Thielecke, Antonia; Whitehouse, Martin J; Fernández-Méndez, Mar: Single cell carbon, nitrate and silicic acid uptake rates of Arctic phytoplankton in response to light and silicic acid interactions (SIMS) [dataset]. PANGAEA, https://doi.pangaea.de/10.1594/PANGAEA.991544 (dataset in review)

This data was collected during the Polarstern cruise PS138 (ArcWatch1) from August 3 to September 30, 2023 to the Central Arctic Ocean. At three stations during the Polarstern cruise PS138 (ArcWatch1) we conducted bioassays on board in order to assess the interactive effects of light and dSi on single cell uptake rates of carbon (C), nitrogen (N), and silicon (Si) for various phytoplankton groups. Single-cell uptake rates were obtained at stations 3, 4 and 5 for each dSi level (0, 2, 5, 10, 20 µM added dSi) at the 80 µmol photons m-2 s-1 light level and for each light level (0, 10, 40, 80, 320 µmol photons m-2 s-1) at the 5 µM added dSi level, resulting in a total of 9 samples for each station. For each bioassay we collected water samples from the chlorophyll maximum (Chl a max) using a CTD rosette, prefiltered the water with a 200 µm mesh and added different concentrations of dSi (0, 2, 5, 10, and 20 µmol L⁻¹ above ambient concentrations) to establish a dSi gradient. Samples were spiked with 13C labelled sodium bicarbonate, 15N labelled potassium nitrate and 30Si-sodium metasilicate at a 10% enrichment level. To avoid insufficient cell densities on the resulting filters, we added concentrated phytoplankton to the cell culture bottles. The phytoplankton community from the same depth was concentrated using reverse filtration and 2 mL of the concentrate corresponding to ~1.5-2.5 L of concentrated volume were added to each cell culture bottle before the incubation. After 24h of incubation the samples were fixed with 2 % EM-grade paraformaldehyde (PFA; EMS, USA) for 24 h in the dark at 4 °C. The fixed cells were then filtered onto 2 μm pore size polycarbonate filters (ø 25 mm; Merck Millipore Ltd., Cork, Ireland) and washed with phosphate-buffered saline (Merck Millipore Ltd., Cork, Ireland ). Single-cell 15N, 13C and 30Si assimilation rates were determined by high resolution secondary ion mass spectrometry (HR-SIMS; IMS 1280, CAMECA, Gennevilliers, France) at the Natural History Museum in Stockholm, Sweden. From the single-cell data we identified five different phytoplankton types (centric diatoms, pennate diatoms, elliptic dinoflagellates, spherical dinoflagellates, silicoflagellates and small flagellates <10µm length). Biovolumes were calculated assuming standard phytoplankton shapes (Hillebrand et al., 1999) and estimated fixed width:height ratios using microscopy and observations of SIMS measurements.