Fig. 1: Field investigation of the Pearl River Estuary in the northern South China Sea.

Photosynthetic light use efficiency [μmol C (μg Chl a)⁻¹ h⁻¹ (μmol photons m⁻² s⁻¹)⁻¹] of phytoplankton assemblages in stations of Pearl River Estuary (a) as a function of dissolved O₂ levels (mg L⁻¹) (b), CO₂ levels (μM) (c), pH_T (d), DIN (NO₃⁻ + NO₂⁻ + NH₄⁺, μM) (e) and SiO₃²⁻ (μM) (f). Samples were collected from 10 m (Green) and 20 m (Purple) depths in stations (Blue) of the Pearl River Estuary in the northern South China Sea (June 2015), detailed parameters for the field observations at the stations are shown in the Supplementary Table 1. Significant (P < 0.0001) negative (b, d) and positive (c) correlations and non-significant (e, f, P = 0.6671, 0.0707, Pearson correlation analysis, two-tailed) relationships with O₂ (b), CO₂ (c), pH_T (d), DIN (e) and SiO₃²⁻ (f) are shown in Supplementary Table 2.