This study explores microbial nitrogen cycling in coastal Antarctica, revealing that the primary source of nitrate (NO₃⁻) is biological nitrification, not atmospheric deposition. The research identifies the dominance of complete ammonia oxidizing (comammox) *Nitrospira* in the nitrification process, which is a key driver of nitrogen cycling in this region. These bacteria are well-adapted to the cold and oligotrophic conditions of coastal Antarctica, utilizing strategies such as trehalose synthesis for cold stress resistance, high substrate affinity for resource utilization, and alternate metabolic pathways under nutrient-scarce conditions. The study also shows that the microbial nitrogen cycle in coastal Antarctica is distinct, encompassing most nitrogen cycling processes except for anaerobic ammonium oxidation (anammox). The absence of anammox functional markers suggests unique microbial nitrogen cycling properties in this remote region. The research further highlights the significant role of comammox *Nitrospira* clade B in nitrification, as confirmed by ¹³C-DNA-based stable isotope probing. The study provides insights into the microbial diversity and metabolic capabilities in coastal Antarctic soils and sediments, revealing the importance of nitrification in the nitrogen budget of this region. The findings underscore the need for further investigation into the impact of global warming on microbial communities and their role in biogeochemical cycles in extreme environments. The study also contributes to the expansion of microbial genomic data for Antarctica, providing valuable resources for future research on microbial interactions and climate change.This study explores microbial nitrogen cycling in coastal Antarctica, revealing that the primary source of nitrate (NO₃⁻) is biological nitrification, not atmospheric deposition. The research identifies the dominance of complete ammonia oxidizing (comammox) *Nitrospira* in the nitrification process, which is a key driver of nitrogen cycling in this region. These bacteria are well-adapted to the cold and oligotrophic conditions of coastal Antarctica, utilizing strategies such as trehalose synthesis for cold stress resistance, high substrate affinity for resource utilization, and alternate metabolic pathways under nutrient-scarce conditions. The study also shows that the microbial nitrogen cycle in coastal Antarctica is distinct, encompassing most nitrogen cycling processes except for anaerobic ammonium oxidation (anammox). The absence of anammox functional markers suggests unique microbial nitrogen cycling properties in this remote region. The research further highlights the significant role of comammox *Nitrospira* clade B in nitrification, as confirmed by ¹³C-DNA-based stable isotope probing. The study provides insights into the microbial diversity and metabolic capabilities in coastal Antarctic soils and sediments, revealing the importance of nitrification in the nitrogen budget of this region. The findings underscore the need for further investigation into the impact of global warming on microbial communities and their role in biogeochemical cycles in extreme environments. The study also contributes to the expansion of microbial genomic data for Antarctica, providing valuable resources for future research on microbial interactions and climate change.