Ocean currents are the continuous movement of seawater across the globe, driven by forces like wind, gravity, and differences in water density. These flows distribute heat around the Earth and influence regional climates. The Peru Current is a key example, shaping the environment and ecosystems along the western coast of South America.
Geographic Positioning
The Peru Current, also known as the Humboldt Current, is a cold, low-salinity ocean current flowing northward along the western coast of South America. It extends from southern Chile, around the 45th parallel south, up to northern Peru, near the 4th parallel south. As an eastern boundary current, it flows along the eastern edge of an ocean basin, moving parallel to the coastline and typically extending 500 to 1,000 kilometers offshore.
The current’s northern trajectory eventually leads it to turn westward, merging with the South Equatorial Current. Its surface speeds are relatively slow, but the Peru Current is a key feature of the Pacific Ocean’s circulation. Sea surface temperatures off Peru can reach as low as 16 °C, which is uncharacteristic for tropical waters that usually measure above 25 °C.
The Mechanism of Cold Water and Nutrients
The cold temperatures and rich nutrient content of the Peru Current are primarily due to upwelling. Upwelling is a wind-driven process where dense, cooler, nutrient-rich water from deeper ocean layers rises to the surface. Along the coast of Peru, prevailing winds blow towards the north, and the Coriolis effect in the Southern Hemisphere deflects surface water offshore.
As surface water is pushed away, colder, nutrient-dense water from below wells up to replace it. These deeper waters are rich in nutrients like nitrates, phosphates, and silicic acid, which are products of decaying organic matter. Once these nutrients reach the sunlit surface waters, they fuel the growth of phytoplankton through photosynthesis, forming the base of a highly productive marine food web.
Impact on Marine Life and Coastal Climate
The nutrient-rich waters brought to the surface by the Peru Current create one of the most productive marine ecosystems globally. This high productivity supports populations of fish, including sardines, anchovies, and jack mackerel, making the region one of the world’s largest fishing grounds. Approximately 18-20% of the total worldwide marine fish catch originates from this system. This abundance also sustains marine mammals, such as seals and cetaceans, and seabird colonies.
The Peru Current influences the climate of adjacent coastal regions. Its cold waters contribute to the aridity of the Atacama Desert in northern Chile and coastal Peru. Marine air passing over the cold current cools, becoming less conducive to generating rain when it reaches the warmer land. The cold current also leads to the formation of coastal fog, locally known as “garúa,” especially during the Southern Hemisphere winter. This moist, cold fog provides moisture to these otherwise extremely dry areas, supporting unique fog oases.
El Niño and the Current’s Fluctuations
The Peru Current’s upwelling process is disrupted during an El Niño event. Occurring every two to seven years, El Niño is characterized by a warming of surface waters in the tropical Pacific Ocean. During El Niño, the trade winds, which normally drive upwelling, weaken or even reverse.
This weakening allows warm surface water to accumulate along the coasts of Peru and Chile, increasing sea surface temperatures, sometimes by 4 to 8 °C warmer than normal. The influx of warm, nutrient-poor water reduces the availability of nutrients at the surface, which suppresses phytoplankton growth. This reduction in primary productivity impacts the entire food web, leading to a decline in fish populations and affecting marine mammals and seabirds that rely on them. Altered ocean temperatures and disrupted upwelling during El Niño events can have ecological and economic consequences for the region.