11:8 class notes - • O18 represents the concentration of...

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11/8 Milankovitch cycles and Pleistocene glaciations evidence of climate changes o glacial deposits o moraines o till o striations Milankovitch orbital cycles o eccentricity changes (~100,000-yr and ~400,000-yr cyclicities) o obliquity changes (~41,000-yr cyclicity) o precession of the equinoxes (~19,000-yr and ~23,000-yr cyclicities) Loess: cold glacial period Costal deposits drowned as sea level rises Ocean has an abundance of O18 and O16; when water evaporates, oxygen 18 is depleted in heavier isotope (water vapor), enriched in O16 o Vapor is transported long distances o Process of evaporation and precipitation tends to leave heavier isotope Oxygen-isotopic composition of seawater
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Unformatted text preview: • O18 represents the concentration of O18 relative to O16 • Evaporation favors the water molecules with the lighter O16 • The heavier isotope, O18, is preferentially lost from vapor in the atmosphere through precipitation • As ice sheets grow, they lock up disproportionately more O16 than O18 in land-based ice • Consequently, during times of large global ice volume (glacials), the oceans have greater O18 than during interglacial times • When ice sheets melt, the O16-rich meltwater runs back to the oceans and dilutes the ocean water which is then no longer so relatively high in O18...
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This note was uploaded on 11/08/2011 for the course GEOSCI 100 taught by Professor Williammccoy during the Fall '11 term at UMass (Amherst).

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