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Mardi, 28 Septembre 2010 21:00

Tiny Plankton Could Steer Giant Hurricanes

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By Duncan Geere, Wired UK

Microscopic plants less than half a centimeter across may be

able to change the paths of 300-mile-wide tropical storms, due to their ability to change the color of the surface of the sea.

Phytoplankton is as common in the oceans as grass is on land, and blooms when cold, nutrient-rich water upwells from the depths. That bloom turns the oceans surface from a deep dark blue to a murky turquoise, henceforth known as murkquoise.

The murkquoise stops the sun from penetrating as far as it normally does into the surface of the sea, making the surface layer much warmer, and the depths cooler. As a result, hurricanes tend to be stronger and last longer.

While these results haven’t been isolated in the real world, and there are plenty of other factors affecting hurricane formation too, results from numerical models suggest that reducing the amount of phytoplankton could also keep hurricanes weaker and confine them to equatorial latitudes.

At the Geophysical Fluid Dynamics Laboratory at the US National Oceanic and Atmospheric Administration, researchers simulated a large-scale “phytocide” in the Pacific Ocean and observed the effects on the sea surface and atmosphere. The results were clear — a 15 percent drop in the number of hurricanes that formed each year.

Those that did form didn’t track as far north, either. Instead, they wobbled along the equator before fizzling out. Hurricane activity in the subtropical north-west of the Pacific dropped a whopping 70 percent.

But why? Well, removing the murkquoise and allowing the sun deeper into the ocean cools the surface. That in turn cools the air above the surface of the sea, allowing more cool dry air to descend from above. When the hurricane moves into this large-scale cool, dry, air-descending area, its moist, warm upwelling air is countered by it, and so it weakens.

The sinking air is also carried along the surface to the equator, where it rises again, strengthening the already-powerful western winds in the upper atmosphere in the tropics. These winds, if strong enough, can behead storm systems that are beginning to organise into a hurricane by literally blowing them away.

But before you dig out the industrial-strength herbicide to dump into the ocean and reduce the risk of hurricanes, it might be wise to consider the implications. Killing off phytoplankton would be like removing all grass from land. Grazing herbivores would be deprived of their food source and die, depriving carnivores their food source too.

Before too long, the oceans would be barren and sterile. Probably too great a price to pay for a slightly lowered risk of hurricanes.

Source Link: Wired.co.uk

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Authors: Duncan Geere

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