Temperature dependence of grain size in Tibetan ice core

Grain size in ice cores can not only reflect the glacial strain processes but also be linked to climate change. However, the variation of grain size along ice cores in mountain glaciers remains largely unexplored. Here, we continuously measured the ice grain areas along two deep ice cores drilled from the Tibetan Plateau, and found that the two ice cores exhibit vertical grain area differentiation at the hundred-meter scale, analogous to polar ice-core profiles. Relatively higher temperatures significantly accelerate grain growth and result in larger grain areas. Refreezing under warm conditions gives rise to abrupt increases in grain area within melt-refrozen layers, whereas impurities result in abrupt decreases in grain area within impurity layers. Together, these two factors drive centimeter-scale fluctuations in grain area. Even so, we also found that grain area exhibits a significant correlation with δ 18 O in ice layers where Rotation Recrystallization (RRX)-induced refinement is negligible, indicating that the grain size of mountain glacier ice cores can retain temperature signals.