Implications for paleomobility studies of the effects of quaternary volcanism on bioavailable strontium: A case test in North Patagonia (Argentina).

Isótopos de estroncio87Sr /86Sr) se utilizan como trazadores geoquímicos para estudios de paleomovilidad porque muestran patrones predecibles y estables en ecosistemas controlados principalmente por los regímenes geológicos subyacentes. Si bien la geología del lecho de roca es estable durante miles de años, los procesos geomorfológicos pueden influir en la87Sr /86Sr en ecosistemas sobre escalas de tiempo arqueológicamente relevantes. Entre estos procesos geomorfológicos, la deposición y reelaboración de sedimentos volcánicos en escalas de tiempo cuaternarias son poco estudiados, pero podrían ser un control importante de87Sr /86Variaciones de Sr en muchas regiones arqueológicas. La Patagonia Norte es una región arqueológica clave para abordar los movimientos animales y humanos, y un lugar ideal para probar la influencia del vulcanismo cuaternario en87Sr /86Variación Sr, ya que se encuentra a favor del viento de los principales centros volcánicos. En este estudio, nuestro objetivo es evaluar los principales controles ambientales y geológicos de biodisponibles87Sr /86Sr y para construir un isoscape de alta resolución utilizando un marco de regresión de aprendizaje automático para futuros estudios de paleomovilidad. Tomamos muestras de varias ubicaciones y analizamos diferentes tipos de muestras (N = 94). Las proporciones muestran un rango limitado de variación, que no está relacionado con la geología del lecho de roca. Más bien, biodisponible87Sr /86Las variaciones de Sr muestran un aumento progresivo hacia el este (lejos de los Andes), luego de las deposiciones de polvo y las variaciones de elevación (R2 = 0,71, RMSE = 0,00041). Sostenemos que esta tendencia se relaciona con la deposición y reelaboración de sedimentos volcánicos no radiogénicos por erosión eólica, fluvial y glacial durante el Cuaternario. Como la mayor parte de esta reelaboración de sedimentos se produjo durante los períodos glaciales, la biodisponibilidad actual87Sr /86Las variaciones de Sr en el área de estudio probablemente representan un promedio a largo plazo que varió poco durante el Holoceno. En consecuencia, nuestro isoscape proporciona una base sólida para los estudios de paleomovilidad del Holoceno en la Patagonia Norte y subraya la importancia de los procesos de volcanismo cuaternario para la interpretación.87Sr /86Datos de Sr en estudios de paleomovilidad en regiones volcánicas

Small-scale mobility fostering the interaction networks of Patagonia (Argentina) hunter-gatherers during the Late Holocene: Perspectives from strontium isotopes and exotic items

During the Late Holocene, hunter-gatherer interaction networks significantly grew in intensity and extension across Patagonia. Although this growth is evidenced by the increased flow of exotic items across the region, the mechanisms behind these strengthening social networks remain unclear. Since evidence suggests that some individuals might have performed long-distance trips, this article aims to address the potential relationship between these individuals and the flows of exotic items in North Patagonia. We analyzed 54 enamel teeth for strontium isotopes and reconstructed their probable mobility using mixed-effect models and isotope-based geographic assignments. We inferred population and individual mobility trends and compared them against the flow of exotic items built from a standardized compilation. Our results indicate that most individuals have isotopic composition compatible with residence within their burial and surrounding areas. However, a few individuals show isotopic composition incompatible with their burial areas, which suggests axes -from the burial location to the most likely isotope integration area- of extraordinary mobility. At the same time, the flows of exotic items overlap with these axes around the eastern sector of the study area suggesting that this location could have been a central point of convergence for people and items. We argue that small-scale socially driven mobility could have played a relevant role as a general mechanism of interaction that fostered and materialized Patagonian interaction networks during the Late Holocene

Mapping of bioavailable strontium isotope ratios in France for archaeological provenance studies

Strontium isotope ratios (⁸⁷Sr/⁸⁶Sr) of archaeological samples (teeth and bones) can be used to track mobility and migration across geologically distinct landscapes. However, traditional interpolation algorithms and classification approaches used to generate Sr isoscapes are often limited in predicting multiscale ⁸⁷Sr/⁸⁶Sr patterning. Here we investigate the suitability of plant samples and soil leachates from the IRHUM database (www.irhumdatabase.com) to create a bioavailable ⁸⁷Sr/⁸⁶Sr map using a novel geostatistical framework. First, we generated an ⁸⁷Sr/⁸⁶Sr map by classifying ⁸⁷Sr/⁸⁶Sr values into five geologically-representative isotope groups using cluster analysis. The isotope groups were then used as a covariate in kriging to integrate prior geological knowledge of Sr cycling with the information contained in the bioavailable dataset and enhance ⁸⁷Sr/⁸⁶Sr predictions. Our approach couples the strengths of classification and geostatistical methods to generate more accurate ⁸⁷Sr/⁸⁶Sr predictions (Root Mean Squared Error = 0.0029) with an estimate of spatial uncertainty based on lithology and sample density. This bioavailable Sr isoscape is applicable for provenance studies in France, and the method is transferable to other areas with high sampling density. While our method is a step forward in generating accurate ⁸⁷Sr/⁸⁶Sr isoscapes, the remaining uncertainty also demonstrates that fine-modelling of ⁸⁷Sr/⁸⁶Sr variability is challenging and requires more than geological maps for accurately predicting ⁸⁷Sr/⁸⁶Sr variations across the landscape. Future efforts should focus on increasing sampling density and developing predictive models to further quantify and predict the processes that lead to ⁸⁷Sr/⁸⁶Sr variability.Funding was provided by ARC DP110101415 (Grün, Spriggs, Armstrong, Maureille and Falguères) Understanding the migrations of prehistoric populations through direct dating and isotopic tracking of their mobility patterns. Part of this research was supported by the Australian French Association for Science & Technology through the ACT Science Fellowship program (2013) to M. Willme

Implications for paleomobility studies of the effects of quaternary volcanism on bioavailable strontium: a test case in North Patagonia (Argentina)

Strontium isotopes (⁸⁷Sr/⁸⁶Sr) are used as geochemical tracers for paleomobility studies because they display predictable and stable patterns in ecosystems primarily controlled by the underlying geological regimes. While bedrock geology is stable over thousands of years, geomorphological processes can influence the ⁸⁷Sr/⁸⁶Sr in ecosystems over archeologically relevant timescales. Among these geomorphological processes, the deposition and reworking of volcanic sediments over Quaternary timescales are little studied but could be an important control of ⁸⁷Sr/⁸⁶Sr variations in many archeological regions. North Patagonia is a key archeological region to address animal and human movements, and an ideal location to test the influence of Quaternary volcanism on ⁸⁷Sr/⁸⁶Sr variation as it is located downwind of major volcanic centers. In this study, we aim to assess the main environmental and geological controls of bioavailable ⁸⁷Sr/⁸⁶Sr and to build a high-resolution isoscape using a machine learning regression framework for forthcoming paleomobility studies. We sampled several locations and analyzed different types of samples (N = 94). The ratios show a limited range of variation, which is not related to the bedrock geology. Rather, bioavailable ⁸⁷Sr/⁸⁶Sr variations display a progressive increase going eastward (away from the Andes), following dust aerosol deposition and elevation variations (R² = 0.71, RMSE = 0.00041). We argue that this trend relates to the deposition and reworking of unradiogenic volcanic sediments by aeolian, fluvial and glacial erosion during the Quaternary. As most of this sediment reworking occurred during glacial periods, the current bioavailable ⁸⁷Sr/⁸⁶Sr variations across the study area likely represent a long-term average that varied little during the Holocene. Consequently, our isoscape provides a solid base for Holocene paleomobility studies in North Patagonia and underlines the importance of Quaternary volcanism processes for interpreting ⁸⁷Sr/⁸⁶Sr data in paleomobility studies in volcanic regions.Facultad de Ciencias Naturales y Muse

Mapping of bioavailable strontium isotope ratios in France for archaeological provenance studies

© 2017 Elsevier. This manuscript version is made available under the CC-BY-NC-ND 4.0 license: http://creativecommons.org/licenses/by-nc-nd/4.0/ This author accepted manuscript is made available following 24 month embargo from date of publication (Dec 2017) in accordance with the publisher’s archiving policyStrontium isotope ratios (87Sr/86Sr) of archaeological samples (teeth and bones) can be used to track mobility and migration across geologically distinct landscapes. However, traditional interpolation algorithms and classification approaches used to generate Sr isoscapes are often limited in predicting multiscale 87Sr/86Sr patterning. Here we investigate the suitability of plant samples and soil leachates from the IRHUM database (www.irhumdatabase.com) to create a bioavailable 87Sr/86Sr map using a novel geostatistical framework. First, we generated an 87Sr/86Sr map by classifying 87Sr/86Sr values into five geologically-representative isotope groups using cluster analysis. The isotope groups were then used as a covariate in kriging to integrate prior geological knowledge of Sr cycling with the information contained in the bioavailable dataset and enhance 87Sr/86Sr predictions. Our approach couples the strengths of classification and geostatistical methods to generate more accurate 87Sr/86Sr predictions (Root Mean Squared Error = 0.0029) with an estimate of spatial uncertainty based on lithology and sample density. This bioavailable Sr isoscape is applicable for provenance studies in France, and the method is transferable to other areas with high sampling density. While our method is a step forward in generating accurate 87Sr/86Sr isoscapes, the remaining uncertainty also demonstrates that fine-modelling of 87Sr/86Sr variability is challenging and requires more than geological maps for accurately predicting 87Sr/86Sr variations across the landscape. Future efforts should focus on increasing sampling density and developing predictive models to further quantify and predict the processes that lead to 87Sr/86Sr variability

Harmonizing and Extending Fragmented 100 Year Flood Hazard Maps in Canada’s Capital Region Using Random Forest Classification

With the record breaking flood experienced in Canada’s capital region in 2017 and 2019, there is an urgent need to update and harmonize existing flood hazard maps and fill in the spatial gaps between them to improve flood mitigation strategies. To achieve this goal, we aim to develop a novel approach using machine learning classification (i.e., random forest). We used existing fragmented flood hazard maps along the Ottawa River to train a random forest classification model using a range of flood conditioning factors. We then applied this classification across the Capital Region to fill in the spatial gaps between existing flood hazard maps and generate a harmonized high-resolution (1 m) 100 year flood susceptibility map. When validated against recently produced 100 year flood hazard maps across the capital region, we find that this random forest classification approach yields a highly accurate flood susceptibility map. We argue that the machine learning classification approach is a promising technique to fill in the spatial gaps between existing flood hazard maps and create harmonized high-resolution flood susceptibility maps across flood-vulnerable areas. However, caution must be taken in selecting suitable flood conditioning factors and extrapolating classification to areas with similar characteristics to the training sites. The resulted harmonized and spatially continuous flood susceptibility map has wide-reaching relevance for flood mitigation planning in the capital region. The machine learning approach and flood classification optimization method developed in this study is also a first step toward Natural Resources Canada’s aim of creating a spatially continuous flood susceptibility map across the Ottawa River watershed. Our modeling approach is transferable to harmonize flood maps and fill in spatial gaps in other regions of the world and will help mitigate flood disasters by providing accurate flood data for urban planning

Harmonizing and Extending Fragmented 100 Year Flood Hazard Maps in Canada’s Capital Region Using Random Forest Classification

With the record breaking flood experienced in Canada’s capital region in 2017 and 2019, there is an urgent need to update and harmonize existing flood hazard maps and fill in the spatial gaps between them to improve flood mitigation strategies. To achieve this goal, we aim to develop a novel approach using machine learning classification (i.e., random forest). We used existing fragmented flood hazard maps along the Ottawa River to train a random forest classification model using a range of flood conditioning factors. We then applied this classification across the Capital Region to fill in the spatial gaps between existing flood hazard maps and generate a harmonized high-resolution (1 m) 100 year flood susceptibility map. When validated against recently produced 100 year flood hazard maps across the capital region, we find that this random forest classification approach yields a highly accurate flood susceptibility map. We argue that the machine learning classification approach is a promising technique to fill in the spatial gaps between existing flood hazard maps and create harmonized high-resolution flood susceptibility maps across flood-vulnerable areas. However, caution must be taken in selecting suitable flood conditioning factors and extrapolating classification to areas with similar characteristics to the training sites. The resulted harmonized and spatially continuous flood susceptibility map has wide-reaching relevance for flood mitigation planning in the capital region. The machine learning approach and flood classification optimization method developed in this study is also a first step toward Natural Resources Canada’s aim of creating a spatially continuous flood susceptibility map across the Ottawa River watershed. Our modeling approach is transferable to harmonize flood maps and fill in spatial gaps in other regions of the world and will help mitigate flood disasters by providing accurate flood data for urban planning

Assessing geographic controls of hair isotopic variability in human populations: A case-study in Canada.

Studying the isotope variability in fast-growing human tissues (e.g., hair, nails) is a powerful tool to investigate human nutrition. However, interpreting the controls of this isotopic variability at the population scale is often challenging as multiple factors can superimpose on the isotopic signals of a current population. Here, we analyse carbon, nitrogen, and sulphur isotopes in hair from 590 Canadian resident volunteers along with demographics, dietary and geographic information about each participant. We use a series of machine-learning regressions to demonstrate that the isotopic values in Canadian residents' hair are not only influenced by dietary choices but by geographic controls. First, we show that isotopic values in Canadian residents' hair have a limited range of variability consistent with the homogenization of Canadian dietary habits (as in other industrialized countries). As expected, some of the isotopic variability within the population correlates with recorded individual dietary choices. More interestingly, some regional spatial patterns emerge from carbon and sulphur isotope variations. The high carbon isotope composition of the hair of eastern Canadians relative to that of western Canadians correlates with the dominance of corn in the eastern Canadian food-industry. The gradient of sulphur isotope composition in Canadian hair from coast to inland regions correlates with the increasing soil pH and decreasing deposition of marine-derived sulphate aerosols in local food systems. We conclude that part of the isotopic variability found in the hair of Canadian residents reflects the isotopic signature associated with specific environmental conditions and agricultural practices of regional food systems transmitted to humans through the high consumption rate of intra-provincial food in Canada. Our study also underscores the strong potential of sulphur isotopes as tracers of human and food provenance

A bioavailable strontium isoscape for Western Europe:A machine learning approach

Strontium isotope ratios (87Sr/86Sr) are gaining considerable interest as a geolocation tool and are now widely applied in archaeology, ecology, and forensic research. However, their application for provenance requires the development of baseline models predicting surficial 87Sr/86Sr variations (“isoscapes”). A variety of empirically-based and process-based models have been proposed to build terrestrial 87Sr/86Sr isoscapes but, in their current forms, those models are not mature enough to be integrated with continuous-probability surface models used in geographic assignment. In this study, we aim to overcome those limitations and to predict 87Sr/86Sr variations across Western Europe by combining process-based models and a series of remote-sensing geospatial products into a regression framework. We find that random forest regression significantly outperforms other commonly used regression and interpolation methods, and efficiently predicts the multi-scale patterning of 87Sr/86Sr variations by accounting for geological, geomorphological and atmospheric controls. Random forest regression also provides an easily interpretable and flexible framework to integrate different types of environmental auxiliary variables required to model the multi-scale patterning of 87Sr/86Sr variability. The method is transferable to different scales and resolutions and can be applied to the large collection of geospatial data available at local and global levels. The isoscape generated in this study provides the most accurate 87Sr/86Sr predictions in bioavailable strontium for Western Europe (R2 = 0.58 and RMSE = 0.0023) to date, as well as a conservative estimate of spatial uncertainty by applying quantile regression forest. We anticipate that the method presented in this study combined with the growing numbers of bioavailable 87Sr/86Sr data and satellite geospatial products will extend the applicability of the 87Sr/86Sr geo-profiling tool in provenance applications