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The sampling stations where in situ NPP (open circle, N = 928, 1959–2011) and nitrate (1, N = 663, 1979–2011) weremeasured during the periods of (a) 1959–1989, (b) 1990–1999, and (c) 2000–2011. In each plot, the stations were also grouped by seasons: March–June (green), July (blue), August (black), and September–November (red).
