When do upwellings occur

Diagram illustrating the principle of equatorial upwelling. Winds along the equator dotted line create currents, which are then diverted north and south by the Coriolis force. The cold, deep waters from below rise to the surface to replace these diverted waters, causing upwelling. Composite image of satellite photos since depicting phytoplankton concentration along North and South America. The key for the image is in units of milligrams of phytoplankton pigment per cubic meter of seawater.

In winter, winds blow from the south to the north, resulting in downwelling. During the summer, winds blow from the north to the south, and water moves offshore, resulting in upwelling along the coast.

This summer upwelling produces cold coastal waters in the San Francisco area, contributing to the frequent summer fogs. Duxbury, et al, Home Education Currents Upwelling. Upwelling Currents Tutorial. Upwelling is the movement of cold, deep, often nutrient-rich water to the surface mixed layer; and downwelling is the movement of surface water to deeper depths.

Downwelling occurs when surface waters converge come together , pushing the surface water downwards. Regions of downwelling have low productivity because of the nutrients get used up and are not continuously resupplied by the cold, nutrient-rich water from below the surface. Upwelling occurs when surface waters diverge move apart , enabling upward movement of water. Upwelling brings water to the surface that is enriched with nutrients important for primary productivity algal growth that in turn supports richly productive marine ecosystems.

Upwelling regions are often measured by their productivity due to the influx of nutrients to the surface mixed layer and euphotic zone sunlit layer by upwelling currents.

This drives photosynthesis of phytoplankton tiny alga , which form the base of the ocean food web. Some of the most important upwelling regions are along the coasts of continents.