Since the 1980’s Dr. Joseph M. Prospero, professor of Marine and Atmospheric Chemistry at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science, has pioneered studies in the worldwide measurement of aerosols, fine particles suspended in the atmosphere and carried by winds.
His team’s work focuses on the aerosol chemistry of the marine atmosphere. They are particularly interested in the long-range transport of pollutants from the continents to the oceans and their impact on climate and on biogeochemical processes in ocean waters.
Starting in 1980 Prospero established a network of island stations in the North and South Pacific Oceans. These stations made continuous measurements of the concentration of major aerosol species that play a role in climate: mineral dust, nitrate, sulfate, and sea salt. The network was eventually extended to the Indian Ocean and Antarctica. Throughout the 80’s and into the late 90’s the UM team maintained a total of 30 stations in constant operation in all ocean regions. The data obtained are unique and they have played a critical role in the development and testing of the global chemical transport models used in the recent climate assessment carried out by Intergovernmental Panel on Climate Change.
Prospero’s data plays a central role in a paper that appears in the May 16 issue of Science, “Impacts of Atmospheric Anthropogenic Nitrogen on the Open Ocean”. Spearheaded by Dr. Robert Duce from Texas A&M, the study highlights the importance of the Earth’s nitrogen cycle, and its vital link to the global carbon cycle, especially the atmospheric concentration of CO2, the greenhouse gas responsible for most of the global warming effects observed during the past century.
Scientists have long known that biological processes in the ocean play an important role in the global carbon cycle. Algae and other forms of marine life take up CO2 and nutrients from ocean surface waters and, through the process of photosynthesis, reproduce and grow rapidly in total mass. This process draws CO2 from the atmosphere and partially offsets the growth of CO2 from human activities. Every year approximately one-third of the CO2 released into the atmosphere because of human activities, is taken up by the oceans.
Consequently any processes that affect the ocean uptake of CO2 can have an effect on global warming.
Various nitrogen compounds, especially nitrates and ammonium, play an important role in ocean’s photosynthesis by acting as fertilizers that stimulate the growth of marine organisms. Because of human activities, the emission rates of these compounds have increased greatly over the last 100 years. The transport of these compounds to the oceans, mostly through the atmosphere, have acted to increase the draw-down of CO2 from the atmosphere.
The paper in Science compares emissions of nitrogen compounds in the year 1860, before humans had a great impact on pollution emissions, with current emissions. Today pollutant nitrogen deposition to the oceans accounts for about ten percent of the draw-down of CO2 from the atmosphere to the ocean. However, the deposition of these pollutants also results in the increased emissions of nitrous oxide, N2O, which is also a potent greenhouse gas. The net effect is that the N2O emissions offset about one-third of the effects of the increased drawdown of CO2 due to pollution deposition.
The team who wrote the paper appearing in Science also estimates emissions for the year 2020 using scenarios from the IPCC report. “All of us are concerned that the amount of anthropogenic nitrogen transported to the oceans will to continue to rise in the future,” commented Prospero.