Updated: Sep 22
Weather forecasting suggests that there will be an El Niño climate event in 2023. This could create a huge number of problems for our oceans, as these events result in raised sea temperatures, pushing coral reefs and other ecosystems to the edge of disaster, and lead to coral bleaching events and impacts on the amount of dissolved CO2 in the oceans.
What is El Niño ?
El Niño Southern Oscillation (ENSO) is a naturally occurring ocean-atmosphere phenomenon that occurs every two to seven years. It is one of the most significant climate patterns that affects the marine environment, as well as many other parts of the world.
ENSO is characterised by the warming of the central and eastern equatorial Pacific Ocean and a cooling of the western Pacific. This warming and cooling results in changes in the atmospheric circulation and the ocean currents, which in turn affects the global climate. During an El Niño event, the ocean currents that normally move warm water from the western Pacific to the east are disrupted, causing a large amount of warm water to remain in the central and eastern Pacific. This leads to an increase in sea surface temperatures and a decrease in the upwelling of cold water from the deep ocean, which can have significant impacts on the marine environment.
How will it affect marine life?
One of the primary impacts of El Niño on the marine environment is a reduction in the productivity of the ocean. During an El Niño event, the reduction in upwelling of cold, nutrient-rich water from the deep ocean reduces the availability of nutrients for phytoplankton, which are the base of the marine food chain. This leads to a decline in the populations of zooplankton and other small organisms, which in turn affects the populations of larger organisms such as fish, birds, and mammals.
In addition to its effects on productivity, El Niño can also have significant impacts on the distribution and abundance of marine species. For example, during an El Niño event, many fish species that are normally found in the eastern Pacific, may move to the west to escape the warm water. This can result in changes in the fishing industry, as some species may become more abundant in certain areas, while others may become scarce.
How does it cause coral bleaching?
El Niño can also have impacts on the physical environment of the ocean, such as altering the water temperatures and causing changes in the ocean currents. These changes can result in the movement of warmer water into areas where it is normally cold, which can impact the distribution and abundance of certain species, such as causing coral bleaching. When water temperatures rise, the coral polyps become stressed and expel the colourful algae (zooxanthellae) that live inside of them and provide them with food and their vibrant colour. Without the zooxanthellae, the coral polyps turn white. Coral bleaching can have devastating effects on coral reefs, as they provide important habitats for a wide range of marine species and play a crucial role in maintaining the health of the ocean.
Additionally, El Niño can result in increased ocean stratification, which can limit the exchange of nutrients between the surface and deep waters and further reduce the productivity of the ocean.
El Niño is a complex and powerful climate phenomenon that has significant impacts on the marine environment. From reducing ocean productivity to altering the distribution and abundance of marine species, its effects are far-reaching and can have significant consequences for the ecosystem and the people that depend on it. Understanding the mechanisms of ENSO and how it impacts the marine environment is important for predicting and mitigating its impacts, and for managing the resources that depend on the health of the ocean. We must also remember that the impacts of human emission driven climate change only serve to make these events more extreme and push species and ecosystems further and further from their ideal environmental conditions, resulting in environmental damage to greater levels.