ENV234H1 Lecture Notes - Lecture 7: Dendrochronology, Statistical Hypothesis Testing, Uniformitarianism
Document Summary
Stable isotopes of oxygen: 18o in temperature, ice, volume. Element ratios: can measure mg/c ratios. Will tell us temperatures: can measure cd/ca ratios. Biogeochemical proxies: can reconstruct temperatures using organic compounds. O-16 is stable: majority of all oxygen isotopes are found in this form. O-18 is not stable: heavier than o-16 because there are more neutrons. Can measure amount of oxygen isotopes in a rock (e. g. in calcium carbonate: measure ratio with formula, heavier values have more o-18, while lighter values have less o-18. Can measure ratio of oxygen isotopes: positive ratio values indicate more 18-o in isotopes (heavier, negative values indicate depletion of sample in 18-o (lighter) Shows o-18 ratios: ratios fluctuates between 3 and 5. See temperature indication and ice volume indication at top of diagram: where line hits blue peak = ice age, where line hits red peak = interglacial. Generally minerals exchange more readily with free water phase than with each other.
