Reef Report for Wednesday, January 10, 2007
New Scientific Research Links Global Warming and Declining Productivity of Oceans
The results of a landmark study were released this week, which further strengthened the threat of global warming to ocean ecosystems.
The ten-year study was a collaborative effort involving scientists from five institutions, and led by Dr.
Michael Behrenfeld, a professor of Botany at Oregon State University. Dr. Behrenfeldís specialty is the use of remote sensing technology to measure plant growth, and his team devised a way to use satellite data to measure the growth rate of algae in oceans worldwide then use ocean temperature data to calculate the effect of warmer ocean temperatures on the growth of marine algae.
You might wonder why the growth of marine algae, also known as phytoplankton, is so important. These small microscopic algae are the food that nearly all marine organisms depend on. They are the base of the oceanís food web; the majority of animals in the ocean feed on phytoplankton, and the larger ocean organisms we are most familiar with (fish, whales, etc) feed on these animals. A decline in the growth rate of phytoplankton means that there is less food available for nearly every other organism in the ocean.
To measure phytoplankton growth rates the team used data collected by NASAís SeaWiFS satellite, which was launched in 1997. The satellite measures the amount and frequency of wavelength of light reflected by the ocean. Phytoplankton absorb light, which means that the more phytoplankton there are in the ocean and the faster they are growing, the more light they absorb during the process of photosynthesis, and this data can be calculated using the satellite data.
Because the satellite has been collecting this data since 1997, the productivity of any patch of ocean can be compared over that time, a process used by the research team to make their conclusions.
"This clearly showed that overall ocean productivity decreases when the climate warms," said lead author Michael Behrenfeld, an Oregon State University professor of botany and expert on remote sensing of marine biology.
It is thought that reason warmer ocean waters cause a decline in phytoplankton productivity is because warmer oceans do not mix well; the surface layers containing phytoplankton do not mix with the deeper, more nutrient-rich water, and the lack of nutrients causes the slower growth rates.
The rising ocean temperatures could be causing further global warming because of the slower algal growth rates. Phytoplankton performs more than half the photosynthesis on earth, and the process photosynthesis converts carbon dioxide, a gas connected with global warming, into organic compounds. "Rising levels of carbon dioxide in the atmosphere play a big part in global warming," said Behrenfeld. "This study shows that as the climate warms, phytoplankton growth rates go down and along with them the amount of carbon dioxide these ocean plants consume. That allows carbon dioxide to accumulate more rapidly in the atmosphere, which would produce more warming."
Coverage by the Guardian.
Coverage by the Environmental News Service.
Coverage by Eureka Alert
Coverage by National Public Radio.
Coverage by Oregon State University.
About Dr. Behrenfeld.
The weekly reef report is written by Joel Groberg of DiveTheReef.com,
who compiles them from the many conversations he has with dive staff in the area, as well as† many other local sources in the dive
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