Nov. 21, 2009 (The Yomiuri Shimbun) -- Waters near Japan are becoming less alkaline, and the change is so sudden that if the pace of acidification keeps up, it could threaten the ecosystem in 100 years, according to researchers studying the phenomenon.
Ocean water is mildly alkaline by nature, but when the amount of carbon dioxide in seawater increases, the water becomes less alkaline. On the pH scale, ocean water is usually about 8.1, which is alkaline. Depending on location, however, seawater alkalinity is getting closer to the neutral figure of 7.
The drop in alkaline levels is believed to be caused by CO2, the amount of which in the atmosphere has surged due to large consumption of fossil fuels, among other factors.
A group of scientists, led by Takashi Midorikawa of the Meteorological Research Institute in Tsukuba, Ibaraki Prefecture, has checked the pH readings of surface seawater off the Kii Peninsula at 30 degrees north latitude that have been made since 1986. They have found that the pH has dropped by 0.04 during this period, a considerable change. Such ocean acidification has been observed elsewhere as well, such as off Hawaii.
Midorikawa's group used data collected on a survey ship that observed seawater from near Japan down to near the equator, following a line of 137 degrees east longitude. The data were provided by the Meteorological Agency, which has long monitored ocean pH twice every year as part of its regular duties. ===
Most basic creatures in danger
The growing acidification of ocean water raises concern over its effect on marine life. Shellfish and plankton use calcium in the seawater to build their shells and outer bodies. Many experts say a more acidic ocean could harm this process.
For example, a type of phytoplankton has cells covered by plates of calcium carbonate, while some mollusk pteropods swim using featherlike limbs. It is believed that these creatures either protect themselves with a tough shell of calcium carbonate, or control their buoyancy with the weight in their shells.
There also are concerns over the acidification on coral colonies, which are collections of tiny coral insects that are closely related to sea anemone. Acidification is feared to affect their ability to build structures made of calcium carbonate. ===
Too complex to pin down
The figures in the data the group collected for this study are not serious, but the pace of acidification is causing concern.
Since the Industrial Revolution, humans have heavily burned fossil fuels that emit CO2, half of which is believed to be absorbed by the oceans. As a result, it is estimated that world ocean water pH has dropped by 0.1 point from about 200 years ago. The results of the group's research suggest the pace of ocean acidification over the past quarter century has tripled.
The scientists therefore decided to run a simulation to see what would happen in a century if ocean acidification continues at its current pace. Their model for CO2 density in the atmosphere was based on a scenario from the Intergovernmental Panel on Climate Change, which sums up opinions on global warming by scientists from around the world.
The simulation showed a considerable change in seawater pH, which would go down by 0.4 point from its current level, or to 7.7. This could pose a serious threat to shellfish and plankton.
To learn more about how acidification could affect sea life, researchers both at home and abroad are experimenting with various levels of CO2 density in seawater. The results have apparently shown that the growth rate dropped for some creatures, but for others, it actually increased.
In fact, it is not fully understood how reducing emissions of CO2 and other greenhouse gases would affect ocean acidification, partly because of the complexities of the global environment, including weather phenomena. Add to this the influences acidification could have on sea life, and it becomes clear that a huge amount of research and funding will be needed to better grasp the whole picture.
Midorikawa's group is tackling this puzzle together with Tsukuba University Prof. Takeo Hama and the Japan Hydrographic Association.
"Before any life in waters off Japanese coasts is affected in some way, we'd like to pave the way for clarifying the complex system of how acidification develops," Midorikawa said.
