Seasonal and periodic upwelling of deep nutrient-rich water to shallow depths plays a major role in supporting marine organisms worldwide. Upwelling occurs when cold nutrient-rich deep water replaces warmer nutrient-poor surface water. Increases in nutrients promote growth of marine algae and phytoplankton, which in turn provide the basis of the food web for many fish, marine mammals, and marine birds. These shifts in resources influence the abundance of marine organisms throughout the world. Upwelling events provide animals such as humpback whales, shearwaters (a largely pelagic bird), many tuna, and other primary and secondary consumers, with a significant portion of their annual energy requirements.
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