The dataset contains incubation results on carbon uptake rates in water column samples collected by the CTD–water sampler unit while exploring the hydrothermal plumes of the Lucky B site (81°N, Lena Trough) in June–July 2023 during RV Polarstern expedition PS137. Samples include Lucky B's shallow plume (station PS137/061) and reference Arctic seawater (station PS137/018). Specifically, this dataset has 14C-bicarbonate and 3H-leucine uptake rates, indicative of chemoautotrophic and heterotrophic microbial activity. Microbial autotrophic and heterotrophic activities were assessed by applying bicarbonate and leucine incorporation-based methodologies. Rates of dark CO2 fixation and microbial heterotrophic activity were derived following incubation periods of 6 h and 12 h, respectively.