What is upwelling and downwelling in the ocean

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. In these coastal upwelling regions, surface winds push water away from the shore and create a divergence at the coast, which is replaced by water from depth.

For coastal upwelling to occur, the wind must be parallel to the coast because water is deflected to the left of the wind in the southern hemisphere, and the right of the wind in the northern hemisphere. Equatorial upwelling involves the Trade Winds blowing across the equator and the Coriolis effect taking over as diverging currents move away from the equator.

The continental margins of the world are places where coastal upwelling and downwelling are taking place Figure 9. Coastal upwelling is influenced by coastal geometry, wind directions, and the influence of the Coriolis effect Ekman transport. Figures and illustrate how the direction of wind movement determines how coastal upwelling and downwelling takes place in the Northern Hemisphere such as in California.

Upwelling water along the coastline is colder than waters farther offshore. Upwelling and Downwelling Upwelling is the vertical movement of cold, nutrient-rich water from deep water to the surface, resulting in high productivity plankton growth.

The movement of surface currents also plays a role in the vertical movements of deeper water, mixing the upper water column. Upwelling is the process that brings deeper water to the surface, and its major significance is that it brings nutrient -rich deep water to the nutrient-deprived surface, stimulating primary production see section 7. Downwelling is where surface water is forced downwards, where it may deliver oxygen to deeper water.

Downwelling leads to reduced productivity, as it extends the depth of the nutrient-limited layer. Upwelling occurs where surface currents are diverging, or moving away from each other.

As the surface waters diverge, deeper water must be brought to the surface to replace it, creating upwelling zones. The upwelled water is cold and rich in nutrients, leading to high productivity.

Many of the most productive regions on Earth are found in upwelling zones. In the equatorial Pacific, the trade winds blow the North and South Equatorial Currents towards the west, while Ekman transport causes the upper layers to move to the north and south in their respective hemispheres.

This creates a divergence zone, and a region of upwelling and high productivity Figure 9.