Foraminifera samples.

δ18O ppm in deep sea sediment foraminifera carbonates over time from 0-600,000 years. Averaged over a large number of cores in order to isolate a global signal.

In geochemistry, paleoclimatology and paleoceanography δ¹⁸O is a measure of the ratio of stable isotopes ¹⁸O:¹⁶O. The field of geochemistry involves study of the chemical composition of the Earth and other Planets chemical processes and reactions that govern the composition Paleoclimatology (also Palaeoclimatology) is the study of Climate change taken on the scale of the entire History of Earth. Paleoceanography is the study of the history of the Oceans in the geologic past with regard to circulation Chemistry, Biology, geology and patterns Stable isotopes are chemical isotopes that are not Radioactive (to current knowledge The definition is δ¹⁸O (in per mil) = 10³[(R_sample/R_standard)-1], where R_x = (¹⁸O)/(¹⁶O) is the ratio of isotopic composition of a sample compared to that of an established standard, such as ocean water. It is commonly used as a measure of the temperature of precipitation, as a measure of groundwater/mineral interactions, as an indicator of processes that show isotopic fractionation, like methanogenesis. In paleosciences, foraminifera and ice core data ¹⁸O:¹⁶O is used as a proxy for temperature. The Foraminifera, ("Hole Bearers" or forams for short are a large group of Amoeboid Protists with reticulating Pseudopods fine An ice core is a Core sample from the accumulation of snow and ice over many years that have re-crystallized and have trapped air bubbles from previous time periods In Climate research a proxy variable is something that is probably not in itself of any great interest but from which a variable of interest can be obtained

Mechanism

Foraminifera shells of calcium carbonate (CaCO₃), having oxygen in them, and being found in many common geological features, are most commonly used to do tests on. Calcium carbonate is a Chemical compound with the Chemical formula Ca[[Carbon C]] O 3 The ratio of ¹⁸O to ¹⁶O is used to tell the temperature of the surrounding water of the time solidified, indirectly. The ratio varies slightly depending on the temperature of the surrounding water, as well as other factors such as the water's salinity, and the volume of water locked up in ice sheets.

δ¹⁸O also reflects local evaporation and freshwater input, as rainwater is ¹⁶O enriched - a result of ¹⁶O's preferential evaporation from seawater. Consequently, the surface ocean contains greater amounts of ¹⁸O around the subtropics and tropics where there is more evaporation, and lesser amounts of ¹⁸O in the mid-latitudes where it rains more.

Similarly, when water vapor condenses, heavier water molecules holding ¹⁸O atoms tend to condense and precipitate first. The water vapor gradient heading from the tropics to the poles gradually becomes more and more depleted of ¹⁸O. Snow falling in Canada has much less H₂¹⁸O than rain in Florida; similarly, snow falling in the center of ice sheets has a lighter δ¹⁸O signature than that at its margins, since heavier ¹⁸O precipitates first. "Snowfall" redirects here For other uses see Snow (disambiguation or Snowfall (disambiguation. Country to "Dominion of Canada" or "Canadian Federation" or anything else please read the Talk Page Florida ( is a state located in the southeastern region of the United States, bordering Alabama to the northwest and Georgia to the

Changes in climate alter global patterns of evaporation and precipitation therefore change the background δ¹⁸O ratio.

Calculations

If the signal can be attributed to temperature change alone, with the effects of salinity and ice volume change ignored, a δ¹⁸O increase of 0. 22‰ is equivalent to a 1 °C cooling. ^[1] Temperature can also be calculated using the equation:

T (°C) = 16. 9 - 4. 0(δ¹⁸O_calcite - δ¹⁸O_seawater)

During the Pleistocene, a 0. 11‰ δ¹⁸O signature correlates to 10m of sea level change as a consequence of changing ice volume.

See also

• δ¹³C

References

• Clark, Ian D. and Peter Fritz (1997) Environmental Isotopes in Hydrogeology, CRC Press: 1997, ISBN 1566702496
• Schmidt, G. A. (1999). "Forward Modeling of Carbonate Proxy Data from Planktonic Foraminifera Using Oxygen Isotope Tracers in a Global Ocean Model Paleoceanography 14,": 482-497.