Chlorophyll concentrations worldwide; Image via SeaWiFS satellite of NASA
Recent research shows that the color of the ocean can have a big influence on the occurence of hurricanes -- the greener the ocean, the more hurricanes. And that's a good thing. The ocean's tint comes from the presence of chlorophyll, the green pigment in phytoplankton that helps the organisms convert sunlight into food, and thus forms the foundation of the oceanic food chain, as well as a prime environment for hurricanes. However, as we recently pointed out in another study, warming temperatures of the oceans are having a negative impact on phytoplankton populations, which have dropped 40% over the last 60 years. And that means fewer hurricanes as well. According to a press release from the American Geophysical Union, "In a simulation of such a change [in color of the ocean] in one region of the North Pacific, the study finds that hurricane formation decreases by 70 percent. That would be a big drop for a region that accounts for more than half the world's reported hurricane-force winds."
Anand Gnanadesikan, a researcher with the National Oceanic and Atmospheric Administration's Geophysical Fluid Dynamics Laboratory in Princeton, New Jersey, and his team are publishing the study in the next issue of Geophysical Research Letters. They describe how a decrease in chlorophyll concentration, and thus a drop in the greenish hue of the ocean, directly causes a drop in the formation of hurricanes in that area.
The discovery occurred when the team used computer simulations of real conditions of chlorophyll concentrations in the North Pacific, and simulations where chlorophyll concentrations in the subtropical gyre of the of the North Pacific were set to zero. They found that the absence of chlorophyll in the subtropical gyre modified air circulation and heat distribution patterns enough that hurricane formations were impacted. Outside the gyre, hurricanes increased by 20%, yet there was a 70% decrease in storms further north -- more hurricanes would hit the Philippines and Vietnam, but fewer would make landfall in South China and Japan.
Why is this the case? It's all in how chlorophyll moderates how sunlight penetrates the ocean:
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.
The drop in phytoplankton numbers due to warming water stretches far beyond the food chain -- which alone is frightening enough -- but also into weather patterns. And changes in weather patterns can have unknown and wide-reaching affects on land.
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