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Nachrichten, Termine, Experten
Nachrichten, Termine, Experten
Yesterday, an international team of researchers from various disciplines set off aboard the German research vessel METEOR for an expedition along the west coast of Africa, led by the GEOMAR Helmholtz Centre for Ocean Research Kiel. The expedition focuses on two poorly understood phenomena: the Benguela upwelling system off the coasts of Angola and Namibia, which partly operates independently of the wind, and the recurring marine heatwaves known as Benguela Niños, which have a significant impact on the local climate and cause flooding in Angola and Namibia.
Tropical upwelling regions play an active role in climate and oceanic biogeochemical cycles as well as supporting the most productive oceanic food chains. They support the world’s largest fisheries and are home to a biodiverse marine environment. Climate change, fishing pressure and pollution will alter the tropical upwelling systems in the future. However, despite intense research activities in the past, process understanding and their interactions remains poor hampering prediction of future changes.
Eastern boundary upwelling regions are usually formed by winds blowing parallel to the coast towards lower latitudes, which push warm surface water out to sea. This causes cold, nutrient-rich water from greater depth to rise, promoting the growth of phytoplankton, which forms the basis of marine food web providing a food source for a rich fish population.
Upwelling without wind off Angola
This explanation does not hold in the Benguela upwelling system: “Off Angola we observe a seasonal upwelling that begins in July, when there is almost no wind,” says Dr Marcus Dengler, a physical oceanographer at GEOMAR Helmholtz Centre for Ocean Research Kiel. He is the chief scientist on the M217 “BOCABENO” expedition (Boundary Circulation off Angola and Benguela Niños), which departed from Las Palmas today bound for Namibia.
Coastal Kelvin waves play a key role here. Forming by wind variability at the equator, these waves propagate polewards along the eastern edges of the oceans. Extending for several thousand kilometres, they alter coastal currents and vertically displace ocean properties in the deeper ocean, while the sea surface height fluctuates by only a few centimetres.
Additionally, vertical mixing in the upper ocean supports the upwelling of cold deeper water reaching the surface.
In order to gain a better understanding of the interplay of these processes, the researchers are studying the ocean currents and hydrography along the continental slope as well as the intensity of turbulence, which drives vertical mixing, particularly caused by the tides.
Benguela Niños: Marine heatwaves and their impact
The second key research question addressed by the expedition concerns the causes of marine heatwaves off the south-west African coast. Every few years, sea surface temperatures in this region rise suddenly by up to three degrees Celsius above the climatological norm. These events, known as Benguela Niños, cause flooding in Angola and Namibia, increased rainfall in the arid Namib Desert and disruption to the fragile marine ecosystem.
“An interesting and strong Benguela Niño event occurred in 2021. It appeared later than usual shifting into the main upwelling season significantly reducing the growth of plankton. Consequently, there was less food available for fish,” says Dr Rodrigue Imbol Koungue, a physical oceanographer at GEOMAR. While potential causes include coastal Kelvin wave impulses, changes in local winds, or increased freshwater input from the Congo River, the phenomenon is still poorly understood. A better understanding is essential in order to predict such extreme events.
Methods: Measuring, observing, comparing
In order to investigate the upwelling off the coast of Angola and the formation of Benguela Niños, the researchers on METEOR are combining multiple oceanographic measurement methods. They are servicing existing moored long-term instruments and deploying new devices to the ocean floor. These moorings continuously measure currents, temperature, salinity, pressure, and oxygen from near the surface down to a depth of around 1,200 metres. The instruments remain in the ocean for years while continuously recording data.
In addition, vertical profiles are taken at various stations using a CTD rosette. A ring sampler equipped with sensors is lowered almost to the seabed to measure temperature, salinity and oxygen levels, while collecting water samples from different depths. These samples are later analysed in the laboratory for nutrients, dissolved gases, and biological components. Special sensors also detect small-scale turbulence in the water, shedding light on how cold deep water can reach the surface without strong winds.
Expedition at a glance
• Name: M217/1 BOCABENO (Boundary Circulation off Angola and Benguela Niños)
• Dates: 12 February – 7 March 2026
• Chief Scientist: Dr Marcus Dengler
• Departure: Las Palmas
• Arrival: Walvis Bay
• Area: Tropical Atlantic
https://www.geomar.de/n10173 – images for download
https://www.geomar.de/en/atlantic-ocean-upwelling Atlantic Ocean Upwelling
https://www.geomar.de/en/research/expeditions/detail-view/exp/394300?cHash=03555... Expedition ;217/1
RV METEOR in the port of Las Palmas: Yesterday, it set sail for Namibia to investigate two phenomena ...
Source: Philipp Henning, GEOMAR
Copyright: GEOMAR
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RV METEOR in the port of Las Palmas: Yesterday, it set sail for Namibia to investigate two phenomena ...
Source: Philipp Henning, GEOMAR
Copyright: GEOMAR
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