The Equatorial Undercurrent

At the equator, trade winds push a surface current from east to west. About 100 to 200 meters below, a swift countercurrent flows in the opposite direction. This Equatorial Undercurrent (EUC) is cooler and rich in nutrients. When it hits an island, like a current hitting a rock in a river, water is deflected upward on the islands western flank and around the islands. This wellknown upwelling process brings cooler water and nutrients to the sunlit surface, creating localized areas where tiny chlorophyll-rich marine plants and corals thrive. (Illustration by Amy Caracappa-Qubeck, © Woods Hole Oceanographic Institution)