Human activity, particularly in industrial and agricultural processes, has had significant impacts on the upper ocean nitrogen cycle, a new study warns.
Human-induced changes to Earth's carbon cycle - for example, rising atmospheric carbon dioxide and ocean acidification - have been observed for decades.
To dig further, David Karl, professor of oceanography at the University of Hawaii teamed up with researchers to assess changes in nitrate concentration between the 1960s and 2000s across the open North Pacific Ocean.
Their analysis revealed that the oceanic nitrate concentration increased significantly over the last 30 years in surface waters of the North Pacific largely due to the enhanced deposition of nitrogen from the atmosphere.
"The burgeoning human population needs energy and food. Unfortunately, nitrogen pollution is an unintended consequence and not even the open ocean is immune from our daily industrial activities," Karl noted.
The team's assessment revealed a consistent picture of increasing nitrate concentrations, the magnitude and pattern of which can only be explained by the observed increase in atmospheric nitrogen deposition.
Enhanced nitrogen deposition has several potential ecological ramifications.
Because biological activity is limited by nitrate availability in the North Pacific Ocean, the input of new nitrogen from the atmosphere may increase photosynthesis in the sunlit layers and export of carbon-rich organic material out of the surface ocean into the deep.
Researchers from Korea, Switzerland and the US National Oceanic and Atmospheric Administration were part of the study that appeared in the journal Science.
