Ocean upwellings are caused by a variety of different mechanisms. The most common is wind-driven, where the winds push against the surface of the ocean and cause water to flow towards the shore. This can lead to an accumulation of water at the coastline, which then flows back out to sea as an upwelling. Another mechanism is thermohaline circulation, where differences in temperature and salinity drive deep water upwards towards the surface.
These upwellings bring deep, cold water to the surface, which is rich in nutrients that promote the growth of microscopic plankton. Plankton are key players in ocean ecosystems, providing food for larger animals and helping to regulate atmospheric carbon dioxide levels. Without them, our oceans would be very different places.