Oxic-Anoxic Transition Zones:

1. Oxic-Anoxic Transition Zones: synergy between geochemistry and (micro)biology Brian T. Glazer Postdoctoral Fellow University of Hawaii NASA Astrobiology Institute glazer@hawaii.edu

2. Presentation Outline Oxic-anoxic transition zones (OATZ) Sulfur cycling introductory material

3. Presentation Outline In situ voltammetry – overview, rationale, & examples method development

4. Presentation Outline Cyanobacterial mats Oceanic hydrothermal vents 2 case studies Recap and overall conclusions

5. Oxic-anoxic transition zones (OATZ) Atmospheric O2 rose to 21% ~2 billion years ago Combined influence of slow diffusion through water and organic matter ensures OATZ persistence Photosynthesis and chemosynthesis = redox gradients Redox gradients = respiration & metabolism Life is a big, constant, redox equation

6. Some perspective • Life history on earth is overwhelmingly microbial • The earth is ~4.5 billion yrs old, • microbes arose ~3.5 billion years ago (bya) • animals-0.7 bya -- humans-0.001 bya Jan. 1-Earth Forms The Microbial Age-3.1 Billion Years Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Late Feb-Microbes ~Nov. 5th-Animals (oceans) Dec. 11th-Land Plants Dec. 27th-Mammals Dec. 31st- 10:00 PM Humans 11:59:30 PM Written History

7. Types of metabolism • Light is used directly by phototrophs • Hydrothermal energy is utilized mainly via heat-catalyzed production of reduced inorganics Nealson and Rye 2004

8. Oxic-anoxic transition zones(OATZ)

9. O2 NO3- Mn++ has been traditionally oversimplified to SO42- and H2S Fe++ SO42- S2- NH4+ CH4 Redox profiling Vertical scale changes across environments General guideline for OATZ progression Nealson and Stahl 1997

10. SO42- sulfate S0 elemental sulfur Sulfur reduction oxidation H2S oxidation hydrogen sulfide Sulfate reduction (dissimilatory) Sulfate reduction (assimilatory) mineralization organic S Sulfur redox cycling general overview Megonigal et al. 2004

11. Dissimilatory sulfate reduction: SO42- + 2CH2O  2HCO3- + HS- + H+ Sulfur redox cycling Accounts for half or more of the total organic carbon mineralization in many environments significance Highly reactive HS- is geochemically relevant because of its involvement in precipitation of metal sulfides and potential for reoxidation

12. H2S oxidation (ph >6): O2+ Fe2+ Fe3+ Fe3+ + H2S  Fe2+ + S(0) as S8 and Sx2- FeS formation and dissociation: Fe2+ + H2S  FeSaq + 2H+ (FeSaq formation is enhanced with increasing temperature) Pyrite formation: FeSaq + H2S  FeS2 + H2 or under milder reducing conditions: FeS(s) + S2O32-  FeS2 + SO32- Sulfur redox cycling important Fe/S chemistry

13. Manganese catalytic cycling: Mn2+ + ½ O2+ H2O  MnO2 + 2H+ MnO2 + HS- + 3H+  Mn2+ + 2H2O + S(0) as S8 and Sx2- Sulfur redox cycling important Mn/S chemistry

14. Sulfur redox cycling Other pathways for S oxidation: HS- + 2O2 SO42- + H+ 5HS- + 8NO3-  5SO42- + 4N2 + 3OH- + H2O HS- + 2CO2 + 2H2O  SO42- + 2CH2O + H+ partially oxidized intermediates S2O32- + H2O  SO42- + HS- + H+ 4S0 + 4H2O  SO42- + 3HS- + 5H+ 4SO32- + H+ 3SO42- + HS-

15. Methods & analytical evaluation “the science of the interaction of electrical and chemical phenomena” electrochemistry …blurring the lines between methods & results…

16. Au wire – 100mm diameter Polished epoxy surface Voltammetry 101 100 mm gold wire sealed in PEEK or glass using marine epoxy, plated with mercury O2, Fe2+, Mn2+, H2S, H2O2, I-, Sx2-, S2O32-, FeSaq, Fe(III) are all measurable in one scan, if present

17. H2O2 + 2H+ + 2e- H2O O2 + 2H+ + 2e- H2O2 Argon purged Voltammetry 101 Glazer et al. 2004

18. In situ voltammetry analytical comparison Glazer et al. 2004

19. In situ voltammetry analytical comparison Glazer et al. 2004

20. In situ voltammetry analytical comparison Glazer et al. 2004

21. In situ voltammetry field application Coastal bays and sediments Luther et al. 2004, Taillefert et al. 2002, Rozan et al. 2002,

22. In situ voltammetry field application Hydroelectric power generation Luther et al. 2003

23. In situ voltammetry application Laboratory microbial cultures Sobolev et al. 2001, Roden et al. 2004

24. In situ voltammetry field application Black Sea - world’s largest anoxic basin photo: Murray, 2003

25. In situ voltammetry field application microbial mats - steep gradients photo: Glazer, 2002

26. Riftia plume electrode In situ voltammetry field application Hydrothermal vents photo: Glazer, 2003

27. In situ voltammetry 1) no need to collect samples 2) a small amount of analyte is used, allowing multiple measurements advantages 3) microelectrodes can be used to obtain a high spatial resolution

28. In situ voltammetry 4) relatively high data acquisition in a short period of time 5) electrodes can be deployed in a variety of water column, sediment, or laboratory environments advantages 6) simultaneous detection of several analytes

29. In situ voltammetry 1) labor intensive construction, preparation, maintenance, and data interpretation 2) expensive 3) relatively high data acquisition in a short period of time (is actually a two edged sword) disadvantages

30. Microbial Mats steep gradients

31. 2 bya gunflint chert, Michigan

32. Wisconsin & Australia

33. Hamelin Bay, Australia

34. Microbial Mat OATZ Questions: Are transient partially-oxidized sulfur intermediates a measureable component of the redox transition? How is the redoxocline affected by the diurnal cycle? How are the geochemical gradients reflected by the microbial consortia?

35. Microbial Mat OATZ Technique: In situ voltammetry should give resolution & sensitivity required to identify partially-oxidized sulfide intermediates and other redox analytes. DGGE, sequencing analysis, and metabolic gene-specific PCR will allow for community characterization on the same vertical scale as the in situ profiles.

36. CO2 CO2 O2 O2 CH4 H2S SO4 CH2O O2 SO4 Sx2-, S8 HS- FeS CO2 Organic acids & H2 FeS2 precipitation & burial CH4 Mat Surface cyanobacteria aerobic heterotrophs chemolithotrophic S-bacteria phototrophic S-bacteria fermenters sulfate/sulfur reducers methanogens

37. Field deployments Glazer et al., 2004

38. H2O2 O2 Redox speciation (surface) Glazer et al., 2004

39. H2O2 Redox speciation (-0.5 mm) Glazer et al., 2004

40. H2O2 S0 (S8) O2 AVS Redox speciation (-2.0 mm) Glazer et al., 2004

41. S0(Sx2-) S2- (H2S, Sx2-) FeS 2000 mVs-1 S4O62- AVS Redox speciation (-4.0 mm) Glazer et al., 2004

42. S2- (H2S, Sx2-) FeS 2000 mVs-1 AVS Redox speciation (-6.0 mm) Glazer et al., 2004

43. Redox profiles Glazer et al., 2004

44. Spatial variability Vertical heterogeneity of up to 1 mm may account for disparity between geochemistry & microbial sampling Glazer et al., 2004

45. Diurnal (& tidal) variability four-electrode array: surface, -2.0 mm, -4.0 mm, -6.0 mm Glazer et al., 2004

46. Surface oxidation & dehydration, 20:00 Tidal inundation, 13:00 Surface Glazer et al., 2004

47. Surface oxidation & dehydration, 20:00 photoinhibition, 12:00 photosynthesis, 06:50 - 2.0 mm Glazer et al., 2004

48. More oxidized, 09:30 More reduced, 22:00 Overnight precipitation of FeS & FeS2 - 4.0 mm Glazer et al., 2004

49. Partially oxidized, 10:00 Reduced, 22:40 Overnight precipitation of FeS & FeS2 - 6.0 mm Glazer et al., 2004

50. FeS S0 (Sx2-) S2- (Sx2-, H2S) Polysulfide dynamics (-4.0 mm) Glazer et al., 2004