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| {{DISPLAYTITLE:δ<sup>18</sup>O}}
| | Greetings. Let me start by telling you the writer's title - Phebe. For a while she's been in South Dakota. Hiring is his profession. One of the things he loves most is ice skating but he is having difficulties to find time for it.<br><br>Have a look at my page: [http://www.Videokeren.com/blog/71062 www.Videokeren.com] |
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| | [[File:Benthic foraminifera.jpg|thumb|right|200px|Foraminifera samples.]]
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| | [[File:Delta-O-18_in_deep_sea_sediment.png|thumb|right|200px|δ<sup>18</sup>O (in permil;‰) 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.]]
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| | [[File:Five Myr Climate Change.png|thumb|right|200px|Climate record of Lisiecki and Raymo (2005) constructed by combining measurements from 57 globally distributed deep sea sediment cores. The measured quantity is oxygen [[isotope fractionation]] (δ<sup>18</sup>O) in benthic foraminifera.<ref>{{Cite doi|10.1029.2F2004PA001071}}</ref>]]
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| In [[geochemistry]], [[paleoclimatology]] and [[paleoceanography]] '''δ<sup>18</sup>O''' or '''delta-O-18''' is a measure of the ratio of [[stable isotope]]s '''<sup>18</sup>O:<sup>16</sup>O''' ([[oxygen-18]]:[[oxygen-16]]). It is commonly used as a measure of the temperature of [[precipitation (meteorology)|precipitation]], as a measure of groundwater/mineral interactions, as an indicator of processes that show [[isotope fractionation|isotopic fractionation]], like [[methanogenesis]]. In paleosciences, <sup>18</sup>O:<sup>16</sup>O data from [[coral]]s, [[foraminifera]] and [[ice cores]] are used as a [[proxy (climate)|proxy]] for temperature. The definition is, in "per mil" (‰, parts per thousand):
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| :<math>\delta ^{18}O = \Biggl( \frac{\bigl( \frac{^{18}O}{^{16}O} \bigr)_{sample}}{\bigl( \frac{^{18}O}{^{16}O} \bigr)_{standard}} -1 \Biggr) * 1000\ ^{o}\!/\!_{oo}</math>
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| where the standard has a known isotopic composition, such as [[Vienna Standard Mean Ocean Water]] (VSMOW).<ref name="usgs_isotope_tracers">
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| {{cite web
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| |url= http://wwwrcamnl.wr.usgs.gov/isoig/res/funda.html
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| |title= USGS -- Isotope Tracers -- Resources -- Isotope Geochemistry
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| |accessdate=2009-01-18
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| }}</ref> The fractionation can arise from [[Kinetic fractionation|kinetic]], [[Equilibrium fractionation|equilibrium]], or [[Mass-independent fractionation|mass-independent]] [[isotope fractionation|fractionation]].
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| == Mechanism ==
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| Foraminifera shells of [[calcium carbonate]] (CaCO<sub>3</sub>), having oxygen in them, and being found in many common geological features, are most commonly tested. The ratio of <sup>18</sup>O to <sup>16</sup>O 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.
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| {{delta|18|O|}} also reflects local evaporation and freshwater input, as rainwater is <sup>16</sup>O enriched—a result of <sup>16</sup>O's preferential evaporation from seawater. Consequently, the surface ocean contains greater amounts of <sup>18</sup>O around the subtropics and tropics where there is more evaporation, and lesser amounts of <sup>18</sup>O in the mid-latitudes where it rains more.
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| Similarly, when water vapor condenses, heavier water molecules holding <sup>18</sup>O 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 <sup>18</sup>O. [[Snow]] falling in [[Canada]] has much less H<sub>2</sub><sup>18</sup>O than rain in [[Florida]]; similarly, snow falling in the center of ice sheets has a lighter {{delta|18|O|}} signature than that at its margins, since heavier <sup>18</sup>O precipitates first.
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| Changes in climate that alter global patterns of evaporation and precipitation therefore change the background δ<sup>18</sup>O ratio.
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| ==Calculations==
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| If the signal can be attributed to temperature change alone, with the effects of salinity and ice volume change ignored, a {{delta|18|O|}} increase of 0.22‰ is equivalent to a 1 °C (1.8 °F) cooling.<!-- Do not convert the temperature with a template or AWB. --><ref>
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| {{cite journal
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| |author=Visser, K.
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| |year=2003
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| |last2=Thunell
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| |first2=Robert
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| |last3=Stott
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| |first3=Lowell
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| |title=Magnitude and timing of temperature change in the Indo-Pacific warm pool during deglaciation
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| |journal=[[Nature (journal)|Nature]]
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| |volume=421 |pages=152
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| |doi=10.1038/nature01297
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| |issue=6919
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| |bibcode = 2003Natur.421..152V }}</ref> Temperature can also be calculated using the equation:
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| :<math>T( \text{deg C}) = 16.9 - 4.0 \times \mathrm{\delta^{18}O_{calcite}} - \mathrm{\delta^{18}O_{seawater}}</math>
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| During the [[Pleistocene]], a 0.11‰ {{delta|18|O|}} signature correlates to 10 m of sea level change as a consequence of changing ice volume (higher {{delta|18|O|}} correlates with a lower mean temperature and lower sea level).
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| ==See also==
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| * {{delta|13|C|link}}
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| * {{delta|15|N|link}}
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| * [[Isotopic signature]]
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| * [[Isotope analysis]]
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| * [[Isotope geochemistry]]
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| ==References==
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| {{reflist}}
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| *{{cite book
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| |author=Clark, I.D. and Fritz, P
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| |year=1997
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| |title=Environmental Isotopes in Hydrogeology
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| |publisher=[[CRC Press]]
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| |isbn=1-56670-249-6
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| }}
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| *{{cite journal
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| |author=Schmidt, G.A.
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| |year=1999
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| |url=http://www.agu.org/pubs/crossref/1999/1999PA900025.shtml
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| |title=Forward Modeling of Carbonate Proxy Data from Planktonic Foraminifera Using Oxygen Isotope Tracers in a Global Ocean Model
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| |journal=[[Paleoceanography (journal)|Paleoceanography]]
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| |volume=14 |pages=482–497
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| |doi=10.1029/1999PA900025
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| |bibcode=1999PalOc..14..482S
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| |issue=4
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| }}
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| {{DEFAULTSORT:Delta18O}}
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| [[Category:Bioindicators]]
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| [[Category:Oxygen]]
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| [[Category:Isotopes of oxygen]]
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| [[Category:Environmental isotopes]]
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| [[Category:Geochemistry]]
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Greetings. Let me start by telling you the writer's title - Phebe. For a while she's been in South Dakota. Hiring is his profession. One of the things he loves most is ice skating but he is having difficulties to find time for it.
Have a look at my page: www.Videokeren.com