EVOLUTION OF THE CHEMISTRY OF OUR EARTH ’ S OCEANS

1. EVOLUTION OF THE CHEMISTRY OF OUR EARTH’S OCEANS “Weathering”portion based on lecture by David Montgomery

2. EVOLUTION OF THE CHEMISTRY OF OUR EARTH’S OCEANS HAVE THE OCEANS ALWAYS BEEN THE SAME?

3. WHAT MIGHT CAUSE DIFFERENCES IN OCEAN COMPOSITION THROUGH TIME ?

4. “IN THE BEGINNING” OCEAN WATER PROBABLY WAS DIFFERENT FROM PRESENT BUT IT IS DIFFICULT TO SAY HOW DIFFERENT…. OUR RECORD REALLY IS ONLY VALID FROM THE NEOPROTEROZOIC (IN RELATIVLY UNALTERED MATERIALS)

5. Conservative vs. Nonconservative Elements Conservative Non-reactive Long residence time Major ions (conservative) Na+, K+, Mg2+, Sr2+, Cl-, Br-

6. Chemical composition of modern seawater Major ions in seawater of salinity 35 Symbol Name % total (wt) mmol/kg g/kg seawater seawater Cl- Chloride 55.29% 545.87 19.353 Na+ Sodium 30.81% 469.07 10.784 SO42- Sulfate 7.75% 28.24 2.712 Mg2+ Magnesium 3.67 52.82 1.284 Ca2+ Calcium 1.18% 10.28 0.412 K+ Potassium 1.14% 10.21 0.399 Total 99.84%

7. A GOOD RECORD COMES FROM PRIMARY FLUID INCLUSIONS IN UNDEFORMED HALITE BUT THERE IS NO UNDEFORMED HALITE OLDER THAN THE NEOPROTEROZOIC

9. Secular variation in marine aragonite ooids, early marine aragonite cements, and MgSO4- bearing potash evaporites. Histogram is based on data by Sandberg (1983, 1985a, 1985b) with additional Vendianooid data from Singh (1987). Evaporite data are based on 62 potash deposits (Zharkov, 1984; Hardie, 1990)

10. FIRST POSSIBLE CONTROLS ARE BASED ON THE IONS COMING FROM THE EVOLUTION OF OCEANIC AND CONTINENTAL (granitic) IGNEOUS ROCKS

11. (Hardie, 1996)

13. Spencer and Hardie (1990) showed that the composition of modern seawater can be accounted for by steady-state mixing of the two major contributors to ocean chemistry, river water (RW) and hydrothermal brines from Mid-Ocean-Ridges (MOR)

14. spring Regional map of the Juan de Fuca Plate showing the location of the “Three Bares” and ODP sites 1026 and 1027. Dashed lines represent the basement topographic high of 2 ridges. From Wheat and Mottl,, 2000

15. Based on results of Alt,

16. Central Atlantic, mid-ocean ridge Teagle et al., 1998, Chem. Geol. V. 149 Northwest-southeast cross-section of a MOR mound (TAG). The stratigraphy of TAG-5 (borehole) has been projected onto the mound cross-section . Paragonite = yellow/green mineral of the mica group. Usually formed by hydrothermal alteration. The rock, here termed paragonite, is similar to talc. (NaAl 2(AlSi 10)(OH)2) Humphris et al., 1995

17. Alt et al., 1986, J.G.R. v. 91

18. ADDITIONALLYWe must consider surface and atmospheric processes

21. WAS THE OCEAN WATER ALWAYS THE SAME? HOW DID WE BEGIN TO TEASE APART ALL THE SEGMENTS OF MARINE EARTH HISTORY? FIRST: GEOLOGISTS NOTICED THAT FOSSIL AND OTHER CARBONATE GROUPINGS CHANGED THROUGH TIME example. Reefs were made up of bryozoan, then corals, then rudistids. Then back again to corals (different families however). Why?

22. WAS THE OCEAN WATER ALWAYS THE SAME? HOW DID WE BEGIN TO TEASE APART ALL THE SEGMENTS OF MARINE EARTH HISTORY? FIRST: GEOLOGISTS NOTICED THAT FOSSIL AND OTHER CARBONATE GROUPINGS CHANGED THROUGH TIME example. Reefs were made up of bryozoan, then corals, then rudistids. Then back again to corals (different families however). Why? SECOND: WE NOTED THAT OOLITES SOMETIMES WERE RADIAL AND AT OTHER TIMES TANGENTIAL. Why?

23. WAS THE OCEAN WATER ALWAYS THE SAME? HOW DID WE BEGIN TO TEASE APART ALL THE SEGMENTS OF MARINE EARTH HISTORY? FIRST: GEOLOGISTS NOTICED THAT FOSSIL AND OTHER CARBONATE GROUPINGS CHANGED THROUGH TIME example. Reefs were made up of bryozoan, then corals, then rudistids. Then back again to corals (different families however). Why? SECOND: WE NOTED THAT OOLITES SOMETIMES WERE RADIAL AND AT OTHER TIMES TANGENTIAL. Why? THIRD: WE HAD ENOUGH SALT SAMPLES FROM DIFFERENT AGES TO EXAMINE SALT TYPES, THEIR PRIMARY FLUID AND SOLID INCLUSIONS, AND EVEN SOME ISOTOPIC COMPOSITIONS

24. High Mg/Ca ratio produces an ARAGONITE SEA

25. High Mg/Ca ratio produces an ARAGONITE SEA Lowenstein et al., 2003

27. CAN WE SET UP A DEFINITIVE PROOF IN A MODERN CONTROLLED SETTING? YES! AN ARAGONITIC CODIACIAN ALGA, GROWN IN LOWERED Mg WATER, WILL CAUSE SLOWER GROWTH AND WEAKENED ALGAE (prone to disease etc) AND THIS COMMON ARAGONITE- PRODUCING FORM WOULD DIE OUT IF THE Mg/Ca RATIO WOULD SHIFT PERMANENTLY J. B. Ries, 2006 J.S.R. v.76, 515-523

28. If there are so many variations in seawater with time, what actually makes it happen? 1. Changes in climate especially due to the geographic redistribution of continents 2. Removal of components due to sedimentation 3. Result of increased/decreased rates of seafloor spreading with an influx/decrease of new components 4. Topographic changes leading to more or less land surface available for weathering.

29. Aqueous trace- metal concentration profiles for the modern open ocean OMZ= Oxygen Minimum Zone

31. Long term climate change and ocean chemistry. On million year time scales, climate is driven by the Input of CO2 to the atmosphere by plate tectonics. The atmospheric CO2 reservoir is small & would raise global temperatures unchecked without a chemical weathering carbon feedback. This global Mg cycle shares some similarities with the carbon cycle. Elderfield, 2011: Coggon et al. 2010

32. WEATHERING PROCESSES & THE ORIGIN OF SEDIMENTS AND THE CHANGES IN SEAWATER OVER EARTH’S HISTORY

33. Weathering

34. Weathering: the disintegration, or breakdown of rock material

35. Weathering Rates of weathering • Climate • Temperature and moisture characteristics • Mechanical weathering • Enhanced where there are frequent freeze-thaw cycles • Chemical weathering • Most effective in areas of warm, moist climates – decaying vegetation creates acids that enhance weathering • Least effective in polar regions (water is locked up as ice) and arid regions (little water)

36. Weathering Rates of weathering • Climate • Temperature and moisture characteristics • Mechanical weathering • Enhanced where there are frequent freeze-thaw cycles • Chemical weathering • Most effective in areas of warm, moist climates – decaying vegetation creates acids that enhance weathering • Least effective in polar regions (water is locked up as ice) and arid regions (little water)

37. CLIMATE/TEMPERATURE CONTROL

38. WEATHERING THROUGH TIME (Jurassic)

39. DAVID MONTGOMERY

40. Alaska Seattle Amazon Altiplano DAVID MONTGOMERY

41. Role of Physical Weathering • Reduces rock material to smaller fragments that are easier to transport 2) Increases the exposed surface area of rock, making it more vulnerable to further physical and chemical weathering

42. Mechanical Weathering • Physical breakup • pressure release • water: freeze - thaw cycles • crystallization of salt in cracks • thermal expansion and contraction • All this increases the total surface area exposed to weathering processes.

43. Surface Area and Weathering

44. Frost Wedging: rock breakdown caused by expansion of ice in cracks and joints

45. Mechanical Weathering: no change in chemical composition--just disintegration into smaller pieces

46. Chemical Weathering • Definition: transformation/decomposition of one mineral into another • Mineral breakdown • carbonate dissolves • primary minerals --> secondary minerals (mostly • clays) • Net loss of elements retained in the soil (leached).

47. Chemical Weathering • Water is the main operator: • Dissolution • Many ionic and organic compounds dissolve in water • Silica, K, Na, Mg, Ca, Cl, CO3, SO4 • Acid Reactions • Water + carbon dioxide <---> carbonic acid • Water + sulfur <---> sulphuric acid • H+ effective at breaking down minerals

48. Chemical Weathering: breakdown as a result of chemical reactions One example: CaCO3+CO2+H2O ---> Ca2+ + 2HCO3-

49. Resistance to Weathering First to Crystallize FastWeathering Bowen’s Reaction Series Goldrich Stability Series Last to Crystallize SlowWeathering

50. Chemical Weathering Solution: process by which rock is dissolved in water • Is strongly influenced by pH and temperature • When water becomes saturated, chemicals may precipitate out forming carbonate and evaporite deposits. • Calcium carbonate (calcite, limestone), sodium chloride (salt), and calcium sulfate (gypsum) are particularly vulnerable to solution weathering.