Tree-ring isotopes adjacent to Lake Superior reveal cold winter anomalies for the Great Lakes region of North America.

Tree-ring carbon isotope discrimination (ΔC) and oxygen isotopes (δO) collected from white pine (Pinus strobus) trees adjacent to Lake Superior show potential to produce the first winter-specific paleoclimate reconstruction with inter-annual resolution for this region. Isotopic signatures from 1976 to 2015 were strongly linked to antecedent winter minimum temperatures (T), Lake Superior peak ice cover, and regional to continental-scale atmospheric winter pressure variability including the North American Dipole. The immense thermal inertia of Lake Superior underlies the unique connection between winter conditions and tree-ring ΔC and δO signals from the following growing season in trees located near the lake. By combining these signals, we demonstrate feasibility to reconstruct variability in T, ice cover, and continental-scale atmospheric circulation patterns (r ≥ 0.65, P < 0.001).