Increase of anthropogenic NOx emissions stimulate the productivity on global ocean deserts

Abstract

Abstract The decline in ocean productivity has become a consensus due to the weakening vertical supply of nutrients to the upper ocean under global warming. However, ocean productivity in the subtropical gyres, regarded as ocean deserts, has increased over the past few decades. We speculated that the continuous increase in anthropogenic NOx emissions is the key factor for such an inconsistent trend. Herein, aerosol nitrate dual isotopes covering the global oceans were analysed and we found that nitrate concentrations in the Northern Hemisphere (NH) are nearly twice higher than in the Southern Hemisphere (SH) due to intensive human activities in the NH. Although atmospheric nitrate deposition only accounts for 2.1% of nitrate inventory in the global upper ocean, its contribution is up to 31.5% in the subtropical gyres, with much higher contribution in the NH (over 50%), indicating the significant contribution of atmospheric deposition to the ocean productivity in these regions.