Fig. 1. Lake Cadagno chemocline nutrient, δ¹⁵N and turbidity depth profile, bulk CO₂ and N₂ fixation rates, and PSB abundance.

a Molybdenum (light blue) and sulfide (yellow) depth profiles. b Ammonium (dark blue) and δ¹⁵N values of bulk biomass (red circles, duplicate measurements at depths 13.7 m and 14 m, single measurement at 15.5 m). c Bulk N₂ fixation rates (green) and bulk CO₂ fixation rates (blue, determined in the same samples as N₂ fixation rates). All rate measurements were performed in biological triplicates (except 15.5 m where one replicate was lost), individual replicates are shown as small circles, and the average rate is shown in large circles with the respective standard deviation. N₂ fixation rates at 15.5 m depth were below the detection limit. d Abundances of key PSB populations (stacked bars, cell numbers based on FISH counts) and turbidity (gray line, a measure of total cell abundance). The location of the chemocline, as determined from the conductivity profile, is indicated by gray shading (a–d).