GEOL 103 Study Guide - Oxygen-18, Pleistocene, Antarctica
Document Summary
Methane gas = -90 ; carbonates (methanogenic bacteria) = +10 - +20 . Air = -7 to -10 corg: surface ocean = -22 deep ocean = -22 . Cinorg: surface ocean = +1 deep ocean = 0 . Most hydrocarbons derived from marine phytoplankton ( 13c = -22 ) Photosynthesis = conversion of inorganic c (co2) into an organic form (ch2o)n. Fractionation = a process favoring the transfer of one isotope of an element more than another. Biological (13c/12c) discrimination within living systems to conserve energy. C3 plants - 3 carbon intermediate product -25 . C4 plants - 4 carbon intermediate product -13 . Ocean water = 0 meteoric water = -40 - +10 . Chemical fractionation (18o/16o) discrimination by temperature, evaporation and condensation. Clouds form from isotopically light vapor, the resulting rain is in heavy 18o. Rain then gets successively lighter as you lose the heaviest isotopes.
