The Agulhas Current and Europe's climate
The Agulhas Current transports water from the Indian Ocean along the east coast of southern Africa. At the southern tip of the continent, immediately before entering the South Atlantic it turns around and flows back into the Indian Ocean. However, some water enters the South Atlantic in the form of mega-eddies up to 400 km wide known as Agulhas Rings, which carry warm salty Indian Ocean water. This causes an anomaly across the South Atlantic, which affects the strength of the Gulf Stream and is therefore a potential driver of climate in Europe. The GATEWAYS (Multi-level assessment of ocean-climate dynamics: A gateway to interdisciplinary training and analysis) project was established to better understand the Agulhas Current. Project partners used modern observations, ocean reconstructions and climate modelling to investigate the relationship between the Current and climate, including weather systems and rainfall patterns. GATEWAYS brought together an international group of marine and continental palaeoclimatologists who studied deep-sea sediments to detect and quantify past variations in the Agulhas Current. Reconstructions were combined with computer model experiments that acted as a reference for comparison with analytical data. Results showed that the Agulhas Current underwent regular swings that matched global ice age/warm age cycles. Recurrent millennium-long periods of wet climates on land were evidenced by river sediments found offshore. The periods occurred when the North Atlantic experienced extremely cold conditions due to a weakened Gulf Stream. These humid episodes coincided with periods of technological and behavioural innovation in southern Africa. This revealed a possible link between the Agulhas Current's behaviour and the evolution of modern humans. Computer models conducted accurate simulations of the Agulhas Current and were instrumental in highlighting the sensitivity of the leakages to the South Atlantic to changing winds. Comparisons between the palaeo data and model simulations led to improved understanding of past climates. This gave scientists a better understanding of how Agulhas water enters the Atlantic Ocean, influencing the overall Atlantic Ocean circulation, including the Gulf Stream. The GATEWAYS project improved understanding of ocean dynamics, resulting in a clearer understanding of climate sensitivity over different timescales. This is extremely important for making climate predictions. The initiative also showed the essential nature of collaboration between climate modelling, observational oceanography and palaeo data communities.
Keywords
Agulhas Current, Indian Ocean, South Atlantic, Gulf Stream, ocean-climate dynamics
