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Chapter 8—Part 2 Basics of ocean structure The Inorganic Carbon Cycle/

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1 Chapter 8—Part 2 Basics of ocean structure The Inorganic Carbon Cycle/
Marine Organic Carbon Cycle

2 Basics of ocean structure
Surface Ocean Deep Ocean ~100 m Well mixed by winds Mixing occurs as a result of density differences due to temperature and salinity -- the thermohaline circulation ~4 km

3 The thermocline Ocean temperature decreases with depth between ~100 m (the bottom of the mixed layer) and 1 km. This is termed the thermocline Salinity also increases with depth, also increasing the density of seawater. The increase in density with depth is termed the pycnocline /Water/temp.html

4 Deep Ocean Circulation

5 Radiocarbon Age of Deep Water
Ref: Broecker and Peng, Tracers in the Sea (1982), p. 269

6 How Carbon-14 is made 14N: 7 p, 7 n 14C: 6 p, 8 n C-14 production:
14N + n  14C + p C-14 decay: 14C  14N + e (Beta decay)

7 The Inorganic Carbon Cycle
Carbon Uptake by the Oceans: 1. The biological pump 2. Air-sea gas exchange

8 Atm. CO2 Surface Ocean Deep Ocean DIC = Dissolved inorganic carbon
Air-sea exchange Surface Ocean DIC Deep Ocean ~100 m Biological pump ~4 km DIC = Dissolved inorganic carbon

9 The Biological Pump transfer of CO2 to the deep ocean: Photosynthesis creates organic matter; this sinks to the deep ocean, where it decays back to CO2

10

11 transfer of CO2 to the deep ocean:
The Biological Pump transfer of CO2 to the deep ocean: Photosynthesis creates organic matter; this sinks to the deep ocean, where it decays back to CO2 North Atlantic Pacific Ocean Deep water

12 transfer of CO2 to the deep ocean:
The Biological Pump transfer of CO2 to the deep ocean: Photosynthesis creates organic matter; this sinks to the deep ocean, where it decays back to CO2 photosynthesis North Atlantic Pacific Ocean Transfer of carbon Deep water

13 transfer of CO2 to the deep ocean: Deep water becomes enriched in CO2
The Biological Pump transfer of CO2 to the deep ocean: Deep water becomes enriched in CO2 The carbon is recycled to the surface ca. 1,000 years photosynthesis North Atlantic Pacific Ocean Transfer of carbon Deep water

14 surface water Photosynthesis CO2 + H2O  CH2O + O2 sinking particles Respiration CH2O + O2  CO2 + H2O deep water

15 surface water Photosynthesis CO2 + H2O  CH2O + O2 sinking particles Respiration CH2O + O2  CO2 + H2O deep water This pumps up the CO2 partial pressure of deep water…

16 Atm. CO2 pCO2 = 370 ppmv Surface Ocean pCO2 = 370 ppmv Deep Ocean
DIC Deep Ocean pCO2 = 370 ppmv Biological pump pCO2  1000 ppmv Deep water has a higher CO2 partial pressure than does surface water

17 Dissolved inorganic carbon
Atm. CO2 Air-sea exchange 60 Gt(C)/yr Ocean Dissolved inorganic carbon

18 How CO2 is dissolved into sea water:
+ H2O H2CO3 carbon dioxide carbonic acid

19 How CO2 is dissolved into sea water:
+ H2O H2CO3 HCO3- + H+ carbon dioxide carbonic acid bicarbonate ion

20 How CO2 is dissolved into sea water:
+ H2O H2CO3 HCO3- + H+ CO3= + 2H+ carbon dioxide carbonic acid bicarbonate ion carbonate ion

21 Buffer reaction helps dissolve CO2 into sea water:
CO2 + CO3= + H2O HCO3-

22 Buffer reaction helps dissolve CO2 into sea water:
CO2 + CO3= + H2O HCO3- This reaction removes CO2 from the atmosphere, with no change in the amount of H+ (i.e., no change in pH) Definition: pH =  log10[H+] So, low pH = high [H+]  acidic high ph = low [H+]  basic

23 Other Common Acids Hydrochloric acid: HCl  H+ + Cl−
Nitric acid: HNO3  H+ + NO3− Sulfuric acid: H2SO4  2 H+ + SO4= All of these reactions release H+ ions (protons) into solution

24 How much carbon is dissolved in the ocean?

25 How much carbon is dissolved in the ocean?
Gt C Atmospheric CO

26 How much carbon is dissolved in the ocean?
Gt C Atmospheric CO Carbonic acid (H2CO3) Bicarbonate ion 37,000 (HCO3-) Carbonate ion ,300 (CO3=)

27 How much carbon is dissolved in the ocean?
Gt C Atmospheric CO Carbonic acid (H2CO3) Bicarbonate ion 37,000 (HCO3-) Carbonate ion ,300 (CO3=) 39,040 Gton C

28 Inorganic Carbon in Marine Sediments:
Sea shells Reefs Carbonate minerals (CaCO3) Algae tests

29

30

31 The Inorganic Carbon Cycle (Carbonate-silicate Cycle)
The rest of this lecture will be done slightly differently on the board. I will leave these slides in, though, for the benefit of anyone who missed the lecture.

32 Silicate Mineral Weathering:
Based on dissolution of calcium silicate minerals (CaSiO3) Silicate weathering removes CO2 from the atmosphere. Globally, it removes about 0.03 Gton C/year

33 Silicate Mineral Weathering:
Based on dissolution of calcium silicate minerals (CaSiO3) Silicate weathering removes CO2 from the atmosphere. Globally, it removes about 0.03 Gton C/year

34 CaSiO3 + 2 H2O + 2 CO2  Ca2+ + 2 HCO3- + SiO2 + H2O
Silicate weathering: CaSiO3 + 2 H2O + 2 CO2  Ca HCO3- + SiO2 + H2O

35 CaSiO3 + 2 H2O + 2 CO2  Ca2+ + 2 HCO3- + SiO2 + H2O
Silicate weathering: CaSiO3 + 2 H2O + 2 CO2  Ca HCO3- + SiO2 + H2O Carbonate precipitation: Ca HCO3-  CaCO3 + H2O + CO2

36 CaSiO3 + 2 H2O + 2 CO2  Ca2+ + 2 HCO3- + SiO2 + H2O
Silicate weathering: CaSiO3 + 2 H2O + 2 CO2  Ca HCO3- + SiO2 + H2O Carbonate precipitation: Ca HCO3-  CaCO3 + H2O + CO2 Net Reaction

37 CaSiO3 + 2 H2O + 2 CO2  Ca2+ + 2 HCO3- + SiO2 + H2O
Silicate weathering: CaSiO3 + 2 H2O + 2 CO2  Ca HCO3- + SiO2 + H2O Carbonate precipitation: Ca HCO3-  CaCO3 + H2O + CO2 Net Reaction

38 CaSiO3 + 2 H2O + 2 CO2  Ca2+ + 2 HCO3- + SiO2 + H2O
Silicate weathering: CaSiO3 + 2 H2O + 2 CO2  Ca HCO3- + SiO2 + H2O Carbonate precipitation: Ca HCO3-  CaCO3 + H2O + CO2 Net Reaction

39 CaSiO3 + 2 H2O + 2 CO2  Ca2+ + 2 HCO3- + SiO2 + H2O
Silicate weathering: CaSiO3 + 2 H2O + 2 CO2  Ca HCO3- + SiO2 + H2O Carbonate precipitation: Ca HCO3-  CaCO3 + H2O + CO2 Net Reaction

40 CaSiO3 + 2 H2O + 2 CO2  Ca2+ + 2 HCO3- + SiO2 + H2O
Silicate weathering: CaSiO3 + 2 H2O + 2 CO2  Ca HCO3- + SiO2 + H2O Carbonate precipitation: Ca HCO3-  CaCO3 + H2O + CO2 Net Reaction CaSiO3 + CO2  CaCO3 + SiO2

41 CaSiO3 + 2 H2O + 2 CO2  Ca2+ + 2 HCO3- + SiO2 + H2O
Silicate weathering: CaSiO3 + 2 H2O + 2 CO2  Ca HCO3- + SiO2 + H2O Carbonate precipitation: Ca HCO3-  CaCO3 + H2O + CO2 Net Reaction CaSiO3 + CO2  CaCO3 + SiO2

42 Silicate weathering results in a net loss of CO2
This contrasts with carbonate weathering, which does not remove atmospheric CO2

43 Dissolved inorganic carbon
Silicate Weathering 0.03 Atm. CO2 Carbonate Weathering 0.17 Air-sea exchange Volcanism 0.03 60 Gt/yr Ocean Dissolved inorganic carbon 39,040 Gton Dissolution 0.3 Deposition 0.5 Marine Sediments 2,500 Gton Carbonate Weathering 0.17 Burial 0.2 Sedimentary Rocks 40,000,000 Gton C

44 Weathering Volcanism The Long-term Inorganic Carbon Cycle:
CaSiO3 + CO2 CaCO3 + SiO2 Volcanism

45 Weathering Volcanism The Long-term Inorganic Carbon Cycle:
CaSiO3 + CO2 CaCO3 + SiO2 Volcanism

46 Weathering Volcanism The Long-term Inorganic Carbon Cycle: 0.03
GtonC/yr CaSiO3 + CO2 CaCO3 + SiO2 0.03 GtonC/yr Volcanism

47 What controls silicate weathering rates?
Time Temperature Rainfall Exposure of fresh rock surfaces Vegetation (roots provide acid)

48 Weathering Feedback Loop:
Atm. CO2 Silicate weathering Rates Surface Temperature Weathering rates increase with increased temperature

49 Weathering Feedback Loop:
Atm. CO2 Silicate weathering Rates Surface Temperature Weathering reactions remove CO2, and as CO2 declines, planet temperatures go down

50 Weathering Feedback Loop:
Atm. CO2 Silicate weathering Rates Surface Temperature This is a negative feedback loop, or a stable system. This loop is a key control on climate over long time scales (i.e., millions of years).

51 The Inorganic Carbon Cycle Atm. CO2 Fast Air-sea exchange Med. Slow Marine sediments Sedimentary rocks

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