Fig. 6: Seasonal rates and long-term trends of colour, N and P across oxygen regimes.

a–d, Estimates of ice-free seasonal rates (within years, orange) and long-term trends (across years, cyan) of bottom-water colour (a), TN (b), TP (c) and NH₄ (d) within distinct oxygen regimes: anoxic (≤0.5 mg l⁻¹), hypoxic (0.5–2 mg l⁻¹), low oxic (2–5 mg l⁻¹), mid oxic (5–8 mg l⁻¹), high oxic (>8 mg l⁻¹) and ‘All’ (no oxygen criterion). Long-term surface-water trends are shown for comparison as open symbols. In the y axis labels, f stands for frequency (d⁻¹ and yr⁻¹). The category ‘All’ includes all bottom-water samples. Error bars mark 95% CIs of the means. Statistics associated with this figure are summarized in Extended Data Table 1.