We used more than 25,000 nutrient samples to elucidate for the first time basin-scale distributions and seasonal changes of surface ammonium (NH4 +) and nitrite (NO2 −) concentrations in the Pacific Ocean. The highest NH4 +, NO2 −, and nitrate (NO3 −) concentrations were observed north of 40°N, in the coastal upwelling region off the coast of Mexico, and in the Tasman Sea. NH4 + concentrations were elevated during May–October in the western subarctic North Pacific, May–December in the eastern subarctic North Pacific, and June–September in the subtropical South Pacific. NO2 − concentrations were highest in winter in both hemispheres. The seasonal cycle of NH4 + was synchronous with NO2 −, NO3 −, and satellite chlorophyll a concentrations in the western subtropical South Pacific, whereas it was synchronous with chlorophyll-a but out of phase with NO2 − and NO3 − in the subarctic regions.
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