The Age of El Nino

Murtugudde explained that the rotation of the Earth causes currents on opposite sides of the equator to move away from each other. Any moving water just north of the equator is pushed further north and any water just south of the equator goes further south. During a normal year the currents produce equatorial upwelling and give rise to beds of algae. When El Niño hits, warm water prevents this upwelling, as it does in many other parts of the ocean, and the algae die off. At the end of the cycle the algal bloom should re-establish themselves at the equator.

In order to understand what was going on, the scientists looked at measurements of the wind speed and water temperature for March and April. The readings not only verified the scientists’ suspicions that the warm waters were retreating to the western Pacific, but also gave them an explanation for the position of the algae. Apparently, El Niño-related changes were also creating changes in the air above the ocean. The winds were not blowing east or west across the equator, but south, and they were pushing warm surface water into the equator.

"If you blow warm water into the equator, it cannot go further south. The water tends to pile up there," he said. Since these winds had blown away the surface waters north of the equator, the upwelling currents shifted and they ended up emerging 200-300 kilometers away. Within days the phytoplankton started to grow north of the equator.

Reading the Future in a Bed of Algae

"For the first time we are seeing the transition from El Niño to La Niña well before other measurements become available," Murtugudde said. The researchers had to look at sea surface temperature, sea surface heights and wind speed to verify the results shown on the SeaWiFS satellite maps in January and February. Though the northerly winds and lower temperatures existed during these earlier months, they had not changed enough for the scientists to get a bead on them using standard monitoring equipment, he explained. "The biology reacts much more to sub-surface conditions of the ocean than these other parameters do," Murtugudde said.