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Global climate change scenarios predict not only higher temperatures, but also increased climatic variability. In cold regions, these changes may bring about a shift in the frequency of soil freeze-thaw cycles (FTCs), which represent a significant physiological challenge, especially for small, poikilothermic animals with limited mobility. To assess the impact of FTCs on cold-adapted soil biota, we evaluated freeze-thaw dynamics (i.e., 0 A degrees C crossings) and demographics of the dominant nematode Scottnema lindsayae (proportion of adults, population size) over 20 years in soils at two locations in Taylor Valley, Antarctica. Based on hourly soil temperature data, we demonstrate that FTCs are a frequent feature in Taylor Valley, but with high inter-annual and spatial variability. Valley topography and soil moisture were found to impact FTC frequency, suggesting that basins within Taylor Valley have different susceptibilities to environmental variability. Increased FTC frequency in 1999-2001 coincided with a shift in S. lindsayae populations, with fewer juveniles reaching maturity. In the years following decreased adult proportions, overall S. lindsayae numbers were reduced, implying a strong negative effect of FTCs on in situ recruitment. Our results suggest that increased FTC frequency in the Dry Valleys slows S. lindsayae development, reducing reproductive success, and may take years to impact population size, which demonstrates the importance of long-term research to accurately predict the consequences of climate change on soil biota and biogeochemical cycling in the cold regions.