Galapagos Ocean Upwelling
There is another reason for the peculiar climate of the Galapagos, that is ocean upwelling. Upwelling refers to the rise of deep water to the surface; this can occur as a result of both current patterns and winds. Though the actual cause is complex, a simple explanation goes as follows.
As water of the Humbolt Current turns westward, it spreads out, or diverges. Since the water is spread out over a greater area, extra water must come from below, or upwell, to make up the difference.
A more important reason for upwelling, however, has to do with winds and a phenomenon known as Ekman Transport. The trade winds blow from southeast to northwest in the southern hemisphere and from northeast to southwest in the northern hemisphere. Therefore, both blow towards the equator. However, the winds push water not straight ahead, but at a 45° angle to the wind direction (45° to the left in the southern hemisphere and 45° to the right in the northern hemisphere).
This Ekman Transport, which, like the Coriolis Force, is a result of the Earths rotation. Therefore, although the trade winds are blowing towards the equator, they push water away from it. Once again, the divergence in surface water allows deep water to rise to the surface.
The oceans are thermally stratified, so that the water rising from depth is colder than the surface water. In some areas, the water temperature can fall below 20° C (68° F), particularly west of island Isabela. For most people, this is too cold for comfortable swimming.
Another interesting and important aspect of deep ocean water is that it is rich in nutrients. Most marine organisms live near the surface. When they die, their bodies sink. As they sink, they are slowly decomposed by bacteria, releasing nutrients back into the deep water. Therefore, the deep water in the ocean is enriched in nutrients. When upwelling occurs, these nutrients are carried to the surface.
The nutrients stimulate growth of the algae, or phytoplankton, living in the surface water. The phytoplankton are the base of the food chain in the ocean so when they flourish, everything else does as well. Because of upwelling, the waters around the Galapagos are remarkably productive and rich in marine life.