Peatland trees record strong and temporally stable hydroclimate information in tree-ring δ¹³C and δ¹⁸O

Abstract. Peatland trees are valuable archives of paleoclimatic information; however, gaps persist in understanding the relationships between tree growth, peatland hydrology, and hydroclimate variables. While previous research in peatlands has mainly focused on tree-ring widths (TRW), yielding inconclusive results, the potential of stable carbon (δ¹³C) and oxygen (δ¹⁸O) isotopes in tree rings remains unexplored. In this study, we develop TRW, δ¹³C, and δ¹⁸O chronologies of Scots pine trees located in a Swedish peatland and a reference site on bedrock with a mineral soil layer. We assess their responses to hydroclimate conditions and evaluate their potential for reconstructing hydroclimate variations. Our findings show significant differences in mean TRW and δ¹³C values between the peatland and reference sites. Moreover, while all three proxies exhibit uniform year-to-year variations across sites, we observe discrepancies in long-term trends, particularly in δ¹³C. Although the climate sensitivity of TRW is weak and non-homogenous, the δ¹³C and δ¹⁸O peatland and reference chronologies contain robust and consistent signals, with a maximum sensitivity to water table, precipitation, and vapor pressure deficit (VPD) variations during summer. Both δ¹³C and δ¹⁸O chronologies show stable relationships with three key hydroclimate variables over time. In conclusion, while TRWs from living peatland pines at our sites have limited potential to record high-frequency hydroclimate information, δ¹³C and δ¹⁸O chronologies can serve as excellent proxies for the reconstruction of past hydroclimate changes.