Reassessing Arctic 137Cs deposition history with a 70-year Greenland ice core archive

Accelerated Arctic warming may remobilize legacy radioactive contaminants preserved in the cryosphere, increasing the need for reliable historical baselines. Here, we report a previously unrecognized systematic bias in environmental radionuclide measurements, and demonstrate its impact through reconstruction of a high-resolution 137 Cs record (1947–2015) in an ice core collected at Camp Century, Greenland. Ultra-low-background gamma-ray spectrometry in the underground HADES laboratory enabled robust detection of ultra-low-level post-1975 137 Cs signals that are difficult to resolve using conventional aboveground spectrometry. Comparisons between direct measurements and processed meltwater analysis reveal systematic underestimations of 137 Cs activity by 25–50% in processed water. Direct measurement of storage bags identifies adsorption onto low-density polyethylene bags as the dominant loss mechanism. This finding highlights the need to account for often-overlooked storage to avoid bias in future environmental 137 Cs analysis. Correcting these biases resolves discrepancies with previous monitoring data and yields the first inland 137 Cs record for northwest Greenland. Spatial patterns indicate that deposition is controlled by latitudinal transport gradients, precipitation driven scavenging, and enhanced in-cloud removal at high altitude sites, providing a mechanistic basis for future environmental risk assessments under Arctic warming.