Rising anthropogenic nitrate levels in North Pacific Ocean due to human activities

Human-induced changes to Earth’s carbon cycle like, the rising atmospheric carbon dioxide and ocean acidification which has been observed for decades. However, a new study has shown that human activities, in particular industrial and agricultural processes, have also had significant impacts on the upper ocean nitrogen cycle. The rate of deposition of reactive nitrogen i.e. nitrogen oxides from fossil fuel burning and ammonia compounds from fertilizer use, from the atmosphere to the open ocean has more than doubled globally over the last 100 years. This anthropogenic addition of nitrogen has reached a magnitude comparable to about half of global ocean nitrogen fixation, the natural process by which atmospheric nitrogen gas becomes a useful nutrient for organisms. Their analysis, which could discern human-derived nitrogen from natural nitrogen fixation, revealed that the oceanic nitrate concentration increased significantly over the last 30 years in surface waters of the North Pacific due to the enhanced deposition of nitrogen from the atmosphere. In particular, the shift in nutrient availability could favor marine organisms that thrive under the high nitrate and low phosphorus conditions. If similar trends are confirmed in the Atlantic and Indian Oceans, it would constitute another example of a global-scale alteration of Earth system. Further, the findings of this study of the North Pacific highlight the need for greater controls on the emission of nitrogen compounds during combustion and agricultural processes.