Fig. 5: Biomarkers of physiological state cluster according to bloom phase and stratification.

(Top) Conceptual illustration of changes in mixed layer depths and water column stratification associated with seasonal bloom phases in the North Atlantic. (Bottom) Heatmap of different biomarkers (organized as rows). Row shading represents the median of each variable throughout a phase, normalized to the entire cycle. Rows are clustered by an optimal leaf algorithm to minimize the distance between normalized distributions of each variable (leaves). Phytoplankton accumulation day⁻¹ = cell concentration-based accumulation rate (day⁻¹); Triacylglycerol ChlA⁻¹ = triacylglycerol concentration (pM) normalized to chlorophyll A; Metacaspase activity = µmol metacaspase substrate cleaved h⁻¹ µg protein⁻¹; Phytoplankton cells L⁻¹ = phytoplankton concentration (cells L⁻¹); Reactive oxygen species = log₁₀ fold change from unstained phytoplankton population; Oxidized mem. lipids = oxidized phosphatidylcholine normalized to total phosphatidylcholine; Transparent exopolymers cell⁻¹ = transparent exopolymer particles (µg XG eq. L⁻¹) normalized to bacteria and phytoplankton cell concentrations; Phytoplankton biovolume L⁻¹ = phytoplankton biovolume (µL L⁻¹); Stratification = measured buoyancy frequency (s⁻¹); Virus cell⁻¹ = virus concentration normalized to phytoplankton and bacterial cell concentrations; Caspase activity = µmol caspase substrate cleaved h⁻¹ µg protein⁻¹; % Compromised membranes = % of phytoplankton population with compromised membranes; Dissolved organic carbon_SA = seasonally accumulated dissolved organic carbon (µM change from minimum value per bloom phase).