Carbon Dioxide
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Fundamental ingredient in photosynthesis
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Highly soluble in water
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50X more in ocean than atmosphere
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most stored as calcium and magnesium carbonates in animal shells or sediments
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carbonate compounds reservoir in sea
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concentration relatively constant at 45 – 54 ml/L
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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
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2nd , Carbonic acid dissociates into bicarbonate and then to carbonate ions releasing
hydrogen ions
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H2CO3  H+ + HCO3-  CO3-2
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carbonic acid  Hydrogen icon + Bicarbonate ion  Hyrdogen Ion + Carbonate Ion
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3rd – Carbonate ions react with calcium and magnesium in seawater to form calcium
carbonate and magnesium carbonate
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CO3-2 + Mg+2 + Ca+2  MgCO3 + CaCO3
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carbonate ion + magnesium ion + calcium ion  magnesium carbonate + calcium
carbonate
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pH values and carbonate buffer system
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reversible reactions associated with dissolved carbon dioxide regulate the number of
hydrogen ions in the ocean
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concentration of hydrogen ions is pH
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Carbonate buffer acts as a source of hydrogen ions if too basic and removes hydrogen
ions if too acid
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If seawater becomes too basic: H2CO3  H+ + HCO3-
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if seawater becomes too acid: H+ + HCO3-  H2CO3
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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
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Nitrate – nutrient
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Depth profiles
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Depth (Z) vs. nitrate
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Phytoplankton use nitrates so low at surface
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As depth increases, so does nitrates
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Levels off
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Similar to Compensation depth
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Poop (fecal pellets) sink
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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
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N:P in ocean – Redfield Ratio (mole ratio) = C:N:P 106:16:1
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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
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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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