Particulate trace metals

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 47mm 142mm filter holder 142mm 293mm Gas line to over-pressure 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) 47mm or 25mm filter holder goes here GO-Flo filtration: 10L, size fractions hard

5. Sampling for sinking particles PIT-style surface-tethered sediment trap, adapted for trace metal clean collection (Carl Lamborg) Using 234Th/238U 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)” Fe Al Dissolved Al, Fe from BATS in 2008 (GEOTRACES IC1, Bruland website) Dissimilar dissolved profile shapes but similar particulate profile shapes--increase until ~1000m, then constant until nepheloid layer at bottom Particulate Al, Fe from BATS in 1987 (Sherrell and Boyle, 1992) Strong nepheloid layers with concentrations 7x higher than water column profile

9. Mn, Co, Pb, Zn, Cu, Ni: the “Minor minors (pM)” • 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 (Sherrell and Boyle, 1992)

10. Lithogenic contribution to pTMs % 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 (Sherrell and Boyle, 1992)

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

12. Modelling scavenging and removal (II) -repackaging flux (FR) 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 (FS) (Sherrell and Boyle, 1992)

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

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

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. 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 Frew et al. 2006

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

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

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

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

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

22. PyriteFe2+Fe3+ 1-21k0.1-20.1k.7-20.7k Gamma=0.69 SIA14C aerosol--OUT SIRENA Core Top--OUT 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.

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

24. References