Isotope analysis
Isotopic oxygen is incorporated into the body primarily through ingestion at which point it is used in the formation of, for archaeological purposes, bones and teeth.
Although the rate of turnover of isotopic oxygen in hydroxyapatite is not fully known, it is assumed to be similar to that of collagen; approximately 10 years.
Teeth are not subject to continual remodelling and so their isotopic oxygen ratios remain constant from the time of formation.
Archaeological materials, such as bone, organic residues, hair, or sea shells, can serve as substrates for isotopic analysis.
A complication is that enrichment also occurs as a result of environmental factors, such as wetland denitrification, salinity, aridity, microbes, and clearance.
[7] δ13C and δ15N measurements on medieval manor soils has shown that stable isotopes can differentiate between crop cultivation and grazing activities, revealing land use types such as cereal production and the presence of fertilization practices at historical sites.
[8] To obtain an accurate picture of palaeodiets, it is important to understand processes of diagenesis that may affect the original isotopic signal.
A wide range of archaeological materials such as metals, glass and lead-based pigments have been sourced using isotopic characterization.
[9] Particularly in the Bronze Age Mediterranean, lead isotope analysis has been a useful tool for determining the sources of metals and an important indicator of trade patterns.
The ratio of the two isotopes may be altered by biological and geophysical processes, and these differences can be utilized in a number of ways by ecologists.
The main elements used in isotope ecology are carbon, nitrogen, oxygen, hydrogen and sulfur, but also include silicon, iron, and strontium.
Certain isotopes can signify distinct primary producers forming the bases of food webs and trophic level positioning.
The stable isotope compositions are expressed in terms of delta values (δ) in permil (‰), i.e. parts per thousand differences from a standard.
Muscle or protein fractions have become the most common animal tissue used to examine the isotopes because they represent the assimilated nutrients in their diet.
Hydrogen isotopes in plant tissue are correlated with local water values but vary based on fractionation during photosynthesis, transpiration, and other processes in the formation of cellulose.
[14] Hydrogen isotope ratios in animal tissue reflect diet, including drinking water, and have been used to study bird migration[15] and aquatic food webs.
[16][17] Carbon isotopes aid us in determining the primary production source responsible for the energy flow in an ecosystem.
δ13C has been used in determining migration of juvenile animals from sheltered inshore areas to offshore locations by examining the changes in their diets.
[20] In addition to trophic positioning of organisms, δ15N values have become commonly used in distinguishing between land derived and natural sources of nutrients.
Thus, due to bacteria's preference when performing biogeochemical processes such as denitrification and volatilization of ammonia, 14N is removed from the water at a faster rate than 15N, resulting in more 15N entering the aquifer.
[citation needed] Isotope analysis can be used by forensic investigators to determine whether two or more samples of explosives are of a common origin.
Most high explosives contain carbon, hydrogen, nitrogen and oxygen atoms and thus comparing their relative abundances of isotopes can reveal the existence of a common origin.
[34][35][36] The ratio of 18O to 16O in ice and deep sea cores is temperature dependent, and can be used as a proxy measure for reconstructing climate change.
Organisms such as foraminifera which combine oxygen dissolved in the surrounding water with carbon and calcium to build their shells therefore incorporate the temperature-dependent 18O to 16O ratio.
When these organisms die, they settle out on the sea bed, preserving a long and invaluable record of global climate change through much of the Quaternary.
