Fig. 2. Seasonal phases have distinct physiological state signatures.

a, c Concentration of phytoplankton cells sampled within the mixed layer at depths associated with 40, 20, or 1% surface irradiance during different seasonal phases (W.Tran = Winter Transition; Acc = Accumulation; Clim = Climax; Decl = Decline). Data are shown for in situ water (grey bars) and on-deck incubations (open bars). Population-wide levels of a, b cellular reactive oxygen species (colored by fluorescence fold change from unstained; median per population) and c, d cell death (colored by % compromised membrane). Plots (b) and (d) are contoured with ridgeline smoothing to represent the relative in situ distribution of biomarker levels within each phase. The size of contour peaks is driven by frequency of observations. e, f In situ inventories of live (e; green) and dead (f; red) cells within the mixed layer through the different phases. Individual circles denote biological replicates. Box plots in (a), (c), (e) and (f) represent the median value bounded by the upper and lower quartiles with whiskers representing median + quartile × 1.5. Different letters denote statistically significant groups (p < 0.05, Kruskal−Wallis test with Dunn corrections for multiple comparisons). Intergroup comparisons with more than one letter denote no significant difference between the two groups. Number of biological replicates, by bloom phase/cast type (from left to right) = 10/9, 13/33, 17/36, 19/36 (a), 11/25, 13/36, 17/36, 19/36 (c), 11, 13, 17, 19 (e, f). Exact p values can be found in Source Data file.