National and EU legislation codifies wine production areas in the Czech Republic. Accordingly, there exist two regions, “Morava” (Moravia) with four sub-regions (Znojmo, Mikulov, Velké Pavlovice, Slovácko, Figure 1) and “Čechy” (Bohemia) with two sub-regions (Mělník, Litoměřice).

The Morava region, with its four sub-regions, is a continuous area in Southern Moravia, roughly around and between the cities of Brno, Uherské Hradiště, Hodonín, Břeclav, and Znojmo. The region straddles the NE–SW trending contact of two large geological units, the Bohemian Massif in the west and the Western Carpathians in the east. This main boundary also controls the orientation of almost all geological units in the area, which, in map view, forms parallel bands.

Sedimentary rocks such as loess deposits, siliciclastic deposits, Pliocene marine and continental sediments of the Vienna Basin, mudstones, sandstones, and carbonates predominate in the region. The NE part of Znojmo and Velké Pavlovice sub-regions is formed by Cadomian igneous (granites) and various Variscan metamorphosed units (orthogneiss), partly covered by Upper Paleozoic sediments (Šimíček et al., 2021). Loess and its derivatives cover about 20 % of the Moravian surface and are an important part of the European loess belt (Šimíček et al., 2021).

The studied vineyards are located on loess deposits (Figure 1C), which are more than 20 m thick (Šimíček et al., 2021; Waroszewski et al., 2021). Source regions for Pleistocene aeolian loess deposits of these sediments are expected to be in the Variscan part of the Bohemian Massif (Lisá and Uher, 2006).

Schaller (2017) described the modern concept of terroir in agriculture and concluded that many variables contribute to the landscape imprint on a particular product. Ideally, at least some of those variables would be a set of quantifiable parameters that could be unambiguously tested. Wine-growing areas are characterised by natural environmental conditions, such as climate, soil conditions, and the human factor, which is decisive in selecting variety and agrotechnical practices. The "soil-plant-atmosphere" connection significantly determines the character and results of a certain vineyard (Santos et al., 2020).

Modern geochemistry could provide a powerful toolkit for wine "terroir" specification. Trace element composition of wines (Kment et al., 2005), such as Sr (Epova et al., 2019), could be characteristic of different viticulture areas. However, Sr isotopic composition is only effective in complex geological investigations. The composition of the local rainwater (Figure 6) is an essential parameter contributing to the overall isotopic characteristics of the terroir. Analysis of a groundwater sample gives an overview of the isotopic composition of the available Sr and simplifies the investigation with the complicated geological structure of the bedrock. Information on ⁸⁷Sr/⁸⁶Sr of bio-available Sr in the local soil and ⁸⁷Sr/⁸⁶Sr composition of wines (or juices or musts) of different vintages could mark the characteristic limit values of ⁸⁷Sr/⁸⁶Sr for a specific locality. Together, these parameters allow identification of wine's geographical origin and authenticity.

Santos et al. (2020) assume that all factors can influence wine quality and composition. Therefore, future wine studies could focus on these factors and their impact on ⁸⁷Sr/⁸⁶Sr. Despite numerous publications about wine's ⁸⁷Sr/⁸⁶Sr composition, there is not yet sufficient evidence to connect the wine-soil-bedrock signatures. Unfortunately, a large proportion of the previously measured Sr isotopic dataset was measured on instruments (single collector ICP-MS, even optical emission spectrometers ICP-OES) that are not specifically intended for precise isotopic ratio measurements. For the most part, those instruments lack the mass resolution required to resolve neighbouring peaks and make it difficult to collect the entire peak in the detector at once (i.e., have a "flat-topped" peak). Therefore, these data are largely unusable, given the relatively small differences in isotopic signatures of the geochemical reservoirs involved. Consequently, we agree with Epova et al. (2019) and Rosner (2010) that only isotopic analyses at TIMS and MC-ICP-MS quality levels are comparable to geological studies, with precision and accuracy. Only these data should be used for modelling rock-soil-water-wine processes and determining the origin of wines.

The geology of the studied Moravian region is very heterogeneous. In addition to loess sediments, other rocks with contrasting ⁸⁷Sr/⁸⁶Sr composition also occur in South Moravia, such as marine sediments, granitic rocks, and flysch. The whole rock Sr ratios of the marine sediments can thus be estimated from the published global marine Sr evolution curve for the Phanerozoic (McArthur et al., 2012). In general, seawater ⁸⁷Sr/⁸⁶Sr was < 0.709 during the Mesozoic and Cenozoic (McArthur et al., 2012), similar to or lower than local rainwater ⁸⁷Sr/⁸⁶Sr = 0.7097 (Novak et al., 2020a; Novak et al., 2020b).

Cretaceous to Neogene flysch sediments, characterised by a heterogeneous ⁸⁷Sr/⁸⁶Sr composition (Mason et al., 1996), range from 0.7078 to 0.7170 for the Eastern Carpathian samples. Modern ⁸⁷Sr/⁸⁶Sr of granitic rocks of the Bohemian Massif are more radiogenic than seawater carbonates, flysch, and loess sediment, with ⁸⁷Sr/⁸⁶Sr compositions of up to 0.730 (Janoušek et al., 2022; Janoušek et al., 2020). In some cases, values are extremely high (over 0.8; (Erban Kochergina et al., 2021; Hasalová et al., 2008). The heterogeneous ⁸⁷Sr/⁸⁶Sr composition of Southern Moravia bedrock allows us to test the hypothesis that such heterogeneity will be reflected in the ⁸⁷Sr/⁸⁶Sr of wines.

A recent study (Erban Kochergina et al., 2021) focused on the relationships between the Sr isotopic composition of the bedrock, water input, and plant tissue. The authors examined different tree species (oak, pine, spruce) from the contrasting geological sites without evolved soil horizons, for example, quarries and rock outcrops. The authors offered a simplified model for determining plant origin based on Sr isotopic ratios. We used this model to describe the relationship between the isotopic composition of wine, rainwater and bedrock (Figure 4). The determinative factor for this model is the relative Sr isotopic compositions of rock and rainwater. While the isotopic composition of the local rainwater varies between 0.709 and 0.710, similar to sea spray ⁸⁷Sr/⁸⁶Sr, we can divide all rocks into two groups: (i) rocks with ⁸⁷Sr/⁸⁶Sr lower than the local rainwater composition and (ii) rocks with more radiogenic ⁸⁷Sr/⁸⁶Sr than the local rainwater. The authors suggest that the plant's final ⁸⁷Sr/⁸⁶Sr composition is located on the mixing line between ⁸⁷Sr/⁸⁶Sr of rainwater and ⁸⁷Sr/⁸⁶Sr of bedrock.

The tendency of plant material to have isotopic compositions, which are a mixture of bedrock and atmospheric deposition (rain) compositions, may be used to find the origin of a wine sample from among a set of putative localities. The isotopic composition of rainfall is uniform relative to the highly variable contribution derived from the local geology. Because of this, the relative positions along the ⁸⁷Sr/⁸⁶Sr axis where the wine sample, precipitation, and bedrock of the various candidate localities plot determine whether the origin of the wine sample can be identified. This is shown in the following three cases, each involving two candidate sites: (i) The bedrock of the candidate sites falls on opposite sides of the rainfall value. Since the wine sample is a mixture of precipitation and bedrock isotopic values, the locality plotting on the opposite side of the rainfall value from the wine sample can be excluded (Figure 4A). (ii) If there are two sites with bedrock values on the same side of the rainfall value and similar to the wine sample, the wine sample could have originated from either of the two sites (Figure 4B). (iii) If there are no putative localities with bedrock on the same side of the rainfall value, there is high confidence that none of the sites is the actual origin (Figure 4B).

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The model considers simple scenarios, whereby different Sr isotope signatures of the bedrock and overlapping ranges of wine ⁸⁷Sr/⁸⁶Sr ratios due to partial uptake of atmospheric Sr (adopted from Erban Kochergina et al., 2021). This model can also be used to determine the origin of the wine. Knowing the composition of the wine and the bedrock candidates, we can determine the putative origin of the wine: (i) if the Sr isotopic signatures of bedrock/bulk soil at two candidate sites plot in opposite directions relative to the ⁸⁷Sr/⁸⁶Sr ratio of rainfall (~ 0.710), the Sr isotope analysis of the plant (wine) sample shows the probable place of origin (Figure 4A); (ii) if the ⁸⁷Sr/⁸⁶Sr ratio of the plant (wine) sample is more/less radiogenic than local rainfall, compared to the two candidate sites, it is likely that neither of the candidate sites was the place of the plant (wine) origin (Figure 4B); (iii) if the ⁸⁷Sr/⁸⁶Sr ratios of wines and two candidate sites are similar, there is no way to indicate the likely place of origin (Figure 4B).

Almeida and Vasconcelos (2004), Tescione et al. (2020), and Marchionni et al. (2016) conclude that the winemaking process does not affect the ⁸⁷Sr/⁸⁶Sr composition of the wine. These studies also confirm that the differences in ⁸⁷Sr/⁸⁶Sr isotope ratios are the result of heterogeneity of the soil/bedrock composition and, therefore, Sr isotope composition could be a good tool to trace the origin of the wine. Taking these results into account, we were able to rule out the influence of winemaking on the ⁸⁷Sr/⁸⁶Sr isotope heterogeneity of the Moravian wines. It also allows us to compare samples from different wineries.

The ⁸⁷Sr/⁸⁶Sr of the wine samples (Figure 3) from Groups A and B are almost identical and comparable to groundwater and bio-available ⁸⁷Sr/⁸⁶Sr. The Group A and B wines belong to different sub-regions of Mikulov and Velké Pavlovice, respectively. This indicates that the geographical/historical divisions into wine (sub-) regions do not correspond to the chemical composition of wines, resulting from the locality's geological characteristics. The low heterogeneity of the wine samples is comparable to the changes in the ⁸⁷Sr/⁸⁶Sr with depth.

Group C and D samples have lower ⁸⁷Sr/⁸⁶Sr ratios than Groups A and B. However, these differences are insufficient to distinguish production from these localities.

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The indistinguishable isotopic compositions of grape juices, must, and wine enables us to see connections between them (Tescione et al., 2020). Therefore, two wine samples from the same winery, vintage, and locality should have an identical Sr isotopic composition. We can also recognise two samples from geologically different localities (e.g., basalts and granites, Figure 4). In addition, we describe the geological limitation of the connection between bedrock, soil, and wine Sr isotopic composition.