In a resolute determination to prove the old adage that ‘when life gives you lemons’, you really should ‘make lemonade’, it would appear that increasing drought events in southern Africa are delivering “unprecedented” benefits to phytoplankton and therefore marine life and atmospheric carbon removal in the Indian Ocean.

If ever you needed proof of the inter-connectedness of Earth’s mechanical systems, then surely these latest findings – derived from a new study led by scientists at the University of Athens in partnership with experts from the UK’s National Oceanography Centre – will be it?

In observations made of recent Madagascar bloom events – famed for being one of the world’s largest recorded phytoplankton bloom events – researchers have now linked recent “unprecedented levels” of algal bloom to an influx of nutrient-dense dust blown from southern Africa over the Indian Ocean. 

According to authors of the new study – published this week in PNAS Nexus – the event witnessed phytoplankton levels at three times the level normally expected at the time of year it occurred, spreading from southeast of Madagascar into the wider Indian Ocean for three weeks longer than normal.

It’s this phytoplankton – a marine algae – that forms the basis of the marine food chain, helping to remove carbon dioxide from the atmosphere by using it to grow then by being eaten or dying and falling as organic matter to the seafloor.

The National Oceanography Centre’s Dr Fatma Jebri, co-author on this new study, said the results “show how African desert dust being blown over and deposited onto the ocean surface was key in triggering this unprecedented oceanic phytoplankton bloom in the Southeast of Madagascar, at a time of year when blooms are uncommon.”

The study used satellite data to study the causes of major phytoplankton blooms, focusing on the unprecedented Madagascar bloom in late 2019 to early 2020, which was found to be the largest on record going back 24 years. 

It has been long understood that dust from the Sahara Desert often crosses the Atlantic Ocean to the Americas and that when these particles settle on land or in the ocean, they deliver essential nutrients that may boost plant and marine life growth.

However, the relationship between desertification, dust emissions, and ocean fertilisation has been poorly understood. This new study therefore marks a significant step in unravelling these connections.

“And this is important as it suggests that as deserts release more dust into the air and that dust settles on the ocean’s surface, it could help phytoplankton growth, potentially increasing the amount of CO2 the ocean absorbs from the atmosphere,” said the National Oceanographic Centre’s Professor Meric Srokosz.

Measurements were taken using satellite data collated through the European Space Agency’s Living Planet Fellowships Poseidon and Pyroplankton. In addition to data from the European Space Agency’s Climate Change Initiative Ocean Colour project, information from its Climate Change Initiative Soil Moisture project and Science for Society Biological Pump and Carbon Exchange Processes projects were also used. On top of this, data from both the Copernicus Atmosphere Monitoring Service and the Copernicus Marine Service was incorporated.

“Having access to such rich satellite datasets enabled us to clearly track the extent of this massive bloom and pinpoint the dust events responsible for it,” said the study’s lead author, John Gittings from the University of Athens.

“While this extensive phytoplankton bloom was highly unusual, trends in rising air temperatures, aridity, and dust emissions in southern Africa indicate that such events may become more frequent in the future.

“Alongside recent discoveries of ocean fertilisation caused by drought-induced megafires in Australia, our findings suggest a potential connection between climate change, drought, aerosols, and ocean blooms.”

Ocean applications scientist at the European Space Agency, Marie-Helene Rio, added: “Oceans cover two-thirds of our planet and are vital to the health of our ecosystems. Understanding how climate change is altering their biological processes is not just a matter of scientific inquiry, it’s crucial for life on Earth.”

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