Up to a third of the nitrogen entering the world’s oceans is man-made and could have significant effects on the global climate, scientists said.
Nitrogen from agricultural fertilisers and the burning of fossil fuels entering the seas through the atmosphere is increasing, the study published in the journal Science said.
It has significant implications for climate change, because the extra nitrogen increases the level of marine biological activity by an estimated 3% – which in turn boosts the oceans’ ability to absorb carbon dioxide.
The man-made nitrogen could account for as much as 10% of the CO2 emitted by human activities which is captured by oceans, the scientists suggest. But it could also increase levels of nitrous oxide, a potent greenhouse gas, they warn.
As much as a third of the total nitrous oxide given out by the oceans could be caused by man-made nitrogen deposits in the sea.
The effect of these emissions could cancel out as much as two thirds of reductions in CO2, the researchers said.
With ever increasing levels of nitrogen being released by humans into the atmosphere, their impact on the world’s seas is expected to grow in the future.
Peter Liss, environmental scientist at the University of East Anglia and one of the study’s authors, said: “Anyone concerned about climate change will be alarmed at the scale of man’s impact on the oceans.
“The natural nitrogen cycle has been very heavily influenced by human activity over the last century – perhaps even more so than the carbon cycle – and we expect the damaging effects to continue to grow.”
He said it was vital policy makers took action to stop the growth of nitrogen in the oceans, by controlling the use of nitrogen fertilisers and tackling pollution from growing numbers of cars.