Trace 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 ID: 196733
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Lecture 3Trace Elements in Seawater
What are trace elements?
Why are they important?Principal of Oceanographic Consistency.Profiles shapes as clues for controlling processes.Slide2
A first look at spatial variation
What are the different “types” of elements?Slide3
Trace elements in seawaterDefinition: Those elements that do not contribute to salinity
All 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.Slide4
Oceanographic consistencyAcceptance of data must satisfy two criteria:
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
NO3Slide5Slide6
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 minimum Manganese (Mn) Iron (Fe)Near Bottom Enrichment – sediment source North Sea Metals (Cd, Cu, Mn)Deep Depletion - scavenging Lead-210 Aluminum (Al) Manganese (Mn) Copper (Cu)Slide7
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 ProfilesSlide8
Example: Comparison of vertical profiles of nutrients from the Atlantic and Pacific
PO
4
Si
Notice differences in shapeSlide9
Nutrient Like Examples
Cd, Zn, Cu, Ni
But what aboutMn, Pb ??Slide10
Ba and Si strongly
correlated.Q. But Why??
BaNutrient Like-Deep Regeneration-Hard PartsSlide11
Cd and PO
4 stronglycorrelated.Q. But Why??
CdNutrient Like-Shallow Regeneration-Soft PartsSlide12
Use the Cd-PO
4 correlationas a tool to determine paleoPO4 concentrations.
Modern Data
Paleo
Reconstruction using Cd in the shells
o
f benthic foraminiferaSlide13
Al profilesMediterranean toAtlantic to Pacific
Al
Atmospheric InputandScavengingSlide14
Depth (km)
Depth (km)
Mid-depth Maximum (~200 – 1000m)
Mn
Murray et al (1981)
Dissolved
Total
Oxygen Minimum Zone - ETNPSlide15
MOR Hydrothermal System – Mid-Depth Maximum and ScavengingSlide16
Fe and Mn
Hydrothermal plume from the Juan de Fuca Ridge
Fe
Mn
T anomaly
particles
Coale et al (1991) Nature, 352, 325
Mid-Depth Maximum (~2000m)Slide17
Saito et al (2013) Nature GeosciencesSlide18
Atmospheric input
Pb in Greenland snow
PbSlide19
Atmospheric Input
Anthropogenic OriginPbSurface Maximum
Flegal and Patterson, 1983Slide20
Pb – Ocean ProfilesSlide21
Pb Profiles at Bermudain North AtlanticHow have profiles of Pb changed with time?Boyle et al 2014Oceanography MagazineSlide22
Echegoyen-Sanz and Boyle (unpublished).
(Boyle and Jenkins, in preparation), Pb profiles in South PacificSlide23
Extend the record for Pb Back in time using corals.Kelly et al (2009) EPSL283, 93Surface 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 DPSlide24
Another Anthropogenic Example – Mercury (total)Lamborg et al (2014) Nature, 512, 65NASANEPacDeep water with no contaminationWe 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.Slide25
Sediment SourceHigh Trace Metal Concentrationson the Continental Shelf
Kremling (1983) Nature 303, 225
Cd
Cu
Mn
Si
PO4
SSlide26
Ocean Periodic Table (from Ken Johnson, MBARI)http://www.mbari.org/chemsensor/pteo.htmThen click on any element of interest for example profiles
.GEOTRACEShttp://www.geotraces.org/Latest literature from GEOTRACEShttp://www.geotraces.org/science/science-highlight/science-highlights-archiveSlide27Slide28
MIT Pb concentration data (Boyle) from US GT NAT-2010 transect compared to MIT data from nearby stations from 1989 and 1999.Slide29Slide30
Bruland BATSSlide31Slide32
pCu = - log Cu
2+ Cutotal = Cu2+ + inorganic complexes + organic complexes
Metal Limitation and Toxicity
– Cu – Role of Free Metal Ion
Cu Speciation
and
Plankton GrowthSlide33
Cu Speciation – Ocean Distributions
Total Copper
Strong Organic LigandsFree Cu2+
Total CuSlide34
Mn
Multiple ControlsSlide35Slide36
Vertical profile of
PCuSlide37
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)Slide38Slide39