This is a time-series record of nitrate + nitrite (∑NOx) concentrations measured using an in situ lab-on-chip sensor that was deployed in a glacier-fed fjord (Nuup Kangerlua) between 14th June to 13th September 2019. The sensor (along with a conductivity, temperature and depth (CTD) probe and a silicic acid sensor) was attached to a frame that was anchored to a cliff and submerged at an average depth of 5 m. The sensor was programmed to draw in ambient water (through 0.45 µm pore-size 13 mm diameter polyethersulfone inlet filters) and measure its nitrate + nitrite concentration every 12 hours. Each measurement was accompanied by the measurement of an onboard calibration standard and a blank solution (artificial seawater). During a three-month monitoring period ∑NOx varied between 0.05 and 10.07 µM (± 0.2 μM).