Upwelling describes an oceanographic process where deep, cold, and nutrient-rich water rises to the surface, replacing warmer, nutrient-depleted surface waters. This upward movement brings essential elements from the ocean depths into the sunlit zone, playing a fundamental role in marine ecosystems and influencing global processes.
Fueling Ocean Life
The primary importance of upwelling stems from its ability to fertilize the ocean’s surface waters. Deep ocean waters accumulate essential dissolved nutrients from the decomposition of organic matter. When upwelling brings these deep waters to the surface, these nutrients become available in the sunlit upper layers where photosynthesis can occur.
This influx of nutrients acts as a natural fertilizer, stimulating massive blooms of phytoplankton. Phytoplankton are microscopic marine plants that form the base of the marine food web. They use sunlight and carbon dioxide to produce organic compounds through photosynthesis, initiating the flow of energy in the ocean.
The abundant phytoplankton then support a thriving ecosystem. Zooplankton, tiny marine animals, graze on these phytoplankton. In turn, these zooplankton become a food source for small fish, crustaceans, and larger marine animals, including predatory fish, marine mammals, and seabirds. Upwelling zones therefore represent areas of high primary productivity, supporting a rich and complex food chain.
Supporting Global Fisheries and Biodiversity
The high primary productivity fueled by upwelling translates directly into some of the most productive fishing grounds worldwide. Upwelling regions, although covering only about one percent of the ocean surface, contribute roughly 50 percent of the world’s fisheries landings.
Examples of these highly productive upwelling regions include the California Current, the Humboldt Current off Peru and Chile, the Benguela Current off southern Africa, and the Canary Current off Northwest Africa. These areas support significant commercial fisheries for species such as anchovy and sardine, vital for global food security.
Beyond fisheries, upwelling zones are also recognized as hotspots of marine biodiversity. The rich food supply attracts a wide array of species, from tiny invertebrates to large marine mammals and seabirds. These areas provide important foraging habitats and support dense populations of marine life, making them ecologically diverse and important for ecosystem health.
Influencing Earth’s Climate
Upwelling also plays a role in regulating Earth’s climate, primarily through its influence on the global carbon cycle. The vast phytoplankton blooms in upwelling zones absorb substantial amounts of atmospheric carbon dioxide (CO2) during photosynthesis. This process removes CO2 from the atmosphere and incorporates it into organic matter.
When these phytoplankton and the organisms that consume them die, their organic carbon can sink to the deep ocean, a process known as the biological carbon pump. This downward transport of carbon sequesters it away from the atmosphere for periods ranging from months to millennia, helping to regulate atmospheric CO2 levels. Even small changes in the efficiency of this pump can impact atmospheric CO2.
Upwelling also brings cold water from the ocean depths to the surface. This cold water can locally influence air temperatures and weather patterns in coastal regions. For example, the upwelling off the coast of California contributes to the cool and foggy climate characteristic of that area. This cooling effect can also reduce precipitation and influence atmospheric circulation, contributing to regional climate regulation.