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The mystery of the cold current: Why does the Humboldt current have such a huge impact on the climate of South America?
The Humboldt Current, also known as the Peruvian Current, is a cooling, low-salinity warm ocean current that flows along the west coast of South America. This cold current is an eastern boundary flow that extends toward the equator and extends about 500 to 1,000 kilometers beyond the coastline. Although this cold current was discovered 250 years ago by Spanish natural historian Hamil de Acosta, it was named after German naturalist Alexander Humboldt. Humboldt reported the measurement of this cold current in his 1846 book "Cosmos". This cold current extends from southern Chile (about 45 degrees south latitude) to northern Peru (about 4 degrees south latitude), where the upwelling of cold water forms an equatorial front, where cold water intersects with warm tropical water. Sea surface temperatures along the Peruvian coast can be as low as 16°C, which is quite unusual in tropical waters as most other areas have water temperatures above 25°C.
Upwelling brings nutrients to the surface, supporting the growth of phytoplankton and ultimately increasing biological productivity.
The Humboldt Cold Current is an extremely productive ecosystem and is considered the most productive eastern boundary cold current system. Its contribution to the world's total marine fisheries accounts for approximately 18% to 20%. The species here are mainly pelagic: for example sardines, anchovies and bonito. In addition, the system's high productivity supports other important fisheries resources, as well as marine mammals (eared dolphins and cetaceans) and seabirds. Whenever the Southern Oscillation is delayed, known as an El Niño event, the upwelling that drives the system's productivity is disrupted, often with significant social and economic impacts.
The Humboldt Current significantly affects the climate of Chile, Peru and Ecuador. It is one of the main causes of drought in the Atacama Desert of Chile and along the southern coasts of Peru and Ecuador. Cooling ocean air makes these areas less prone to precipitation, although clouds and fog can form.
Trade winds are the main driving force of the Humboldt Cold Current circulation, and its system changes are affected by the north-south movement of trade winds at the equator and in the north.
Changes in trade winds drive changes in this first-rate system. The high pressure system in south Pyongyang, cyclonic storms and the movement of westerly winds in the south all play an important role in the changes in this system. The air-sea changes in central Chile are intensified by the low-pressure system between the ocean boundary layer and the coastal mountains. This situation is especially obvious between 27 degrees south latitude and 42 degrees south latitude. The Humboldt Current occupies the upper ocean and flows equatorially, carrying fresh, cooled subantarctic surface water along the edges of the subtropical gyre. In southern Peru, this main flow deviates toward the coast, while a weaker branch continues to flow toward the equator. When the flow reaches 18 degrees south latitude, cool low-salt water mixes with warm high-salt water, causing partial submergence.
There is a coastal transition zone (CTZ) with high eddy kinetic energy off the coast of central Chile. This energy forms mesoscale eddies extending 600 to 800 kilometers outward. This area is divided into three distinct areas: a high chlorophyll concentration area near the coast of Chile, a high chlorophyll concentration area on the Peruvian coast, and a high concentration area in northern southern Chile. High chlorophyll concentrations are usually observed within 50 kilometers of water bodies.
The branches of the Humboldt Current flowing towards the Peruvian coast reduce the ventilation within this system, thereby forming a strong oxygen minimum zone.
The formation of the oxygen minimum zone is affected by multiple factors, including the subsidence and decline of major production resources. Therefore, many organisms are forced to search for nutrients and oxygen near the water surface, limiting the migration of zooplankton in the water body. In the water layer between 0 and 600 meters, many species of zooplankton gather in the oxygen minimum zone, promoting carbon exchange between the planktonic layer and the oxygen minimum zone. 75% of the total zooplankton biomass here moves back and forth in and out of the oxygen minimum zone. This area also provides shelter for organisms that can live in oxygen-depleted conditions.
Coastal upwelling is the main reason for the high biological productivity of the Humboldt Current, and this upwelling system is not uniform. This current system creates three significant upwelling subsystems, including a seasonal upwelling in Chile only in spring and summer, an upwelling shadow in northern Chile and southern Peru, and a strong upwelling that is productive year-round in Peru.
The Humboldt Current's profitability comes from its unique ecosystem, such as a successful fishery for a variety of fish including sardines, anchovies and bonito.
The Humboldt Current produces one of the most successful commercial fisheries in the world. The main catches include sardines, anchovies and seabass, and the fish resources in northern Peru mainly consist of a special kind of anchovy. These fisheries influence the direction of global fisheries, and population changes in these species can have far-reaching economic consequences based on environmental changes such as El Niño.
El Niño and La Niña events have a great impact on the productivity of the Humboldt Cold Current system. During an El Niño event, the upper layers of thermosalt and low-oxygen waters deepen to depths of more than 600 meters, releasing nitrogen and reducing carbon export, significantly affecting the abundance and distribution of many fish species. Conversely, in non-El Niño years, productivity remains high and coastal areas are richer in nutrients.
Such changes not only affect the local fishery, but also affect the social and economic conditions of South America as a whole, and at the same time trigger people's reflection on environmental changes. How do you think we can continue to utilize the resources of the Humboldt Cold Current while protecting the ecosystem?
