Final answer:
Vigorous upwelling along the coast of Ecuador and Peru occurs during El Niño, a warm ocean current event that disrupts normal nutrient cycling by rising deep ocean waters full of nutrients.
Step-by-step explanation:
Exceptionally vigorous upwelling along the coast of Ecuador and Peru occurs during an event known as El Niño. This phenomenon is characterized by the warming of ocean currents along the west coast of South America, leading to remarkable changes in weather patterns that can trigger extreme weather in various regions.
During normal years, ocean upwelling is a crucial process that recycles nutrients and energy in the ocean, with the wind driving surface waters away from the coastline and prompting the rising of deep ocean waters that are rich in nutrients to the surface. But during El Niño, the warm waters take over, disrupting this natural upwelling and potentially causing large die-offs of fish and marine mammals.