The Benguela System under climate change - Effects of Variability in physical forcing on carbon and oxygen budgets

01.02.2022 – Upwelling

The Benguela upwelling area stretches off the coast of South Africa, Namibia and Angola and is one of the most fertile or productive areas of our oceans. In total, there are four major coastal upwelling systems on Earth, known as the Eastern Boundaries Upwelling Systems, the other three being off the coast of north-west Africa, off the west coast of the USA and the north-west coast of South America. These four regions account for the majority of all fish catches that take place on Earth. Of the four, the Benguela upwelling area is the largest and most important. But what happens here? There is a permanent area of high pressure over the South Atlantic. In combination with heat-low pressure areas over the African continent, this leads to a constantly prevailing trade wind off the coast that blows in a north-westerly direction. This trade wind pushes the surface water off the coast towards the open sea, causing cold deep water to flow to the surface. With this deep water, many important nutrients such as nitrate and phosphate come to the surface, providing the basis for the growth of microscopic marine algae, the phytoplankton. The phytoplankton is the basis for the entire food chain and for all other life in this part of the coast. This is why large schools of fish are found here, which are an important source of protein for people living on the west coast. With the upwelling of cold deep-sea water, CO2 also reaches the surface and enters the atmosphere. However, this CO2 is also bound again by the algae through photosynthesis. When the phyto- and zooplankton and other organisms die, they slowly sink to the seabed. There and on their way down, their organic material is degraded by other organisms and processes. This happens with the consumption of oxygen, so that oxygen-poor (suboxic) and oxygen-free (anoxic) areas can form on the seabed. Off the coast of Namibia, this is further reinforced by the fact that oxygen-poor and nutrient-rich water is physically sucked in from the huge Angoladome. If oxygen is not present, nitrate, for example, can be used by certain bacteria to break down organic material. If you want to learn more about the system, we recommend you watch the video "How does the Benguela Upwelling System work?", which was produced as part of the Genus project a few years ago.

 

 

Text: Fabian J., Braun P. (both IOW)