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The West Antarctic Peninsula is among the fastest-warming regions on Earth and may be approaching a climatic tipping point [1,2]. Ongoing warming threatens the stability of frozen ground and permafrost, with potentially important consequences for terrestrial carbon and nutrient cycling. In Antarctic terrestrial ecosystems soil microorganisms represent the dominant biological drivers of biogeochemical processes. However, their role in regulating carbon turnover and greenhouse gas production during summer thaw remains poorly constrained. Here, we present observations from eight terrestrial sites along the West Antarctic Peninsula, where the last seven years have been the warmest on record [2]. Soil surface temperatures ranged from 2.3 to 17.1 °C (mean 8.5 °C). We combined shotgun metagenomics with soil geochemistry, geological context, and interstitial soil gas composition and isotopic fingerprint to characterize microbial taxonomic and functional diversity and its environmental controls. Microbial community composition and metabolic potential differed markedly among sites and showed a strong relationship with soil temperature. Metagenomic data reveal widespread genetic potential for the degradation of complex and refractory organic matter, indicating that Antarctic soil microbial communities actively contribute to carbon mobilization and greenhouse gas production under sustained warming. By integrating microbial, geochemical, and geological observations, this study provides new process-level insights into terrestrial ecosystem responses to climate change in polar regions. Our results offer empirical constraints on microbial-driven soil carbon dynamics that are currently underrepresented in ecosystem and Earth system models, highlighting the need to explicitly account for Antarctic soil microbial processes when predicting future biogeochemical cycling in a warming climate.Masson-Delmotte, V. et al. (eds) IPCC (Cambridge University Press, 2021).Gorodetskaya, I.V., Durán-Alarcón, C., González-Herrero, S. et al. npj Climate and Atmospheric Science 6, 202 (2023).