Lecture 3 Trace Elements in Seawater What are

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. 2. 3. 4. 5. many are micronutrients (e. g. Fe, Cu) – speciation is important others are toxic (e. g. Cu, Hg) some are tracers for redox conditions (Mn, Fe, Cr, I, Re, Mo, V, U) some are enriched in economic deposits such as manganese nodules (e. g. Cu, Co, Ni, Cd) 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) PO 4 NO 3 Si SST

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)

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

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 Nutrient Like. Deep Regeneration. Hard Parts Ba and Si strongly correlated. Q. But Why? ?

Cd Nutrient Like. Shallow Regeneration. Soft Parts Cd and PO 4 strongly correlated. Q. But Why? ?

Modern Data Use the Cd-PO 4 correlation as a tool to determine paleo PO 4 concentrations. Paleo Reconstruction using Cd in the shells of benthic foraminifera

Al Atmospheric Input and Scavenging Al profiles Mediterranean to Atlantic to Pacific

Mid-depth Maximum (~200 – 1000 m) Mn Depth (km) Total Dissolved Oxygen Minimum Zone - ETNP Murray et al (1981)

MOR Hydrothermal System – Mid-Depth Maximum and Scavenging

Mid-Depth Maximum (~2000 m) Fe and Mn Hydrothermal plume from the Juan de Fuca Ridge T anomaly particles Fe Mn Coale et al (1991) Nature, 352, 325

Saito et al (2013) Nature Geosciences

Pb Atmospheric input Pb in Greenland snow

Atmospheric Input Anthropogenic Origin Pb Surface Maximum Flegal and Patterson, 1983

Pb – Ocean Profiles

Pb Profiles at Bermuda in North Atlantic How have profiles of Pb changed with time? Boyle et al 2014 Oceanography Magazine

Pb profiles in South Pacific Echegoyen-Sanz and Boyle (unpublished). (Boyle and Jenkins, in preparation),

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 DP values. Pb. SW = (Pb/Ca)coral* Ca. SW DP

Another Anthropogenic Example – Mercury (total) Lamborg et al (2014) Nature, 512, 65 NA p w at er w ith n o co nt am in at io n NEPac D ee SA 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 S PO 4 Si Cd Cu Mn Kremling (1983) Nature 303, 225

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-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

Metal Limitation and Toxicity – Cu – Role of Free Metal Ion Cu Speciation and Plankton Growth p. Cu = - log Cu 2+ Cutotal = Cu 2+ + inorganic complexes + organic complexes

Cu Speciation – Ocean Distributions Total Copper Strong Organic Ligands Free Cu 2+ Total Cu

Mn Multiple Controls

Vertical profile of PCu

Classification of elements Conservative Bio-limiting (or “bio-unlimited”) (and “biointermediate”) Scavenged Some have a style of their own (e. g. O, Ar, Bi, Hg)