Climate impacts on tree-ring stable isotopes across the Northern Hemispheric boreal zone

Boreal regions are changing rapidly with anthropogenic global warming. In order to assess risks and impacts of this process, it is crucial to put these observed changes into a long-term perspective. Summer air temperature variability can be well reconstructed from conifer tree rings. While the application of stable isotopes can potentially provide com-plementary climatic information over different seasons.In this study, we developed new triple stable isotope chronologies in tree-ring cellulose (813Ctrc, 818Otrc, 82Htrc) from a study site in Canada. Additionally, we performed regional aggregated analysis of available stable isotope chronologies from 6 conifers' tree species across high-latitudinal (HL) and -altitudinal (HA) as well as Siberian (SIB) transects of the Northern Hemispheric boreal zone.Our results show that summer air temperature still plays an important role in determining tree-ring isotope variability at 11 out of 24 sites for 813Ctrc, 6 out of 18 sites for 818Otrc and 1 out of 6 sites for 82Htrc. Precipitation, relative humidity and vapor pressure deficit are significantly and consistently recorded in both 813Ctrc and 818Otrc along HL. Summer sunshine duration is captured by all isotopes, mainly for HL and HA transects, indicating an indirect link with an increase in air and leaf temperature. A mixed temperature-precipitation signal is preserved in 813Ctrc and 818Otrc along SIB transect. The 82Htrcdata obtained for HL-transect provide information not only about growing seasonal moisture and temperature, but also capture autumn, winter and spring sunshine duration signals. We conclude that a combination of triple stable isotopes in tree-ring studies can provide a comprehensive description of climate variabil-ity across the boreal forest zone and improve ecohydrological reconstructions.

Automated summary

This study analyzed stable isotopes in tree rings from Canada and found that summer air temperature plays a crucial role in determining tree ring isotope variability. The study also identified the effects of precipitation, relative humidity, vapor pressure deficit, and sunshine duration on tree ring isotopes. By combining multiple stable isotopes in tree ring studies, a comprehensive description of climate variability in boreal regions can be achieved.