1. Particulate trace metals Phoebe Lam Marine Bioinorganic Chemistry lecture October 5, 2009

2. outline Why are particles important How do we sample for particulate trace metals (suspended, sinking) Techniques for analysis Sample profiles (bulk) Sample profiles (speciation)

3. Why are particles important to trace metal (TM) cycling? Source of lithogenic TMs (dust, mobilization of continental margin and benthic sediments) Participate in internal cycling of TMs: release some TMs into solution, provide surfaces for scavenging TMs out of solution; biological uptake and remineralization Are the ultimate sink of dissolved trace metals (vertical particle export and removal to sediments)

4. Sampling for suspended particles McLane battery- operated in-situ pump: <1000L, size fractionated MULVFS: Multiple Unit Large Volume in-situ Filtration System (ship power): <12,000L, 3 flow paths, size fractionated (Jim Bishop) GO-Flo filtration: 10L, size fractions hard Gas line to over- pressure 47mm or 25mm filter holder goes here 142mm filter holder 142mm 293mm 47mm

5. Sampling for sinking particles PIT-style surface-tethered sediment trap, adapted for trace metal clean collection (Carl Lamborg) Using 234 Th/ 238 U disequilibrium and particulate 234Th:TM ratios (Weinstein and Moran 2005)

6. The basic analysis: applying crustal ratios to total digests Total digests using (sub)boiling strong acids with HF to dissolve aluminosilicates Sherrell and Boyle, 1992, after Taylor 1964 GCA

7. Nutrient(-like) dissolved profiles have mirror image particulate profiles Nozaki 2001 Dissolved profiles from N.Pacific Sherrell and Boyle 1992 Particulate profiles, BATS

8. Al, Fe: The “Major minors (nM)” Dissolved Al, Fe from BATS in 2008 (GEOTRACES IC1, Bruland website) Al Fe Particulate Al, Fe from BATS in 1987 (Sherrell and Boyle, 1992) Dissimilar dissolved profile shapes but similar particulate profile shapes--increase until ~1000m, then constant until nepheloid layer at bottom Strong nepheloid layers with concentrations 7x higher than water column profile

9. Mn, Co, Pb, Zn, Cu, Ni: the “Minor minors (pM)” (Sherrell and Boyle, 1992) Similar profiles: Generally low at the surface, increasing to max at 500m Authigenic Mn as host phase for scavenged metals? Nepheloid layers in most pTMs (Mn, Co, Zn, Ni), but not Pb, Cu, and not nearly as strong as for Fe, Al

10. Lithogenic contribution to pTMs (Sherrell and Boyle, 1992) % particulate Al: <10% Fe: ~50% Mn: <25% Co: <10% Zn: <5% Cu: <5% Ni: <5% Cd: <5% Pb: <5% Lithogenics are strong sources for Al, Fe everywhere, moderate for Mn and Co, not at all for Zn, Cu, Ni (?), Cd, Pb Fe has the highest %particulate

11. Modelling scavenging and removal (I) (Sherrell and Boyle, 1992) Use slope of particulate 230 Th profile to estimate the mean particle sinking speed, S;  p =D/S F T =F S +F R F R =(Me P *D)/  p = Me P *S How much of total flux is due to sinking from the surface vs. repacking in the water column?

12. Modelling scavenging and removal (II) (Sherrell and Boyle, 1992) -repackaging flux (F R ) provides ~30% of total flux out of surface (except Cd: 80%, Zn: 10%); i.e. Most of total flux due to flux out of surface (F S )

13. Pools of particulate trace metals Biological Surface adsorbed Authigenic particles Lithogenic particles

14. Simplified Fe cycle Terrigenous (clays (dust), oceanic crustal material, volcanic sediments) Biota Atmospheric deposition Dissolved (Fe-L) Lateral transport (from rivers, continental margin) Authigenic (hydroxides) Uptake/scavenging Sinking Dissolved Pool Particulate Pool Remineral- ization

15. How to distinguish between different pools?? Leaching methods (not exhaustive!): “biogenic”: weak acid+mild reductant+heat (Berger et al. 2007); total-lithogenic (Frew et al. 2006) “surface adsorbed”: oxalate wash (Tovar-Sanchez et al. 2004) “authigenic”: mild reductant+acid (eg. Poulton and Canfield 2005) “lithogenic”: strong acid digest (w/ HF) and crustal Al:TM ratio (eg. Sherrell and Boyle 1992; Frew et al. 2006) Biological Surface adsorbed Authigenic particles Lithogenic particles

16. Transformation between pools? Frew et al. 2006 Frew et al. applied a crustal Al:Fe ratio to total pFe (HNO3/HF) to partition between “lithogenic” and “biogenic”. Surface samples were 80% “lithogenic”; trap samples were only 50% “lithogenic” Conclude biologically-mediated conversion of “lithogenic” to “biogenic” pFe

17. X-Ray Fluorescence (XRF) microprobe: spatial distribution of elements Incident x-rays Sample Detector Fluor- escent x-rays Wikipedia Incident beam of 10keV

18. Synchrotron X-Ray microprobe: spatial distribution of pTM 71m 1 mm Red=Fe Blue=Ca Lam et al. GBC 2006 Silicoflagellate (scale bar = 20  m) c/o Ben Twining Cellular scaleAggregate scale

19. Speciation from X-Ray Absorption Spectroscopy: valence EXAFS region Energy (eV) Absorption XANES region Position of edge depends on valence Energy (eV) Absorption Fe

20. Speciation from X-Ray Absorption Spectroscopy: mineralogy Fe EXAFS region Energy (eV) Absorption XANES region Clay Olivine Hydroxide Organic Fe

21. Chemical mapping combines XRF and XAS all 3 species more or less equal at 7160eV at 7122eV, Fe3+ is significantly lower than Fe2+ or pyrite at 7117eV, pyrite is signicantly higher than Fe2+ or Fe3+ This set of energies minimizes error estimates 7105: everyone is low 7117: pyrite only is high 7122: pyrite,Fe 2+ are high (Fe 3+ is low) 7160: everyone is high

22. Figure 3: Preliminary x-ray fluorescence maps showing the relative abundance of Fe3+ oxides (blue), Fe2+ silicates (green), and pyrite (red) in end member (aerosol and sediment core) samples. Aerosol samples are a mix of Fe3+ oxides and Fe2+ silicates, whereas core top samples have abundant pyrite. Scale bar is 200um. PyriteFe2+Fe3+ 1-21k0.1-20.1k.7-20.7k Gamma=0.69 SIA14C aerosol--OUTSIRENA Core Top--OUT

23. SIM87T d11 125m--IN SIM84T d10 20m--IN SIM89T d11 200m--IN, low RGB 1 2 3 4 6 5 PyriteFe2+Fe3+ 1-21k0.1-20.1k.7-20.7k Gamma=0.69

24. References