Isotope Diet Analysis

At the Viking burial site of Birka in Sweden, archaeologists found a skeleton buried with a full set of weapons and dismissed for over a century as a male warrior. In 2017, a bone-chemistry test called DNA analysis proved it was a woman. A closely related technique, isotope analysis, has done something just as powerful for Viking-Age skeletons: it can reveal exactly what a person ate, and even where they grew up, just by testing their bones and teeth.

- What an isotope is and why different foods leave different chemical signatures - How carbon and nitrogen isotopes reveal whether a Viking ate mostly land food or seafood - How oxygen and strontium isotopes in tooth enamel reveal where someone was born - How this evidence has changed what historians know about Viking trade and migration

An isotope is a version of an element with a different number of neutrons, giving it slightly different weight. Carbon exists mostly as carbon-12, but a small amount is the heavier carbon-13. As you eat and your bones rebuild themselves over years, the ratio of carbon-13 to carbon-12 in your bone collagen locks in based on what you ate. Marine food chains and land food chains carry different carbon and nitrogen isotope ratios, so a skeleton's bone chemistry is like a decade-long diet diary written in atoms.

Researchers studying skeletons from Viking-Age Scandinavia, roughly 793 to 1066 CE, measure carbon-13 and nitrogen-15 levels in bone collagen. High nitrogen-15 combined with a particular carbon signature points to a diet heavy in fish and marine mammals, common in coastal trading towns like Hedeby and Ribe. Lower marine signatures paired with certain plant-based carbon ratios point to inland farming communities eating mostly barley, rye, and livestock. Isotope studies from sites in Denmark have shown that coastal Viking populations got as much as 40 to 50 percent of their protein from the sea.

Tooth enamel forms in childhood and never remodels, so it locks in a permanent record of the water and local rock a person grew up around. Oxygen isotopes in enamel reflect the local rainfall and climate, while strontium isotopes reflect the geology of the local bedrock, which enters the body through plants and water. By comparing a skeleton's tooth enamel signature to known regional isotope maps, researchers can tell whether someone buried in England, for instance, actually grew up in Norway, Sweden, or the Baltic region, evidence used to confirm real Viking migration into places like the Danelaw in England during the 9th and 10th centuries.