Tuesday, 16 September 2025

Correcting the Record: Misrepresenting the Lead Isoscape

 Once again, our favourite critic, Brian John, has managed to seize on a minor caveat in scientific work and inflate it into a grand conspiracy of incompetence. This time, the target is the UK lead isotope map — or “lead isoscape” — painstakingly developed by Evans et al. (2022) and published in PLOS ONE. John's blog post, dated 16 September 2025, argues that the map is “misleading” because it relies on bedrock geology and mineral deposits rather than superficial deposits like glacial till, potentially misplacing contour lines due to ice-flow redistribution of isotopic signatures. He draws on examples from Sweden and the Netherlands to bolster his case, suggesting the map's flaws undermine provenance claims, such as those for a Neolithic cattle tooth linked to Stonehenge.

Sounds damning — until you actually read the paper and the broader context. John's critique, while highlighting a valid point about glacial influences, overreaches by portraying the map as fundamentally flawed and ignoring how the authors addressed limitations. Crucially, his proposed alternative base map — complete with generalised ice-flow arrows extending glacial influences unusually far south, such as Irish Sea ice into the Bristol Channel and local ice caps in southwest England — is not the peer-reviewed figure from Booth et al. (2015) as implied in parts of his post, but appears to be his own unsupported compilation. This fabrication shows ice flows much further than the evidence in Booth et al. (2015) and other peer-reviewed sources supports, aligning more with John's controversial views on extensive glaciation than with mainstream Quaternary geology. Let's dissect this step by step.

What Evans et al. Actually Said

Evans and colleagues (2022) were completely transparent about their methods, as outlined in their open-access paper. They explain that the isoscape is constructed from a dataset of many lead isotope measurements, primarily from ore minerals (like galena) and rock-forming minerals, because modern biosphere samples — such as soils, plants, and waters — are heavily contaminated by anthropogenic lead from industrial sources, including leaded petrol with distinctive Australian ore signatures. This pollution masks the natural geogenic signals, making direct biosphere mapping unreliable for pre-industrial archaeological applications.

To validate the map, they cross-checked it against archaeological samples from low-lead tissues (e.g., tooth enamel from Neolithic pigs and Roman sheep), ensuring it reflects bioavailable signals at a regional scale. They explicitly call the map a “first step” towards a comprehensive Pb isoscape, acknowledging limitations such as data gaps in certain regions (e.g., Scotland) and the need for further refinement. For instance, they note that while ore data provide a robust geological baseline, biosphere transfer can introduce variability, and they define domains at 1 standard deviation to allow for probabilistic interpretations rather than pinpoint accuracy.

In other words, the very “flaws” our critic trumpets — the reliance on bedrock proxies and potential decoupling from surface deposits — were already recognised and openly discussed by the map’s creators. The British Geological Survey (BGS) news release accompanying the paper reinforces this, describing it as a tool to "determine lead isotope ratios in soil and rock" for provenance studies, while noting its innovative use in archaeology. John's dismissal ignores this nuance, treating acknowledged caveats as evidence of oversight.

Glacial Sleight of Hand

John's alternative hinges on what he presents as a superior base map for isoscapes: one showing "generalised ice movement directions and the distribution of glacial sediments," with bold arrows indicating flows from sources like the "Irish Sea Glacier," "Welsh Ice Cap," and "Northern Ice." He references Booth et al. (2015) earlier in the post for a coloured Quaternary provinces map, but the arrow-laden schematic he promotes as the ideal replacement lacks a citation and diverges significantly from Booth's work. Booth et al. (2015) indeed provides a peer-reviewed classification of Britain's landscape into provinces and domains based on Quaternary processes, with a map dividing the UK into glaciated and non-glaciated areas (e.g., the non-glaciated province south of the Devensian limit, roughly from the Thames to the Bristol Channel). However, Booth's map focuses on broad domains with limited glacial indicators (such as a red dashed line for Last Glacial Irish Sea glaciers in some versions), not the extensive, speculative arrows John employs, which push ice influences implausibly far into unglaciated southern England.

Fair enough — glacial redistribution is indeed a factor in bioavailable isotopes, particularly for grazing animals ingesting soil and dust. However, John's version exaggerates this, fabricating flows beyond established evidence. Standard Quaternary mapping, including Booth et al., places the Devensian glacial limit such that southwest Wales and the Scilly Isles mark the southern reach of Irish Sea ice, with no major glaciation in the Cotswolds, Thames Valley, or southwest England proper during the Last Glacial Maximum. John's arrows, by contrast, imply inherited signatures from Welsh or northern ice far south, supporting his fringe theories on glacial transport of Stonehenge bluestones but lacking empirical backing from peer-reviewed sources.

Moreover, studies in Sweden (Schjerven et al., 2024) and the Netherlands do prioritise superficial deposits for Sr and other isotopes, but these regions have less industrial Pb pollution, allowing modern biosphere sampling — a luxury not available in Britain, as Evans explains. British research does account for this. For strontium (a close analogue to Pb in provenance work), Müldner et al. (2022) created a dedicated biosphere map for South-West England using 98 modern samples (plants, waters, and soils), identifying highly radiogenic ⁸⁷Sr/⁸⁶Sr values influenced by local geology and superficial sediments. This builds on BGS's biosphere isotope domains dataset, which integrates superficial deposits for Sr, O, and S across Great Britain, using GIS layers to model bioavailable signals decoupled from bedrock where thick tills dominate. If glacial effects are as transformative as John claims, why not engage with these peer-reviewed refinements rather than implying the entire Pb map is invalid?

Yes, glacial transport can redistribute isotopic signatures — that is well known. But to leap from “superficial deposits matter” to “the isoscape is wrong everywhere” is pure misrepresentation. The Evans map excels at broad regional distinctions (e.g., Chalk vs. Palaeozoic domains), where superficial mixing may homogenise but not erase tectonic signals.

Recognised Quibbles vs. Misleading Spin

Let’s be clear: the scientific community recognises that ore-derived Pb isoscapes have limitations for biosphere applications, especially in glaciated areas. That’s why ongoing BGS work on biosphere isotope domains continues to incorporate superficial sediments and biosphere samples as data allow, with interactive maps for querying Sr, O, and S variations that explicitly address Quaternary deposits. Recent reviews, like Spies et al. (2025), advocate for such integrations in Sr isoscapes, and similar efforts could extend to Pb once pollution-corrected datasets mature.

John misrepresents this nuance by treating a limitation as a fatal flaw, while offering his unsupported ice-flow map as a superior alternative — despite it lacking direct isotope data or alignment with Booth's actual figures. It’s a familiar pattern: selective reading, inflation of caveats into catastrophes, and an odd refusal to engage with what the peer-reviewed sources actually say. For the Stonehenge cattle tooth, Evans' map supports multiple potential sources, but John dismisses it to favour local origins, overlooking how multi-isotope approaches (Pb + Sr + O) mitigate individual weaknesses.

Conclusion

The UK lead isoscape is not perfect — no one ever claimed it was. But it is a carefully constructed, transparent, peer-reviewed starting point for provenance work. Its limitations are acknowledged, its methods are justified given pollution constraints, and it is being refined through BGS initiatives. To brand it “misleading” while waving around an unsupported glacial fabrication (masquerading as derived from Booth et al.) as if it overrules the isotope-specific literature is, frankly, to have grasped the wrong end of the stick yet again.

If John's goal is constructive dialogue, perhaps he could collaborate on sampling tills for Pb — that would advance the field far more than blog polemics.

References

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