Climate Change Can Slow Ocean's Absorption of Carbon Dioxide Gas
Perkins, S., Science News
A decrease in precipitation over the Pacific Ocean just north of Hawaii in recent years has left the ocean there saltier and has diminished its capacity to soak up planet-warming carbon dioxide, a new analysis shows.
Each month since the late 1980s, researchers have recorded ocean conditions about 100 kilometers north of Oahu, far enough out that waters aren't affected by nutrients washed from any island. At 5 km deep, the water at this site--which scientists have dubbed station ALOHA--has ocean layers that mix just as much as they do in more remote waters, says David M. Karl, a biogeochemist at the University of Hawaii in Honolulu.
The scientists' measurements indicate that, averaged over a year, surface waters at the site soak up carbon dioxide from the atmosphere. However, the rate of absorption of that greenhouse gas has been slowing in recent years. In 2001, the ocean at station ALOHA absorbed only about 15 percent of the carbon dioxide that it did in 1989, says Karl.
Other changes in the water during that same period--together with simple thermodynamics--help explain why. From 1989 to 2001, the ocean-surface salinity at station ALOHA went up about 1 percent. That's because in recent years there's been less rainfall and more evaporation in the area, both of which concentrate salt in the surface water. When the concentration of dissolved substances goes up, it becomes more difficult for a liquid to absorb a gas, says Karl. …