Tree-ring cellulose oxygen isotope reveals summer hydroclimate variability across the East European Plain

Abstract. Hydroclimate variability across the East European Plain plays a critical role in regional ecosystems and climate dynamics, yet moisture-sensitive tree-ring proxies remain scarce in this region, particularly at high latitudes where tree-ring width (TRW) and density are primarily controlled by temperature. Tree-ring cellulose oxygen isotopes (δ¹⁸O_TRC) have the potential to serve as a useful hydroclimate proxy, but their climatic signal in this region remain poorly understood. Here, we developed three δ¹⁸O_TRC chronologies of Scots pine (Pinus sylvestris L.) from the northern, central, and southern East European Plain to assess their climate signals. The δ¹⁸O_TRC chronologies from the three sites show similar response to summer moisture condition. The northern δ¹⁸O_TRC shows the strongest relationship with vapor pressure deficit (VPD), the central δ¹⁸O_TRC records both hydroclimate variability and precipitation oxygen isotopes (δ¹⁸O_p) signals, and the southern δ¹⁸O_TRC mainly reflects the Standardized Precipitation Evapotranspiration Index (SPEI). In contrast, TRW shows weak hydroclimate sensitivity at the northern and central sites, whereas at the southern site it mainly reflects soil moisture. Overall, compared with TRW, δ¹⁸O_TRC better captures regional summer hydroclimate signals, particularly capturing signals related to atmospheric drought.