View source for Isotopic signature

{{short description|Mathematical ratio used in analysis of radioactive materials}}
An '''isotopic signature''' (also '''isotopic fingerprint''') is a ratio of non-radiogenic '[[Stable isotope ratio|stable isotopes]]', stable [[Radiogenic nuclide|radiogenic isotopes]], or unstable [[radioactive]] isotopes of particular elements in an investigated material. The ratios of isotopes in a sample material are measured by [[isotope-ratio mass spectrometry]] against an [[Reference Materials for Stable Isotope Analysis|isotopic reference material]]. This process is called [[isotope analysis]].

==Stable isotopes==
The [[atomic mass]] of different isotopes affect their [[chemical kinetics|chemical kinetic]] behavior, leading to natural [[isotope separation]] processes.

===Carbon isotopes===
{{Hatnote|1=Main article: [[δ13C|δ<sup>13</sup>C]]}} <!--Can't get superscript to work otherwise with template: {{Main article|δ13C}} -->

{{Algal carbon isotopes}}
For example, different sources and sinks of [[methane]] have different affinity for the [[Carbon-12|<sup>12</sup>C]] and [[carbon-13|<sup>13</sup>C]] isotopes, which allows distinguishing between different sources by the <sup>13</sup>C/<sup>12</sup>C ratio in methane in the air. In [[geochemistry]], [[paleoclimatology]] and [[paleoceanography]] this ratio is called [[Δ13C|δ<sup>13</sup>C]]. The ratio is calculated with respect to [[Δ13C#Reference standard|Pee Dee Belemnite]] (PDB) [[Reference Materials for Stable Isotope Analysis|standard]]:

:<math chem>\delta \ce{^{13}C}_\mathrm{sample} = \left(\frac{\ce{^{13}C/^{12}C}_\ce{sample}}{\ce{^{13}C/^{12}C}_\mathrm{standard}} - 1\right) \cdot 1000</math> ‰

Similarly, carbon in inorganic [[carbonate]]s shows little isotopic fractionation, while carbon in materials originated by [[photosynthesis]] is depleted of the heavier isotopes. In addition, there are two types of plants with different biochemical pathways; the [[C3 carbon fixation]], where the isotope separation effect is more pronounced, [[C4 carbon fixation]], where the heavier <sup>13</sup>C is less depleted, and [[Crassulacean Acid Metabolism]] (CAM) plants, where the effect is similar but less pronounced than with C<sub>4</sub> plants. Isotopic fractionation in plants is caused by physical (slower diffusion of <sup>13</sup>C in plant tissues due to increased atomic weight) and biochemical (preference of <sup>12</sup>C by two enzymes: [[RuBisCO]] and [[phosphoenolpyruvate carboxylase]]) factors.<ref>{{cite book |url=https://books.google.com/books?id=RXX8FwhAsngC&pg=PA411 |first=Park S. |last=Nobel |title=Physicochemical and Environmental Plant Physiology |date=7 February 2005 |page=411|publisher=Academic Press |isbn=978-0-12-520026-4 }}</ref> The different isotope ratios for the two kinds of plants propagate through the [[food chain]], thus it is possible to determine if the principal diet of a human or an animal consists primarily of C<sub>3</sub> plants ([[rice]], [[wheat]], [[soybeans]], [[potato]]es) or C<sub>4</sub> plants ([[maize|corn]], or [[corn-fed beef]]) by [[isotope analysis]] of their flesh and bone collagen (however, to obtain more accurate determinations, carbon isotopic fractionation must be also taken into account, since several studies have reported significant <sup>13</sup>C discrimination during biodegradation of simple and complex substrates).<ref name="FernandezCadisch2003">{{cite journal|last1=Fernandez|first1=Irene|last2=Cadisch|first2=Georg|title=Discrimination against13C during degradation of simple and complex substrates by two white rot fungi|journal=Rapid Communications in Mass Spectrometry|volume=17|issue=23|year=2003|pages=2614–2620|issn=0951-4198|doi=10.1002/rcm.1234|pmid=14648898|bibcode=2003RCMS...17.2614F}}</ref><ref name="FernandezMahieu2003">{{cite journal|last1=Fernandez|first1=I.|last2=Mahieu|first2=N.|last3=Cadisch|first3=G.|title=Carbon isotopic fractionation during decomposition of plant materials of different quality|journal=Global Biogeochemical Cycles|volume=17|issue=3|year=2003|pages=n/a|issn=0886-6236|doi=10.1029/2001GB001834|bibcode = 2003GBioC..17.1075F |doi-access=free}}</ref>
Within C3 plants processes regulating changes in δ<sup>13</sup>C are well understood, particularly at the leaf level,<ref name="FarquharEhleringer1989">{{cite journal|last1=Farquhar|first1=G D|last2=Ehleringer|first2=J R|last3=Hubick|first3=K T|title=Carbon Isotope Discrimination and Photosynthesis|journal=Annual Review of Plant Physiology and Plant Molecular Biology|volume=40|issue=1|year=1989|pages=503–537|issn=1040-2519|doi=10.1146/annurev.pp.40.060189.002443|s2cid=12988287}}</ref> but also during wood formation.<ref name="McCarrollLoader2004">{{cite journal|last1=McCarroll|first1=Danny|last2=Loader|first2=Neil J.|title=Stable isotopes in tree rings|journal=Quaternary Science Reviews|volume=23|issue=7–8|year=2004|pages=771–801|issn=0277-3791|doi=10.1016/j.quascirev.2003.06.017|bibcode = 2004QSRv...23..771M |citeseerx=10.1.1.336.2011}}</ref><ref name="Eweda Silveira Lobo Sternberg1999">{{cite journal|last1=Ewe|first1=Sharon M.L|last2=da Silveira Lobo Sternberg|first2=Leonel|last3=Busch|first3=David E|title=Water-use patterns of woody species in pineland and hammock communities of South Florida|journal=Forest Ecology and Management|volume=118|issue=1–3|year=1999|pages=139–148|issn=0378-1127|doi=10.1016/S0378-1127(98)00493-9|doi-access=free|bibcode=1999ForEM.118..139E }}</ref> Many recent studies combine leaf level isotopic fractionation with annual patterns of wood formation (i.e. tree ring δ<sup>13</sup>C) to quantify the impacts of climatic variations and atmospheric composition<ref name="CabaneiroFernandez2015">{{cite journal|last1=Cabaneiro|first1=Ana|last2=Fernandez|first2=Irene|title=Disclosing biome sensitivity to atmospheric changes: Stable C isotope ecophysiological dependences during photosynthetic uptake in Maritime pine and Scots pine ecosystems from southwestern Europe|journal=Environmental Technology & Innovation|volume=4|year=2015|pages=52–61|issn=2352-1864|doi=10.1016/j.eti.2015.04.007|doi-access=free}}</ref> on physiological processes of individual trees and forest stands.<ref name="SilvaAnand2013">{{cite journal|last1=Silva|first1=Lucas C. R.|last2=Anand|first2=Madhur|last3=Shipley|first3=Bill|title=Probing for the influence of atmospheric CO2and climate change on forest ecosystems across biomes|journal=Global Ecology and Biogeography|volume=22|issue=1|year=2013|pages=83–92|issn=1466-822X|doi=10.1111/j.1466-8238.2012.00783.x|bibcode=2013GloEB..22...83S }}</ref> The next phase of understanding, in terrestrial ecosystems at least, seems to be the combination of multiple isotopic proxies to decipher interactions between plants, soils and the atmosphere, and predict how changes in land use will affect climate change.<ref name="Gómez-GuerreroSilva2013">{{cite journal|last1=Gómez-Guerrero|first1=Armando|last2=Silva|first2=Lucas C. R.|last3=Barrera-Reyes|first3=Miguel|last4=Kishchuk|first4=Barbara|last5=Velázquez-Martínez|first5=Alejandro|last6=Martínez-Trinidad|first6=Tomás|last7=Plascencia-Escalante|first7=Francisca Ofelia|last8=Horwath|first8=William R.|title=Growth decline and divergent tree ring isotopic composition (δ13C and δ18O) contradict predictions of CO2 stimulation in high altitudinal forests|journal=Global Change Biology|volume=19|issue=6|year=2013|pages=1748–1758|issn=1354-1013|doi=10.1111/gcb.12170|pmid=23504983|bibcode=2013GCBio..19.1748G|s2cid=39714321 }}</ref>
Similarly, marine fish contain more <sup>13</sup>C than freshwater fish, with values approximating the C<sub>4</sub> and C<sub>3</sub> plants respectively.<!--bones are composed of an inorganic matrix and organic collagen -->

The ratio of carbon-13 and carbon-12 isotopes in these types of plants is as follows:<ref>{{Cite journal| last1 = O'Leary | first1 = M. H.| title = Carbon Isotopes in Photosynthesis| jstor = 1310735| journal = BioScience| volume = 38| issue = 5| pages = 328–336| year = 1988| doi = 10.2307/1310735| s2cid = 29110460}}</ref>
* C<sub>4</sub> plants: {{val|-16 |to| -10 |u=‰}}
* CAM plants: {{val|-20 |to| -10 |u=‰}}
* C<sub>3</sub> plants: {{val|-33 |to| -24 |u=‰}}

[[Limestone]]s formed by precipitation in [[sea]]s from the atmospheric carbon dioxide contain normal proportion of <sup>13</sup>C. Conversely, [[calcite]] found in [[salt dome]]s originates from carbon dioxide formed by [[oxidation]] of [[petroleum]], which due to its plant origin is <sup>13</sup>C-depleted. The layer of limestone deposited at the Permian extinction 252 Mya can be identified by the 1% drop in <sup>13</sup>C/<sup>12</sup>C.

The [[carbon-14|<sup>14</sup>C isotope]] is important in distinguishing [[biosynthetized]] materials from man-made ones. [[Biogenic]] chemicals are derived from biospheric carbon, which contains <sup>14</sup>C. Carbon in artificially made chemicals is usually derived from [[fossil fuel]]s like [[coal]] or [[petroleum]], where the <sup>14</sup>C originally present has decayed below detectable limits. The amount of <sup>14</sup>C currently present in a sample therefore indicates the proportion of carbon of biogenic origin.

===Nitrogen isotopes===
{{hatnote|1=Main article: [[δ15N|δ<sup>15</sup>N]]}}
[[Isotopes of nitrogen#Nitrogen-15|Nitrogen-15]], or <sup>15</sup>N, is often used in [[agriculture|agricultural]] and [[medicine|medical]] research, for example in the [[Meselson–Stahl experiment]] to establish the nature of [[DNA replication]].<ref>{{cite journal | last1 = Meselson |first1=M. |last2=Stahl |first2=F. W. | year = 1958 | title = The replication of DNA in ''E. coli'' | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 44 | issue = 7| pages = 671–682 | pmc=528642|doi=10.1073/pnas.44.7.671 | pmid=16590258|bibcode = 1958PNAS...44..671M |doi-access=free }}</ref> An extension of this research resulted in development of DNA-based stable-isotope probing, which allows examination of links between [[metabolic]] function and [[Taxonomy (biology)|taxonomic]] identity of [[microorganisms]] in the environment, without the need for [[Microbiological culture|culture]] isolation.<ref>{{cite journal |last1 = Radajewski |first1=S. |last2=McDonald |first2=I. R. |last3=Murrell |first3=J. C. | year = 2003 | title = Stable-isotope probing of nucleic acids: a window to the function of uncultured microorganisms | journal = Current Opinion in Biotechnology | volume = 14 | issue = 3| pages = 296–302 | doi=10.1016/s0958-1669(03)00064-8|pmid=12849783 }}</ref><ref>{{cite journal | last1 = Cupples | first1 = A. M. | last2 = Shaffer | first2 = E. A. | last3 = Chee-Sanford | first3 = J. C. | last4 = Sims | first4 = G. K. | year = 2007 | title = DNA buoyant density shifts during <sup>15</sup>N DNA stable isotope probing | journal = Microbiological Research | volume = 162 | issue = 4| pages = 328–334 | doi=10.1016/j.micres.2006.01.016| pmid = 16563712 | doi-access = free }}</ref> [[Proteins]] can be isotopically labelled by cultivating them in a medium containing <sup>15</sup>N as the only source of nitrogen, e.g., in quantitative [[proteomics]] such as [[SILAC]].

Nitrogen-15 is extensively used to trace [[Ammoniacal nitrogen#Mineral nitrogen|mineral nitrogen]] compounds (particularly [[fertilizers]]) in the environment.<ref>{{cite journal |last1=Janovský |first1=Martin |title=Stable isotope analysis in soil prospection reveals the type of historic land ‑ use under contemporary temperate forests in Europe |journal=Scientific Reports |volume=14 |doi=10.1038/s41598-024-63563-1|pmc=11208554 }}</ref>  When combined with the use of other isotopic labels, <sup>15</sup>N is also a very important [[Isotopic tracer|tracer]] for describing the fate of nitrogenous [[Persistent organic pollutant|organic pollutants]].<ref>{{cite journal | last1 = Marsh | first1 = K. L. | last2 = Sims | first2 = G. K. | last3 = Mulvaney | first3 = R. L. | year = 2005 | title = Availability of urea to autotrophic ammonia-oxidizing bacteria as related to the fate of <sup>14</sup>C- and <sup>15</sup>N-labeled urea added to soil | journal = Biology and Fertility of Soils | volume = 42 | issue = 2| pages = 137–145 | doi=10.1007/s00374-005-0004-2| bibcode = 2005BioFS..42..137M | s2cid = 6245255 }}</ref><ref>{{cite journal | last1 = Bichat | first1 = F. | last2 = Sims | first2 = G. K. | last3 = Mulvaney | first3 = R. L. | year = 1999 | title = Microbial utilization of heterocyclic nitrogen from atrazine | journal = Soil Science Society of America Journal | volume = 63 | issue = 1| pages = 100–110 | doi=10.2136/sssaj1999.03615995006300010016x| bibcode = 1999SSASJ..63..100B }}</ref> [[Nitrogen-15 tracing]] is an important method used in [[biogeochemistry]].

The ratio of stable nitrogen isotopes, <sup>15</sup>N/[[Isotopes of nitrogen#Nitrogen-14|<sup>14</sup>N]] or [[δ15N|δ<sup>15</sup>N]], tends to increase with [[trophic level]], such that [[herbivore]]s have higher nitrogen isotope values than [[plant]]s, and [[carnivore]]s have higher nitrogen isotope values than herbivores. Depending on the [[Tissue (biology)|tissue]] being examined, there tends to be an increase of 3-4 parts per thousand with each increase in trophic level.<ref name="Adams">{{Cite journal
 |last1        = Adams
 |first1       = Thomas S.
 |last2       = Sterner
 |first2      = Robert W.
 |date        = 2000
 |title       = The effect of dietary nitrogen content on trophic level <sup>15</sup>N enrichment
 |journal     = Limnol. Oceanogr.
 |volume      = 45
 |issue       = 3
 |pages       = 601–607
 |doi         = 10.4319/lo.2000.45.3.0601
 |bibcode     = 2000LimOc..45..601A
 |doi-access= free
 }}</ref> The tissues and [[hair]] of [[vegan]]s therefore contain significantly lower δ<sup>15</sup>N than the bodies of people who eat mostly meat. Similarly, a terrestrial diet produces a different signature than a marine-based diet. Isotopic [[hair analysis|analysis of hair]] is an important source of information for [[archaeology|archaeologists]], providing clues about the ancient diets and differing cultural attitudes to food sources.<ref>{{cite journal |doi=10.1073/pnas.0903821106 |title=Isotopic evidence for the diets of European Neanderthals and early modern humans |year=2009 |last1=Richards |first1=M. P. |last2=Trinkaus |first2=E. |journal=Proceedings of the National Academy of Sciences |volume=106 |issue=38 |pages=16034–16039 |pmid=19706482 |pmc=2752538 |doi-access=free |bibcode=2009PNAS..10616034R }}</ref>

A number of other environmental and physiological factors can influence the nitrogen isotopic composition at the base of the [[food web]] (i.e. in plants) or at the level of individual animals. For example, in arid regions, the [[nitrogen cycle]] tends to be more 'open' and prone to the loss of <sup>14</sup>N, increasing δ<sup>15</sup>N in soils and plants.<ref name="Handley">{{Cite journal |last1=Handley |first1=L.L |last2=Austin |first2=A. T. |last3=Stewart |first3=G.R. |last4=Robinson |first4=D. |last5=Scrimgeour |first5=C.M. |last6=Raven |first6=J.A. |last7=Heaton |first7=T.H.E. |last8=Schmidt |first8=S. |year=1999 |title=The 15N natural abundance (δ15N) of ecosystem samples reflects measures of water availability |journal=Aust. J. Plant Physiol. |issn=0310-7841 |volume=26 |issue=2 |pages=185–199 |doi=10.1071/pp98146}}{{closed access}}</ref> This leads to relatively high δ<sup>15</sup>N values in plants and animals in hot and arid ecosystems relative to cooler and moister ecosystems.<ref name="Szpak2013PLoSOne">{{Cite journal |last1=Szpak |first1=Paul |last2=White |first2=Christine D. |last3=Longstaffe |first3=Fred J. |last4=Millaire |first4=Jean-Francois |last5=Vásquez Sánchez |first5=Victor F. |year=2013 |title=Carbon and Nitrogen Isotopic Survey of Northern Peruvian Plants: Baselines for Paleodietary and Paleoecological Studies |journal=[[PLOS ONE]] |volume=8 |issue=1 |pages=e53763 |doi=10.1371/journal.pone.0053763 |pmid=23341996 |pmc=3547067 |bibcode = 2013PLoSO...853763S |doi-access=free }}</ref> Furthermore, elevated δ<sup>15</sup>N have been linked to the preferential excretion of 14N and reutilization of already enriched 15N tissues in the body under prolonged water stress conditions or insufficient protein intake.<ref>{{cite journal | last1 = Ambrose | first1 = Stanley H. | last2 = DeNiro | first2 = Michael J. | year = 1986 | title = The isotopic ecology of East African mammals | journal = Oecologia | volume = 69 | issue = 3| pages = 395–406 | doi = 10.1007/bf00377062 | pmid = 28311342 | bibcode = 1986Oecol..69..395A | s2cid = 22660367 }}</ref><ref>{{cite journal | last1 = Hobson | first1 = Keith A. | last2 = Alisauskas | first2 = Ray T. | last3 = Clark | first3 = Robert G. | year = 1993 | title = Stable-Nitrogen Isotope Enrichment in Avian Tissues Due to Fasting and Nutritional Stress: Implications for Isotopic Analyses of Diet | journal = The Condor | volume = 95 | issue = 2| page = 388 | doi = 10.2307/1369361 | jstor = 1369361 }}</ref>

δ<sup>15</sup>N also provides a diagnostic tool in [[planetary science]] as the ratio exhibited in atmospheres and surface materials "is closely tied to the conditions under which materials form".<ref name="NASA-201450623">{{cite press release |last1=Dyches |first1=Preston |last2=Clavin |first2=Whitney |title=Titan's Building Blocks Might Pre-date Saturn |url=http://www.jpl.nasa.gov/news/news.php?release=2014-200 |date=June 23, 2014 |publisher=[[Jet Propulsion Laboratory]] |access-date=June 28, 2014 }}</ref>

===Oxygen isotopes===
{{hatnote|1=Main article: [[δ18O|δ<sup>18</sup>O]]}}
Oxygen occurs naturally in three variants, but [[oxygen-17|<sup>17</sup>O]] is so rare that it is very difficult to detect (~0.04% abundant).<ref name="iupac_abundance">{{CIAAW2003}}</ref> The ratio of [[oxygen-18|<sup>18</sup>O]]/[[oxygen-16|<sup>16</sup>O]] in water depends on the amount of evaporation the water experienced (as <sup>18</sup>O is heavier and therefore less likely to vaporize). As the vapor tension depends on the concentration of dissolved salts, the <sup>18</sup>O/<sup>16</sup>O ratio shows correlation on the [[salinity]] and temperature of water. As oxygen is incorporated into the shells of [[calcium carbonate]]-secreting organisms, such sediments provide a chronological record of temperature and salinity of the water in the area.

The oxygen isotope ratio in the atmosphere varies predictably with time of year and geographic location; e.g. there is a 2% difference between <sup>18</sup>O-rich precipitation in Montana and <sup>18</sup>O-depleted precipitation in Florida Keys. This variability can be used for approximate determination of geographic location of origin of a material; e.g. it is possible to determine where a shipment of [[uranium oxide]] was produced. The rate of exchange of surface isotopes with the environment has to be taken in account.<ref name="nucfor">{{cite book |url=https://books.google.com/books?id=W3FnEOg8tS4C&pg=PA399 |title=Nuclear Forensic Analysis |first1=Kenton J. |last1=Moody |first2=Ian D. |last2=Hutcheon |first3=Patrick M. |last3=Grant |date=28 February 2005 |page=399|publisher=CRC Press |isbn=978-0-203-50780-3 }}</ref>

The oxygen isotopic signatures of solid samples (organic and inorganic) are usually measured with [[pyrolysis]] and [[mass spectrometry]].<ref name=":0">{{Cite journal|last1=Tsang|first1=Man-Yin|last2=Yao|first2=Weiqi|last3=Tse|first3=Kevin|date=2020|editor-last=Kim|editor-first=Il-Nam|title=Oxidized silver cups can skew oxygen isotope results of small samples|journal=Experimental Results|language=en|volume=1|pages=e12|doi=10.1017/exp.2020.15|issn=2516-712X|doi-access=free}}</ref> Improper or prolonged storage of samples can lead to inaccurate measurements.<ref name=":0" />

=== Sulfur Isotopes ===
{{hatnote|1=Main article: [[δ34S|δ<sup>34</sup>S]], [[Isotopes of sulfur]]}}
Sulfur has four stable isotopes, <sup>32</sup>[[Sulfur|S]], <sup>33</sup>S, <sup>34</sup>S, and <sup>36</sup>S, of which <sup>32</sup>S is the most abundant by a large margin due to the fact it is [[Silicon-burning process|created by the very common <sup>12</sup>C in supernovas]]. Sulfur isotope ratios are almost always expressed as ratios relative to <sup>32</sup>S due to this major relative abundance (95.0%). Sulfur isotope fractionations are usually measured in terms of [[Δ34S|δ<sup>34</sup>S]] due to its higher abundance (4.25%) compared to the [[Isotopes of sulfur|other stable isotopes of sulfur]], though δ<sup>33</sup>S is also sometimes measured. Differences in sulfur isotope ratios are thought to exist primarily due to [[kinetic fractionation]] during reactions and transformations.

Sulfur isotopes are generally measured against standards; prior to 1993, the [[Canyon Diablo (meteorite)|Canyon Diablo]] [[troilite]] standard (abbreviated to [[Canyon Diablo Troilite|CDT]]), which has a <sup>32</sup>S:<sup>34</sup>S equal to 22.220, was used as both a reference material and the zero point for the isotopic scale. Since 1993, the Vienna-CDT standard has been used as a zero point, and there are several materials used as [[Reference materials for stable isotope analysis|reference materials for sulfur isotope measurements]]. Sulfur fractionations by natural processes measured against these standards have been shown to exist between −72‰ and +147‰,<ref name=":02">{{Cite journal |last1=Lever |first1=Mark A. |last2=Rouxel |first2=Olivier |last3=Alt |first3=Jeffrey C. |last4=Shimizu |first4=Nobumichi |last5=Ono |first5=Shuhei |last6=Coggon |first6=Rosalind M. |last7=Shanks |first7=Wayne C. |last8=Lapham |first8=Laura |last9=Elvert |first9=Marcus |last10=Prieto-Mollar |first10=Xavier |last11=Hinrichs |first11=Kai-Uwe |date=2013-03-01 |title=Evidence for Microbial Carbon and Sulfur Cycling in Deeply Buried Ridge Flank Basalt |url=https://archimer.ifremer.fr/doc/00176/28767/ |journal=Science |language=en |volume=339 |issue=6125 |pages=1305–1308 |doi=10.1126/science.1229240 |pmid=23493710 |bibcode=2013Sci...339.1305L |s2cid=10728606 |issn=0036-8075}}</ref><ref name=":1">{{Cite journal |last1=Drake |first1=Henrik |last2=Roberts |first2=Nick M. W. |last3=Reinhardt |first3=Manuel |last4=Whitehouse |first4=Martin |last5=Ivarsson |first5=Magnus |last6=Karlsson |first6=Andreas |last7=Kooijman |first7=Ellen |last8=Kielman-Schmitt |first8=Melanie |date=2021-06-03 |title=Biosignatures of ancient microbial life are present across the igneous crust of the Fennoscandian shield |journal=Communications Earth & Environment |language=en |volume=2 |issue=1 |pages=1–13 |doi=10.1038/s43247-021-00170-2 |s2cid=235307116 |issn=2662-4435|doi-access=free }}</ref> as calculated by the following equation:

<math chem display="block">\delta \ce{^{34}S}_\mathrm{sample} = \left(\frac{\ce{^{34}S/^{32}S}_\ce{sample}}{\ce{^{34}S/^{32}S}_\mathrm{standard}} - 1\right) \cdot 1000</math>
<div style=display:inline-table>
{| class="wikitable"
|+Natural sulfur isotope values
!Natural Source
![[Δ34S|δ<sup>34</sup>S]] range
|-
|Petroleum<ref>{{Citation |last=Hannan |first=Keith |title=Sulfur isotopes in geochemistry |date=1998 |work=Geochemistry |series=Encyclopedia of Earth Science |pages=610–615 |place=Dordrecht |publisher=Springer Netherlands |language=en |doi=10.1007/1-4020-4496-8_309 |isbn=978-1-4020-4496-0 }}</ref>
| {{val|-32 |to| -8|u=‰}}
|-
|River water<ref name=":12">{{Cite book |series=Springer Textbooks in Earth Sciences, Geography and Environment |year=2021 |url=https://link.springer.com/content/pdf/10.1007/978-3-030-77692-3.pdf |language=en-gb |doi=10.1007/978-3-030-77692-3|isbn=978-3-030-77691-6 |s2cid=238480248 |title=Stable Isotope Geochemistry }}</ref>
| {{val|-8| to| 10|u=‰}}
|-
|Lunar rocks<ref name=":12" />
| {{val|-2| to |2.5|u=‰}}
|-
|Meteorites<ref name=":12" />
| {{val|0| to |2|u=‰}}
|-
|Ocean water<ref name=":12" />
| {{val|17| to |20|u=‰}}
|}
</div> 
<div style=display:inline-table>
{| class="wikitable"
|+Most relevant isotopes of sulfur
![[Isotope]]
!Abundance
![[Half-life]]
|-
|<sup>32</sup>S
|94.99%
|Stable
|-
|<sup>33</sup>S
|0.75%
|Stable
|-
|<sup>34</sup>S
|4.25%
|Stable
|-
|<sup>35</sup>S
|<0.1%
|87.4 days
|-
|<sup>36</sup>S
|0.01%
|Stable
|}
</div>

As a very [[Redox|redox-active]] element, sulfur can be useful for recording major chemistry-altering events throughout [[History of Earth|Earth's history]], such as marine [[evaporite]]s which reflect the change in the atmosphere's redox state brought about by the [[Great Oxidation Event|Oxygen Crisis]].<ref name=":22">{{Cite journal |last=Seal |first=Robert R. II |date=2006-01-01 |title=Sulfur Isotope Geochemistry of Sulfide Minerals |journal=Reviews in Mineralogy and Geochemistry |volume=61 |issue=1 |pages=633–677 |doi=10.2138/rmg.2006.61.12 |bibcode=2006RvMG...61..633S |issn=1529-6466}}</ref><ref name=":3">{{Cite journal |last1=Farquhar |first1=James |last2=Bao |first2=Huiming |last3=Thiemens |first3=Mark |date=2000-08-04 |title=Atmospheric Influence of Earth's Earliest Sulfur Cycle |url=https://www.science.org/doi/10.1126/science.289.5480.756 |journal=Science |language=en |volume=289 |issue=5480 |pages=756–758 |doi=10.1126/science.289.5480.756 |pmid=10926533 |bibcode=2000Sci...289..756F |issn=0036-8075}}</ref>

==Radiogenic isotopes==

===Lead isotopes===
Lead consists of four stable [[isotopes of lead|isotopes]]: <sup>204</sup>Pb, <sup>206</sup>Pb, <sup>207</sup>Pb, and <sup>208</sup>Pb. Local variations in [[uranium]]/[[thorium]]/[[lead]] content cause a wide location-specific variation of isotopic ratios for lead from different localities. Lead emitted to the atmosphere by industrial processes has an isotopic composition different from lead in minerals. Combustion of [[gasoline]] with [[tetraethyllead]] additive led to formation of ubiquitous micrometer-sized lead-rich [[particulate]]s in car exhaust [[smoke]]; especially in urban areas the man-made lead particles are much more common than natural ones. The differences in isotopic content in particles found in objects can be used for approximate geolocation of the object's origin.<ref name="nucfor"/>

==Radioactive isotopes==
[[Hot particle]]s, radioactive particles of [[nuclear fallout]] and [[radioactive waste]], also exhibit distinct isotopic signatures. Their radionuclide composition (and thus their age and origin) can be determined by [[mass spectrometry]] or by [[gamma ray spectrometer|gamma spectrometry]]. For example, particles generated by a nuclear blast contain detectable amounts of <sup>60</sup>[[Cobalt|Co]] and <sup>152</sup>[[Europium|Eu]]. The [[Chernobyl accident]] did not release these particles but did release <sup>125</sup>[[Antimony|Sb]] and <sup>144</sup>[[Cerium|Ce]]. Particles from underwater bursts will consist mostly of irradiated sea salts. Ratios of <sup>152</sup>[[Europium|Eu]]/<sup>155</sup>Eu, <sup>154</sup>Eu/<sup>155</sup>Eu, and <sup>238</sup>[[Plutonium|Pu]]/<sup>239</sup>Pu are also different for fusion and fission [[nuclear weapon]]s, which allows identification of hot particles of unknown origin.

Uranium has a relatively constant isotope ratio in all natural samples with ~0.72% {{chem|235|U}}, some 55&nbsp;[[parts per million|ppm]] {{chem|234|U}} (in [[secular equilibrium]] with its [[parent nuclide]] {{chem|238|U}}), and the balance made up by {{chem|238|U}}. Isotopic compositions that diverge significantly from those values are evidence for the uranium having been subject to depletion or [[uranium enrichment|enrichment]] in some fashion or of (part of it) having participated in a nuclear fission reaction. While the latter is almost as universally due to human influence as the former two, the [[natural nuclear fission reactor]] at [[Oklo]], Gabon was detected through a significant diversion of {{chem|235|U}} concentration in samples from Oklo compared to those of all other known deposits on earth. Given that {{chem|235|U}} is a [[special nuclear material|material of proliferation concern]] then as now every [[International Atomic Energy Agency|IAEA]]-approved supplier of Uranium fuel keeps track of the isotopic composition of uranium to ensure none is diverted for nefarious purposes. It would thus become apparent quickly if another Uranium deposit besides Oklo proves to have once been a natural nuclear fission reactor.

==Applications==

===Archaeological studies===
In archaeological studies, stable isotope ratios have been used to track diet within the time span formation of analyzed tissues (10–15 years for bone collagen and intra-annual periods for tooth enamel bioapatite) from individuals; "recipes" of foodstuffs (ceramic vessel residues); locations of cultivation and types of plants grown (chemical extractions from sediments); and migration of individuals (dental material).{{citation needed|date=March 2018}}

===Forensics===
With the advent of stable [[isotope ratio mass spectrometry]], isotopic signatures of materials find increasing use in [[forensics]], distinguishing the origin of otherwise similar materials and tracking the materials to their common source. For example, the isotope signatures of plants can be to a degree influenced by the growth conditions, including moisture and nutrient availability. In case of synthetic materials, the signature is influenced by the conditions during the chemical reaction. The isotopic signature profiling is useful in cases where other kinds of profiling, e.g. characterization of [[impurities]], are not optimal. Electronics coupled with scintillator detectors are routinely used to evaluate isotope signatures and identify unknown sources.

A study was published demonstrating the possibility of determination of the origin of a common brown [[pressure sensitive adhesive|PSA]] [[packaging tape]] by using the carbon, oxygen, and hydrogen isotopic signature of the backing polymer, additives, and [[adhesive]].<ref>{{cite journal | last1 = Carter | first1 = James F. | last2 = Grundy | first2 = Polly L. | last3 = Hill | first3 = Jenny C. | last4 = Ronan | first4 = Neil C. | last5 = Titterton | first5 = Emma L. | last6 = Sleeman | first6 = Richard | year = 2004 | title = Forensic isotope ratio mass spectrometry of packaging tapes | journal = Analyst | volume = 129 | issue = 12| pages = 1206–1210 | doi = 10.1039/b409341k | pmid = 15565219 | bibcode = 2004Ana...129.1206C }}</ref>

Measurement of carbon isotopic ratios can be used for detection of [[adulteration]] of [[honey]]. Addition of sugars originated from corn or sugar cane (C4 plants) skews the isotopic ratio of sugars present in honey, but does not influence the isotopic ratio of proteins; in an unadulterated honey the carbon isotopic ratios of sugars and proteins should match.<ref>{{Cite journal| last1 = González Martín | first1 = I.| last2 = Marqués Macías | first2 = E.| last3 = Sánchez Sánchez | first3 = J.| last4 = González Rivera | first4 = B.| title = Detection of honey adulteration with beet sugar using stable isotope methodology| journal = Food Chemistry| volume = 61| issue = 3| pages = 281–286| year = 1998| doi = 10.1016/S0308-8146(97)00101-5}}</ref> As low as 7% level of addition can be detected.<ref name="honeycouncil.ca">{{cite web |url=http://www.honeycouncil.ca/documents/HivelightsNov2004.pdf |work=Canadian Honey Council |date=November 2004 |volume=17 |number=4 |access-date=30 April 2021 |title=Tracking Nature: Geographical fingerprints in food ingredients add transparency to organic chain|pages=10–11 |archive-url=https://web.archive.org/web/20140101171222/http://www.honeycouncil.ca/documents/HivelightsNov2004.pdf |archive-date=2014-01-01 }}</ref>

Nuclear explosions form [[Beryllium-10|<sup>10</sup>Be]] by a reaction of fast neutrons with <sup>13</sup>C in the carbon dioxide in air. This is one of the historical indicators of past activity at nuclear test sites.<ref>{{cite journal|doi=10.1016/j.jenvrad.2007.07.016|year=2008|author1=Whitehead, Ne |author2=Endo, S |author3=Tanaka, K |author4=Takatsuji, T |author5=Hoshi, M |author6=Fukutani, S |author7=Ditchburn, Rg |author8=Zondervan, A |title=A preliminary study on the use of (10)Be in forensic radioecology of nuclear explosion sites.|volume=99|issue=2|pages=260–70|pmid=17904707|journal=Journal of Environmental Radioactivity}}</ref>

===Solar System origins===
{{Main|Origin of the Moon}}
Isotopic fingerprints are used to study the origin of materials in the Solar System.<ref name=airspace/>  For example, the [[Moon]]'s [[Isotopes of oxygen|oxygen isotopic]] ratios seem to be essentially identical to Earth's.<ref name=wiechert>{{Cite journal | title=Oxygen Isotopes and the Moon-Forming Giant Impact | display-authors=1 | last1=Wiechert | first1=U. | last2=Halliday | first2=A. N. | last3=Lee | first3=D.-C. | last4=Snyder | first4=G. A. | last5=Taylor | first5=L. A. | last6=Rumble | first6=D. | volume=294 | issue=12 | pages=345–348 |date=October 2001 | doi=10.1126/science.1063037 | pmid=11598294 | journal=Science |bibcode = 2001Sci...294..345W | s2cid=29835446 }}</ref> Oxygen isotopic ratios, which may be measured very precisely, yield a unique and distinct signature for each Solar System body.<ref name=scott010312>{{cite journal | url=http://www.psrd.hawaii.edu/Dec01/Oisotopes.html | title=Oxygen Isotopes Give Clues to the Formation of Planets, Moons, and Asteroids | journal=Planetary Science Research Discoveries Report | page=55 | last=Scott | first=Edward R. D. | bibcode=2001psrd.reptE..55S | date=December 3, 2001 | access-date=2014-01-01 }}</ref> Different oxygen isotopic signatures can indicate the origin of material ejected into space.<ref name=moonwalk>{{cite web | url=http://www.geolsoc.org.uk/Geoscientist/Archive/September-2009/Moonwalk | first=Ted | last=Nield | title=Moonwalk | publisher=Geological Society of London | page=8 |date=September 2009 | access-date=2014-01-01 }}</ref> The Moon's [[titanium isotope]] ratio (<sup>50</sup>Ti/<sup>47</sup>Ti) appears close to the Earth's (within 4 ppm).<ref>{{cite journal | title = The proto-Earth as a significant source of lunar material | journal = Nature Geoscience | date = 25 March 2012 | first = Junjun | last = Zhang |author2=Nicolas Dauphas |author3=Andrew M. Davis |author4=Ingo Leya |author5=Alexei Fedkin  | volume = 5 | issue = 4 | pages = 251–255| doi= 10.1038/ngeo1429 |bibcode = 2012NatGe...5..251Z | s2cid = 38921983 }}</ref><ref>{{cite web | url=https://news.uchicago.edu/article/2012/03/28/titanium-paternity-test-fingers-earth-moon-s-sole-parent | title=Titanium paternity test fingers Earth as moon's sole parent | publisher=The University of Chicago | work=Zhang, Junjun | date=March 28, 2012 | author=Koppes, Steve | access-date=2014-01-01}}</ref> In 2013, a study was released that indicated water in lunar magma was 'indistinguishable' from carbonaceous chondrites and nearly the same as Earth's, based on the composition of water isotopes.<ref name=airspace>{{cite web |url=https://www.airspacemag.com/daily-planet/earth-moon-a-watery-double-planet-60919196/ |title=Earth-Moon: A Watery "Double-Planet" |archive-url=https://web.archive.org/web/20130807172422/http://blogs.airspacemag.com/moon/2013/05/earth-moon-a-watery-double-planet/ |archive-date=2013-08-07 |date=May 14, 2013 |first=Paul D. |last=Spudis |access-date=April 30, 2021 }}</ref><ref>{{cite journal |doi=10.1126/science.1235142 |title=Hydrogen Isotopes in Lunar Volcanic Glasses and Melt Inclusions Reveal a Carbonaceous Chondrite Heritage |year=2013 |last1=Saal |first1=A. E. |last2=Hauri |first2=E. H. |last3=Van Orman |first3=J. A. |last4=Rutherford |first4=M. J. |journal=Science |volume=340 |issue=6138 |pages=1317–1320 |pmid=23661641 |bibcode=2013Sci...340.1317S |s2cid=9092975 }}</ref>

=== Records of early life on Earth ===
{{Main|Timeline of the evolutionary history of life}}

[[Isotope geochemistry|Isotope biogeochemistry]] has been used to investigate the timeline surrounding life and its [[Early evolution of life|earliest iterations on Earth]]. Isotopic fingerprints typical of life, preserved in sediments, have been used to suggest, but do not necessarily prove, that life was already in existence on Earth by 3.85 billion years ago.<ref>{{Cite journal |last1=Mojzsis |first1=S. J. |last2=Arrhenius |first2=G. |last3=McKeegan |first3=K. D. |last4=Harrison |first4=T. M. |last5=Nutman |first5=A. P. |last6=Friend |first6=C. R. L. |date=November 1996 |title=Evidence for life on Earth before 3,800 million years ago |url=https://www.nature.com/articles/384055a0 |journal=Nature |language=en |volume=384 |issue=6604 |pages=55–59 |doi=10.1038/384055a0 |pmid=8900275 |bibcode=1996Natur.384...55M |hdl=2060/19980037618 |s2cid=4342620 |issn=1476-4687|hdl-access=free }}</ref>

Sulfur isotope evidence has also been used to corroborate the timing of the [[Great Oxidation Event]], during which the [[Atmosphere of Earth|Earth's atmosphere]] experienced a measurable rise in oxygen (to about 9% of modern values<ref>{{Cite journal |last=Holland |first=Heinrich D |date=2006-06-29 |title=The oxygenation of the atmosphere and oceans |journal=Philosophical Transactions of the Royal Society B: Biological Sciences |volume=361 |issue=1470 |pages=903–915 |doi=10.1098/rstb.2006.1838 |pmc=1578726 |pmid=16754606}}</ref>) for the first time about 2.3–2.4 billion years ago. Mass-independent sulfur isotope fractionations are found to be widespread in the geologic record before about 2.45&nbsp;billion years ago, and these isotopic signatures have since ceded to mass-dependent fractionation, providing strong evidence that the atmosphere shifted from anoxic to oxygenated at that threshold.<ref>{{Cite journal |last1=Papineau |first1=Dominic |last2=Mojzsis |first2=Stephen J. |last3=Schmitt |first3=Axel K. |date=2007-03-15 |title=Multiple sulfur isotopes from Paleoproterozoic Huronian interglacial sediments and the rise of atmospheric oxygen |url=https://www.sciencedirect.com/science/article/pii/S0012821X06008910 |journal=Earth and Planetary Science Letters |language=en |volume=255 |issue=1 |pages=188–212 |doi=10.1016/j.epsl.2006.12.015 |bibcode=2007E&PSL.255..188P |issn=0012-821X}}</ref>

Modern [[sulfate-reducing bacteria]] are known to favorably reduce lighter <sup>32</sup>S instead of <sup>34</sup>S, and the presence of these microorganisms can measurably alter the sulfur isotope composition of the ocean.<ref name=":22"/> Because the δ<sup>34</sup>S values of [[sulfide mineral]]s is primarily influenced by the presence of [[Sulfate-reducing microorganism|sulfate-reducing bacteria]],<ref>{{Cite journal |last=Canfield |first=D. E. |date=2001-01-01 |title=Biogeochemistry of Sulfur Isotopes |journal=Reviews in Mineralogy and Geochemistry |volume=43 |issue=1 |pages=607–636 |doi=10.2138/gsrmg.43.1.607 |bibcode=2001RvMG...43..607C |issn=1529-6466}}</ref> the absence of sulfur isotope fractionations in sulfide minerals suggests the absence of these bacterial processes or the absence of freely available sulfate. Some have used this knowledge of microbial sulfur fractionation to suggest that minerals (namely [[pyrite]]) with large sulfur isotope fractionations relative to the inferred seawater composition may be evidence of life.<ref name=":4">{{Cite journal |last1=Archer |first1=Corey |last2=Vance |first2=Derek |date=2006-03-01 |title=Coupled Fe and S isotope evidence for Archean microbial Fe(III) and sulfate reduction |journal=Geology |volume=34 |issue=3 |pages=153–156 |doi=10.1130/G22067.1 |bibcode=2006Geo....34..153A |issn=0091-7613}}</ref><ref name=":5">{{Cite journal |last1=Wacey |first1=David |last2=McLoughlin |first2=Nicola |last3=Whitehouse |first3=Martin J. |last4=Kilburn |first4=Matt R. |date=2010-12-01 |title=Two coexisting sulfur metabolisms in a ca. 3400 Ma sandstone |journal=Geology |volume=38 |issue=12 |pages=1115–1118 |doi=10.1130/G31329.1 |bibcode=2010Geo....38.1115W |issn=0091-7613}}</ref> This claim is not clear-cut, however, and is sometimes contested using geologic evidence from the ~3.49&nbsp;Ga [[sulfide mineral]]s found in the [[Dresser Formation]] of Western Australia, which are found to have δ<sup>34</sup>S values as negative as −22‰.<ref name=":6">{{Cite journal |last1=Philippot |first1=Pascal |last2=Zuilen |first2=Mark |last3=Lepot |first3=Kevin |last4=Thomazo |first4=Christophe |last5=Farquhar |first5=James |last6=Van Kranendonk |first6=Martin |date=2007-09-14 |title=Early Archaean Microorganisms Preferred Elemental Sulfur, Not Sulfate |url=https://www.researchgate.net/publication/5970453 |journal=Science |volume=317 |issue=5844 |pages=1534–1537 |doi=10.1126/science.1145861|pmid=17872441 |bibcode=2007Sci...317.1534P |s2cid=41254565 }}</ref> Because it has not been proven that the sulfide and barite minerals formed in the absence of major hydrothermal input, it is not conclusive evidence of life or of the microbial sulfate reduction pathway in the Archean.<ref name=":7">{{Cite book |series=Topics in Geobiology |year=2009 |volume=31 |url=https://link.springer.com/content/pdf/10.1007/978-1-4020-9389-0.pdf |language=en-gb |doi=10.1007/978-1-4020-9389-0|isbn=978-1-4020-9388-3 |title=Early Life on Earth }}</ref>

==See also==
*[[Isoscapes]]
*[[Isotope electrochemistry]]
*[[Isotope geochemistry]]
*[[Radiometric dating]]

==References==
{{reflist|30em}}

==Further reading==
* [http://ethomas.web.wesleyan.edu/ees123/carboniso.htm Carbon isotopes: you are what you eat]
* [https://web.archive.org/web/20010221233242/http://www.evsc.virginia.edu/news/esreport99/hair.htm Hair-rising research]
* [https://sites.google.com/site/brianfinucane/ayacuchoarchaeo-isotopeproject Ayacucho Archaeo Isotope Project]
* [https://journals.uair.arizona.edu/index.php/radiocarbon/article/view/2025 The pursuit of isotopic and molecular fire tracers in the polar atmosphere and cryosphere]

[[Category:Radiometric dating]]
[[Category:Bioindicators]]
[[Category:Anthropology]]
[[Category:Isotopes]]
[[Category:Forensic evidence]]