LAUSR

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.