Reconstructing 15,000 years of Arctic sea ice dynamics: High-resolution bromine records from the late Glacial to the Holocene

Arctic sea ice is a critical component of the climate system, yet its long-term variability and drivers remain poorly understood due to the scarcity of direct paleoclimate records. In this study, we utilize bromine records preserved in four Greenland ice cores—NEEM, DYE-3, EGRIP, and RECAP—to reconstruct changes in Arctic sea ice cover over the past 15,000 years. Bromine in polar snow and ice is primarily derived from "bromine explosions" occurring over seasonal sea ice surfaces. These are autocatalytic photochemical reactions in which sea salt from brine and frost flowers on newly formed sea ice is activated, releasing reactive bromine into the atmosphere. Because these processes are strongly linked to the presence of first-year (seasonal) sea ice, bromine enrichment in ice cores reflects the extent and variability of seasonal sea ice cover. The combined records provide a high-resolution, multi-site perspective on sea ice variability during the late glacial–Holocene transition and throughout the Holocene. By integrating these records, we explore the spatial variability of sea ice changes and highlight the heterogeneous response of the Arctic Ocean to climatic perturbation. These results offer new insights into the mechanisms controlling past sea ice variability, providing important context for evaluating future Arctic change.