Carbon Dioxide and Buffer System

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Carbon Dioxide
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Fundamental ingredient in photosynthesis

Highly soluble in water

50X more in ocean than atmosphere

most stored as calcium and magnesium carbonates in animal shells or sediments

carbonate compounds reservoir in sea

concentration relatively constant at 45 – 54 ml/L

phytoplankton blooms – decrease CO2
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Reacts with water
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1st Carbon dioxide reacts with water forming carbonic acid
o H2O + CO2  H2CO3

2nd , Carbonic acid dissociates into bicarbonate and then to carbonate ions releasing
hydrogen ions

H2CO3  H+ + HCO3-  CO3-2

carbonic acid  Hydrogen icon + Bicarbonate ion  Hyrdogen Ion + Carbonate Ion

3rd – Carbonate ions react with calcium and magnesium in seawater to form calcium
carbonate and magnesium carbonate

CO3-2 + Mg+2 + Ca+2  MgCO3 + CaCO3

carbonate ion + magnesium ion + calcium ion  magnesium carbonate + calcium
carbonate
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pH values and carbonate buffer system

reversible reactions associated with dissolved carbon dioxide regulate the number of
hydrogen ions in the ocean

concentration of hydrogen ions is pH

Carbonate buffer acts as a source of hydrogen ions if too basic and removes hydrogen
ions if too acid

If seawater becomes too basic: H2CO3  H+ + HCO3-

if seawater becomes too acid: H+ + HCO3-  H2CO3

Even though carbonic acid is a weak acid, its amount of ionization is so slight that it
acts to decrease the number of hydrogen ions in solution

Nitrate – nutrient

Depth profiles
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Depth (Z) vs. nitrate

Phytoplankton use nitrates so low at surface
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As depth increases, so does nitrates

Levels off

Similar to Compensation depth

Poop (fecal pellets) sink

Remineralized
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Oxygen minimum zone
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Compensation – photo and resp are equal
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Critical – no photo
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Lot of theories re: why Oxygen has minimum zone
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About 1000 m

N:P in ocean – Redfield Ratio (mole ratio) = C:N:P 106:16:1

16X N than P in ocean
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Lysocline, CaCO3 compensation depth
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At some point it goes below a critical

Lysocline – dissolution
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CCD – calcium carbonate compesation depth – no CaCO3
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Reservoirs – inventory of various chemicals
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