In the latter scenario, the absence of chlorophyll in the subtropical gyre affected hurricane formation by modifying air circulation and heat distribution patterns both within and beyond the gyre. In fact, along the equator, those new patterns outside the gyre led to an increase in hurricane formation of about 20 percent. Yet, this rise was more than made up for by the 70 percent decrease in storms further north, over and near the gyre. The model showed that more hurricanes would hit the Philippines and Vietnam, but fewer would make landfall in South China and Japan.
In the no-chlorophyll scenario, sunlight is able to penetrate deeper into the ocean, leaving the surface water cooler. The drop in the surface temperature in the model affects hurricane formation in three main ways: cold water provides less energy; air circulation patterns change, leading to more dry air aloft which makes it hard for hurricanes to grow. The changes in air circulation trigger strong winds aloft, which tend to prevent thunderstorms from developing the necessary superstructure that allows them to grow into hurricanes.
A decrease in hurricanes in the North Pacific is just one example of how changing chlorophyll concentrations can have far-reaching, previously unconsidered, effects. The specific outcomes over different patches of the ocean will vary based on local currents and ocean conditions, said Gnanadesikan.
A complete absence of chlorophyll in parts of the ocean would be a drastic change, Gnanadesikan admits. Yet, its potential impact is still important to consider, he maintains. The northern Pacific gyre that he studied is already the "biological desert of the ocean," he said. So the surprise, then, is that "even in this region that is apparently clear, biologically-mediated heating is importan
|Contact: Colin Schultz|
American Geophysical Union