布朗大学同位素地球化学Applications-in-paleoclimate-studies-1.ppt

Ice core studies Antarctic ice sheet sites (domes) Antarctic ice drilling sites Greenland sites Ice core studies Ice core studies Ice core studies Ice core d18O variations Ice core information Vostok Records (Petit et al., 1999, Nature 399, 429-436) CO2 and CH4 in Vostok (Petit et al., 1999, Nature 399, 429-436) Dome C, Antarctica EPICA community members*, Nature, 429, 623 (2004) Limitations/problems of ice core Sites limited to where there is continuous ice sheet accumulation; high latitude, or altitude. Few people live in close proximity Records shorter than ocean cores Chronology, often flow of ice causes problems (especially when away from summit) Speleothems Speleothem d18O Wang et al., Science 294, 2345 (2001) Applications/limitations Need caves. Caves are common in Karts regions but uncommon in humid regions with non-carbonate bedrocks. Isotopic equilibrium has to be established, not easily attained, not known until analyses are done Samplings of speleothems in developed counties are highly regulated Datings are done after sampling, hence high uncertainty of the ages at the time of sampling Application of oxygen and hydrogen isotopes in paleoclimate studies:An introduction Topics in this section Basis for paleoclimate reconstructions from isotope ratios Common inorganic proxies for paleoclimate studies based on O and H isotope ratios δ18O of hard fossils in marine sediment, coral (annual bands) δ18O andδD of ice cores Objectives Understand the basic principles of paleoclimate reconstruction using stable isotopes A general understanding of different (inorganic) approaches for paleoclimate reconstructions Isotopic fractionation factor α=f(T) Equilibrium isotope fractionation is strongly dependent on the temperature of the reaction, because it is a thermodynamic reaction Empirical relationship (overleaf of the text) 1000lnαx-y≈dx-dy=a?106/T2 + b?103/T + c Basis I: temperature dependency of equilibrium isotope fractionation Two phases, one re