CORVALLIS, Ore. -- A 10-year, satellite-based analysis has shown for the first time that primary biological productivity in the oceans - the growth of phytoplankton that forms the basis for the rest of the marine food chain - is tightly linked to climate change, and would be reduced by global warming.
The study, published this week in the journal Nature by researchers from Oregon State University and five other institutions, found that on a global scale, a warmer climate could cause a rapid, overall reduction in marine life.
This clearly showed that overall ocean productivity decreases when the climate warms, said lead author Michael Behrenfeld, an OSU professor of botany and expert on remote sensing of marine biology.
There is significant regional variability, with some areas showing enhanced production and some area losses, Behrenfeld said. But on a global basis there is an inverse relationship increased temperatures cause decreased marine phytoplankton production.
This climate response can be traced to increased stratification in the oceans, the study showed. When the ocean surface warms, it essentially becomes lighter than the cold, dense water below, which is loaded with nutrients. This process effectively separates phytoplankton in the surface layer - which need light for photosynthesis - from the nutrients below them, which they also need for growth.
The satellite data used in the study were from NASAs SeaWiFS satellite, or Sea-viewing Wide-Field-of-view Sensor. Since its launch in 1997, SeaWiFS has measured changes in the color of the ocean - as more and more phytoplankton are added, the color shifts from blue toward green. By studying these color changes from space, scientists can calculate how much phytoplankton pigment is in the water, relate this to photosynthetic rate, and correlate these changes to simultaneous changes in climate.