Samplings: June 2009

Print

Email

Massive storm blows dust from Africa into the Atlantic Ocean.

NASA/courtesy Amato Evan

The surface temperature of the tropical North Atlantic Ocean—between Senegal and the Lesser Antilles—has risen faster than that of any other tropical ocean basin. It’s been warming by about one-half a Fahrenheit degree per decade since 1980. Global warming or changes in ocean circulation have been taking the blame, but new research links most of the rise to decreasing dust and volcanic particles in the air.

Such airborne particles, called aerosols, reflect sunlight and thus shield the ocean’s upper layers from heat. The tropical North Atlantic gets bombarded with dust from Africa’s Sahara and Sahel regions, receiving more dust than any other ocean basin. But the volume varies greatly by season and year, and it has been trending downward.

Amato T. Evan of the University of Wisconsin at Madison and several colleagues analyzed twenty-six years of satellite data on sea-surface temperature and atmospheric conditions. The researchers attribute a fifth of the region’s upward temperature trend to a long-term decrease in dust from Africa. A full half they attribute to the gradual subsidence of dust and volcanic sulfuric-acid particles from the eruptions of El Chichón in Mexico in 1982 and Mt. Pinatubo in the Philippines in 1991. The remainder—just 31 percent—is due to other factors, including climate change, the team says.

Warming North Atlantic waters have spawned intense hurricanes in recent years. Dust from Africa and volcanic eruptions—both difficult to predict—may affect the number and force of future storms. (Science)