Δ18O

In geochemistry, paleoclimatology and paleoceanography δ18O or delta -O -18 is a measure of the ratio of the stable oxygen isotopes 18O/16O. Determining the ratio is referred to as isotope analysis. δ18O is suitable for the reconstruction of the temperature of precipitation, but also serves as a measure of the interaction between groundwater and minerals; it is also used as an indicator of the isotopic fractionation processes such as methanogenesis. 18O/16O-Daten of corals, foraminifera, ice cores and sediments of freshwater lakes are used in the Paläowissenschaften as a temperature proxy. It is defined as:

The unit is parts per thousand (‰, parts per thousand). The standard has a known isotopic composition, such as the Vienna Standard Mean Ocean Water ( VSMOW ).

Fractionation can be done by a kinetic fractionation, Gleichgewichtsfraktionierung or mass-independent fractionation.

Mechanism and application

δ18O reflects the local evaporation rate and the fresh water influx. Since preferably from sea water evaporates 16O, rain water is rich in 16O. Consequently, in the subtropics, the surface water of the oceans contains larger amounts of 18O, because there the evaporation rate is increased. Lesser amounts of 18O are in the mid-latitude ocean water, where it rains more.

The like can be observed in the condensation: water molecules, which contain the heavier 18O atoms tend to condense the first and auszuregnen. The gradient of the water shows moisture from the tropics to the poles of a decrease in the 18O content. Snow Falling in Canada, contains much less H218O as rain which descends in Florida; accordingly carries snow falling in the center of an ice rink, a lighter δ18O signature than at the edges of the ice, because the heavier 18O rains out first. A climate change which alters the global pattern of evaporation and precipitation changes, for this reason the basic δ18O ratio.

These relationships have been discovered and published by Harold C. Urey in 1947. Cesare Emiliani analyzed on this basis in the 1950s, large-scale cores and classified on the basis of δ18O signatures found the geological ages in so-called oxygen - isotope stages.

Suitable proxies

Most often, the shells of foraminifera were studied. They are composed of calcium carbonate ( CaCO3), can be found and contain oxygen in many geological structures. The ratio of 18O to 16O is used to control the temperature of the surrounding water to the crystallization time point to determine indirectly. The ratio varies depending on the temperature of the surrounding water easily; but other factors influence the relationship such as the salinity and the amount of water trapped in ice sheets. However, reconstructions are also possible with the use of corals, lake sediments and stalagmites. In addition, the ice from ice cores and the sugar fossil plants can be examined.

While the suitability of δ18O from Eisbohrkernproben to reconstruct temperatures of past times is amply documented, it can be at a temperature reconstruction in the biogenic phosphate material such as Bone and tooth material is used to get distorted by diagenesis.

Analysis of sugar

Add the sugars ( arabinose, xylose and fucose ) of deposited in lake sediments plants a clear δ18O signature is using a new procedure can also be seen, which probably reflects the local temperature or precipitation situation. In the Himalayan region, this signature can be used for example as a proxy for the intensity and variability of the summer monsoon.

Review of food

A further application is the verification of authenticity of food products. As recorded water is stored by plants in water, wearing every other plant foods in the water it contains the signature of its growth place. For example, wine diluted with tap water or juice, which was previously converted to a cost effective transport into a concentrate, diluted back with tap water, it is detectable on the determination of δ18O. Plenty of loungers in front of accurate data on a growing area, so it is possible with the method to also check information on the installation location. Example, it is checked whether a Bordeaux wine actually comes from grapes grown in Bordeaux.

Calculations

If the effect of changing salinity and ice volume are ignored and the signal is therefore solely attributed to changes in temperature, representing an increase of 0.22 ‰ δ18O of cooling by 1 ° C.

Also, the temperature can be calculated using this equation:

During the Pleistocene correlated a δ 18O signature of 0.11 ‰ with a sea level change of 10 m, which resulted from the change in ice volume.