Anomalously high activities of short-lived radium isotope ²²⁴Ra, measured in the summer surface water of the Arctic Ocean, have long been enigmatic. Through experiments, we demonstrate that sea ice effectively absorbs dissolved ²²⁸Ra during formation, enabling in-situ production of ²²⁴Ra via a complete chain of radioactive decay within the ice matrix. The accumulated ²²⁴Ra in sea ice gets released to surface water upon melting. We develop a coupled sea ice-radium dynamics model to simulate this seasonal production-and-release mechanism. The model reproduces the observed ²²⁴Ra signals, as amplified by the seasonal sea ice freezing-melting cycle. Using satellite-derived sea ice records along with model predictions, we further show that shifts in sea ice extent and seasonality caused by climate change drive significant changes of ²²⁴Ra dynamics, in addition to the effect due to rising continental input of ²²⁸Ra from thawing permafrost. The ²²⁴Ra activity encodes the cumulative effects of seasonal ice freezing–melting cycle shift and permafrost thaw, and serves as an integrative tracer of climate change impacts on the Arctic cryosphere and hydrosphere.

暂无