Thielecke, Antonia; Krause, Jeffrey W; Stefels, Jacqueline; Torres-Valdés, Sinhué; Bryan, Natasha; Fernández-Méndez, Mar: Bulk carbon, nitrate and silicic acid uptake rates of Arctic phytoplankton in response to interactive light and silicic acid gradients (CNSiUptake): [dataset]. PANGAEA, https://doi.pangaea.de/10.1594/PANGAEA.991536 (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 five stations 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). 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. All samples were subsequently incubated for 24 hours under a light gradient (0, 10, 40, 80, 320 µmol photons m-2 s-1) creating a 5x5 gradient of light and dSi. After incubation, subsamples were taken for analysis of 13C labelled dissolved inorganic carbon (13C-DIC) and inorganic nutrients. The remaining volume was divided and filtered for 13C- and 15N-labelled particulate organic carbon and nitrogen (13C-POC and 15N-PON) and 30Si-labelled biogenic silica (30Si-BSi). Samples for 13C-POC and 15N-PON were filtered onto a 0.7 µm pre-combusted glass-fiber filters (GFF, Whatmann). The filters were acidified, then dried in the oven at 60 °C and later measured using an elemental analyzer (Flash IRMS, ThermoFisher) connected to a mass spectrometer (Delta V Advantage Isotope Ratio MS, ThermoFisher) with the ConFlo IV (ThermoFisher). Carbon and nitrogen uptake rates were calculated based on Slawyk et al. (1977). Samples for 30Si-BSi were filtered on 2 µm polycarbonate filters (Merck Millipore Ltd., Cork, Ireland), dried at 60°C and measured using alkaline digestion following Krause et al., (2023).The isotopic composition was measured using a high-resolution sector field inductively coupled plasma mass spectrometer (Element XR; Thermo Fisher Scientific, Waltham, US) following Fripiat et al., (2009). Si uptake rates were calculated following Nelson and Goering, (1977).