Everything about 18o totally explained
In
geochemistry,
paleoclimatology and
paleoceanography δ18O is a measure of the ratio of
stable isotopes
18O:16O. The definition is δ
18O (in per mil) = 10
3[(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.
Detail
Foraminifera shells of
calcium carbonate (CaCO
3), having oxygen in them, and being found in many common geological features, such as the
White Cliffs of Dover that were once at the bottom of the ocean, are most commonly used to do tests on. 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. Although the change is only about 0.2
parts per thousand decrease for each degree
Celsius of temperature increase, this is sufficient to estimate the temperature of the water in which the foraminifera lived in millions of years ago.
δ
18O value of the shells depends on the δ
18O in the surrounding water, which can be as variable as its temperature. This variability arises because of when water evaporates the lighter molecules of water—those with
16O atoms instead of
18O—tend to evaporate first, because of their lower mass. This makes the water vapor more depleted of
18O than the ocean from which it evaporates. The ocean contains greater amounts of
18O around the subtropics and tropics where there's 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 H
218O than rain in
Florida.
Changes in climate alter global patterns of evaporation and precipitation therefore change the background δ
18O ratio.
Further Information
Get more info on '18o'.
|
External Link Exchanges
Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:
<a href="http://__18o.totallyexplained.com">Δ18O Totally Explained</a>
Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned. |
