The organic carbon that reaches the sediments
             drives sedimentary diagenesis. 2% of expor is buried. 
             98% of export is respired in the water column. Consumes O2.
  Many elements in the periodic table can exist in more than one oxidation state. 
  Oxidation States are indicated by Roman numerals (e.g. (+I), (-II), etc). 
  The oxidation state represents the "electron content" of an element which 
  can be expressed as the excess or deficiency of electrons relative to the 
  elemental state.
             Oxidation States
                                                                                         How to determine:
             Element           Oxidation State          Species                          Assign 0 = -II
                                                                                         Assign H = +I
             Nitrogen          N (+V)             NO-
                                                      3                                  Charge on species
                         N (+III)           NO-                                          Calculate Oxidation State
                                                2
                         N (O)              N
                                              2                                                   V
                         N (-III)           NH, NH+
                                                3      4                                          IV       d
             Sulfur            S (+VI)            SO2-                                                     e
                                                     4                                            III      c
                                                                                                           u
                         S (+II)            S O 2-                                                         d
                                             2  3                                           d     II       e
                                                                                            e              r
                         S (O)              S                                              z
                                                                                            i     I
                                                                                            d
                                                      -  2-                                 i
                         S(-II)             HS, HS, S                                       x     O
                                              2                                             o
             Iron        Fe (+III)          Fe3+                                                  -I
                         Fe (+II)           Fe2+                                                  -II
             Manganese         Mn (+VI)           MnO2-                                           -III  more e-
                                                        4
                         Mn (+IV)           MnO (s)
                                                  2
                         Mn (+III)          Mn3+, MnOOH (s)
                         Mn (+II)           Mn2+
      Oxidation / Reduction Reactions
      One Reactant:
                                            -
          is oxidized – it loses electrons = the e  donor (a reductant)
          is reduced – it gains electrons = the e- acceptor (an oxidant)
      Electrons are conserved!
      Example:
      CHO      +      O         ↔      CO      +       H O
          2           2             2          2
       -         -               -            -
      e donor    e acceptor         e  acceptor     e  donor
      (e- rich)                                       Reactions always 
                                                      coupled. No free e-.
                                                      No free H+.
      Compare with acid / base reactions:
      HCl         +       H O             Cl-      +       H O+
                      2                        3
        +          +             +             +
      H donor    H  acceptor    H  acceptor    H  donor
   The driver of ocean redox chemistry 
   is organic matter.
   Why is organic matter an electron donor?
        photosynthesis
    Z-scheme for photosynthetic electron transport
                                                                    Falkowski and Raven (1997/2007)
                                                                      ADP→ATP
                                                                                   Ferredoxin
      e
      l
      a                                                                      to Calvin cycle
      c
      S
                                                                             and carbohydrate 
      y
      g
      r                                                                      formation
      e                                      ADP→ATP
      n
      E
                                       photooxidation
                                       of water  H O to O
                                                 2     2
   2e- from water
   H2O   O = -II
   O2      O =   0
                energy from sun converted to C-C, energy rich, chemical bonds
                inside chloroplasts of plants. Two photons absorbed.