Covariance and climate signals among state-of-the-art tree-ring proxies

Tree-ring stable isotopes and wood anatomical traits emerged as powerful proxies for paleoclimate reconstructions, providing information beyond traditional ring width and wood density chronologies. However, comprehensive comparisons of these state-of-the-art tree-ring proxies derived from the same trees have yet to be performed to identify and differentiate their full paleoclimatic skill. Here, we assess covariance and climate signals in tree-ring width (TRW), maximum latewood density (MXD), cellulose stable carbon (δ13Cc) and oxygen (δ18Oc) isotopes, lignin methoxy carbon (δ13Cm) and hydrogen (δ2Hm) isotopes, radial cell lumen diameter (Drad), and radial and tangential cell wall thickness (CWTrad/CWTtan) of ten Bosnian pines (Pinus heldreichii) from a treeline site on Mt. Smolikas, Greece. Proxy cross-comparison over the period 1861–2020 CE reveals strong covariance between detrended δ13Cc and δ13Cm (r ≥ 0.81). δ13Cc and δ18Oc exhibit the highest inter-series correlations (r ≥ 0.61) among all proxies. δ13Cc, δ13Cm, δ18Oc, together with Drad, show considerable skill for reconstructing summer precipitation, whereas MXD and δ2Hm may be used for summer temperature reconstructions. Enhanced inter-series and hydroclimate correlations, along with a prolonged seasonality are significant advances of the isotopic and wood anatomical measurements compared to TRW. Our findings highlight the importance of integrating new isotopic, particularly δ13Cc, and xylem anatomical data into existing TRW networks to enhance our understanding of past hydroclimate variability and contextualize the recent aridification of the Mediterranean region.