Palaeobiodiversity research based on stable isotopes: Correction of the sea spray effect on bone carbonate δ13C and δ18O by Gaussian Mixture Model clustering

Rationale The use of multi‐isotopic analysis (δ2H, δ13C, δ15N, δ18O, and δ34S values) of modern human body tissues for provenancing of unknown individuals in forensics is increasing. Tooth dentine develops during childhood and adolescence, therefore providing geographical information from that period of life. Tooth apatite δ18O values are commonly used for the reconstruction of drinking water values, and H–C–N–S isotope ratios in collagen supply additional information about the composition of diet. We tested if dentine collagen δ2H values provide similar information to apatite δ18O values with a proof‐of‐concept study. Methods Tooth samples were taken from modern‐day individuals born in different regions of the world. Apatite and collagen were prepared from dentine. Stable isotope analyses were performed on apatite phosphate oxygen (δ18Ophos); oxygen and carbon of the structural carbonate (δ18Ocarb, δ13Ccarb); and hydrogen, carbon, nitrogen, and sulfur of the collagen (δ2Hcoll, δ13Ccoll, δ15N, δ34S). Results δ18Ophos, δ18Ocarb, and δ2Hcoll values are highly correlated in modern human dentine. There are significant relationships of δ18O values in the apatite fraction and δ2H values in the collagen fraction with local δ18O and δ2H precipitation values, respectively. Pearson correlation coefficients indicate no direct relationship between δ15N values and the isotope ratios of any other element. Weak relationships exist between collagen δ34S values and δ18Ocarb or δ18Ophos values. Conclusions The highly significant correlation of δ18Ophos, δ18Ocarb, and δ2Hcoll values in the modern human dentine implies that measurement of δ2H values in collagen or δ18O values in bioapatite will provide reliable information about the climate at the person's whereabouts.

Section: Discussionsupporting

confidence: 53%

Stable isotope relationships between apatite phosphate (δ¹⁸O), structural carbonate (δ¹⁸O, δ¹³C), and collagen (δ²H, δ¹³C, δ¹⁵N, δ³⁴S) in modern human dentine

Lehn

Roßmann

Mayr

2020

“…The relatively low information content detected for δ 18 O carbonate values can probably be explained by a quite strong “sea spray” effect in this isotopic system as detected by Göhring et al This effect causes a distinct enrichment in 18 O in terrestrial mammals from Haithabu and Schleswig, thus leading to an overlap of herbivores, carnivores, and omnivores. Although this effect has also been verified for δ 13 C carbonate and δ 18 O phosphate values, it is much stronger in δ 18 O carbonate values . Consequently, the high entropy values for δ 18 O carbonate might be a site‐specific result and must be verified for other datasets.…”

Section: Discussionmentioning

confidence: 78%

“…This might, however, usually not be a necessary step when applying the feature ranking method, but serves as a validation tool for implementing the entropy‐based feature ranking described in this paper. Nevertheless, GMM cluster analysis was validated as a useful tool for the interpretation of multi‐isotope datasets, previously …”

Section: Discussionmentioning

confidence: 99%

Which isotopes should we choose? Entropy‐based feature ranking enables evaluation of the information content of stable isotopes in archaeofaunal material

Göhring

Mauder

Kröger

et al. 2020

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Rationale Methods for multi‐isotope analyses are gaining in importance in anthropological, archaeological, and ecological studies. However, when material is limited (i.e., archaeological remains), it is obligatory to decide a priori which isotopic system(s) could be omitted without losing information. Methods We introduce a method that enables feature ranking of isotopic systems on the basis of distance‐based entropy. The feature ranking method is evaluated using Gaussian Mixture Model (GMM) clustering as well as a cluster validation index (“trace index”). Results Combinations of features resulting in high entropy values are less important than those resulting in low entropy values structuring the dataset into more distinct clusters. Therefore, this method allows us to rank isotopic systems. The isotope ranking depends on the analyzed dataset, for example, consisting of terrestrial mammals or fish. The feature ranking results were verified by cluster analysis. Conclusions Entropy‐based feature ranking can be used to a priori select the isotopic systems that should be analyzed. Consequently, we strongly suggest that this method should be applied if only limited material is available.

“…Therefore, an in-depth interpretation of particular burials with regard to their archaeological context is beyond the scope of this manuscript. We were able to show that GMM clustering, a method that has recently been successfully applied by our research group in the frame of palaeoenvironmental studies, 30,58 is also a promising method for a definition of multi-isotopic similarities which agree with the spatial distribution of the samples in the reference area we studied. At the same time, significant multi-isotopic dissimilarities between individuals excavated at the same site confirm the absence of diagenetic alterations that could obscure the data interpretation.…”

Section: Discussionmentioning

confidence: 79%

“…The Expectation Maximization Algorithm served for an estimation of the model parameters . This similarity analysis has proved successful previously with regard to stable isotopes of light elements and proved superior to more common methods such as principal component analysis . In this way, animal and human bones were grouped separately into clusters the members of which share the highest similarity in terms of the seven‐ (animals) to six‐ (humans) dimensional isotopic fingerprints.…”

Section: Methodsmentioning

confidence: 99%

Multi‐isotope provenancing of archaeological skeletons including cremations in a reference area of the European Alps

Grupe

Klaut

Mauder

et al. 2018

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