Marine Geochemical

1. Marine Geochemical/Biogeochemical Cycles Working up to sedimentation Understanding chemistry of the oceans Lead to biogenic and chemical sedimentation Cycles Dissolved constituents Particulate- Organic and inorganic Colloidal material- dissolved? particulate?

2. Marine Geochemical Cycles Almost entire periodic table of elements can be found in the ocean (ions in solution) Concentrations are not equivalent to riverine input

5. Marine Cycles

6. Marine Cycles Inputs: Particulate Terrestrial- riverine, eolian, volcanic Cosmogenic Dissolved constituents Continental weathering (including ground water flux) Hydrothermal reactions (ocean crust weathering) Diagenetic reactions (sediment) Gases Volcanic Air/sea exchange Excess volatiles

7. Marine Cycles

8. Marine Cycles Cycling Cyclic salts- from ocean ? atmosphere ? rivers or rainout ? oceans Aerosols (Sea spray) Biological cycling nutrients Sediment cycling

10. Marine Cycles Outputs Sedimentation (biogenic, lithogenic, chemical) Burial Reverse weathering Lithification Subduction Diagenetic reactions Hydrothermal reactions (Seafloor weathering of basalt) Gas exchange

11. Marine Cycles Removal to sediment Biogenic precipitation- �reverse weathering� Hard parts Also photosynthesis ? Organic matter Adsorption on clays Important for Fe, Mn and Co cycles

12. Marine Cycles Hydrothermal and diagenetic cycles Both process add and remove cations Hydrothermal Mg2+ removed from and Ca2+ added to solutions Carbonate diagenesis Ca2+ removed from and Sr2+ and Mg2+ added to solutions

14. Marine Cycles

15. Marine Cycles Process approach Global cycle- includes passage through oceans Weathering Removal to sediments Cycling through hydrothermal systems or marine sediments Uplift or burial/metamorphism

16. Marine Cycles Weathering

17. Marine cycles To close the loop From the marine realm back to continent/atmosphere/(biosphere) Burial and metamorphism Uplift Volcanism

19. Dissolved Constituents Salinity- The sum of all the dissolved salts in seawater Amount of dissolved inorganic solids Average 35% 35g salt in 1000g water (g/kg) 35 ppt 35 per mil (% ) 35 psu (practical salinity units)

20. Salts divided into major constituents (> 1 ppm) minor constituents (1 ppb � 1 ppm) trace constituents (< 1 ppb) 7 Major constituents account for >99.9% of the salts Cl-, Na+, Mg2+, SO4 2-, Ca2+, K+, HCO3- (Earth�s crust- O, Si, Al, Fe, Ca, Na, Mg, K, Ti, H) Dissolved Constituents

21. Salinity

22. Salinity Law of constant proportions Salinity will vary with evaporation and precipitation (add and remove H2O), but the ratio of the major salts does not change conservative behavior- not altered by biological or chemical reactions within the ocean

23. Conservative Behavior (mostly major elements) Altered only by processes at the boundaries Within the ocean only altered by mixing Examples �major elements; salinity, potential temperature and pressure Non-conservative Behavior (most minor and trace) Altered by physical, chemical or biological processes within the ocean Examples- nutrients, silica, dissolved oxygen Dissolved Constituents

24. Conservative - Non-conservative

25. Steady State Steady State Inputs = outputs Chemical budget is balanced Believed to be true in a gross sense for major constituents and many minor/trace for the Phanerozoic Sediment/organisms haven�t changed Fluid inclusions

26. Permian/Triassic Evaporites

27. Steady State Balanced cycles Example- Mg cycle If HT circulation decreases (less seafloor spreading) Less Mg uptake at the ridge Increased Mg uptake elsewhere (carbonates, evaporites�) Related to distribution coefficient KD = conc in solid/conc in seawater

28. Mg and Ca Seas

29. Residence Time If elements are in steady state, it is possible to determine how long they stay in dissolved form- the residence time Reactivity of an element

30. Residence Time

31. Major constituents tend to have long residence times Residence Time

32. Particulate Fluxes Most of the organic matter and particulate cycles takes place in the upper water column Photic zone ~ 100-200 m Phytoplankton photosynthesize (most of the biomass) Zooplankton eat phytoplankton (fecal pellets) Bacteria consume and decompose small particles and pellets Input of eolian material

33. Particle Scavenging Metal ions and ionic complexes are adsorbed on particles and transferred to the seafloor Adsorption = ionic attraction Bacteria- small size, large surface area ? sites of adsorption Clays- charged surfaces Elements that are commonly scavenged Th, Pb, Co Have short residence times (<100 � 1000 yrs)

34. Particle Scavenging

35. Particulate Fluxes Transfer to the seafloor Settle at ~ 1m/hr, 166 days to reach seafloor Yet sediment on seafloor reflects particles in overlying water column Packaged as: Fecal pellets (~100-200m/day) Marine snow (aggregates)

36. Marine Flux

37. Nutrient Cycles Biological Pump Downward movement of nutrients out of the photic zone as particles Release into deeper waters by decay Combines particle and dissolved fluxes LoLo

38. Biological Pump- Nutrient Cycles

40. Biological Particle Formation

41. Worked through 2 box model for PO4 in MBCWorked through 2 box model for PO4 in MBC

42. Nutrient Profiles

43. Nutrient Profiles

45. Preformed Nutrients Preformed nutrients- Nutrients that are advected into the deep ocean rather than produced by decay Common in Southern Ocean (HNLC areas) Low light levels Lack of biolimiting trace elements- Fe?

46. High Nutrient-Low Chlorophyll Regions

47. PO4* (Broecker) ~ initial phosphate (related to preformed phosphate) Distinct value for NCW and SCW SCW >NCW Conservative property Preformed Nutrients

48. O2 Profiles

49. Apparent Oxygen Utilization (AOU) ~ Know dissolved oxygen content of water when it sinks That value decreases through oxidation of organic matter Difference between expected value at saturation and observed value = amount used for oxidation

50. Dissolved O2

51. AOU

52. O2 Profile

53. Dissolved Profiles- Summary