This data was collected during the Polarstern cruise PS138 (ArcWatch1) from August 3 to September 30, 2023 to the Central Arctic Ocean. At five stations during the Polarstern cruise PS138 (ArcWatch1) we conducted bioassays on board in order to assess the interactive effects of light and dSi on the uptake rates of carbon (C), nitrogen (N), and silicon (Si). The resulting bulk and single-cell uptake rates from the bioassays were supported and put into context using environmental data collected at the same stations. At each stations ice cover and meltpond cover were assessed using the Arctic Shipborne Sea Ice Standardization Tool. Ice and snow thickness were estimated using snow depth and core length averaged across at least 9 cores collected at a representative coring site on a nearby ice floe. Surface light intensity was measured continuously using a pyranometer (Kipp & Zonen, Delft, Netherlands) mounted near the bridge of the vessel. Surface light intensity and ice and snow thickness were used to estimate the euphotic depth and light intensity at the sampling depth following Fernández-Méndez et al., 2015. At the same time, location and depth as the incubation experiment information on salinity and temperature was collected from the CTD and additional water samples were taken for analysis of photosynthetic pigments for Chl a analysis, particulate organic carbon and nitrogen (POC/PON) and particulate organic phosphate (POP) by filtering 1-2L on pre-combusted glass-fiber filters (GFF, Whatman, UK). Photosynthetic pigments were analysed using reverse-phase HPLC performed using a Waters Alliance e2695 separation module (Waters Corporation, Milford, USA), equipped with a PDA detector (2998, Waters Corporation, Milford, USA). POC/PON were analysed using a Euro EA Elemental Analyzer (Hekatech, Wegberg, Germany) and POP was analyzed by conveting it to phosphate by autoclaving with an oxidizing agent, followed by spectrophotometrical analysis following Hansen and Koroleff, 1999. Samples for inorganic nutrients were analysed onboard using a continuous flow autoanalyser (AA500, SEAL Analytical, Norderstedt, Germany).