Stable hydrogen isotope ratios (δ2H values) in structural hydroxyl groups of pedogenic clay minerals are inherited from the surrounding water at the time of their formation. Only non‐exchangeable H preserves the environmental forensic and paleoclimate information (δ2Hn value). To measure δ2Hn values in structural H of clay minerals and soil clay fractions, we adapted a steam equilibration method by accounting for high hygroscopicity. Our δ2Hn values for USGS57 biotite (−95.3 ± SD 0.9‰) and USGS58 muscovite (30.7 ± 1.4‰) differed slightly but significantly from the reported δ2H values (−91.5 ± 2.4‰ and −28.4 ± 1.6‰), because the minerals contained 1.1%–4.4% of exchangeable H. The low SD of replicate measurements (n = 3) confirmed a high precision. The clay separation method including destruction of Fe oxides, carbonates and soil organic matter, and dispersion did not significantly change the δ2Hn values of five different clay minerals. However, we were unable to remove all organic matter from the soil clay fractions resulting in an estimated bias of 1‰ in two samples and 15‰ in the carbon‐richest sample. Our results demonstrate that δ2Hn values of structural H of clay minerals and soil clay fractions can be reliably measured without interference from atmospheric water and the method used to separate the soil clay fraction. Highlights We tested steam equilibration to determine stable isotope ratios of structural H in clay. Gas‐tight capsule sealing in Ar atmosphere was necessary to avoid remoistening. Our steam equilibration method showed a high accuracy and precision. The clay separation method did not change stable isotope ratios of structural H in clay.

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The stable isotope ratios of C-bonded H (δ2Hn values) can be used to locate soil samples for forensic purposes because of their close correlation with the δ2H values of precipitation. Post-sampling bacterial activity might change the δ2Hn values via glycolysis. We tested to which degree C-bonded H is replaced by H from ambient water under favorable and unfavorable growing conditions. We provided two heterotrophic bacteria (Bacillus atrophaeus, Escherichia coli) with glucose (favorable) or lysine (unfavorable) under aerobic conditions. We assessed the H incorporation from ambient water via 2H labeling. We found that the H incorporation into bacterial biomass in the glucose treatment was 79 ± 5.9% (B. atrophaeus) and 43 ± 3.0% (E. coli), likely as a consequence of glycolysis and conservation of the δ2H value in the anabolic mode of the tricarboxylic acid (TCA) cycle. Differences between species were possibly related with different compositions of metabolite mixtures. The bacteria did hardly grow with lysine while respiration continued, and we found no H incorporation because the catabolic mode of the TCA cycle, which was active when the bacteria grew on lysine, is associated with CO2 release and a complete cleavage of former C–2H bonds. Our results support the glycolysis pathway as a mechanism underlying the incorporation of ambient-water H into the C-bonded H pool of bacteria. Stressful conditions forcing bacteria into a catabolism-dominated metabolism disable the incorporation of ambient-water H, and δ2Hn values can be applied to identify the origin of soil samples in forensics.

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Although Rapa Nui has been proposed as a classic example of cultural collapse, this hypothesis has been repeatedly questioned. This paper investigates cultural continuity on Rapa Nui following the onset of deforestation through a study of red ochre pits. Red ochre pigments are well-known from various contexts on Rapa Nui, but until recently its origin and the extraction process involved in their production were not precisely understood. New excavations have revealed the presence of multiple pits used for pigment production and storage by the island’s prehistoric culture. Previous geoarchaeological studies, including geomorphological, pedological, geochemical and micromorphological analyses, have shown that the pits contain fine layers of reddish iron oxides (ochre), which result from repeated intentional burning. The oxide layers alternate with thin layers of phytoliths, interpreted as the remains of plant material used as fuel, and diatoms. This paper presents new phytolith and diatom data from the previously described site of Vaipú East, complemented with data from similar pits at the new sites of Vaipú West and Poike. New 14C dates are also presented from these sites. The phytolith and diatom data provide crucial information about the chaîne opératoire of the ochre production and the formation processes associated with the pits. The evidence of pigment production and storage at Vaipú East shows that labour-intensive ochre production took place on Rapa Nui during at least two separate phases after deforestation, while the pits discovered at other sites indicate that Vaipú East did not stand alone. This provides a further line of evidence in favour of cultural continuity rather than collapse following deforestation in the island’s late prehistory.