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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.

Earth’s plate-tectonic activity regulates the carbon cycle and, hence, climate, via volcanic outgassing and silicate-rock weathering. Mountain building, arc–continent collisions and clustering of continents in the tropics have all been invoked as controlling the weathering flux, with arcs also acting as a major contributor of carbon dioxide to the atmosphere. However, these processes have largely been considered in isolation when in reality they are all tightly coupled. To properly account for interactions among these processes, and the inherent multi-million-year time lags at play in the Earth system, we need to characterize their complex interdependencies. Here we analyse these interdependencies over the past 400 million years using a Bayesian network to identify primary relationships, time lags and drivers of the global chemical weathering signal. We find that the length of continental volcanic arcs—the fastest-eroding surface features on Earth—exerts the strongest control on global chemical weathering fluxes. We propose that the rapid drawdown of carbon dioxide tied to arc weathering stabilizes surface temperatures over geological time, contrary to the widely held view that this stability is achieved mainly by a delicate balance between weathering of the seafloor and the continental interiors. Earth’s surface temperature is stabilized by the drawdown of CO2 owing to weathering of continental arcs, whose length is shown to be a primary control on global weathering fluxes, according to a probabilistic analysis of interdependencies.

While the identity of a victim of a localized disaster – such as a train or bus crash – may be established quickly through personal effects, fingerprints, dental records, and a comparison of decedent DNA to family reference specimen DNA, a different scenario presents itself in mass disasters, such as the Asian Tsunami of 2004. In the aftermath of the tsunami, visual appearance was initially used to assign “foreign” or “indigenous” classifications to the remains of thousands of victims. However, this visual identification approach was undermined by the speed with which bodies deteriorated under the hot and humid conditions. Time was spent populating ante-mortem DNA databases for different nationalities, which led to problems when creating a post-mortem DNA database because recovery of viable DNA was compromised due to rapid decomposition. As a consequence, only 1.3% of victims were identified by DNA; in contrast, 61% were identified based on dental examination, although this process took several months and a significant number of deceased from the 2004 Asian Tsunami still remain to be identified.

Understanding seasonal mobility, population connectivity, and site fidelity is critical for managing and preserving migratory species. We investigated the potential of coupling strontium (87Sr/86Sr) and hydrogen (δ2H) isotopes in feathers for quantitatively constraining natal origin for juvenile migratory predatory birds (raptors) using a probabilistic framework. We first calibrated single‐isotope models that predict spatial isotope variability in raptor feathers (called isoscapes) by analyzing and compiling isotope data for juvenile birds with known origins in North America and comparing their values to existing isotopic baselines in precipitation (for δ2H) and bioavailable strontium (for 87Sr/86Sr). We then compared the potential of hydrogen and strontium isotopes for refining geographic assignments either independently or combined. While yielding very different probability maps, hydrogen and strontium isotopes performed equally well at constraining regions of natal origin. However, thanks to the complementarity of these isotopes, dual δ2H and 87Sr/86Sr assignments increased predictive precision by an order of magnitude compared to either isotope alone. Lastly, we used the models to predict natal origin for juveniles with unknown origins that were sampled in southwestern Idaho, USA, during their autumn migration. The precision of geographic assignments for birds with unknown origins varied. Nevertheless, dual‐isotope assignments clearly distinguished individuals born outside of southwestern Idaho, and overall, predicted geographic assignments matched breeding ranges for the study species. Quantitative dual‐isotope geographic assignments enhance our ability to predict natal range of migratory raptors and complement other methods for monitoring movement and population connectivity. Combining isotopic data from feathers with other intrinsic geochemical and genetic data, as well as extrinsic markers, such as transmitters or bands, and niche‐modeling approaches will further refine key nesting areas for migratory birds.

Rationale Strontium isotope ratios (87 Sr/86 Sr) of hair may be a valuable tool to estimate human provenance. However, the systematics and mechanisms controlling spatial variation in 87 Sr/86 Sr of modern human hair remain unclear. Here, we measure 87 Sr/86 Sr of hair specimens from across the USA to assess the presence of geospatial relationships. Methods Ninety-eight human hair specimens were collected from salon/barbershop floors in 48 municipalities throughout the conterminous USA. [Sr] and 87 Sr/86 Sr ratios were measured from hair using quadrupole and multi-collector inductively coupled plasma mass spectrometers, respectively. The [Sr] and 87 Sr/86 Sr ratios of hair were compared with the measured [Sr] and 87 Sr/86 Sr ratios of tap waters from the collection locations. In addition, the 87 Sr/86 Sr ratio of hair was compared with the modeled ratios of bedrock and surface waters. Results Hair color was independent of the 87 Sr/86 Sr ratio, but related to [Sr]. The 87 Sr/86 Sr ratios of hair and leachate were not statistically different and were positively correlated; however, in several hair-leachate pairs, the ratios were conspicuously different. The 87 Sr/86 Sr ratios of both hair and leachate were linearly correlated with tap water. The 87 Sr/86 Sr ratio of hair was also significantly correlated with the modeled ratio of bedrock and surface waters, although the 87 Sr/86 Sr ratio of hair was most strongly correlated with the measured ratio of tap water. Conclusions The 87 Sr/86 Sr ratio of hair is related to the ratio of tap water, which varied geographically. The ratio of hair provided geographic information about an individual's recent residence. Differences in the 87 Sr/86 Sr ratios of hair and hair leachate may be concomitant with travel and could potentially be used as a screening tool to identify recent movements.

Mass graves are usually key historical markers with strong incentive for archeological investigations. The identification of individuals buried in mass graves has long benefitted from traditional historical, archaeological, anthropological and paleopathological techniques. The addition of novel methods including genetic, genomic and isotopic geochemistry have renewed interest in solving unidentified mass graves. In this study, we demonstrate that the combined use of these techniques allows the identification of the individuals found in two Breton historical mass graves, where one method alone would not have revealed the importance of this discovery. The skeletons likely belong to soldiers from the two enemy armies who fought during a major event of Breton history: the siege of Rennes in 1491, which ended by the wedding of the Duchess of Brittany with the King of France and signaled the end of the independence of the region. Our study highlights the value of interdisciplinary approaches with a particular emphasis on increasingly accurate isotopic markers. The development of the sulfur isoscape and testing of the triple isotope geographic assignment are detailed in a companion paper [1].

International audience; Mass graves are usually key historical markers with strong incentive for archeological investigations. The identification of individuals buried in mass graves has long benefitted from traditional historical, archaeological, anthropological and paleopathological techniques. The addition of novel methods including genetic, genomic and isotopic geochemistry have renewed interest in solving unidentified mass graves. In this study, we demonstrate that the combined use of these techniques allows the identification of the individuals found in two Breton historical mass graves, where one method alone would not have revealed the importance of this discovery. The skeletons likely belong to soldiers from the two enemy armies who fought during a major event of Breton history: the siege of Rennes in 1491, which ended by the wedding of the Duchess of Brittany with the King of France and signaled the end of the independence of the region. Our study highlights the value of interdisciplinary approaches with a particular emphasis on increasingly accurate isotopic markers. The development of the sulfur isoscape and testing of the triple isotope geographic assignment are detailed in a companion paper [13].

Little is known about woolly mammoth (Mammuthus primigenius) mobility and range. Here we use high temporal resolution sequential analyses of strontium isotope ratios along an entire 1.7-meter-long tusk to reconstruct the movements of an Arctic woolly mammoth that lived 17,100 years ago, during the last ice age. We use an isotope-guided random walk approach to compare the tusk’s strontium and oxygen isotope profiles to isotopic maps. Our modeling reveals patterns of movement across a geographically extensive range during the animal’s ~28-year life span that varied with life stages. Maintenance of this level of mobility by megafaunal species such as mammoth would have been increasingly difficult as the ice age ended and the environment changed at high latitudes.

Forensic practitioners, archeologists, and ecologists increasingly use hair isotope profiles and isotope databases and maps to reconstruct the life history of unidentified individuals. Relationships between hair isotope profiles with travel history have been primarily investigated through controlled laboratory experiments. However, those controlled studies do not reflect the complex life history of modern individuals who often travel between multiple locations over different periods. Here, we collect one bundle of hairs from a volunteer whose primary residence is in Ottawa (Canada) but who traveled to multiple destinations over a period of 18 months. Those travels include multi-week trips to distant locations and multi-day trips to more local areas. We use multi-isotope profiles on the individual’s hairs coupled with isotope databases across the world to reconstruct travel history at sub-monthly temporal resolution. We compare the isotopic interpretation of mobility with the recorded travel history. A prominent shift in δ2H values is interpreted as a westward movement towards central Canada, which corresponds to a month-long road-trip to the Prairie. We observed a marked negative excursion in δ13C values along the hairs profile, which was related to a multi-week-long trip to several countries in Europe. Except for an exceptionally variable interval likely driven by health issues, δ15N values show very little fluctuation across the entire profile, indicating consumption of consistent amounts of animal or marine-based protein at different locations. The isotopic shifts in the proximal part of the hair reveal a clearer picture of traveling destinations than the shifts in the distal part, which have larger uncertainty in terms of timing and amplitude. Except for the last couple of months before collection, 87Sr/86Sr ratios show little variation throughout the profile likely due to recent exchange with Ottawa tap water during bathing or showering. The different 87Sr/86Sr ratios in the month preceding collection appear to partially preserve the 87Sr/86Sr ratio of the volunteer’s diet. This study demonstrates the interest of using multi-isotope systems and large isotopic databases to reconstruct individual mobility. This study also underlines the challenges in linking isotope data to mobility, particularly in rapidly growing keratinous tissues.

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.

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 Museo

The environmental impact of Three Gorges Dam (TGD) in the Changjiang (Yangtze River) is an important topic of concern for scientific communities and the public. However, the changes in river water chemistry in response to the dam construction remain poorly constrained. This study presents the seasonal variability of all major cations and some anions in the lower Changjiang during a full hydrological year from 2010 to 2011. The concentrations of all ions, except for HCO3 −, are higher after the TGD operation than before (p < 0.01), implying that the TGD has modified the river water chemistry in the mid-lower mainstream. Dissolved silicate (DSi) fluxes at Datong station thus increase slightly since the beginning of TGD impoundment. The change of mixing pattern of different water sources and alteration of hydrological and biogeochemical processes could cause the change of solute concentrations in the mid-lower Changjiang after the TGD operation. The mass balance model suggests that two factors primarily account for this increase of DSi observed at Datong: 1) an increasing loading of DSi downstream TGD due to erosion by “clean water”, and 2) an enhanced “Source” role of Lake Poyang in the mid-lower reaches. Our study would provide insights into the damming effect on river water chemistry and the complexity of a large river system facing rapid climate change and strong human activities.

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.

Human remains, later named “Madame Victoria”, were discovered in 2001 near the Royal Victoria hospital in Montreal but were never identified by forensic practitioners. We use multi-isotope hair profiles to investigate Madame Victoria’s travel and diet history. Based on carbon isotope abundances, Madame Victoria had a stable diet and values typical of eastern Canada. Nitrogen isotope ratios are more positive than average Canadians, and increase sharply over the last two months of her life, likely reflecting a rapid health deterioration. Hydrogen isotope abundances are typical of eastern Canada, and become stepwise more positive throughout the hair profile. Based on hydrogen isotope data, Madame Victoria moved progressively from either a western Ontario or northern Quebec locality towards Montreal over the last 3 years of her life stopping multiple times along the way. The strontium isotope ratios are constant throughout the hair profile and equal to the isotopic value of the soil exchangeable strontium at the site where the body was discovered. This observation, combined with hair major and trace elemental data, indicates that strontium from soil diffused and replaced the original hair strontium post-mortem. This study shows the interest of multi-isotope hair profiles to focus investigations on cold cases but also underlines the need for further work to take advantage of metal and metal isotope data.

Radiogenic strontium isotope ratios (87 Sr:86 Sr) in otoliths were compared with isotope ratios predicted from models and observed in water sampling to reconstruct the movement histories of smallmouth bass Micropterus dolomieu between main-river and adjacent tributary habitats. A mechanistic model incorporating isotope geochemistry, weathering processes and basin accumulation reasonably predicted observed river 87 Sr:86 Sr across the study area and provided the foundations for experimental design and inferring fish provenance. Exchange between rivers occurred frequently, with nearly half (48%) of the 209 individuals displaying changes in otolith 87 Sr:86 Sr reflecting movement between isotopically distinct rivers. The majority of between-river movements occurred in the first year and often within the first few months of life. Although more individuals were observed moving from the main river into tributaries, this pattern did not necessarily reflect asymmetry in exchange. Several individuals made multiple movements between rivers over their lifetimes; no patterns were found, however, that suggest seasonal or migratory movement. The main-river sport fishery is strongly supported by recruitment from tributary spawning, as 26% of stock size individuals in the main river were spawned in tributaries. The prevailing pattern of early juvenile dispersal documented in this study has not been observed previously for this species and suggests that the process of establishing seasonal home-range areas occurs up to 2 years earlier than originally hypothesized. Extensive exchange between rivers would have substantial implications for management of M. dolomieu populations in river-tributary networks.

The expression of global climate trends (10 6 to 10 7 years) and events (10 5 years) in terrestrial sedimentary sections can only be assessed from long, continuous continental records. Such records are rare due to the paucity of well-dated terrestrial deposits covering millions of years. This study uses isotope chemostratigraphy to develop an age model for fluvial sedimentary rocks of the Tornillo Group (Tornillo Basin, TX) and to decipher the potential expression of global climate variations in this sub-tropical paleo-fluvial system. The carbon isotope ratio (δ 13 C) of Tornillo Group pedogenic carbonate correlates well with δ 13 C variations from benthic foraminifera and suggests deposition between ~ 69 Ma and ~ 52 Ma for the studied stratigraphic interval. Higher sediment accumulation rates occurred in the greenhouse period of the early Eocene than during the cooler middle Paleocene. Carbon isotope excursions associated with Eocene hyperthermals were not identified, but their predicted stratigraphic positions coincide with thick sand bodies. We interpret the long-term sediment accumulation rates and rapid shifts in facies distribution as reflecting change in sediment supply in the basin, possibly driven by fluctuations in precipitation seasonality and intensity driven associated with global temperature changes. Carbon and oxygen isotope ratios from pedogenic carbonates display a strong correlation throughout the section, interpreted as an expression of coupling between the hydrological cycle and soil processes. Those observations suggest that global climate variations, along with tectonic and eustatic sea-level changes, may be an important control of stratigraphic variations of the Tornillo Group at multiple timescales.

Eastern Africa is a key region for studying archaeological, palaeontological, and ecological movements. This region hosts critical developments in hominin and human evolution, the dispersal of food-producing populations across the continent, and some of the largest known contemporary mammalian migrations on the planet. Strontium isotope analysis of biominerals such as tooth enamel, eggshell, and other tissues in modern animals have been used to reconstruct migration, residential mobility, and provenience. The diverse geologies of Kenya and Tanzania, ranging from the Archaean Basement System rocks of the Tanzania Craton to the recent volcanics of rift valleys, make it a highly promising area for mobility and provenience studies using strontium isotope ratios (87Sr/86Sr). Nevertheless, the application of strontium isotope analysis to reconstruct migration and individual mobility has been limited in the region due to the lack of a map predicting biologically available (bioavailable) 87Sr/86Sr. We present bioavailable 87Sr/86Sr data from a variety of modern and archaeological materials throughout Kenya and northern Tanzania. We show that 87Sr/86Sr of living organisms in the study area range from as low as 0.70439 for samples collected from Neogene volcanics to 0.72796 for samples collected from Precambrian Basement System rocks. We also present an 87Sr/86Sr map (isoscape) of Kenya and Tanzania developed using a machine-learning framework and a compilation of bioavailable 87Sr/86Sr data from Africa. This map provides the first predictions of bioavailable 87Sr/86Sr for East Africa, and represents a crucial resource for future work on ancient and modern animal and human mobility.

Strontium isotope ratios (87Sr/86Sr) are a popular tool in provenance applications in archeology, forensics, paleoecology, and environmental sciences. Using bioavailable 87Sr/86Sr in provenance studies requires comparing the 87Sr/86Sr of a sample of interest to that of 87Sr/86Sr baselines. Historically, these baselines required building empirical datasets from plants or local animals to characterize the 87Sr/86Sr available to local ecosystems (bioavailable 87Sr/86Sr). However, researchers are increasingly relying on modeled bioavailable 87Sr/86Sr maps (called isoscapes). We review the advantages and limitations of existing approaches to mapping bioavailable 87Sr/86Sr for provenance studies and propose a globally applicable, scalable, and editable framework for creating bioavailable 87Sr/86Sr isoscapes. This framework relies on: 1) Compiling global bioavailable 87Sr/86Sr data; 2) Mapping 87Sr/86Sr variability in rocks; 3) Leveraging global environmental covariates; and 4) Applying a random forest regression method that integrates these data to predict bioavailable 87Sr/86Sr. When the random-forest model is applied at the global scale it performs well (explaining 60% of the variance of the global bioavailable 87Sr/86Sr dataset), and accounts for geological, geomorphological and atmospheric controls. In data-rich regions (e.g., Europe), the global bioavailable 87Sr/86Sr isoscape can be successfully extrapolated to broad regions without bioavailable 87Sr/86Sr data. However, we also show that this extrapolation may not be valid in exceptionally geologically complex and data-poor regions (e.g., Madagascar). We suggest research directions to improve the accuracy of global bioavailable 87Sr/86Sr isoscapes, which include: 1) Increasing the collection of bioavailable datasets in data-poor regions; 2) Harmonizing data management practices and metadata collection for bioavailable 87Sr/86Sr data; and 3) Relying on advances in remote sensing and geological mapping techniques to improve geological covariates. While significant potential to refine 87Sr/86Sr isoscapes remains, the data products provided in this review form a basis for using 87Sr/86Sr data in large-scale provenance studies, opening new research avenues in a range of fields.

Yttrium and rare earth elements (REY) in aqueous environments have been intensively studied because they record important geochemical information. For example, the cerium anomaly, measured in marine sedimentary rocks, has been widely applied as a paleoredox indicator. Marine carbonates are the main substrate used to reconstruct REY signal in paleo-oceans with the underlying assumption that REY incorporated into carbonate minerals preserve the authigenic seawater signal. However, extracting authigenic REY signals from carbonate rocks are challenging. It requires dissolving carbonate phases using acid leaching procedures without contamination from other non‑carbonate phases such as Mn/Fe oxides (hydroxides), clay minerals, siliciclastic and organic phases. Multiple dissolution protocols, especially partial leaching, were proposed to eliminate potential contaminations. Yet, the efficiency of these procedures in reducing contamination remains ambiguous. Additionally, no systematic study on how each non‑carbonate phase can modify the authigenic REY signal from carbonates. First, we systematically investigated the efficiency of using ammonium acetate buffer pre-treatment to remove exchangeable ions prior to dissolution. We tested a range of concentration, pH, and reaction time of the buffer and we found that ammonium acetate of 1 M with a pH slightly 75% CaCO3) using two steps of ammonium acetate pre-leaching followed by three steps of 0.3 M acetic acid leaching.

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.

Changes in the isotopic composition of the continental crust control the strontium isotope ratio in seawater., The composition of igneous rocks in the continental crust has changed throughout Earth’s history. However, the impact of these compositional variations on chemical weathering, and by extension on seawater and atmosphere evolution, is largely unknown. We use the strontium isotope ratio in seawater [(87Sr/86Sr)seawater] as a proxy for chemical weathering, and we test the sensitivity of (87Sr/86Sr)seawater variations to the strontium isotopic composition (87Sr/86Sr) in igneous rocks generated through time. We demonstrate that the 87Sr/86Sr ratio in igneous rocks is correlated to the epsilon hafnium (εHf) of their hosted zircon grains, and we use the detrital zircon record to reconstruct the evolution of the 87Sr/86Sr ratio in zircon-bearing igneous rocks. The reconstructed 87Sr/86Sr variations in igneous rocks are strongly correlated with the (87Sr/86Sr)seawater variations over the last 1000 million years, suggesting a direct control of the isotopic composition of silicic magmatism on (87Sr/86Sr)seawater variations. The correlation decreases during several time periods, likely reflecting changes in the chemical weathering rate associated with paleogeographic, climatic, or tectonic events. We argue that for most of the last 1000 million years, the (87Sr/86Sr)seawater variations are responding to changes in the isotopic composition of silicic magmatism rather than to changes in the global chemical weathering rate. We conclude that the (87Sr/86Sr)seawater variations are of limited utility to reconstruct changes in the global chemical weathering rate in deep times.

Bataille and Bowen (2012) developed models to predict variations in the ratio of 87-strontium to 86-strontium (87Sr/86Sr) in rocks (bedrock model) and rivers (catchment water model) for regional provenance studies. Here, we revisit those models' formulation and calibration and apply them to predict Sr concentrations ([Sr]) and 87Sr/86Sr of Alaskan rivers. In a first step, we add several new components and/or improvements to resolve limitations of the model, including: 1) an independent siliciclastic sediment sub-model, 2) an explicit consideration of 87Sr/86Sr variability at the local scale, and 3) a fully-coupled assessment of prediction uncertainty. Tested against a compilation of 885 87Sr/86Sr rock analyses across Alaska, the new bedrock model significantly improves 87Sr/86Sr prediction accuracy in both igneous and sedimentary settings. In a second step, we develop a fully independent Sr chemical weathering model calibrated using a database of 339 [Sr] analyses from rivers of Northern Hemisphere high-latitude and predicting spatial variations in the rate of Sr release from rocks as a function of lithology, permafrost cover and slope. We combine the bedrock and Sr chemical weathering models to predict [Sr] and 87Sr/86Sr in Alaskan rivers. Tested on a dataset of 61 water samples, the resulting catchment water model explains 82% of 87Sr/86Sr variations in Alaskan rivers. We compare the average [Sr] and 87Sr/86Sr of Alaskan runoff estimated with the catchment water model to observed data of the Yukon River. The estimated average [Sr] and 87Sr/86Sr of Alaskan surface runoff – 104.3 μg/L and 0.7098 respectively – differ significantly from those of the Yukon River — 139.3 μg/L and 0.7137 respectively. This result calls into question the assumption that [Sr] and 87Sr/86Sr values estimated only from large rivers are representative of the Sr weathering flux from the entire Earth surface. The data products from this work provide an alternative basis for estimating 87Sr/86Sr values in rocks and rivers for regional provenance and chemical weathering studies across Alaska.

The characterization of strontium (Sr) isotopic ( 87 Sr/ 86 Sr) variation in surface waters of Alaska (AK) has significant implications for provenance studies aiming to track movement patterns of animals. This study presents 87 Sr/ 86 Sr ratios, concentrations of Sr, Ca, Mg, Na and K, and selected molar ratios (Sr/Na, Ca/Na, Mg/Na and Ca/Sr) from 61 rivers from across AK to characterize regional patterns in i) 87 Sr/ 86 Sr variation and ii) carbonate versus silicate weathering influencing 87 Sr/ 86 Sr ratios. 87 Sr/ 86 Sr ratios range from 0.70422–0.74041 ± 0.00009. Rivers north of the Denali Fault exhibit more radiogenic and variable 87 Sr/ 86 Sr ratios (0.70763 to 0.74041) than rivers to the south (0.70422 to 0.70895), reflecting the tectonic growth of southern AK via accretion of relatively young mafic-rich exotic island arcs along North America's continental margin during the Mesozoic. Within interior AK an east–west gradient exists. Radiogenic 87 Sr/ 86 Sr ratios (> 0.725) in east-central AK and relatively low ratios ( 0.711) than lowland rivers ( 87 Sr/ 86 Sr ratios in high relief watersheds north of the Denali Fault and in watersheds of south-central AK. Elemental and 87 Sr/ 86 Sr ratios indicate silicate weathering is important across AK, but is most influential in lowland basins north of the Denali Fault and in southwestern AK. This study illustrates the large Sr isotopic heterogeneity across AK on multiple spatial scales and provides necessary baseline information for provenance studies.

[1] Carbon isotope ratios of bulk organic matter in sedimentary rocks (δ13CDOM) are a potential source of paleoenvironmental information in terrestrial stratigraphic sequences. However, insufficient understanding of the range of depositional and post-depositional controls on δ13CDOM values makes interpretations of these data difficult. Here we evaluate the effects of organic matter (OM) provenance and preservation on δ13CDOM using records spanning the Paleocene Eocene Thermal Maximum (PETM) in the Bighorn Basin (Wyoming, USA) as a case study. We sampled sedimentary rocks spanning the PETM in two well-studied locations—Polecat Bench (PB) and Highway 16 (HW16)—in the Bighorn Basin. Independent carbon isotope records from biomarkers and pedogenic carbonates at these sites suggest that local shifts in plant and soil δ13C values associated with the PETM CIE were broadly similar and were characterized by an abrupt ∼5‰ decrease followed by a plateau and a eventual return to pre-PETM δ13C values. The δ13CDOM records from both sites differ significantly from these reference curves in both amplitude of change and in preserving high-frequency isotopic fluctuations and large isotopic anomalies superimposed on the general pattern of isotopic change through the CIE. For each location, we separated organo-mineral fractions (MOM), concentrated macerals from 20 stratigraphic levels and analyzed the carbon isotope ratio (δ13C) of each fraction. At both sites the δ13C of the fine and coarse MOM differ significantly from each other and from δ13CDOM. Concentration-weighted mixing of these isotopically distinct OM fractions explains high resolution δ13CDOM fluctuations but does not explain the large isotopic anomalies observed at both sites. At HW16, we identified two thermally and isotopically distinct populations of macerals interpreted as being indigenous and recycled OM. At this site, one over total organic carbon (1/TOC) values correlate with δ13CDOM for pre-PETM and PETM strata and both relationships converge toward the δ13C of recycled OM for low TOC. At PB, macerals display homogeneous thermal maturity, but the proportion of isotopically distinct vitrinite and liptinite varies between facies. Relationships between 1/TOC and δ13CDOM are also present within specific stratigraphic intervals at PB, but values do not converge on a single isotopic value across the sampled interval. These observations are consistent with variable mixing of OM fractions having different provenance—mixing of exotic recycled OM at HW16 and locally reworked OM at PB with indigenous “fresh” OM at both sites—and explain the large anomalies observed in the δ13CDOM records at both sites. Our findings raise questions about the assumption that OM in ancient sediments is indigenous and dominantly records δ13C variations of local plants.

Summary Drainage tiles buried beneath many naturally poorly drained agricultural fields in the Midwestern U.S. are believed to “short circuit” pools of NO 3 - -laden soil water and shallow groundwater directly into streams that eventually discharge to the Mississippi River. Although much is known about the mechanisms controlling this regionally pervasive practice of artificial drainage at the field-plot scale, an integrative assessment of the effect of drainage density (i.e., the number of tile drains per unit area) on the transport of nutrients and solutes in streams at the catchment scale is lacking. In this study, we quantified the flux and hydrological pathways of agricultural NO 3 - and road-salt Cl− from catchments lying within the Wabash River Basin, a major source of NO 3 - to the Mississippi River. The paired catchments differ primarily in drainage density (70% vs. 31%, by catchment area), with essentially all other agricultural management, land use, and soil drainage characteristics remaining equal. Our study revealed two significant hydrological responses to increased drainage density: (1) more near-surface storm event water (dilute in both NO 3 - and Cl - ) was transported early in the storm and (2) higher transport of Cl−-laden pre-event soil water relative to shallow groundwater elevated in NO 3 - occurred later in the storm. These patterns are consistent with a proposed conceptual model in which increased drainage density results in (1) greater transport of soil water to streams and (2) a delayed rise in the water table. With respect to nutrient management implications, these results indicate that increased drainage density impacts subsurface pools of Cl− and NO 3 - differently, a finding that we propose is linked to soil/ground water dynamics in artificially drained agricultural catchments.

Although variation in 87Sr/86Sr has been widely pursued as a tracer of provenance in environmental studies, forensics, archeology and food traceability, accurate methods for mapping variations in environmental 87Sr/86Sr at regional scale are not available. In this paper, we build upon earlier efforts to model 87Sr/86Sr in bedrock by developing GIS-based models for Sr isotopes in rock and water that include the combined effects of lithology and time. Using published data, we fit lithology-specific model parameters for generalized equations describing the concentration of radiogenic Sr in silicate and carbonate rocks. The new model explained more than 50% of the observed variance in measured Sr isotope values from independent global databases of igneous, metaigneous, and carbonate rocks, but performed more poorly (explaining 33% of the variance) for sedimentary and metasedimentary rocks. In comparison, a previously applied model formulation that did not include lithology-specific parameters explained only 20% and 8% of the observed variance for igneous and sedimentary rocks, respectively, and exhibited an inverse relationship with measured carbonate rock values. Building upon the bedrock model, we also developed and applied equations to predict the contribution of different rock types to 87Sr/86Sr variations in water as a function of their weathering rates and strontium content. The resulting water model was compared to data from 68 catchments and shown to give more accurate predictions of stream water 87Sr/86Sr (R2 = 0.70) than models that did not include lithological weathering parameters. We applied these models to produce maps (“isoscapes”) predicting 87Sr/86Sr in bedrock and water across the contiguous USA, and compared the mapped Sr isotope distributions to data on Sr isotope ratios of US marijuana crops. Although the maps produced here are demonstrably imperfect and leave significant scope for further refinement, they provide an enhanced framework for lithology-based Sr isotope modeling and offer a baseline for provenance studies by constraining the 87Sr/86Sr in strontium sources at regional scales.

The Palearctic–African migratory circuit has been typically associated with birds. Very few insects are known to endure annual trans-Saharan circuits, but the Painted Lady butterfly ( Vanessa cardui ) is an exception. While it was demonstrated that this species massively migrates from Europe to the Afrotropics during the autumn, the existence of a reverse migration from the Afrotropics to Europe in the early spring remains hypothetical. Here, we analysed wing stable hydrogen isotope values (δ 2 H) of V. cardui migrants collected from February to April across the circum-Mediterranean region. We assessed their region of natal origin by comparing their wing isotope signature predicted δ 2 H values (isoscape). The results unambiguously demonstrate a sub-Saharan origin for many individuals, especially those collected in February, representing the first tangible evidence for a reverse northwards trans-Saharan migration in spring. This work supports the view that the Afrotropics (mostly exploited from September to February) is key in the V. cardui Palearctic–African population dynamics. This species relies on both temperate and tropical habitats to complete their multigenerational cycle, an unprecedented adaptation for butterflies and for most migratory insects. Such a migratory circuit has strong parallelisms with those of migratory birds.

A method for mapping strontium isotope ratio (87Sr/86Sr) variations in bedrock and water has been recently developed for use in the interpretation of 87Sr/86Sr datasets for provenance studies. The mapping process adopted the simplifying assumption that strontium (Sr) comes exclusively from weathering of the underlying bedrock. The scope of this bedrock-only mapping method is thus limited to systems where the contributions of other sources of Sr are minimal. In this paper, we build on this 87Sr/86Sr mapping method by developing a mixing model of Sr fluxes from multiple sources to the bioavailable Sr pool. The new multiple source model includes: (1) quantitative calculations of Sr fluxes from bedrock weathering using an empirical rock weathering model; and (2) addition of sub-models calculating the contribution of Sr fluxes from atmospheric aerosols based on outputs from global climate model simulations. We compared the performance of the new multiple source model and the bedrock-only mapping method in predicting observed values from two datasets of bioavailable 87Sr/86Sr from the circum-Caribbean region (Antilles and Mesoamerica). Although the bedrock-only method performs relatively well in Mesoamerica (n = 99, MAE = 0.00011, RMSE = 0.00073), its prediction accuracy is lower for the Antillean dataset (n = 287, MAE = 0.0021, RMSE = 0.0027). In comparison, the new multiple source model, which accounts for the deposition of sea salt and mineral dust aerosols, performs comparably well in predicting the observed 87Sr/86Sr values in both datasets (MAE = 0.00040, RMSE = 0.00087 and MAE = 0.00014, RMSE = 0.0010). This study underscores the potential of using process-oriented spatial modeling to improve the predictive power of Sr isoscapes over large spatial scales and to refine sampling strategies and bioavailable Sr dataset interpretations for provenance studies.