Abstract
RationaleStrontium isotope ratios (87Sr/86Sr) in modern‐day marine environments are considered to be homogeneous (~0.7092). However, in the Baltic Sea, the Sr ratios are controlled by mixing seawater and continental drainage from major rivers discharging into the Baltic. This pilot study explores if variations in Sr can be detected in marine mammals from archaeological sites in the Baltic Sea.Methods 87Sr/86Sr ratios were measured in tooth enamel from three seal species by laser ablation multi‐collector inductively coupled plasma mass spectrometry (LA‐MC‐ICP‐MS). The method enables micro‐sampling of solid materials. This is the first time that the method has been applied to marine samples from archaeological collections.ResultsThe analyses showed inter‐tooth 87Sr/86Sr variation suggesting that different ratios can be detected in different regions of the Baltic Sea. Furthermore, the intra‐tooth variation suggests possible different geographic origin or seasonal movement of seals within different regions in the Baltic Sea through their lifetime.ConclusionsThe method was successfully applied to archaeological marine samples showing that: (1) the 87Sr/86Sr ratio in marine environments is not uniform, (2) 87Sr/86Sr differences might reflect differences in ecology and life history of different seal species, and (3) archaeological mobility studies based on 87Sr/86Sr ratios in humans should therefore be evaluated together with diet reconstruction.
Highlights
To establish migratory patterns in prehistoric seals in the Baltic is important for understanding both prehistoric human and seal behaviour and the interaction between them
The fact that there are distinct differences in social, foraging and breeding behaviour of the three seal species included in this pilot study, we predict that sequential in situ measurement of 87Sr/86Sr isotope ratios in seal teeth by laser ablation multi‐collector inductively coupled plasma mass spectrometry (LA‐MC‐ICP‐MS) can provide data on life cycle and migratory patterns within and among species
The two harp seal canines that were analyzed in this study yielded isotope ratios that were significantly different from each other (Figures 2 and 5)
Summary
To establish migratory patterns in prehistoric seals in the Baltic is important for understanding both prehistoric human and seal behaviour and the interaction between them In this pilot study we make use of the fact that the present‐day Baltic Sea displays large variations in 87Sr/86Sr in different parts of the basin. The 87Sr/86Sr in oceanic seawater is globally homogeneous within the limits of analytical precision, averaging 0.70918 This is due to a long residence time of Sr in the oceans (5.0 × 106 years) that causes Sr to homogenize isotopically by mixing on a timescale of about 1000 years.[1] in coastal areas, and in smaller basins such as the Baltic Sea, the 87Sr/86Sr ratios can vary considerably. The rivers drain various sediments ranging from Precambrian in the north to Phanerozoic in the south, having
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