive
MIT Pb concentration data (Boyle) from US GT NAT-2010 transect compared to MIT data from nearby stations from 1989 and 1999.
Bruland BATS
pCu = - log Cu2+ Cutotal = Cu2+ + inorganic complexes + organic complexes
Metal Limitation and Toxicity – Cu – Role of Free Metal Ion
Cu SpeciationandPlankton Growth
Cu Speciation – Ocean Distributions
Total CopperStrong Organic Ligands
Free Cu2+
Total Cu
Mn
Multiple Controls
Vertical profile of PCu
Classification of elementsConservative(or “bio-unlimited”)
Bio-limiting(and “biointermediate”) Scavenged
Some have a style of their own (e.g. O, Ar, Bi, Hg)