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 (δ18OTRC) have the potential to serve as a useful hydroclimate proxy, but their climatic signal in this region remain poorly understood. Here, we developed three δ18OTRC chronologies of Scots pine (Pinus sylvestris L.) from the northern, central, and southern East European Plain to assess their climate signals. The δ18OTRC chronologies from the three sites show similar response to summer moisture condition. The northern δ18OTRC shows the strongest relationship with vapor pressure deficit (VPD), the central δ18OTRC records both hydroclimate variability and precipitation oxygen isotopes (δ18Op) signals, and the southern δ18OTRC 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, δ18OTRC better captures regional summer hydroclimate signals, particularly capturing signals related to atmospheric drought.