Annual radiocarbon variability in southern South America recorded by <i>Fitzroya cupressoides</i> , AD 970–1084

Abstract Annually resolved radiocarbon ( 14 C) records from tree rings provide a high-resolution archive for investigating short-term atmospheric 14 C variations driven by solar and cosmic activity, as well as terrestrial processes, including geomagnetic modulation, stratosphere–troposphere exchange, ocean–atmosphere interactions, and tree physiological traits. While extensive data are available for the Northern Hemisphere, comparable high-resolution records from the Southern Hemisphere are scarce, making it difficult to obtain robust 14 C calibration for the south and to evaluate 14 C distribution models. Here, within the framework of the CHASCA project, we present a new annually resolved 14 C record from Fitzroya cupressoides , a long-lived conifer native to southern South America, spanning AD 970–1084 (RAL060), with samples collected in North Patagonia, Argentina. This is the first annually resolved radiocarbon series from South America and among the longest for the Southern Hemisphere. The CHASCA series shows strong agreement with Northern Hemisphere datasets and with SHCal20 confirming the expected interhemispheric offset. It also captures the AD 993–994 solar particle event, with a statistically significant level (≈ 7 σ), though with reduced amplitude compared to the shorter decade-long records from New Zealand and Chile. This attenuation may reflect a combination of stratospheric–tropospheric dynamics, regional environmental conditions, and species-specific growth dynamics, although these mechanisms remain speculative and require further investigation, underscoring the complexity of local expression of cosmogenic 14 C signals. The CHASCA series thus extends the geographic coverage of annually resolved- 14 C datasets and establishes South America as a key region for detecting and comparing short-term cosmogenic events.