An engine of life
The Humboldt Current System is the most productive eastern boundary current in the world. Extending for over 4,000 kilometers along the western coast of South America, it flows north from Chile to Peru. This cold, low-salinity current is driven by persistent southeasterly trade winds. Due to the Earth's rotation, these winds push surface water offshore in a process called Ekman transport. To replace this displaced surface water, deep, cold water from depths of 100 to 300 meters is pulled up to the sunlit euphotic zone.
This upwelled water has many nutrients like nitrates, phosphates, and silicates, which come from decaying organic matter on the seafloor. When exposed to sunlight, these nutrients fuel massive blooms of phytoplankton, the base of the marine food web. The productivity is immense, classified as a Class I ecosystem with over 300 grams of carbon fixed per square meter per year. These phytoplankton blooms support huge populations of zooplankton, which in turn feed vast schools of small pelagic fish. The most important of these is the Peruvian anchoveta (Engraulis ringens), which has historically represented the largest single-species fishery on Earth. This chain of productivity supports millions of seabirds, marine mammals like sea lions, and larger fish. The system's influence is so great that it is largely responsible for the aridity of the Atacama Desert, as the cold water cools the air above it, preventing the formation of rain.
A delicate balance
The Humboldt Current System is characterized by a significant Oxygen Minimum Zone (OMZ), one of the largest permanent hypoxic zones in the world's oceans. This zone forms because the high productivity leads to a large amount of sinking organic matter, and its decomposition by bacteria consumes vast quantities of oxygen. The OMZ extends from about 100 meters to 600 meters deep, forcing many organisms to live near the surface. This compression of habitat concentrates life into a narrow surface layer, making it highly accessible to fishing fleets and predators.
The system's productivity is highly sensitive to climatic shifts, particularly the El Niño-Southern Oscillation (ENSO). During an El Niño event, warm equatorial waters move into the region, suppressing the normal upwelling process. The thermocline, the boundary between warm surface water and cold deep water, deepens significantly, preventing the nutrient-rich water from reaching the surface. This cuts off the fuel for the ecosystem, leading to a dramatic drop in phytoplankton and a collapse in fish stocks, which has severe economic consequences for the fishing industries of Peru and Chile. Conversely, during La Niña events, the trade winds strengthen, enhancing the upwelling and boosting the ecosystem's productivity even further.