Rising anthropogenic nitrate levels in North Pacific Ocean

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 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). David Karl…teamed up with researchers from Korea, Switzerland and…NOAA…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 nitrogen cycle.”

…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 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 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, nitrogen pollution is an unintended consequence and not even the open ocean 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 atmospheric nitrogen deposition have the potential to alter the base of the marine food web; and, in the long term, the structure of the ecosystem.

…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.

The short answer is – if we don’t succeed in wresting control of the politics and power of our nation from the Know-Nothings – we’re screwed. We will be no different from fishes swimming in a steadily heated cauldron until they are killed and cooked. And the Koch Bros, the John Boehners and Rand Pauls of our political world ain’t even dropping in some onions and garlic to make our end a savory one.

2 thoughts on “Rising anthropogenic nitrate levels in North Pacific Ocean

  1. Cassandra says:

    “Oxygen-depleted toxic oceans had key role in mass extinction over 200 million years ago” http://www.eurekalert.org/pub_releases/2015-04/uos-oto040115.php The University of Southampton’s Professor Jessica Whiteside, who co-authored the study, explains: “As tectonic plates shifted to break up Pangaea, huge volcanic rifts would have spewed carbon dioxide into the atmosphere, leading to rising temperatures from the greenhouse effect. The rapid rises in CO2 would have triggered changes in ocean circulation, acidification and deoxygenation.”
    “These changes have the potential to disrupt nutrient cycles and alter food chains essential for the survival of marine ecosystems. Our data now provides direct evidence that anoxic, and ultimately euxinic, conditions severely affected food chains.”
    “The same CO2 rise that led to the oxygen depleted oceans also led to a mass extinction on land, and ultimately to the ecological take-over by dinosaurs, although the mechanisms are still under study.”
    Although the Earth was very different during the Triassic Period compared to today, the rate of carbon dioxide release from volcanic rifts are similar to those that we are experiencing now through the burning of fossil fuels.

  2. CBL says:

    A new study led by scientists with The University of Texas at Arlington demonstrates for the first time how elemental carbon became an important construction material of some forms of ocean life after one of the greatest mass extinctions in the history of Earth more than 252 million years ago.
    As the Permian Period of the Paleozoic Era ended and the Triassic Period of the Mesozoic Era began, more than 90 percent of terrestrial and marine species became extinct. Various proposals have been suggested for this extinction event, including extensive volcanic activity, global heating, or even one or more extraterrestrial impacts.
    The work is explained in the paper, “High influx of carbon in walls of agglutinated foraminifers during the Permian-Triassic transition in global oceans,” which is published in the March edition of International Geology Review. http://www.eurekalert.org/pub_releases/2015-04/uota-nes040315.php

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