Speaker
Description
Cesium-137 (137Cs), a key anthropogenic radionuclide from global nuclear weapons fallout, is a powerful tracer for studying long-range atmospheric transport and deposition processes. Polar ice cores, particularly from Greenland, are suitable natural archives for reconstructing these historical fallout patterns. However, the reliability of existing 137Cs records is potentially compromised by substantial analytical challenges, including ultra-low concentrations and poorly constrained losses during sample handling.
In this study we investigated the 137Cs record in an ice core collected at Camp Century, Greenland by: (1) performing gamma-ray spectrometry 225 m underground in a quasi-background-free environment; (2) quantifying and mechanistically explaining 137Cs losses during sample preparation; and (3) reconstructing a robust 137Cs deposition profile. Controlled experiments comparing raw meltwater with processed samples reveal a systematic underestimation of 137Cs activity by approximately one-half to one-third in the processed fraction. Direct measurements of storage bags show activities comparable to those in the meltwater, demonstrating that significant adsorption onto low-density polyethylene (LDPE) containers—not filtration or chemical separation steps—is the dominant loss mechanism. This container-induced bias compensates for the observed deficit, suggesting that historical datasets, particularly those using pre-1975 protocols, likely underestimate true 137Cs inventories. Consequently, we recommend that future studies prioritize frozen storage. When melting is unavoidable, immediate acidification, minimized storage time, and avoidance of LDPE are critical. Where LDPE use is necessary, a full mass-balance analysis, including container leachates, is essential.
Applying these corrections, we evaluated the spatial variability of 137Cs inventories across Greenland for the main fallout period (1945–1982). Beyond the traditional perception of a decreasing trend from the mid-latitudes toward the Arctic, a more pronounced latitudinal decline is observed along the coast of Greenland. Moreover, a fast increase is evident from low-elevation surface stations to the higher-elevation inland sites studied. This enhanced deposition efficiency is attributed to orographic effects and more efficient in-cloud scavenging at this higher-elevation inland site (1887 m). Our findings underscore that rigorous methodological control is not merely a precaution but a necessity for accurately reconstructing global nuclear fallout signals and refining our understanding of pollutant transport and scavenging in Greenland. The data calls for new investigations to better understand transport and deposition patterns in Greenland and to ensure good radioprotection around legacy sites linked to global warming effects.