Source of strontium in archaeological mobility studies—marine diet contribution to the isotopic composition

Abstract

The strontium isotope composition of human tissues is widely used in archaeological mobility studies. However, little attention is paid to the relative contributions of terrestrial versus marine sources of strontium in these studies. There is some debate over the role of a solid diet versus drinking water as the most important source of strontium for the human body, with related possibilities of misinterpretation of the archaeological record if only strontium isotope compositions of the biosphere are studied. However, there is a third component, marine strontium, which is commonly not assumed to contribute towards the strontium isotope composition of archaeological skeletal remains, especially in locations that are not directly coastal. To illustrate the potentially obfuscating effects of mixed Sr sources in a human population, we present a case study of twelve individuals from the medieval Finnish site Iin Hamina with a known dietary history. Our study shows that marine consumption is a significant factor explaining the strontium isotope composition of the Iin Hamina human remains, with implication of erroneous conclusions about immigration without prior knowledge of diet composition. Thus, future studies should always incorporate a rigorous analysis of dietary history, with special regard to potential consumption of aquatic resources, when strontium isotope analysis is used as a method in the study of palaeomobility.

Strontium isotopes and concentrations in cremated bones suggest an increased salt consumption in Gallo-Roman diet

“…The Belgian Gallo-Roman individuals tend towards patterns shown in these marine-affected people, whereas this is not the case in the Metal Ages individuals. This marine signal in measured human samples from the Scottish Isles is evidently explained by direct salty sea spray, by Sr-rich seaweed used as a fertilizer 40 , 79 , and/or direct consumption of marine products 58 . Whatever the dominant source of this marine signature is, it consistently reflects the same 87 Sr/ 86 Sr of the sea and warps the other Sr resources an individual consumes at a rate depending on the amount and [Sr] of the marine resource 39 .…”

“…crops) represent the main dietary source of strontium 40 , 57 . Marine resources, especially salt, can also be a major contributor of Sr and heavily alter both 87 Sr/ 86 Sr and [Sr] in human remains 40 , 54 , 56 , 58 , 59 . This influence can easily be recognised since marine resources (and seawater) have a characteristic 87 Sr/ 86 Sr of 0.7092 60 .…”

Divergence, diet, and disease: the identification of group identity, landscape use, health, and mobility in the fifth- to sixth-century AD burial community of Echt, the Netherlands

“…The uptake of calcium, and thus also strontium (Coelho et al 2017), is influenced by a number of factors, such as age (Underwood 1977). During periods of rapid growth, the absorption of calcium is elevated (Brickley et al 2020), and prioritizing calcium over strontium uptake may result in lower [Sr] (Lahtinen et al 2021). This may (partially) explain why [Sr] are lower in nonadults than in adults.…”

Strontium isotope identification of possible rural immigrants in 17th century mass graves at St. Gertrude Church cemetery in Riga, Latvia

“…Strontium (Sr) isotopes were first used to study mobility in past human populations in the mid-1980s (Ericson, 1985), and they have become one of the most effective methods to distinguish local and non-local individuals in early prehistory (Bentley et al, 2002;Cox & Sealy, 1997;Montgomery et al, 2000;Müller et al, 2003) as well as later periods of history (Lahtinen et al, 2021;Montgomery et al, 2005;Scheeres et al, 2013;Shaw et al, 2016). Sr is an alkaline earth metal with three non-radiogenic isotopes ( 84 Sr, 86 Sr and 88 Sr) and one radiogenic isotope ( 87 Sr).…”