Oceanic viticulture across contrasting ENSO phases: A three-year field case study with Albariño and Tannat

Climate change is expected to significantly alter the suitability of winegrowing regions, with direct consequences for grape yield and wine quality. Among the most widely studied adaptation strategies is the relocation of vineyards to cooler sites. In this context, a three-year field study was conducted to evaluate the physiological, agronomic, and metabolic responses of Vitis vinifera L. cvs. Albariño and Tannat across three sites located at the same latitude in southern Uruguay, but differing in topography and proximity to the Atlantic Ocean. The study spanned three growing seasons with contrasting ENSO phases: 2023 (La Niña, with the warmest summer in 50 years), 2024 (El Niño, characterised by temperate and humid conditions), and 2025 (Neutral). Albariño exhibited great stability across sites and vintages; however, oceanic plots consistently showed higher levels of titratable acidity, primarily due to malic acid, which impacted the soluble solids/acidity ratio. This situation occurred despite the fact that harvest dates were systematically later in oceanic areas, with a difference of up to 20 days. This condition favours slow ripening, which is desirable for aroma synthesis. Tannat displayed greater sensitivity to interannual climatic variation and site effects. Notably, within the oceanic plots, the more ocean-exposed site preserved higher malic acid levels, whereas the less exposed site showed higher anthocyanin concentrations. The 2023 growing season led to elevated leaf temperatures and vapour pressure deficits in both varieties, impacting net CO2 assimilation, especially at the traditional inland site. The thermal pressure on both cultivars was associated with earlier harvest, particularly at the inland reference, where Tannat, in particular, showed a decrease in anthocyanins, indicating an imbalance in phenolic/technological ripening. Overall, oceanic conditions moderated thermal stress and reduced interannual variability, highlighting the buffering role of Atlantic influence under warm seasons. These findings suggest cultivar-specific interpretations: Albariño appears comparatively resilient under variable seasons, whereas Tannat may require site- and season-tailored management to maintain the balance between technological and phenolic maturity under warming conditions.