Updated project metadata. Colwellia psychrerythraea Cp34H 13C-Leucine uptake over 8 days at -5Celcius to track new protein synthesis at subzero temperatures Few halophilic strains have been examined in detail for their culturability and metabolic activity at subzero temperatures, within the ice matrix, over the longer term. Here we examine an Arctic strains with strong salinity tolerance: Colwellia psychrerythraea str. 34H (Cp34H). As a proxy for biosignatures, we examine observable cells, metabolic activity and recoverability on 12-month incubations at −5, −10 and −36 °C. To further develop life-detection strategies, we also study for the first time short-term tracking of new protein synthesis on Cp34H at −5 °C, using isotopically labeled 13C6-Leucine and mass spectrometry-based proteomics. Cp34H remained metabolically active after 12 months at −5 °C and recoverabile. At −10 and −36 °C metabolic activity was drastically reduced . Cells were observable at high numbers in all treatments, validating their potential as biosignatures. Newly synthesized proteins were detectable and identifiable after one hour of incubation. Proteins prioritized for synthesis with the provided substrate are involved in motility, protein synthesis, nitrogen and carbohydrate metabolism, with an emphasis on structural proteins, enzymatic activities in central metabolic pathways, and regulatory functions.