Polar marine ammonia-oxidizer can oxidize ammonium to nitrate during the winter in the deeper Antarctic mixed layer. However, that activity and its contribution to regenerated NO3- during the summer in surface coastal Antarctic waters remains unclear. Composition identity and nitrification rates of ammonia-oxidizer bacteria (AOB) and archaea (AOA) were evaluated at the marine surface layer (up to 30m) in Chile Bay (South Shetland Island, Antarctica) for three consecutive late summer years (2017, 2018, and 2019). AOB and AOA amoA gene transcripts and 16S rRNA were sequenced by Illumina.