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.