File:Mauritania (MODIS 2021-12-16).jpg

English: This stunning true-color image of western Mauritania was captured by the Moderate Resolution Imaging Spectroradiometer (MODIS) on board NASA’s Terra satellite on December 15. The clear skies of the sunny spring day permitted a gorgeous view of the country’s orange sands, rugged rock outcroppings, and offshore color.

Mauritania sits on the northwestern coast of Africa, where the arid Sahara Desert meets the semi-arid Sahel. About three-fourths of the country sits solidly within the Sahara Desert, and is comprised of flat plains, a broken plateau made up of mesas (flat-topped hills), and orange-colored sand dunes. The prevailing wind in this part Mauritania blow from the northeast, lending to the sweeping, richly-colored, orange streaks of sand that stretch from northeast to southwest in this image.

The color off the coast is created by a combination of phytoplankton and sediment. Phytoplankton are microscopic plant-like organisms that contain chlorophyll and thrive in nutrient-rich water. The waters off of Mauritania typically are rich in diatoms, one of the most common type of phytoplankton found in oceans. They often reproduce explosively, creating a large “bloom” that can be seen from space, after strong storms mix the oceans and bring nutrients up from the seafloor. The waters off of Mauritania are constantly in motion, thanks to an upwelling caused by near-constant trade winds that roil the surface, causing it to be displaced as it is blown away from the African coast. As this occurs, the cold and nutrient-rich waters from deep below the surface are pulled upward to the surface—carrying nutrient-rich waters that feed a phytoplankton bloom. Because the upwelling in this region is near-constant, phytoplankton feast year-round in this location, and are frequently seen in satellite images.