7_stable_isotopes - Stable Isotopes δ 18 O oxygen isotopes...

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Unformatted text preview: Stable Isotopes δ 18 O- oxygen isotopes temperature ice volume δ 13 C- carbon isotopes Carbon cycle Oxygen Isotopes • Oxygen has 3 isotopes #protons #neutrons isotope 8 8 8 8 9 10 16 O 17 O 18 O • Oxygen isotopes – 16 O = 99.8% – 17 O = 0.08% – 18 O = 0.2% δ 18 O [ 18 O/ 16 O sample - 18 O/ 16 O standard ] δ 18 O (‰) = 18 O/ 16 O standard * 1000 Standard = PeeDee Belemnite (PDB) SMOW (Std Mean Ocean Water) Measure the 2 most abundant isotopes Analyze ratios on stable isotope mass spectrometer • Calcite shells (foraminifera) = CaCO 3 Oxygen Isotopes δ 18 O Seawater: HC 16 O 16 O 16 O HC 18 O 16 O 16 O HC 17 O 16 O 16 O CaC 16 O 16 O 16 O CaC 16 O 16 O 18 O Ratio in the foram CaCO 3 reflects the ratio in the seawater Oxygen Isotopes Ruddiman (App. 1) • Differences in mass are great enough to make the atoms behave differently during physical and chemical processes • 1. Evaporation – 16 O is lighter- evaporates more readily • 2. Incorporation into a solid – 16 O greater vibrational energy- more difficult to incorporate into solid Oxygen Isotopes • Evaporation Effect (Ice volume, salinity) – 16 O preferentially evaporated – incorporated into rain and snow – Stored on land as ice – During glacials- more 16 O removed from the ocean and stored on land – 18 O/ 16 O of remaining ocean becomes “heavier” (or higher δ O) Oxygen Isotopes • Temperature Effect – Differences in vibrational energies are more pronounced at lower temperatures – More discrimination against 16 O when it is colder – Shells incorporate a greater % of 18 O when it is cold (= heavier 18 O/ 16 O or δ 18 O) Oxygen Isotopes •...
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7_stable_isotopes - Stable Isotopes δ 18 O oxygen isotopes...

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