Source structure and site leverage reverse pooled archaeological human δ³⁴S–latitude regressions
Abstract
Abstract Recent IsoMemo / Pandora compilations now make it possible to pool archaeological human stable-isotope data across continents. We tested whether a simple latitudinal gradient is detectable in archaeological human δ³⁴S after pooling six such databases. From SAAID, CIMA, MAIA, NEENA, Isotòpia and CAMBIO we extracted every human bone or tooth record with non-null δ³⁴S, latitude and longitude (n = 2,215). The combined coverage is dominated by European (n = 1,586) and South American (n = 463) samples; no Asian, sub-Saharan African, or Oceanic human δ³⁴S exists in IsoMemo. A naive ordinary-least-squares regression returns a slope of + 0.032‰ per degree latitude (p = 2.4 × 10⁻⁹). After adding source as a fixed-effect category, the same slope reverses to − 0.297‰ per degree (p ≤ 2.9 × 10⁻⁹⁶). All four geographically extended sources return negative within-source slopes (bootstrap 95% CIs strictly below zero: MAIA − 0.62, SAAID − 0.45, Isotòpia − 0.28, CIMA − 0.12). One archaeological site (Tibanica, Colombia, Late Muisca, 2,556 m) contributes 193 of 463 SAAID rows and dominates the SAAID latitudinal slope (R² 0.59 → 0.04 on removal) and the previously reported SAAID altitude signal (r − 0.41 → −0.03). The data caution against naive pooling and against altitude inferences anchored on a single high-density site. The currently available compilations consistently contradict the naive positive pooled slope once source structure is modeled, but the ecological meaning of the…
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