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A study links an unusual plankton bloom off the coast of Madagascar to drought in Southern Africa. Climate warming has intensified droughts around the world.

Phytoplankton significantly influence Earth's climate and carbon cycles. Similar to terrestrial plants, they possess chlorophyll and harness sunlight for energy via photosynthesis. During this process, they generate oxygen and absorb a substantial amount of carbon dioxide.

The study published in the journal PNAS Nexus on October 1, 2024 showed that dust emitted from southern Africa was transported and deposited into the nutrient-limited surface waters southeast of Madagascar, which stimulated the strongest phytoplankton bloom of the last two decades during a period of the year when blooms are not expected.

Key sources of dust sources are Etosha and Makgadikgadi Pans in Namibia and Botswana, respectively, pans and ephemeral rivers in the coastal Namibian desert, as well as the southwestern Kalahari Pan belt.

How dust accumulated in South Africa?

Prolonged and extreme multi-year droughts have occurred in southern Africa over the last decade. This trend culminated in the austral spring (the period from September to November) of 2019, which was among the driest in the last 40 years for parts of Zimbabwe, Namibia, Botswana and South Africa.

From November to December of 2019, strong, positive dust aerosol optical depth anomalies were present over parts of Namibia, Botswana and western South Africa.

The study results demonstrate that multiple potential sources of iron-rich dust aerosols over southern Africa were active during the bloom period.

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