New research calls attention to the human footprint left on the ocean by revealing how industrial and agricultural processes affect its nitrogen cycle.
A recent analysis revealed oceanic nitrate concentration has significantly increased over the past three decades in the North Pacific, the University of Hawaii at Manoa reported.
The rate of deposition of reactive nitrogen (primarily from fossil fuel burning and fertilizer) from the atmosphere to the ocean has more than doubled over the past century in the North Pacific, and the source is believed to be primarily enhanced deposits in the atmosphere.
"This is a sobering result, one that I would not have predicted," said David Karl, Professor of Oceanography and Director of the Daniel K. Inouye Center for Microbial Oceanography at the University of Hawai'i, "The North Pacific is so vast it is hard to imagine that humans could impact the natural nitrogen cycle."
To make their findings the researchers looked at ocean data in conjunction with the state-of-the-art Earth System Mode to reconstruct the recent history of oceanic nitrate levels. The assessment uncovered a significant increase in North Pacific nitrate levels linked to higher rates of nitrogen deposition in the atmosphere. This is a problem because an influx of nitrogen can increase photosynthesis in the sunlit layers of the ocean and the export of carbon-rich material from shallow waters to the ocean deep.
"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 said.
If the trend continues the North Pacific Ocean will most likely develop a surplus of nitrates, altering the base of the marine food web and eventually the entire ecosystem. The marine environment would then favor organisms that thrive under high nitrate and low phosphorus conditions.
The findings call attention to need for greater controls on man-made nitrogen emissions during combustion and agricultural practices.
The findings were published in a recent edition of the journal Science.
