It’s not easy being green – a green ocean to be exact. While a blue ocean may be pretty to look at, a green ocean is a productive ocean powered by phytoplankton, microscopic marine plants that serve as the basis for the ocean food chain and photosynthesize on the surface of the ocean by means of sunlight.
The Sea-viewing Wide Field-of-view Sensor Project, or simply the SeaWiFs project, has generated new quantitative data evaluating the relationship between ocean color and phytoplankton. Additionally, the research has given way to new understandings of both the carbon cycle and global warming.
The SeaWiFs team of David Siegel, a UCSB geography professor; Scott Doney, a numerical modeler at the National Center for Atmospheric Research, and Jim Yoder, the division director of ocean sciences at the National Science Foundation, used the SeaWiFs satellite to assess large-scale data regarding the physical processes driving the observed annual changes in ocean color from the phytoplankton spring bloom in the North Atlantic – one of the largest biological features that can be seen from space. The data can be manipulated to generate a single index number representing the amount of energy the phytoplankton has received from the sun. According to the researchers, when the number reaches a critical point the spring bloom begins.
“In the springtime things get warmer; you’ve got more sunlight that triggers this massive bloom in phytoplankton. What we wanted to see was if we could test, in a quantitative fashion, this theory for what triggers this large greening of the North Atlantic,” Doney said.
The spring bloom grows across Earth’s surface, reaching an area of over 2,000 square kilometers. The blooming spreads north at a rate of 20 kilometers per day, making sampling from boats very difficult.
“What we found was that by looking at the satellite data, we actually got a consistent value for the parameter of community respiration over most of the North Atlantic. We can now say something about a number that is hard to measure if you actually go to see it. It’s very hard to measure bulk rates of the entire community because you can’t put them in a bottle and grow them,” Doney said.
Further research has shown that in addition to acting as a primary food source for the community of organisms in the open ocean, phytoplankton affect the carbon cycle, taking in large amounts of the gas during the spring bloom.
“Phytoplankton live for only a couple of days, tops,” Siegel said. “Their life spans are very short. When they die, they sink on their own, very slowly, up to 100 meters a day, into the deep ocean. When they sink, the phytoplankton exports carbon dioxide into the deep ocean for 1,000 [or more] years, removing it from society during that time.”
The ocean is one of the largest reservoirs to store carbon dioxide emissions. “The ocean has 35,000 gigatons of carbon dioxide already and can store so much more because of its buffering system. The carbon dioxide can go into solution to make carbonates and bicarbonates, so there is a buffering capacity for the ocean of just taking up more and more [carbon dioxide],” Siegel said.
Future stages in the SeaWiFs research involve looking at the processes of the ocean at an annual basis and comparing one spring bloom with the next, in addition to looking at the role of climates in a predictive sense in relation to the spring blooms.
“The SeaWiFs satellite is still flying, and it’s still collecting data. There are also new sensors that are going up that tell us similar information. In the [future] we want to combine those satellite records to get a longer term record of how biology is behaving,” Doney said. “One goal in the long run is to see, if in addition to this year’s variability, whether there are any long-term trends.”
Understanding the spring bloom is an essential aspect of comprehending the ocean’s ecosystem and biological pump in terms of realizing the potential effects of global warming.
“Progress is made slowly. I think these approaches coupled with modeling approaches will give us ideas of how this biological pump works. It’s one of the many pieces in figuring out global warming,” Siegel said.
The SeaWiFs mission is funded by the National Science Foundation and NASA’s Earth Science Enterprise, a project to look at Earth in terms of behavior and evolution.