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Wind‐driven movement of water can also induce vertical circulation, particularly in coastal regions. On the west coasts of land masses in the northern hemisphere, winds out of the north or northwest cause along‐shore water movement, which is moved offshore (clockwise) by Ekman transport. In the southern hemisphere, winds from the south will result in similar coastal upwelling. The water moved offshore is replaced by cooler, nutrient‐laden water welling up from below (Figure 1.10), resulting in an ideal situation for increased productivity. Upwelling regions are the most fertile oceanic areas of the world, often supporting large fisheries for small coastal pelagic fishes such as sardines and anchovies. As we will see later, areas of high ocean productivity are often associated with zones of low oxygen at mid‐depths, resulting from the biological degradation of sinking particulates in a stratified water column. Upwelling can also occur offshore, which it consistently does at the equator where the north and south equatorial currents meet and at the Antarctic divergence. Downwelling, the opposite situation, occurs when winds and Ekman transport cause surface water to converge along a coast.