Oceanic plant life is produced from marine carbon (bicarbonate) in the ocean, and that amount of bicarbonate is in equilibrium with the carbon dioxide in the atmosphere. So when more bicarbonate is used up to produce marine plant life, it disrupts the equilibrium, and carbon dioxide is drawn down to the ocean from the atmosphere to restore the balance, Duce explained.
Thus, the human-caused nitrogen fertilization of the ocean removes some of the most important greenhouse gas carbon dioxide from the atmosphere, Duce said. This gain, however, is offset by the nitrogen compound, nitrous oxide, that also forms in the ocean due to the nitrogen fertilization and is re-emitted into the atmosphere as a powerful greenhouse gas, he added.
If you dont consider the impact of human-caused nitrogen when trying to model climate change, youre missing a possibly significant part of the overall carbon cycle as well as the nitrogen cycle, Duce said. So nitrogen deposition is potentially a very important factor in the climate change issue.
According to the teams calculations, about 54 million tons of nitrogen produced from human activities entered the ocean from the atmosphere in the year 2000. The team also found that the current nitrogen emissions are about 10 times what they were in 1860, Duce said. He added that the amount of nitrogen entering the atmosphere is expected to rise in the coming decades with the increase in demand for energy and fertilizers, and the team estimates that by the year 2030, human-caused nitrogen emissions will have risen to around 62 million tons per year.
Clearly, there is much that we do not know about the extent and timescale of the impacts of this nitrogen deposition on the oceans and the subsequent feedbacks to the climate system, Duce said. The implications are complex and interactive, and this is a very important issue that p
|Contact: Keith Randall|
Texas A&M University