Arctic and North Atlantic Oscillation phase changes are recorded in the isotopes (δ18O and δ13C) of Cassiope tetragona plants

The Arctic and North Atlantic Oscillations (AO/NAO) are large‐scale annual modes of atmospheric circulation that have shifted in the last 30 years. Recent changes in arctic climate, including increasing surface air temperature, declining sea ice extent, and shifts in the amounts seasonality of precipitation are linked to the strong positive phase of the AO/NAO. Here, we show that phase changes in the AO/NAO are recorded in the isotopic (δ¹⁸O and Δ‐carbon isotope discrimination) characteristics of the long‐lived circum‐arctic plant, Cassiope tetragona, as summer rain has become a more important water source than snowmelt water which in turn has lead to decreases in Δ and reductions in plant stem growth. These isotopic records in C. tetragona may facilitate reconstructions of climate, plant–soil water relations, plant gas exchange attributes and a mechanistic understanding of growth responses to shifts in atmospheric circulation. If plant specimens were available for populations across the arctic as part of the International Polar Year, these archives could provide a circum‐arctic record of historical climate change and associated shifts in physiological plant performance and growth.