Another human footprint: Rising anthropogenic nitrate levels in the North Pacific Ocean

November 27, 2014
Hawaii Ocean Time-series Program scientists work aboard the R/V Ka'imikai-O-Kanaloa in the North Pacific Ocean. The HOT Program provided decades of data used to reconstruct historical nitrogen concentrations. Credit: Paul Lethaby, UH SOEST

Human-induced changes to Earth's carbon cycle - for example, rising atmospheric carbon dioxide and ocean acidification - have been observed for decades. However, a study published this week in Science showed 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 (i.e., 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). David Karl, Professor of Oceanography and Director of the Daniel K. Inouye Center for Microbial Oceanography at the University of Hawai'i, teamed up with researchers from Korea, Switzerland and the U.S. National Oceanic and Atmospheric Administration to assess changes in nitrate concentration between the 1960s and 2000s across the open North Pacific Ocean.

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 largely to the enhanced deposition of nitrogen from the atmosphere.

"This is a sobering result, one that I would not have predicted," said Karl. "The North Pacific is so vast it is hard to imagine that humans could impact the natural ."

The researchers used ocean data in conjunction with the state-of-the-art Earth System Model to reconstruct the history of the oceanic nitrate concentration and make predictions about the future state of the North Pacific Ocean. Their assessment revealed a consistent picture of increasing nitrate concentrations, the magnitude and pattern of which can only be explained by the observed increase in .

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 photosysnthesis in the sunlit layers and export of carbon-rich organic material out of the surface ocean into the deep.

"The burgeoning human population needs energy and food - unfortunately, is an unintended consequence and not even the open is immune from our daily industrial activities," said Karl.

Given the likelihood that the magnitude of atmospheric nitrogen deposition will continue to increase in the future, the North Pacific Ocean could rapidly switch to having surplus nitrate. Thus, past and future increases in deposition have the potential to alter the base of the marine food web; and, in the long term, the structure of the ecosystem.

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 the Earth system. Further, the findings of this study of the North Pacific highlight the need for greater controls on the emission of during combustion and agricultural processes.

Explore further: Study measures impacts of nitrogen deposition on coastal waters

More information: I-N Kim, K Lee, N Gruber, D M Karl, J L Bullister, S Yang, T-W Kim (2014). Increasing anthropogenic nitrogen in the North Pacific Ocean. Science: www.sciencemag.org/lookup/doi/ … 1126/science.1258396

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gkam
2.6 / 5 (5) Nov 27, 2014
We can deal with this, and must. Look up the article "The Nitrogen Bomb" from a few years ago.

Anaerobic digesters and other methods to treat and return the natural nutrients to the soil are what are needed, along with nutrient management programs. Digesters complete the digestion process of the cow, extracting the Methane usually lost, converting some nutrients to forms amenable to field application. Doing so includes cellulosic substrates with beneficial bacteria to re-build the soil.

This allows us to stop using potent nitrogen which first suppresses, then kills the natural bacteria which usually fix the nitrogen for the plants.

We must start now.
richard_f_cronin
1 / 5 (1) Nov 28, 2014
All lighter elements ( hydrogen , helium) and simple molecules (N2, CO2) are cooked up within the Earth, in far greater quantities than humanity will ever produce. Methane is also produced within the Earth. If we don't burn it, it lingers in the atmosphere with a half life of 12 years before it slowly oxidizes. Read up on the GeoReactor and the concepts put forward by Dr. J. Marvin Herndon. Entirely dismissed by mainstream science since he first published in 1992, but everything he describes makes so much sense. See www dot nuclearplanet dot com
gkam
2 / 5 (4) Nov 28, 2014
Uh, . .. no.

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