Putting South-West England on the (strontium isotope) map: A possible origin for highly radiogenic 87Sr/86Sr values from southern Britain

Isotopic biographies reveal horse rearing and trading networks in medieval London

“…British biosphere strontium isotope ratios this high have only previously been found in parts of northeast Dartmoor, centered on granite outcrops enriched in rubidium with ratios between 0.7143 and 0.7287. Similarly, high ratios might also occur on other granite outcroppings of the Cornubian batholith including southwest Dartmoor, parts of Bodmin moor, and other locations in central and west Cornwall ( 24 ). These locations could theoretically account for the very high 87 Sr/ 86 Sr profiles in the Elverton horses including Horse 13; however, the δ 18 O data show that Horse 13 consumed drinking waters much too depleted in 18 O to have come from southwest Britain (equation 3 = −10.3‰; equation 4 = −11.0‰), where instead some of the most isotopically enriched (in 18 O) precipitation observed across the whole U.K. is recorded ( 15 ).…”

“…southwest England, discrete parts of the Midlands, and parts of Wales and Scotland (12,20). Biosphere ratios above 0.7132 are observed even more rarely in restricted areas of the landscape such as the Malvern Hills (0.714), other areas close to the English-Welsh border (~0.716), and in the Lake District (15,21,22), with some isolated patches of highly radiogenic geologies producing ratios of up to 0.7165 in Wales (23), between 0.7165 and 0.7182 in Scotland (19,22) and, exceptionally, up to 0.7287 on parts of Dartmoor centered on rubidium-rich granites (24). Further localized areas of highly radiogenic deposits may remain unrecognized in Britain (24); in addition, the so-called forest effect can potentially raise 87 Sr/ 86 Sr ratios by up to 0.003 to 0.004 in areas of ancient forest, which will have affected larger areas in the medieval period compared with today (25).…”

“…Enamel isotopic datasets were interpreted with reference to strontium and oxygen isoscape base maps for mainland U.K. (12,15,24) and continental Europe [see, e.g., (16,31,47,48)]. When differences were observed between the datasets, national base maps were preferred over global summaries, as the former typically incorporate more data and analyses specific to a particular region than do the international summaries.…”

Applying lead (Pb) isotopes to explore mobility in humans and animals

“…Consequently, studies have focused on using the feasting remains from domestic animals as a proxy for human movement. The Sr isotope values from human cremated bone are consistent with a southern British source, but bone represents a longer biological time scale and is therefore subject to biogenic averaging [ 27 ] whereas Sr isotope values suggested that Scotland could not be excluded as a source for the animals, though recent advances in mapping raise other possibilities [ 28 ]. The discovery of highly radiogenic 87 Sr/ 86 Sr values (up to 0.7172) in Neolithic animals at the Wiltshire henges has raised the issue of whether some pigs could have been brought, as livestock, from northern Britain to Wessex during the Neolithic [ 29 , 30 ], a possibility that has sparked debate [ 31 , 32 ].…”

“…Since the publication of Madgwick et al 2019 [ 30 ] new research has uncovered new sources of highly radiogenic Sr in England. Biosphere mapping of southwest England, guided by geochemical soil profiles [ 34 ], has highlighted areas around the granite intrusions in Devon and Cornwall where Sr in plants reaches values of 87 Sr/ 86 Sr = 0.72 [ 28 ] and Roman and Medieval sheep from this region record 87 Sr/ 86 Sr ratios up to 0.717 [ 35 , 36 ]. In addition, it has been shown [ 37 , 38 ] that well-established forest on certain terrains, typically those with soils derived from both siliceous and carbonate bedrock, will leach out the carbonate component over time, resulting in a more radiogenic signature for the forest area.…”