Presentation on theme: "Lecture 3 Trace Elements in Seawater What are trace elements? Why are they important? Principal of Oceanographic Consistency. Profiles shapes as clues."— Presentation transcript:
Lecture 3 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 What are the different “types” of elements?
Trace elements in seawater Definition: 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 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.
Oceanographic consistency Acceptance of data must satisfy two criteria: 1.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) SST - Si PO4 NO3
Shapes of Profiles – clues for controls Conservative - Cesium (Cs); Molybdenum (Mo) - under oxic conditions Nutrient 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)
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 Nutrient Like Profiles
Example: Comparison of vertical profiles of nutrients from the Atlantic and Pacific PO 4 Si Notice differences in shape
Nutrient Like Examples Cd, Zn, Cu, Ni But what about Mn, Pb ??
Ba and Si strongly correlated. Q. But Why?? Ba Nutrient Like- Deep Regeneration- Hard Parts
Cd and PO 4 strongly correlated. Q. But Why?? Cd Nutrient Like- Shallow Regeneration- Soft Parts
Use the Cd-PO 4 correlation as a tool to determine paleo PO 4 concentrations. Modern Data Paleo Reconstruction using Cd in the shells of benthic foraminifera
Al profiles Mediterranean to Atlantic to Pacific Al Atmospheric Input and Scavenging
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 anomaly particles Coale et al (1991) Nature, 352, 325 Mid-Depth Maximum (~2000m)
Pb Profiles at Bermuda in North Atlantic How have profiles of Pb changed with time? Boyle et al 2014 Oceanography 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) EPSL 283, 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 D P values. Pb SW = (Pb/Ca) coral * Ca SW D P
Another Anthropogenic Example – Mercury (total) Lamborg et al (2014) Nature, 512, 65 NA SANEPac Deep water with no contamination 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 Concentrations on 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