Researchers from Princeton University measured nitrogen in coral skeleton samples collected in the open ocean about 620 miles east of the North American continent near the island of Bermuda, a region thought to be strongly influenced by airborne nitrogen released from U.S. mainland sources such as vehicle exhaust and power plants. The team found no evidence that human-made nitrogen was on the rise but noted variations in nitrogen that corresponded to levels expected from a natural climate phenomenon called the North Atlantic Oscillation. Earlier work by the Princeton-based team, however, did find elevated nitrogen pollution in another open ocean site in the South China Sea, coinciding with the dramatic increase in coal production and fertilizer usage in China over the past two decades.
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