Researchers Find El Nino Affects the Global Carbon Cycle

COLLEGE PARK, MD B A new study by scientists from the University of Maryland, Dalhousie University, and the U.S. National Oceanographic and Atmospheric Administration (NOAA) demonstrates that the complex atmosphere-ocean interactions associated with the El Ni¿o/Southern Oscillation (ENSO) have a large impact on biological productivity and the export of organic carbon from the tropical Pacific region.

The work, which is based on a unique combination of ship, buoy and satellite observations in the tropical Pacific, found that during El Ni¿o, much of the Pacific Ocean's capacity to take up and store carbon by biological processes is decreased in the eastern Pacific, but is compensated to some extent by increases in the west. During La Ni¿a, the opposite phase of the oscillation, biological productivity of the east is dramatically increased, while in the west it is diminished. The study, which was published in today's issue of Science, found that the net effect was to decrease the export of carbon into the deep ocean by 30 percent during the 1997-98 El Ni¿o and to increase it by 40 percent during the 1998-99 La Ni¿a.

Largest climate signal on the planet

Feeding the fish

The growth of ocean plants, primarily phytoplankton, is directly responsible for marine fisheries. It also results in the export of organic carbon from the surface to deep waters and sediments. This carbon export has implications for global climate change through its impact on levels of atmospheric CO2, the greenhouse gas believed to be most important in climate change. Only about half of the carbon released in the atmosphere through human activities remains there.

The rest ends up in the ocean, or in plants and soils on land. The ocean contains 50 times more CO2 than the atmosphere, and the vast tropical Pacific is thought to be responsible for 10 to 55 per cent of the export of organic carbon from the all world's oceans. Changes in global carbon sequestration associated with the El Ni¿o/La Ni¿a cycle contribute to the largest known natural year-to-year variations of the global carbon cycle.

Topex/Poseidon satellite

The researchers say their findings are based on high precision satellite observations of the surface of the ocean, together with observations of the ocean interior from buoys and ships. "The measurements of the height of the sea surface from the Topex/Poseidon satellite altimeter provides a large scale view of the dynamics of the interior of the ocean when combined with subsurface measurements of temperature and other variables from buoys," said Dalhousie's Turk.

x/Poseidon sensor (http://topex-www.jpl.nasa.gov/), built by NASA and the Centre National d'¿tudes Spatiales (CNES, France), is a radar that is capable of measuring the height of the sea surface to an accuracy of 2 cm from a distance of over 700 km. The buoy observations were taken from the Tropical Ocean Atmosphere (TAO) array built and operated under leadership of NOAA. This array consists of over 70 automated data collection buoys installed across the tropical Pacific, which provide ocean and weather information on a routine basis (http://www.pmel.noaa.gov/tao/).

Unprecedented basin-scale perspective of El Nino

The combination of data from these different sources provides an unprecedented basin-scale perspective on the net effects of El Ni¿o on biological productivity of the tropical oceans. The Earth System Science Interdisciplinary System is a joint center between the University of Maryland departments of meteorology, geology, and geography together with the Earth Sciences Directorate at the NASA/Goddard Space Flight Center. The goal of ESSIC is to understand how the atmosphere-ocean-land-biosphere components of the Earth interact as a coupled system and what influence human activities have on this system. A recent editorial in Science about the importance of the young discipline of earth system science (ESS) cited the University of Maryland as one of Aa mere handful of U.S. and European institutions that offer graduate programs and the kind of interdisciplinary working environments that are essential for the rapid development ofn ESS."

The research team

The department of oceanography at Dalhousie University is Canada's leading oceanographic institute, and is involved in a wide range of basic and applied research and innovation in the ocean sciences. The Pacific Marine Environmental Laboratory carries out interdisciplinary scientific investigations in oceanography and atmospheric science with programs that focus on open ocean observations in support of long-term monitoring and prediction.

Financial support for the research was provided by: NASA's Mission to Planet Earth Program, the Natural Sciences and Engineering Research Council (Canada) and NOAA's Office of Atmospheric and Oceanic Research.

The full manuscript by Turk et al. can be accessed at: http://www.sciencemag.org/cgi/content/full/293/5529/471.

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