OCE 290A (Topics in Chemical Oceanography) Application of Isotopes in Geological and Environmental Research Class participation 25%, Oral presentation 25%, Mid-term manuscript to review 25%, Final 3-5 page Proposal 25%
INTRODUCTION Isotope = Equal Place, occupy the same place in the periodic table Atoms of a given element with the same number of protons but a different number of neutrons in their nuclei. Chemically identical atoms (same electron configuration) with different atomic weights (different mass). E=mc 2 the energy of a compound is a function of its mass. Molecules composed of different isotopes of the same element will posses different levels of energy, thus will differ in the chemical properties which are directly related to mass (diffusion, evaporation, vapor pressure, physical adsorption, reaction rates etc.) For more details take EART 128
Why do isotopes fractionate (chemically)? Mass-dependent differences in zero-point energy Mass-dependence in equilibrium constants & reaction rates Vibrational spectra provide information about bond energies and hence can be used to predict isotope effects If m 2 > m 1 : Bond strength (m 2 -M) Bond strength (m 1 -M) E 0, 2 E 0, 1
Fractionation mechanisms Equilibrium Isotope Fractionation A quantum-mechanical phenomenon, driven mainly by differences in the vibrational energies of molecules and crystals containing atoms of differing masses. Kinetic Isotope Fractionation Occur in unidirectional, incomplete, or branching reactions due to differences in reaction rate of molecules or atoms containing different masses.
Traditional Stable Isotope Systems Geoscience investigations beginning in 1950 s
Nontraditional Stable Isotope Systems? Geoscience investigations beginning in 1960 s - 1990 s Renaissance beginning in mid-late 1990 s (esp. B, Ca, Li, Se)
Emerging Stable Isotope Systems Geoscience applications beginning in late 1990 s and 2000 s Compare with light stable isotopes in the 1950 s
Radiogenic, Cosmogenic and Nobel Gas Isotope Systems Geoscience applications beginning in late 1990 s and 2000 s Compare with light stable isotopes in the 1950 s
Koch 2007
What makes for a stable isotope system that shows large variation? 1) Low atomic mass 1) A large relative mass differences between stable isotopes 2) Element tends to form highly covalent bonds 3) Element has more than one oxidation state or forms bonds with a variety of different elements 4) Rare isotopes aren t in too low abundance to be measured accurately
Since natural variations in isotope ratios are small, we use δ notation δ H X = ((R sample /R standard ) -1) x 1000 where R = heavy/light isotope ratio for element X and units are parts per thousand (or per mil, ) e.g. δ 18 O (spoken delta O 18) or δ 34 S (spoken delta S 34)
Application of Isotope Systems Formation of the elements in the solar system Radioactive geochronology Reaction and formation temperatures of rocks and minerals Geochemical and biological reaction rates Tracking and tracing pollution sources (hydrosphere, soils, atmosphere) Ground water recharge and water rock interaction processes Biogeochemical cycles (sources, sinks and transformations of elements) Evolution of organisms (methanogenesis) and of the environment (paleo) Microbial ecology Food web structure Migration and distribution of plant and animals Nutrient cycling (in water and soil) Atmospheric chemistry and dynamics Weathering rates and geomorphology Circulation and mixing rates of water masses Forensic studies, detecting extraterrestrial life,. The new and innovative uses of these systems are limited mainly by our insight and imagination.
INTRODUCTION Your name, department, thesis project, specific isotopic system or application of interest Web: pmc.ucsc.edu/~paytan/290a_winter2014 Email or come see with your selected paper for presentation.