Ekaterina N Epova
email: ekaterina.epova@univ-pau.fr

Sylvain Bérail
email: sylvain.berail@univ-pau.fr

Fabienne Séby
email: séby-fabienne.seby@univ-pau.fr

Véronique Vacchina
email: veronique.vacchina@univ-pau.fr

Gilles Bareille
email: bareille-gilles.bareille@univ-pau.fr

Bernard Médina

Laurence Sarthou
email: l.sarthou@labopl.com

Olivier F X Donard
email: .donard-olivier.donard@univ-pau.fr

Fabienne

Gilles

Strontium elemental and isotopic signatures of Bordeaux wines for authenticity and geographical origin assessment

Keywords: Wine authenticity, Geographical origin, Bordeaux wine, 87 Sr/ 86 Sr isotope ratio, Sr concentrations, Terroir, Multi-collector ICP-MS

The 87 Sr/ 86 Sr ratio and Sr concentrations of 43 authentic Bordeaux wines from the world's most prestigious châteaux are presented in the context of their relation to the geographical origin of wine and authenticity.

The results demonstrate relatively narrow spans of variabilities observed for 87 Sr/ 86 Sr ratio and Sr concentrations in authentic Bordeaux wines, which can be used with reasonable certainty as specific parameters for identifying regional wineries. For comparison, a set of imitated Bordeaux wines was studied for Sr isotopic and elemental compositions. A significant excess of both parameters in suspicious wines were found in reference to authentic values. Such natural and anthropogenically induced variations offer an enhanced discriminating potential of Sr. The unique Sr binary signature may detect imitated wines and trace genuine products from different regional wineries. The obtained results shown a promising perspective for wine authenticity control by means of Sr isotopic and elemental composition.

Article

Introduction

Bordeaux, a territory in South West France, is one of the most famous and largest world viticultural regions and constitutes a conglomerate of vineyards extending over 112 000 ha. Its production represents almost half of French wines, far ahead of the rest of other world wine producing regions: a global bulk volume of about 6.5 million hectoliters and more than 850 million bottles of wine that are produced and delivered every year with wine qualities ranging from everyday table wines to some of the most expensive and prestigious wines in the world [START_REF] Lecat | Fraud and counterfeit wines in France: an overview and perspectives[END_REF]. To promote quality, the concept named "appellation" (French: "Appellation d'Origine Contrôlée", AOC) has been developed, and takes into account the very careful selection of grape varieties and the approved winemaking practices for each of the Bordeaux's 57 appellations. The appellations are geographically localized and cover sub-regions, individual villages or even specific vineyards. Bordeaux wines are known by their "terroir" -the combination of various environmental factors that have an impact on the wine taste and link the style of the wines to the specific locations (Médoc, Graves, etc.) [START_REF] Wilson | Terroir: The Role of Geology, Climate and Culture in the Making of French Wines[END_REF][START_REF] Bourrouilh | Geology and terroirs of the Bordeaux wines, France[END_REF]. Individual wineries or "châteaux" -are most of the time a traditional term to name a winemaking estate.

Wine traceability and authenticity are extremely important issues for the wine production and distribution sectors due to enormous economic damage caused by forgeries. Despite of the fact that fake wines have always existed, today the damage from this when assessed only the French wine market is around 36 million euros [START_REF] Lecat | Fraud and counterfeit wines in France: an overview and perspectives[END_REF]. The traceability of prestigious Bordeaux wines is becoming crucial, since they are among the most copied. Anti-counterfeiting technologies such as serial and individual numbering, laser engraving of the glass of the bottle, using variety of stickers, etc., has been introduced in order to reduce the turnover of counterfeited wines. However, all these measures are only applied to wine bottle recognition, even though the wine itself can be falsified. Therefore, wine fraud is still a serious and increasing problem. This leads not only to commercial losses, but also results in important health risks in case the counterfeited wine contains dangerous compounds and contaminants.

The determination of the geographical provenance and definitive authentication of wine requires the use of highly sophisticated analytical techniques. The number of recognized analytical approaches based on determination of elemental composition, organic components, stable isotope ratios of light elements, and genetic specifications of vitis varieties have been successfully applied to provenance determinations of wines (Médina, Salagoïty, Guyon, Gaye, Hubert & Guillaume, 2013; [START_REF] Cozzolino | Analytical and chemometric-based methods to monitor and evaluate wine protected designation[END_REF]). Among the different methods briefly mentioned above, the natural variation of the 87 Sr/ 86 Sr ratio is a relatively new approach addressing its geographical origin [START_REF] Balcaen | Determination of isotope ratios of metals (and metalloids) by means of inductively coupled plasma-mass spectrometry for provenancing purposes -A review[END_REF]. This method initially has been applied to provenance study in archeology, and later approved in the food sector. Indeed, its first attempt for food provenance assessment was performed on wine [START_REF] Horn | 87 Sr/ 86 Sr from rock and soil into vine and wine[END_REF]. Since then, the Sr isotope ratio method has been successfully tested on various food matrices and now, its application in the field of geographical origin identification of food products is growing steadily [START_REF] Baffi | Food traceability using the 87 Sr/ 86 Sr isotopic ratio mass spectrometry[END_REF]; Coelho, Castanheira, Bordado, Donard & Silva, 2017). Strontium (Sr) is neither an essential nor a nutritional element for the vine, which is continuously supplied throughout the plant's growth by uptaking from the water-soluble fraction of soil [START_REF] Horn | 87 Sr/ 86 Sr from rock and soil into vine and wine[END_REF][START_REF] Green | Distinguishing sources of base cations in irrigated and natural soils: evidence from strontium isotopes[END_REF]). Then Sr is assimilated in all parts of the vine including grapes [START_REF] Mercurio | A 'Geo-Pedo-Fingerprint' (GPF) as a tracer to detect univocal parent materialto-wine production chain in high quality vineyard districts, Campi Flegrei (Southern Italy)[END_REF], and transferred into wine without being altered during the winemaking process [START_REF] Almeida | Does the winemaking process influence the wine 87 Sr/ 86 Sr? A case study[END_REF]. Therefore, Sr contained in wine directly originates from soil in which the vine is grown and can be used to refer the plant's geographical origin. Following the first promising results, a series of studies have been performed aimed at the investigation of the correlation between 87 Sr/ 86 Sr ratios in the system soil-water-grapes-wine [START_REF] Almeida | ICP-MS determination of strontium isotope ratio in wine in order to be used as a fingerprint of its regional origin[END_REF] et al., 2016). The scientific and the practical importance of these studies is connected with the clear demonstration of the matching of Sr isotopic ratios in wine and those from the soil substratum of vineyards, obtained with precision and accuracy required for geological studies. Also they hold an extensive data base of Sr isotopic variations in Italian wines and are thus widely cited as main arguments of the Sr isotopes method applicable to wine geographical origin assessment. In 2014-2018, a comprehensive project aimed at establishing the 87 Sr/ 86 Sr specification for Italian Lambrusco PDO wines was implemented [START_REF] Durante | Development of 87Sr/86Sr maps as targeted strategy to support wine quality[END_REF].

Among the analytical methods traditionally used for the Sr isotopic analysis, the first reliable results were produced with thermal ionization mass spectrometry (TIMS). Recent instrumental developments made using multicollection inductively coupled plasma mass spectrometry (MC-ICP-MS) offer competitive information with data obtained by TIMS as the reference technique in the field of isotopic analysis [START_REF] Walczyk | TIMS versus multicollector-ICP-MS: coexistence or struggle for survival?[END_REF]. Since then considerable attention has been devoted to the development of methodologies and strategies with this new analytical detector, which finally made MC-ICP-MS the confirmed technique used to provide highly precise and accurate isotopic measurements (Irrgeher & Prohaska, 2016). In comparison to the previous generation ICP-MS instruments with quadrupole detection (Q-ICP-MS), whose analytical precision was tested and recognized to be insufficient for detection of the small variations of 87 Sr/ 86 Sr in wines [START_REF] Green | Distinguishing sources of base cations in irrigated and natural soils: evidence from strontium isotopes[END_REF], the introducing of MC-ICP-MS has resulted in significant improvements in the field of Sr isotopic analysis. The precision of detection with MC-ICP-MS yields variations between the interval of 0.002-0.005% [START_REF] Mercurio | A 'Geo-Pedo-Fingerprint' (GPF) as a tracer to detect univocal parent materialto-wine production chain in high quality vineyard districts, Campi Flegrei (Southern Italy)[END_REF][START_REF] Durante | An analytical approach to Sr isotope ratio determination in Lambrusco wines for geographical traceability purposes[END_REF] versus 0.53% obtained on Q-ICP-MS instruments [START_REF] Geană | Elemental profile and 87 Sr/ 86 Sr Isotope ratio as fingerprints for geographical traceability of wines: an approach on Romanian wines[END_REF]. The accuracy with MC-ICP-MS varies from 0.004% to 0.016% [START_REF] Horsky | Evaluation strategies and uncertainty calculation of isotope amount ratios measured by MC ICP-MS on the example of Sr[END_REF] and it is far better than that obtained by Q-ICP-MS under the best conditions -0.16% [START_REF] Geană | Elemental profile and 87 Sr/ 86 Sr Isotope ratio as fingerprints for geographical traceability of wines: an approach on Romanian wines[END_REF]. Currently, the Sr isotopic analysis of wine is successfully carried out using both methods, TIMS [START_REF] Marchionni | High-precision 87 Sr/ 86 Sr analyses in wines and their use as a geological fingerprint for tracing geographic provenance[END_REF][START_REF] Petrini | The 87 Sr/ 86 Sr strontium isotopic systematics applied to Glera vineyards: A tracer for the geographical origin of the Prosecco[END_REF][START_REF] Tescione | A comparative 87 Sr/ 86 Sr study in red and white wines to validate its use as geochemical tracer for the geographical origin of wine[END_REF][START_REF] Marchionni | Conservation of 87 Sr/ 86 Sr isotopic ratios during the winemaking processes of 'Red' wines to validate their use as geographic tracer[END_REF][START_REF] Vinciguerra | Strontium isotope characterization of wines from Quebec, Canada[END_REF] and MC-ICP-MS [START_REF] Mercurio | A 'Geo-Pedo-Fingerprint' (GPF) as a tracer to detect univocal parent materialto-wine production chain in high quality vineyard districts, Campi Flegrei (Southern Italy)[END_REF][START_REF] Durante | An analytical approach to Sr isotope ratio determination in Lambrusco wines for geographical traceability purposes[END_REF] to identify the 87 Sr/ 86 Sr ratio as a reliable guaranteed indicator of wine provenance.

In this study, an analytical approach for an accurate and precise determination of 87 Sr/ 86 Sr ratio in wine by ICP-MS has been developed for subsequent application for authenticity issues and geographical origin assessment. It has been tested on a wide selection of Bordeaux wines with the specific objective of identifying their Sr signatures with respect to individual wineries and detecting the imitated wine with a suspicious declaration of provenance.

Materials and method

Sample origins

Authentic Bordeaux wine. In this study, a series of 43 authentic wines from prestigious Bordeaux AOC, produced between 1969 and 2012 (most of them after 2000), some are classified as First Growth (French -"Grand Cru"), were provided by winemaking estates, territorially located on a restricted area of about 50 km radius, encompassing the famous Bordeaux viticultural lands of Médoc, Graves and Libourne. These traditionally grown in soils containing some deep fine clays with a mixture of sand resting on calcareous molasse deposits. Geographically, these two winemaking estates are very close, with the distance not exceeding 5 km, but have very distinctive soil compositions [START_REF] Bourrouilh | Geology and terroirs of the Bordeaux wines, France[END_REF]. Pessac-Léognan and Pauillac represent two viticultural sub-regions of the left bank of the Garonne River -Graves and Médoc, respectively. The vineyards of Pessac-Léognan are located within the Bordeaux urban activity zone, where the typical soil consists of gravel, pebbles and stone, overlaying a complex basis of sand and limestone. The vineyards of Pauillac are situated in the northern section of the viticultural strip of the Médoc peninsula.

The soil on the low gravelly terrace mounds of Pauillac is derived from the ferruginous climatic residual crust, resting on a marly calcareous foundation with inclusions of varying proportions of sand, gravel and significant quantities of unique clay in layers of varying depth [START_REF] Bourrouilh | Geology and terroirs of the Bordeaux wines, France[END_REF].

"Other wines" acquired from China. The discriminative capability of the Sr isotope marker was also tested on a set of 17 red wines, produced in 1998 -2009 and purchased directly from China. This group included 3 samples of wine of authentic Chinese production and 14 samples of wine labeled "Bordeaux". For some bottles, the indicated "Bordeaux" origin caused an evident mistrust due to incorrect labels containing spelling mistakes in the names of the well-known wineries, or even not-existant names of wineries. The real geographical origins for these wines were unknown. Exact names of production regions of original Chinese wines were also not specified. The complete sample list of can be seen in the Supplementary material, Table S1.

Instrumentation

For the Sr elemental quantification analysis, a quadrupole Q-ICP-MS NexION 300X (PerkinElmer, USA) was used in a standard operation mode. For the precise Sr isotopic ratios determination, a high resolution MC-ICP-MS Nu Plasma-HR (Nu Instruments Ltd., UK) equipped with a cyclonic spray chamber, a microconcentric nebulizer with flow rate of 200 µL min -1 , and nickel plasma cones (Type A) were used. The operating conditions for both instruments and the list of elements/isotopes determined are given in Tables S2 andS3 in the Supplementary material. For sample digestion, a microwave Mars 5 (CEM Corporation, USA) was used. A laboratory heating block HotBlock (Environmental Express, USA) was used for sample evaporation.

Reagents and materials

All sample handling was performed in a cleanroom class ISO 7. All FEP and PTFE vessels, vials and tubes were pre-cleaned with HNO 3 (10% v/v, 69.0-70.0%, Instra Analysed Reagent, J.T.Baker®, Fisher Scientific, France) and rinsed with ultrapure water obtained from the Milli-Q system (resistivity of 18.2 MΩ cm, Millipore USA, Molsheim, France) prior to use. Sample pre-digestion was performed in 30 mL PFA Savillex vials (Savillex Corporation, USA) using hydrogen peroxide H 2 O 2 (30%, ULTREX® II Ultrapure Reagent, J.T.Baker®, Fisher Scientific, France) and high purity subboiled HNO 3 , obtain by distillation of analytical reagent grade HNO 3 (69.0-70.0%, Instra Analysed Reagent, J.T.Baker®, Fisher Scientific, France) in an acid distillation system DST 1000 (Savillex, USA). All subsequent dilution steps involved in preparation of standards, samples and reagents for elemental and isotopic analysis were performed with HNO 3 solutions (2% v/v and 3 mol L -1 ), made of ultrapure water and HNO 3 (67-70%, ULTREX® II Ultrapure Reagent, J.T.Baker, Fisher Scientific, France).

For the elemental quantification analysis, a multielemental standard CCS-4 (Inorganic Ventures, USA) and the SLRS-5 certified reference material of river water for trace metals (NRC, Ottawa, Canada) were used for preparation and control of the calibration solutions.

The matrix purification was performed in ion-separation columns (2 mL, Triskem International, France) filled with 100 mg of Sr-selective resin Eichrom® (SR-B50-S, Triskem International, France) using 3 mol L -1 HNO 3 Ultrex® and ultrapure water. The isotopic standard reference material SRM 987, (pure SrCO 3 , NIST, USA), previously dissolved in HNO 3 was used for the quality control and instrumental mass bias correction during isotopic analysis.

Each analytical procedure (including cleaning of all types of equipment, sample digestion, laboratory sample preparation, and instrumental analysis) incorporated blanks and controls to minimize contamination impact and ensure the quality of results.

Elemental analysis Q-ICP-MS

For the elemental quantification of Sr and Rb, 0.5 mL of wine was digested with 0.2 mL of HNO 3 . The obtained solution was then diluted with 10 mL of ultrapure water. A series of calibration solutions was prepared in the range of 0.01-100 µg kg -1 . During ICP-MS analysis a drift correction for ICP-MS data was controlled using normalization to 103 Rh. Three blanks were subjected to a similar analytical procedure, the levels of Sr and Rb were below the method detection limits: 0.005 µg kg -1 and 0.003 µg kg -1 , respectively.

Sample preparation for Sr isotopic analysis

Sample preparation for Sr isotopic analysis consisted of steps of digestion followed by the Sr/matrix separation. In order to ensure quality control, several procedural blanks, counting one for every eleven wine samples mineralized and going through all steps of the procedure, were prepared.

Due to low Sr content in some samples, a pre-concentration was necessary. With that, a complete decomposition of organic matter during mineralization must be achieved, thus is was performed in three phases. Firstly, about of 10 mL of wine were evaporated in a Savillex vial until a volume of approximately 1 mL was reached. A full evaporation of the sample was avoided, since it makes further manipulations more difficult. Secondly, 5 mL of HNO 3 were gradually added to the wine concentrate and left to react at room temperature. Lastly, 1 mL of H 2 O 2 was added the next day, and then the resulting solution was microwaved to a temperature of 200°C and power of 1600W with the following timing: ramping -20 min, heating -20 min, and cooling -20 min. After cooling, the solution was transferred into 50 mL polypropylene tubes and diluted with ultrapure water up to 30 mL.

The presented protocol is a modified version from the one proposed by [START_REF] Durante | An analytical approach to Sr isotope ratio determination in Lambrusco wines for geographical traceability purposes[END_REF], where only 5 mL of wine were combined with 5 mL of HNO 3 and microwaved. In fact, some of Bordeaux wines had such low Sr concentrations that large volumes are required to be mineralized to ensure sufficient amounts of Sr for the isotopic analysis. Additionally, the maximum volume allowed for an effective digestion in the microwave system MARS 5 is limited to 10 mL. Thus, for safety and efficiency reasons, a soft preconcentration combined with the addition of H 2 O 2 has been applied. The low temperature mineralization without heating [START_REF] Durante | An analytical approach to Sr isotope ratio determination in Lambrusco wines for geographical traceability purposes[END_REF] was deemed to be ineffective for studying red wines: after reacting for 12 hours, the solutions containing 5 mL of wine and 5 mL of HNO 3 , were still colored typically for the presence of non-destroyed organic matter (pale yellow color). When these samples were subjected to the subsequent Sr/matrix separation using Eichrom® resin, the fractionation of the solution on the column was observed due to the resin depletion by presented organic matter. Hence, recoveries obtained for Sr after the matrix separation were in the range not acceptable for the isotopic determination (30-50%). In contrast to this, all samples subjected to the presented microwave digestion protocol had a clear uncolored appearance and were carried out easily for the following matrix separation. Finally, this method was considered as the preferred and allowing to reach required efficiency in sample preparation for isotopic analysis.

A precise and accurate determination of Sr isotope ratios by MC-ICP-MS requires a separation of Sr from the sample matrix, specifically from Rb, which can produce an isobaric interference of 87 Rb on 87 Sr. The following procedure was applied: the aliquots of a digested wine samples with an approximate content of 2-2.5 µg of Sr (necessary amount for a reliable isotopic ratio determination) were evaporated in 30 mL Savillex vials using a hot block at 80°C close to dryness and then re-dissolved in 4 mL of 3 mol L -1 HNO 3 . An amount of 100 mg of the Eichrom® Sr-selective resin was put into a 2 mL column fitted with appropriate filters to fix the resin inside the column to ensure a slow constant flow rate of about 0.5 mL min -1 required to obtain an acceptable recovery rate. At first, to avoid any contaminations, the packed resin was prewashed with 5 mL of 3 mol L -1 HNO 3 and rinsed with 20 mL of ultrapure water. Then, the resin was conditioned with 2 mL of 3 mol L -1 HNO 3 to ensure the sufficient activation of the binding groups. Next, the re-dissolved samples were loaded into the columns. The matrix removal was accomplished by flushing each column twice with 4 mL of 3 mol L -1 HNO 3 . Finally, the Sr elution was obtained by rinsing the columns with 10 mL of ultrapure water. The resulting solutions contained Sr in the levels of about 200 µg L -1 , and were ready to be analyzed by MC-ICP-MS without any supplementary dilution. The concentrations of Sr and Rb in wine samples and procedural blanks were controlled using a Q-ICP-MS before and after Sr/matrix separation, the obtained recoveries of Sr were in the range of 90-105% (only for samples containing Sr).

Sr isotope ratio analysis

The operating parameters of the MC-ICP-MS were daily optimized using the standard solution NIST SRM 987 with a concentration of 200 µg L -1 to achieve the maximum sensitivity and stability for Sr beam, the typical signal for the isotope 88 Sr was about 7V. Measurements were performed using a conventional Sample-Standard-Bracketing calibration sequence with the NIST SRM 897 used as bracketing standard. After instrumental blank substraction using the On Peak Zero approach (OPZ), the 87 Sr/ 86 Sr ratio was corrected for mass bias using the constant ratio 86 Sr/ 88 Sr of 0.1194, and from the potential remaining interferences from traces of 87 Rb using the ratio 85 Rb/ 87 Rb of 2.5926. A second correction was then applied to the bracketing standard in agreement with the study of Albarède, Telouk, Blichert-Toft, Boyet, Agranier, & Nelson (2004). The value of 87 Sr/ 86 Sr ratio for NIST SRM 987 applied for data processing was 0.710255, according to [START_REF] Waight | Sr isotope ratio measurements by double-focusing MC-ICPMS: techniques, observations and pitfalls[END_REF].

Contamination from the presence of Sr in the samples was evaluated by preparing two procedural blanks:

(1) -the procedural blank containing only reagents used in mineralisation, and (2) -the same procedural blank but spiked with an amount of SRM NIST 987 up to 200 µg L -1 . Both of them followed all the analytical stages, from mineralization to analysis, including matrix purification. The obtained average voltages on 88 Sr were 0.014 V and 7.4 V for the Sr-free procedural blank and for the spiked procedural blank, respectively.

Comparison of 87 Sr/ 86 Sr in spiked procedural blank (0.710271 ± 0.000018) with the reference value of NIST SRM 987 (0.710255 ± 0.000026) have shown that the influence of Sr contamination can be considered as negligible.

Concentrations of Rb in samples after matrix purification were first controlled using Q-ICP-MS and secondly by monitoring the m/z=85 with MC-ICP-MS. Concentration of Rb in the two procedural blanks were below the limit of quantification of Q-ICP-MS (0.01 µg kg -1 ). MC-ICP-MS showed low and relatively comparable voltages for 85 Rb in procedural blanks (the average is less than 0.0001V) and instrumental blank (the average is less than 0.00002V), respectively. Some samples after matrix purification were still containing Rb in the level up to 0.5 µg kg -1 (the voltage on MC-ICP-MS reached 0.024 V for 85 Rb). However, a ratio Rb/Sr for these samples was ≤ 0.006, which is lower than the maximal acceptable value of 0.015 mentioned by Yang, Wu, Xie, Yang & Zhang (2011), and thus an exponential law using 85 Rb correction can be reasonably applied.

The combination of the different methodological approaches mentioned above allowed to achieve an optimal measurement strategy for high-precision and accurate determination of 87 Sr/ 86 Sr by MC-ICP-MS with an external reproducibility for Sr isotope ratio measurement equivalent to 25 ppm calculated as standard deviation with 95% confidence interval of 75 individual measurements of NIST SRM 987 solution (200 µg L -1 ) under daily altered conditions. The average measured value of NIST SRM 987 was 0.710280 ± 0.000013 which is in good agreement with the reference value of 0.710255 ± 0.000023 [START_REF] Waight | Sr isotope ratio measurements by double-focusing MC-ICPMS: techniques, observations and pitfalls[END_REF].

The 87 Sr/ 86 Sr ratios in the wine samples were calculated as the mean from independently digested triplicates and measurement uncertainties were estimated as 2SD.

Results and Discussion

Strontium elemental concentrations

The Sr elemental content in wine is an important criterion addressed to the geographical origin since its concentrations in grapes are strongly regulated by the vineyard's soil composition [START_REF] Green | Distinguishing sources of base cations in irrigated and natural soils: evidence from strontium isotopes[END_REF]). The box plots in Fig. 2 graphically display the mean values and variation intervals of Sr elemental content across the studied wine samples. In authentic Bordeaux wines, the Sr concentrations are quite homogenous with respect to individual wineries and not exceed the level of 0.52 mg kg -1 . A comparative analysis of variability shows a high degree of consistency of the results obtained for wines from Saint-Émilion, Pessac-Léognan (white, red wines), and Pauillac with the Sr concentrations ranging between 0.16 and 0.19 mg kg -1 .

However, the wines from Pomerol are characterized by a slightly higher level of Sr concentrations detected in the interval of 0.33 -0.52 mg kg -1 .

When comparing the average Sr concentrations in authentic Bordeaux and suspicious "Bordeaux" acquired from China, an obvious difference between those two groups can be seen immediately (Fig. 2). Furthermore, statistical distributions of the groups "suspicious Bordeaux" and "suspicious Pauillac" display a significantly higher degree of dispersion and an evident abnormal skewness. In terms of Sr concentrations, the levels vary in the suspicious samples from 0.29 to 2.16 mg kg -1 with the mean value significantly higher than that for authentic Bordeaux, but similar to wines from the group "China". As mentioned previously, Sr in wine mostly originates from the soil, hence, the large variability of Sr concentration in wine reflects the wide diversity of underlying geological bedrocks and soils formed on them. Therefore, the widely scalable results of Sr concentrations in suspicious wines reflect the substantial heterogenity of geological background of its origin, which is not consistent with the rather homogeneous sedimentary basin of Bordeaux [START_REF] Wilson | Terroir: The Role of Geology, Climate and Culture in the Making of French Wines[END_REF][START_REF] Bourrouilh | Geology and terroirs of the Bordeaux wines, France[END_REF]. And vice versa, a smaller dispersion of Sr concentration observed in authentic Bordeaux achieve full harmonization with the above noted. Thus, comparing only the Sr concentrations in authentic and dubious wines can reveal some significant divergence that can be regarded as a sign of falsely declared geographical origin.

Strontium isotope ratios

Following the Sr elemental analysis, the 87 Sr/ 86 Sr ratios in studied wines were determined for further evaluation of their discriminating potential regarding the geographical origin. The ratios 87 Sr/ 86 Sr obtained for studied wines, authentic and suspicious, are listed in Table S1 (Supplementary material) and graphically presented in Fig. 3.

Authentic Bordeaux wine.

The isotopic ratios 87 Sr/ 86 Sr in the authentic Bordeaux wines vary within a comparatively narrow range, between 0.70829 and 0.71022 (Fig. 3). When considering in detail the samples originating from individual wineries (in recognition of the analytical precision of measurements), the 87 Sr/ 86 Sr ratios measured in wines from Pomerol lies in the range of 0.70968 -0.71022, which is slightly higher than those observed in the wines from Saint-Émilion (0.70829 -0.70895), and moderately overlapped with wines from Pauillac (0.70906 -0.70953) and Pessac-Léognan (0.70900 -0.70980). Indeed, the wine from Saint-Émilion demonstrates a lower 87 Sr/ 86 Sr value due to relatively low content of the radiogenic isotope 87 Sr. Wines of Grand Cru of Saint-Émilion are cultivated in soils developed on a large limestone plateau formed during the Lower Oligocene (about of 32 million years ago), and preserved the 87 Sr/ 86 Sr value of seawater during corresponding period. At that time, the 87 Sr/ 86 Sr ratio was in the range of 0.7078-0.7080 (Jones, Jenkyns, Coe & Hesselbo, 1994), and it has been recorded in these limestones, and therefore it continues to be a major factor contributing for the low values of 87 Sr/ 86 Sr ratios in plants that grow on it, and ultimately becomes apparent in wine (Fig. 4). It is noticeably in wines from Pauillac and Pessac-Léognan, but even to a greater extent with respect to samples from Pomerol. In Pomerol, vines are cultivated on more recent alluvial terraces relating to the Pleistocene (< 2 million years ago) formed of sands, pebbles and clays from the glacial erosion of the Central Massif and the Pyrenees. The slow and continuous dissolution of these siliceous elements of the Earth's crust (the 87 Sr/ 86 Sr ratios ranged from 0.715 to 0.730) can only raise the 87 Sr/ 86 Sr ratio of seawater of the Pleistocene (about 0.7090-0.7092), that can be observed in Pomerol wine: 0.7098 -0.7102.

Comparing early published results, the 87 Sr/ 86 Sr data reported here for wine from Saint-Émilion is consistent with the only reliable study of [START_REF] Barbaste | Precise determination of the strontium isotope ratios in wine by coupled plasma sector field multicollector mass (ICP-SF-MC-MS)[END_REF], where the Sr isotopic composition of four wines from the homonymous appellation (however, unknown vineyards) were recorded within the interval When examining the largest group of red and white wines originating from Pessac-Léognan, the obtained values of 87 Sr/ 86 Sr do not vary significantly for red and white wines: 0.70910 -0.70960 (mean of 0.70939 ± 0.00031, n=15) and 0.70900 -0.70980 (mean of 0.70935 ± 0.00058, n=9), respectively. This 87 Sr/ 86 Sr ratio in wine from a definite vineyard is generally stable from one vintage to another. Indeed, a certain variability observed in the samples of Pessac-Léognan (0.071% for red wines and 0.092% for white wines) represents a variability not depending on the year of production (Fig. C.3), and it is not likely due to the practice of vine varietal blending, because such differences have previously been observed for Italian Cesanese mono-varietal wine, produced during a period of 7 years by a particular winery [START_REF] Marchionni | Conservation of 87 Sr/ 86 Sr isotopic ratios during the winemaking processes of 'Red' wines to validate their use as geographic tracer[END_REF]. However, "Other wines" acquired from China. The wines from this group are characterized by large variations in 87 Sr/ 86 Sr ratio (0.70523 to 0.71266), significantly exceeding the upper and lower limits of the values observed in authentic Bordeaux. From 17 samples included in this set, only 12 wines (specifically: 9 suspicious "Bordeaux" and 3 original from China) have the 87 Sr/ 86 Sr ratio within the reference interval of typical Bordeaux 87 Sr/ 86 Sr values (Fig. 3). The 87 Sr/ 86 Sr values of the remaining 5 samples go beyond the lines defining the limits of typical Bordeaux geology and can be considered most likely as not originating from Bordeaux. According to spatial prediction maps [START_REF] Voerkelius | Strontium isotopic signatures of natural mineral waters, the reference to a simple geological map and its potential for authentication of food[END_REF][START_REF] Marchionni | High-precision 87 Sr/ 86 Sr analyses in wines and their use as a geological fingerprint for tracing geographic provenance[END_REF], a wine with 87 Sr/ 86 Sr value of 0.70523 could be produced from grapes planted in soils developed on volcanic, ophiolites or intrusive rocks. On the contrary, more radiogenic values of 87 Sr/ 86 Sr (0.711 -0.713) can be caused by soils of vineyards developed on igneous or metamorphic, granitoidic rocks. These types of bedrock are very different from the typical geological structure of the Bordeaux region, which is a large sedimentary basin [START_REF] Wilson | Terroir: The Role of Geology, Climate and Culture in the Making of French Wines[END_REF][START_REF] Bourrouilh | Geology and terroirs of the Bordeaux wines, France[END_REF]. Such wide variability of 87 Sr/ 86 Sr was observed also for Italian Prosecco wines 0.70706 -0.71215 [START_REF] Petrini | The 87 Sr/ 86 Sr strontium isotopic systematics applied to Glera vineyards: A tracer for the geographical origin of the Prosecco[END_REF] and wines from Quebec [START_REF] Vinciguerra | Strontium isotope characterization of wines from Quebec, Canada[END_REF], in both cases studied vineyards were planted on territories of a wide geological diversity. These overall results are important since they demonstrate that different wines represent a certain specification of Sr isotopic composition depending on their geographical origin. However, its practical application is partly limited when considering it as the only independent discriminating criterion. In the present case, the declared Bordeaux origin could be contested on the basis of Sr isotopic signatures only for five suspicious wines with obvious outliers of 87 Sr/ 86 Sr values. At the same time, the isotopic signatures of the remaining 9 wines labeled "Bordeaux" acquired from the China market do not detect nonconformities despite the other containing evidence of imitated wine. Moreover, the 87 Sr/ 86 Sr ratio of some Italian wines, such as previously mentioned Cesanese, Lambrusco, Prosecco and Chinese wines from this study have the ratio 87 Sr/ 86 Sr also disposed in the same range as Bordeaux. Thus, it is important to state that the Sr isotope ratio cannot be the distinctive criterion singularly applied for geographical origin assignment due to possible cases of similarity of regional lithology in different regions of the world.

Combination of 87 Sr/ 86 Sr and Sr concentrations

In geosciences, an enhanced discriminating potential of Sr lies with the joint interpretation of its two characteristics -elemental concentration and isotopic composition [START_REF] Green | Distinguishing sources of base cations in irrigated and natural soils: evidence from strontium isotopes[END_REF]). We attempted to find such interaction on example of authentic Bordeaux wines with consideration of relevant wineries, and then to use it for the differentiation of geographical origins of authentic and suspicious Bordeaux wines.

The case of Pomerol wine

At first, the correlation of these two parameters depending on vintages was appraised using an exceptional long-term series of wines produced in a winery in Pomerol in 1969 -2010. This small winemaking estate has kept in-house developed wine production technology for many decades. In these wine samples, a significant mirroring dependency of Sr concentration versus the ratio 87 Sr/ 86 Sr from the years of wine production can be seen in Fig. 5. Indeed, despite rather narrow variations of both parameters, such a trend is clearly observed due to the high precision of isotopic measurements on MC-ICP-MS. For the studied wines, those produced during the first 20 years, from the late 1960s until around 1990, we can note a slight enrichment in the radiogenic isotope 87 Sr, then followed by a moderate depletion in 87 Sr for the wines of more recent production. Such variability would be expected to be seemingly dependent upon the quality of the vintage, since the excellence or poorness of a vintage is directly due to annual meteorological conditions. However, the wine produced in the poor 1969 year (French -"Millésime mediocre") and in the best 2009 year (French -"Millésime exeptionnel") have the same Sr concentrations: 0.429 ± 0.011 mg kg -1 and 0.425 ± 0.012 mg kg -1 , while the values of 87 Sr/ 86 Sr differ fairly: 0.71010 ± 0.00002 and 0.70976 ± 0.00005, both parameters are given respectively for 1969 and 2009.

Such interesting opposite relationship of elemental and isotopic signatures can be explained in particular by changing the source of available Sr either during vine growing or winemaking. Indeed, viticulture and winemaking involve various practices and operations [START_REF] Pohl | What do metals tell us about wine?[END_REF], that can potentially change the Sr elemental and isotopic content in grapes and later those in wine. Taking into consideration the lack of detailed information of vineyard-and winemaking management due to commercial confidentiality, only a hypothesis for explaining such a behavior can be made. For example, the use of substances containing Sr of marine origin for pH regulation purposes on vineyard soil in the 1990's could explain the simultaneous increase in Sr concentrations with the shift of the 87 Sr/ 86 Sr ratio toward the 87 Sr/ 86 Sr value of sea water -0.70918 (Allègre, Louvat, Gaillardet, Meynadier, Rad & Capmas, 2010). Other additives used during winemaking, such as bentonite, can also affect the Sr isotopic composition of wine. These observations clearly underline that even within a narrow range of the 87 Sr/ 86 Sr variability, slight significant differences in the ratio may help to unravel the viticultural and winemaking features when considering a specific set of samples.

Variability of Sr isotope and Sr elemental content and its application to discriminate between

Bordeaux's viticultural sub-regions

To trace regional variabilities of Sr elemental and isotopic signatures in studied wines for further evaluation of their cumulative impact upon provenance discrimination, the ratios 87 Sr/ 86 Sr were plotted versus inverse Sr concentrations (Fig. 6). Such diagrams are primarily used to trace the geochemical development of soils horizons and estimate chronosequences of evaporation/sedimentation processes. In the case of wine samples this allows us to assess their potential origins: whether they are from the same or different geological regions. It can be clearly seen that this graph groups together most of the authentic Bordeaux wine samples with a slight distinction for Pomerol wines due to their higher Sr content. All authentic Bordeaux wines from this study form an elongated cloud of points bounded by limits of typical regional values 87 Sr/ 86 Sr [START_REF] Voerkelius | Strontium isotopic signatures of natural mineral waters, the reference to a simple geological map and its potential for authentication of food[END_REF], which is a true sign of the common geological provenance. (Fig. 6A). On the contrary, the suspicious "Bordeaux" wines are remarkable by the extreme diversity of Sr isotope ratio and Sr concentrations, which can be explained by their likely origins from certainly very distinctive geological areas. Moreover, three suspicious samples from this group are located in close proximity to the wine from Pomerol. From their disposition on the Sr elemental/isotopic scatter plot, the origin of these three dubious wines could be interpreted as from Bordeaux. Nevertheless, these wines have been identified as not veritable Bordeaux origin because they did not comply with the AOC regulations applicable to the labels (indications of production sites, winery's names, and grape varieties).

From the closer examining of the series of Bordeaux wine (Fig. 6B), it can be observed that red wines from Pomerol, Saint-Émilion, and white wines from Pessac-Léognan are characterized by significant variabilities of Sr elemental and isotopic composition, which exceed by several times the measurement uncertainties of analytical determinations. Furthermore, a typical trend applicable to most of the samples and expressed in an inverse relationship between total Sr concentrations and Sr isotopic compositions can be highlighted (Fig. 6B): lesser values of 87 Sr/ 86 Sr correspond to higher Sr elemental levels without a direct correlation with years of wine production. Indeed, samples from Pomerol represent the period of 40 years, white wine from Pessac-Léognan -4 years, and wine from Saint-Émilion were produced from the same vintage. This trend is most likely due to geochemical processes in soils, such behavior has been previously observed in soils from irrigated and non-irrigated vineyards [START_REF] Green | Distinguishing sources of base cations in irrigated and natural soils: evidence from strontium isotopes[END_REF]. Apart from the fact that soil profiles may be constituted by layers differing in the 87 Sr/ 86 Sr ratios, we can hypothesise a difference in Sr isotopes mobility, because the radiogenic isotope 87 Sr is being presented in a larger proportion under a lower Sr total concentrations. This was observed in wines, where Sr transferred through biotic and abiotic processes from soil to water and then to plants and grapes (Fig. 5).

Such correlation between Sr elemental and its isotopic composition gives means to discriminate among

Bordeaux's wine production sub-regions. For the studied Bordeaux wines, a certain distinction when plotting specifically the 87 Sr/ 86 Sr ratios versus inverse Sr concentrations can be seen in Fig. 6B: the wines originating from Pomerol and Saint-Émilion plotted very differently with respect to other samples, mainly due to the difference in geological structures of these two sub-regions that referred in paragraph 3.2. On the contrary, there is a significant overlap for the samples originating from Pessac-Léognan (red wines), Pessac-Léognan (white wines) and Pauillac. Nevertheless, without a special consideration of four samples from Saint-Émilion, the most complete discrimination of a single winery by means of Sr isotopic-and elemental specifications was achieved for the wines from Pomerol.

Testing of wine authenticity by means of 87 Sr/ 86 Sr and Sr concentrations

Sr isotopic specification had already been tested for wine authenticity issues [START_REF] Durante | An analytical approach to Sr isotope ratio determination in Lambrusco wines for geographical traceability purposes[END_REF][START_REF] Geană | Elemental profile and 87 Sr/ 86 Sr Isotope ratio as fingerprints for geographical traceability of wines: an approach on Romanian wines[END_REF]). The authenticity of doubtful "Bordeaux" was verified using Sr elemental-and isotopic approach. In the set of suspicious Bordeaux, four wines were labeled as a prestigious wine of high commercial value from a winery from the Pauillac appellation. By visual control, these bottles were indistinguishable from the authentic ones. In order to evaluate their authenticity, we compared their Sr isotopic and elemental signatures with those of authentic samples from the same winery and the same years of production. Regarding the Sr concentrations in two comparative groups "suspicious Pauillac" and "authentic Pauillac", a significant discrepancy can be observed immediately (Fig. 2): the suspicious samples contained 1.52, 0.74, 0.95, and 0.89 mg kg -1 , while the concentrations for authentic wines were more homogeneous: 0.17, 0.17, 0.19, and 0.18 mg kg -1 , for 2004, 2005, 2006, and 2007 respectively. Further, the 87 Sr/ 86 Sr ratios in suspicious wines varied largely from 0.70523 to 0.71266 (Fig. 3, uncolored circles marked by letters A, B, C and D). The version about Bordeaux provenance of two wines with the maximal (0.71266) and the minimal (0.70523) values can be immediately rejected, because this value do not correspond to the Sr isotopic variation in geology of the region (Fig. 3). Values of the 87 Sr/ 86 Sr ratio for two samples marked by uncolored circles B (0.71014 ± 0.00004) and C (0.70861 ± 0.00009) in Fig. 3, are within the typical range for Bordeaux region, but differ significantly from those of the authentic wine (green circles) ranging in the interval of 0.70906-0.70944. The combination of 87 Sr/ 86 Sr and Sr concentration, presented in the insertion chart in Fig. 6B, immediately clearly indicates that 2 comparing groups do not belong to the same set of samples, and the actual geographical origin of suspicious wines does not correspond to the declared one. This example illustrates how the binary Sr signature, isotopic and elemental, can help to characterize wine for authentic purposes.

Factors of influence on variability of Sr isotopic and Sr elemental content

As presented above, the use of the combined information of Sr elemental-and isotopic composition of wine can give evidence about its geographical origin. In this context it is important to estimate the allowable variation range of both parameters and factors affecting them. Apart from the crucial role of soil, there are several important factors that influence Sr elemental and isotopic variability in wine: climatic conditions, agricultural practices, management of wineries, winemaking techniques may be considered as the most significant.

Climatic conditions. The region of Bordeaux is influenced by atmospheric precipitations forming under the Atlantic Ocean, which can bring significant wet dissolved Sr elemental flux with a strong dependency on seasonal to inter-annual scales (Maneux, Grousset, Buat-Ménard, Lavaux, Rimmelin & Lapaquellerie, 1999). In the case of a high rainfall year, two effects are theoretically possible: 1) the flux of marine Sr with the isotopic signature of sea water -0.70918 [START_REF] Allègre | The fundamental role of island arc weathering in the oceanic Sr isotope budget[END_REF] can result the slight shift of the 87 Sr/ 86 Sr ratio in wine to the value of sea water; 2) considerable precipitations can also change the hydrochemical dynamics in soil horizons resulting in the release of extra-amount of bioavailable Sr sourced from soil or sub-soil substrata [START_REF] Nakano | Strontium isotopes in soil-plantatmosphere continuum (SPAC)[END_REF]. The climatic influence on the 87 Sr/ 86 Sr ratio in wine is a global factor and should be traced to a certain extent in all wines produced in the region.

The global changing of environmental climatic conditions, such as an increasing of ambient air temperature and variation of water regime can potentially lead to changing of Sr elemental and isotopic composition in labile soil fraction and, consequently, the 87 Sr/ 86 Sr ratio in wine.

Managing of vineyards.

The root system of vines from non-irrigated Bordeaux's vineyards develops over the years and can reach 20 meters deep. In search of water, vine roots penetrate different layers of soil and sub-soil and uptake the bioavailable Sr. Therefore, wine produced from young vines with still evolving roots and wine from a mature vineyard can slightly differ in 87 Sr/ 86 Sr due to geological heterogeneity of vineyard's soil profiles. Another factor affected directly Sr quantitative and qualitative content in wine is the application of fertilizers on vineyard soil. For example, lime and clay added for pH regulation purposes, contain some Sr with an individual value of the 87 Sr/ 86 Sr ratio [START_REF] Marchionni | Conservation of 87 Sr/ 86 Sr isotopic ratios during the winemaking processes of 'Red' wines to validate their use as geographic tracer[END_REF].

Managing of wineries.

The increasing/decreasing of vineyards through the purchase/sale of neighboring sites differing by pedological settings, as well as wine-making estate mergers may lead to one-off changes of the 87 Sr/ 86 Sr ratio in the corresponding period. Modification and renovation of winemaking and storing facilities (tanks, reservoirs, etc.), composition of glass bottles and possible migration of Sr, should be also taken into account.

Features of production process. The particular features of winemaking within an individual winery, such as the longtime usage of special equipment, adding of yeasts and bentonite during vinification could cause the specification in both, Sr elemental and isotopic composition of wine, with a certain regularity. Bottling and storage the wine is also an important stage for Sr specification due to possible migration of Sr from the glass (Chesson, Tipple, Mackey, Hynek, Fernandez & Ehleringer, 2012). These factors are the most difficult changes to correct, because of the commercial confidentiality of the process. However, in the context of food authenticity, these features can be used to specify the Sr elemental and/or isotopic signatures of final products (Epova et al., 2018). Analyzing all of the above, the internal variability of 87 Sr/ 86 Sr within the studied wines could have various sources. For the winery from Pomerol, a visible continuous influence from a new source of Sr starting around the late 1990's is apparent, that might be due to application of fertilizers or modification of the winemaking process. For other wineries, it is a difficult to single out a specific idea from the number of those available, thus, further studies are required.

Conclusion

This is the first study that concerns the Sr isotopic and elemental compositions of a large selection of authentic Bordeaux wines. The results of 43 genuine wines from four regional wineries demonstrate a moderate variability of 87 Sr/ 86 Sr ratio and Sr concentrations with a strong possibility to assigned Sr specifications for individual winemaking estates. The 87 Sr/ 86 Sr ratio found to be relatively stable in varietal blended wine and wine from different vintages. However, applied solely, the Sr isotope ratio method is not intended to be relied upon to definitely identify the geographical origin due to world-wide geological diversity and numerous factors masking the geological signature of wine, as it has been demonstrated using the case of imitated Bordeaux wines.

A clearer discrimination of geographical origin can be obtained through a combination of Sr isotopic and elemental signatures of wines. Such an approach provides the specific terroir-inherent and winemakingrelated tracer for authenticity and provenance assessment. With it, the studied wines produced by a winery from Pomerol AOC were successfully distinguished from the other authentic Bordeaux wines, and the wines of doubtful declared Bordeaux origin were denoted as imitated or mislabeled products, due to radically different elemental and isotopic compositions with respect to authentic samples.

To approve this method within the legal and scientific framework and corroborate the Sr isotopic-and elemental compositions as fingerprints for Bordeaux wines, isotopic analyses at TIMS and MC-ICP-MS quality levels, with precision and accuracy comparable to those of geological studies should be performed and compared with isotopic data of control samples from the soil substratum of regional vineyards. With this study authors emphasize a serious potential in the expansion of work aimed to establish the individual Sr isotopic-and elemental signatures of Bordeaux wines which are able to objectively support the authenticity of Bordeaux wines.

  ; Barbaste, Robinson, Guilfoyle, Medina & Lobinski, 2002; Almeida & Vasconcelos, 2004; Vorster, Greeff & Coetzee, 2010; Di Paola-Naranjo et al., 2011, Vinciguerra, Stevenson, Pedneault, Poirier, Hélie & Widory, 2016). In the view of vineyards from around the world, the 87 Sr/ 86 Sr ratio has been applied for the geographical origin classification of wines from South-Africa (Vorster et al., 2010), Argentina (Di Paola-Naranjo et al., 2011), Canada (Vinciguerra et al., 2016), Portugal (Almeida & Vasconcelos, 2001) and Romania (Geană, Sandru, Stanciu & Ionete, 2017). Recently, some new information and interest has been raised on this topic following the publication of a series of studies performed on Italian wines. Using an extra-large sample selection of authentic samples it was confirmed that: 1) Sr isotope composition of wine remained constant for different vintages (Mercurio et al., 2014; Durante et al., 2015; Petrini, Sansone, Slejko, Buccianti, Marcuzzo & Tomasi, 2015; Marchionni et al., 2013; Marchionni et al., 2016); 2) the ratio 87 Sr/ 86 Sr is not altered during the winemaking (Marchionni et al., 2016; Petrini et al., 2015; Tescione, Marchionni, Matte, Tassi, Romano & Conticelli, 2015); and 3) the ratio 87 Sr/ 86 Sr in wine can be forecast on the basis of pedological settings (Durante et al., 2013; Mercurio et al., 2014; Durante et al., 2015, Marchionni et al., 2013; Petrini et al., 2015; Marchionni

  wineries belong to the following appellations: Pomerol (11 red wines, vintages 1969-2010), Saint-Émilion (4 red wines, vintage 2011), Pessac-Léognan (15 red wines and 9 white wines, vintages 2009-2012), and Pauillac (4 red wines, vintages 2004-2007). All wines conform to the applicable AOC regulations, are made entirely on the winery's property from grapes owned by the winery and do not ever leave the property during fermentation, ageing, or bottling. The geographical location of vineyards under consideration can be seen in Fig. 1. Pomerol and Saint-Émilion represent the famous appellations of Bordeaux from the Libournais viticultural sub-region, situated on the right bank of the Dordogne River. The vineyards of Saint-Émilion are located on the slope of a large calcareous plateau where soils is rich in sands and clays. The vineyards of Pomerol are

  of 0.70943 -0.71005. The limited sample size in both studies, and recent improvements of the signal treatment (Waight et al., 2002; Albarède et al., 2004; Horsky et al., 2016) can explain a slight discrepancy between them.

  finding is consistent with the recent observations (Di Paola Naranjo, et al. 2011, Vinciguerra et al., 2016): different grape varieties equally accumulate Sr from the labile fraction of soil within the same geological substrata. With regards to Bordeaux wines, these facts are extremely important since the winemaking traditions in Bordeaux integrate the practice of wine varietal blending (fr. "l'assemblage des cépages"), when a final wine is produced by mixing of mono-varietal wines (i.e., Cabernet Sauvignon, Merlot, Cabernet Franc etc. -for red wines, and Sauvignon blanc, Semillon, Muscadelle, etc. -for white wines), and the assembled proportions may vary according to vintage. Further, as observed earlier (Durante et al., 2015; Petrini et al., 2015; Marchionni et al., 2013; Marchionni et al., 2016), the

Fig. 1 .

 1 Fig. 1. Geographical origins of studied authentic Bordeaux wines, appellation of Pomerol, Saint-

FigureFig. 2 .

 2 Figure(s) Click here to download Figure(s): Figures 1-6 Rev3.docx

Fig. 3 .

 3 Fig.3.87 Sr/ 86 Sr in the studied wines and comparison with wines from different world origins, as reported in the literature. Legend: within individual groups,

Fig. 4 .

 4 Fig. 4. Evolution of 87 Sr/ 86 Sr ratios in Jurassic and Cretaceous sea water with respect of periods of

Fig. 5 .Fig. 6 .

 56 Fig. 5. Time dependent changes of Sr concentrations and 87 Sr/ 86 Sr ratios observed in wines from a winery of Pomerol AOC produced in the period 1965-

Acknowledgements

The work was financially supported by the ORQUE SUDOE INTERREG project № SOE3/P2/F591, MASSTWIN project № 692241 and PROMETROFOOD project № GA 739568. A special thanks to Dr. Francis Grousset for helpful suggestions and discussions. The authors are grateful to the two reviewers whose comments and remarks have contributed to improving the manuscript.

additional contributions to the Sr isotopic compositions of wines from winemaking processes and agricultural practices are possible and will be further discussed.

The studied authentic wines characterized by a relatively narrow range of 87 Sr/ 86 Sr variations mainly attributed to overall homogeneous geological settings of the Bordeaux region. Indeed, the local geology of the region is extensively described, with specific consideration given to the regional viticulture [START_REF] Wilson | Terroir: The Role of Geology, Climate and Culture in the Making of French Wines[END_REF][START_REF] Bourrouilh | Geology and terroirs of the Bordeaux wines, France[END_REF]. This territory is a part of Gironde-Aquitaine sedimentary basin formed by erosion of the Pyrenees and the Massif Central between the end of the Tertiary and the beginning of the Quaternary periods. The soils are formed on a large limestone bedrock originated from expanses of alluvial sediments deposited by the Garonne and Dordogne rivers with gravel inclusions. According to [START_REF] Voerkelius | Strontium isotopic signatures of natural mineral waters, the reference to a simple geological map and its potential for authentication of food[END_REF], the typical values of the 87 Sr/ 86 Sr ratio in geological samples from this region can be expected to range between 0.70701 and 0.71100. All ratios 87 Sr/ 86 Sr obtained in this study for authentic Bordeaux wines are within the predicted limits (Fig. 3).

When comparing the average of Sr isotope ratios obtained for authentic Bordeaux wines and those from other wines worldwide (Fig. 3), it is notable that they have some important overlaps which certainly highlights the similarity of geological and pedological characteristics of provenancing territories. In order to achieve a reliable qualitative comparison, we used only results obtained by MC-ICP-MS and TIMS. Indeed, recent studies on Italian wines report the values of 87 Sr/ 86 Sr that overlap Bordeaux signatures: Cesanese wines 0.70894 -0.71062 [START_REF] Marchionni | Conservation of 87 Sr/ 86 Sr isotopic ratios during the winemaking processes of 'Red' wines to validate their use as geographic tracer[END_REF], and Lambrusco 0.70840 -0.70964 [START_REF] Durante | An analytical approach to Sr isotope ratio determination in Lambrusco wines for geographical traceability purposes[END_REF]. The whole interval of the ratios 87 Sr/ 86 Sr which can be potentially found in Bordeaux wines has been recorded in Prosecco wines [START_REF] Petrini | The 87 Sr/ 86 Sr strontium isotopic systematics applied to Glera vineyards: A tracer for the geographical origin of the Prosecco[END_REF], while a significant overlay with Aglianico wines is unlikely [START_REF] Marchionni | High-precision 87 Sr/ 86 Sr analyses in wines and their use as a geological fingerprint for tracing geographic provenance[END_REF]. When examining the Sr isotopic ratios in wine originated from other continents, the span of the 87 Sr/ 86 Sr expressed in lower values has been recorded for wine from Argentina 0.7071 -0.7093 (Di-Paola Naranjo et al., 2011). On the contrary to studied Bordeaux samples, 87 Sr/ 86 Sr ratios in wines from Quebec vary with a wide range of values, from 0.70988 up to maximum 0.71546, indicating a relative enrichment by the radiogenic isotope 87 Sr in Precambrian intrusive and metamorphic rocks composing the Canadian Shield. [START_REF] Vinciguerra | Strontium isotope characterization of wines from Quebec, Canada[END_REF].

Associated content

Supplementary material: list of studied wines, Sr elemental concentrations and Sr isotope ratios are listed in the Table S1. The operating parameters of the Q-ICP-MS and MC-ICP-MS can be seen on Table S2 andS3, respectively.

Conflict of interest statement

All the authors declare that there are no conflicts of interest.

Supplementary Material

Click here to download Supplementary Material: Supplementary materials Rev3.xlsx

Highlights:

• Sr elemental and isotopic composition of 43 Bordeaux wines is determined • Differentiation of authentic Bordeaux wines on the basis of their 87 Sr/ 86 Sr ratio

• Relationship between Sr concentrations and 87 Sr/ 86 Sr in wine

• Detection of wine counterfeits on the basis of 87 Sr/ 86 Sr and Sr concentrations

• Sr isotope ratio is a promising parameter for wine authenticity control *Highlights (for review)

Conflict of interest statement

All the authors declare that there are no conflicts of interest.

*Declaration of Interest Statement