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18 December 2011

Winds and Waves Stir Dust and Mud

(Click on images for larger view.)

The mingling of winds and deserts often leads to dust storms. But winds do more than stir up the land surface; they also generate waves in the water. In a shallow water body such as the Persian Gulf, wind-driven waves can reach down to perturb the sea floor.

This was the likely sequence of events that occurred in early December 2011, when the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured these natural-color images.

The top image, from December 10, 2011, shows dust plumes blowing across Syria and Iraq. Arising from discrete points, the dust blows in a large arc. Over Syria, skies are mostly clear, but across the Iraq border, the dust thickens enough to hide the Euphrates River. The dust arcs around a cloudbank, which may be associated with the same weather system that led to the dust storm.

In the December 12 (bottom) image, the northwestern end of the Persian Gulf is brightened by shades of tan and peacock green. These green hues could result from phytoplankton—tiny plant-like marine organisms. The chlorophyll content of phytoplankton often appears bright green or blue in natural-color satellite images.

The more likely explanation, though, is that the same winds that stirred up the dust also drove the ocean waves. The churning water then disturbed the sea floor and suspended sediments near the surface. Such sediments would increase the amount of sunlight reflected by the water and enhance the green signal from chlorophyll-rich plankton.

NASA image courtesy LANCE/EOSDIS MODIS Rapid Response Team at NASA GSFC. Caption by Michon Scott based on image interpretation by Norman Kuring, Ocean Color Web.