Fig. 1: Large-scale context of study region.

Climatological distribution over 2002–2020 of (A) Phytoplankton (in mg Chl-a m⁻³), B, C occurrence of weak (resp. strong) fronts (expressed in percent of time a pixel is occupied by a weak/strong front), D relative occurrence of background (non front), weak front and strong front in each biome, E meridional transect (averaged over 40–45^∘W) of phytoplankton concentration (in mg Chl-a m⁻³) in the background (no front) and over weak and strong fronts, F same transect for the relative proportion of phytoplankton sorted into three groups. Latitudinal profiles similar to those shown in panels (E) and (F), covering each of the seven phytoplankton groups and their associated diagnostic pigments, are presented in Supplementary Fig. 1. In (A), the red line marks the continental shelf and values over the shelf have been masked. The thick gray line and dashed line represent the climatological boundaries between the permanent subtropical, seasonal subtropical and subpolar biomes.