New insights into the dynamics of the Atlantic Circulation
High-resolution sediment samples off the coast of Brazil reveal surprising fluctuations in the Atlantic circulation at the end of the last ice age
The Atlantic Meridional Overturning Circulation (AMOC) distributes heat across the Atlantic – particularly in the Northern Hemisphere – like a conveyor belt, thereby influencing precipitation, sea ice, ecosystems, and the global carbon cycle. Researchers continue to debate the potential consequences of an abrupt weakening of the AMOC and whether such a weakening could be irreversible over the long term. “Until now, we have assumed that the AMOC was significantly weaker during the Heinrich Event and did not recover even over several thousand years. However, our data show that the overturning circulation was much more dynamic,” explains Dr. Stefan Mulitza of MARUM – Center for Marine Environmental Sciences at the University of Bremen, who led the study together with his Brazilian colleagues Dr. Partha Sarathi Jena and Dr. Cristiano Mazur Chiessi from the University of São Paulo. The study has now been published in Nature Communications.
Key insights came from sediment samples collected during an expedition off the coast of Brazil. Due to the exceptionally high local sedimentation rates – many particles settle on the ocean floor in a relatively short time – the team was able to recover about three meters of material deposited exclusively during the Heinrich Event. The Heinrich Event lasted about 2,000 to 3,000 years, “but until now we couldn’t say with certainty how stable the AMOC was during that period,” explains Chiessi. Radiocarbon dating of benthic foraminifera plays a key role here; these organisms serve as a particularly sensitive indicator of the residence time of bottom water masses and can thus be used to reconstruct the intensity of the Atlantic Meridional Overturning Circulation.
The analyses show that the Atlantic Meridional Overturning Circulation was by no means always in a weakened state during the Heinrich Event. In fact, the researchers were able to identify two periods during which the AMOC was significantly strengthened for several centuries. These periods had an impact on, among other things, tropical precipitation patterns and carbon storage in the ocean. “The exceptionally high temporal resolution of our data now makes it possible, for the first time, to identify the variability of the AMOC and its consequences on timescales of a few centuries,” says Mulitza.
The study provides important insights for better understanding the role of the AMOC in climate change throughout Earth’s recent history. A future weakening of the AMOC currently appears very likely. However, it is still unclear whether this weakening has already begun and whether it will occur abruptly.
Participating institutions:
- MARUM – Center for Marine Environmental Sciences, University of Bremen
- School of Arts, Sciences and Humanities, University of São Paulo (Brasilien)
- Institute of Geosciences, University of Campinas (Brasilien)
MARUM produces fundamental scientific knowledge about the role of the ocean and the seafloor in the total Earth system. The dynamics of the oceans and the seabed significantly impact the entire Earth system through the interaction of geological, physical, biological and chemical processes. These influence both the climate and the global carbon cycle, resulting in the creation of unique biological systems. MARUM is committed to fundamental and unbiased research in the interests of society, the marine environment, and in accordance with the sustainability goals of the United Nations. It publishes its quality-assured scientific data to make it publicly available. MARUM informs the public about new discoveries in the marine environment and provides practical knowledge through its dialogue with society. MARUM cooperation with companies and industrial partners is carried out in accordance with its goal of protecting the marine environment.
Journal
Nature Communications
Article Title
Centennial-scale intensifications of the Atlantic Meridional Overturning Circulation 1 during Heinrich Stadial 1.
Study reveals that Atlantic climate variability enables the prediction of leishmaniasis outbreaks in North Africa
The study, led by ISGlobal together with the Pasteur Institutes of Tunisia and Morocco, demonstrates for the first time that the Atlantic’s climate memory makes it possible to predict climate-sensitive diseases over the long term in temperate regions
Barcelona Institute for Global Health (ISGlobal)
Barcelona, 19 August, 2026-. Climate variability in the Atlantic Ocean can help predict cutaneous leishmaniasis outbreaks in North Africa several months in advance. This is the finding of a new study led by the Barcelona Institute for Global Health (ISGlobal), a centre supported by the ”la Caixa” Foundation, together with researchers from the Pasteur Institutes of Tunisia, Morocco and France. The study identifies how specific climate patterns affecting rainfall across the region influence, over different timescales, the transmission of this disease and make it possible to develop a seasonal forecasting system with up to one year’s lead time.
Cutaneous leishmaniasis is a parasitic disease transmitted through the bite of Phlebotomine, tiny insects commonly known as “sand flies”. Although it is not usually life-threatening, it causes skin lesions and ulcers that may persist for months or even years and can leave permanent scarring, with significant physical, psychological and social consequences. It is estimated that there are around one million new cases worldwide each year, particularly across the Mediterranean Basin, the Middle East, Central Asia and the Americas.
Until now, early warning systems for climate-sensitive diseases had been developed mainly for tropical regions, where phenomena such as ‘El Niño’ make it possible to produce forecasts several months ahead. In temperate regions, by contrast, the atmosphere has been considered far less predictable, making it difficult to develop similar tools for vector-borne diseases.
The study, published in Science Advances, shows that this limitation can be overcome by incorporating two major patterns of Atlantic climate variability: the North Atlantic Oscillation (NAO) and the Atlantic Multidecadal Variability (AMV). The NAO is an atmospheric phenomenon that modulates winds over the Atlantic and influences winter rainfall across Europe and North Africa, while the AMV describes slow changes in Atlantic sea surface temperatures that unfold over years or even decades. The study’s findings show that the interaction between these two patterns modulates rainfall across North Africa and, indirectly, influences the evolution of leishmaniasis.
From Atlantic climate to disease transmission
Variations in Atlantic sea surface temperatures alter atmospheric circulation and the winds that transport moisture towards North Africa, thereby influencing rainfall. These rains regulate vegetation growth in desert ecosystems and, in turn, the populations of rodents that act as reservoirs for the parasite. Because cutaneous leishmaniasis depends closely on this chain of processes, its occurrence can also be predicted from Atlantic climate signals.
“The desert acts as a natural filter that reveals the Atlantic’s climate memory. Because it is influenced by fewer climate processes, it allows the Atlantic signal in rainfall patterns to be isolated much more clearly. Thanks to this, we identified a region where rainfall is remarkably predictable, the deserts of Tunisia and Morocco, and demonstrated that this predictability is also transferred to an infectious disease,” says Adrià San-José, ISGlobal researcher and first author of the study.
Building on this understanding of disease transmission, the research team developed a dynamic model that reproduces transmission of the parasite between humans, sand flies and rodents. The model integrates local temperature and rainfall with information from both the atmosphere and the Atlantic Ocean. As a result, it was able to predict both the timing and intensity of outbreaks of Leishmania major and Leishmania tropica in Morocco and Tunisia up to 12 months in advance. In Tunisia, however, where the Atlantic’s climatic influence is weaker and more heterogeneous, improvements in forecasting were more modest.
Implications for public health
“It was widely believed that this type of forecasting was only possible in the tropics. What is remarkable is that we have identified a source of predictability in a temperate region as well and incorporated it into a model that is ready for operational use. In this respect, our study is clearly pioneering and opens up new opportunities to develop early warning systems in places where they were previously considered unfeasible,” explains Xavier Rodó, ICREA researcher at ISGlobal and senior author of the study.
The ability to anticipate risk several months in advance provides valuable time to implement preventive measures, such as vector control, management of animal reservoirs and preparation of healthcare systems for potential outbreaks. Beyond leishmaniasis, the research team believes that the methodology developed could also be applied to other rainfall-modulated diseases across both Europe and North Africa.
Reference
San-José, A., Aoun, K.; Lemrani, M., López, L., Idris, M., Bouratbine, A., Paul, R., Rodó, X. Coupled Atlantic Atmosphere–Ocean Variability modulates Cutaneous Leishmaniasis in North Africa, enabling long-lead seasonal forecasts. Science Advances, 2026. DOI: 10.1126/sciadv.aeb0774
Journal
Science Advances
Subject of Research
Not applicable
Article Title
Coupled Atlantic Atmosphere–Ocean Variability modulates Cutaneous Leishmaniasis in North Africa, enabling long-lead seasonal forecasts
Article Publication Date
19-Aug-2026
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