Nitrate+nitrite, phosphate, silicate, chlorophyll a, Fv:Fm data from nutrient addition incubation experiments during cruise DY167 in the Barents Sea, July-August 2023

Nutrient addition experiments were performed during research cruise DY167 to the Barents Sea between 9th July and 13th August 2023. Six experiments were conducted, the first as a test station (T1) then five at locations representing different water characteristics, specifically Atlantic water (N03), ice edge (N08), glacier influenced (N15) and polar waters north of the polar front (N07 and N07Y). Twenty four 20L carboys were filled with unfiltered seawater using seawater collected from the 12th of July to the 6th of August using the trace metal clean towed-FISH. Nitrate, phosphate and iron chloride were added alone or in combination to a final concentration of 10 µM, 0.8 µM and 2 nM. Experimental setup and subsampling was performed under trace metal clean conditions. Experiments were performed in triplicate (3 carboys per control or treatment). Carboys were incubated in a temperature and light controlled refrigerated container, with incubation temperature set to sea surface temperature. LED light panels (Part no: LED-PANEL-300-1200-DW and LED-PANEL-200-6-DW, Daylight White, supplier Power Pax UK Limited) delivered a photon flux ranging from 180 to 220 µmol photons m-2 s-1 and were on 24 hours to mimic light at this time of year in the Arctic. Carboys were subsampled for nutrients, chlorophyll a, and variable fluorescence vs maximum fluorescence (Fv:Fm) at time zero and then once a day for the duration of the experiment. Experiments were conducted for between 4 and 7 days depending on the rate of change of chlorophyll and Fv:Fm. Nutrients were measured using standard colorimetric methods and a Seal Analytical QuAAtro 5 channel autoanalyser. Chlorophyll a was measured using acetone extraction and fluorimetric analysis via a Turner 10Au fluorometer. Fv:Fm values were calculated from measurements made using a Chelsea Technology Group FRRF II Sensor. The experiments were conducted to investigate the macro and micronutrient control on primary productivity in the Barents Sea, under Natural Environment Research Council (NERC) Discovery grant Nitrogen fixation in the Arctic Ocean, N-ARC (grant numbers NE/T000570/1 and NE/T001240/1).