Greenland ice core isotope variability is controlled by systematic changes of depositional noise

Ice core stable water isotopes are among the few proxies capable of capturing past climate variability at timescales up to decades throughout and beyond the last Glacial period. They are therefore used to assess climate variability across different global mean temperatures and climate states. However, a significant portion of the isotope variability in ice cores can be attributed to noise, originating, for example, from stratigraphic disturbances at the snow surface and irregular, patchy precipitation events (i.e., precipitation intermittency). This additive noise is influenced by climate system components like accumulation, precipitation, or wind, which can systematically shift over time and across different climate states. Still, most recent studies on isotope variability have largely overlooked the impact of changing noise levels. In this study, we therefore use data from the Greenland ice cores GRIP, GISP2, and NGRIP to show how the common (signal) variability and the independent (noise) variability have evolved over the past 100,000 years and how these variations correlate with the prevailing climate state and accumulation rates. Our findings highlight that systematic fluctuations in noise levels must be accounted for as an additional source of uncertainty when comparing isotope variability across both high and low frequencies between different time periods.