[Science news] - An extinction wave of microalgae due to climate change in Antarctica

During the Early Miocene, about twenty million years ago, the Antarctic Continent had a temperate to subpolar climate. The continent was largely covered with tundra vegetation and Nothofagus forests. This situation changed abruptly when fourteen million years ago, the continent began to cool down rapidly with ice sheets expanding over Antarctica, and plants and animals becoming extinct on a massive scale.

For a long time, scientists assumed that microorganisms, due to their broad distribution patterns, were much less affected by such climatic changes than plants and animals that often present very limited distribution areas. By examining fossils of Antarctic microorganisms, an international team led by researchers from Ghent University and Meise Botanic Garden showed that this assumption is incorrect.

Figure 1. Mount Boreas in the Olympus Range (western Dry Valleys, Antarctica) where part of the material analysed in this study was collected (photo ©Allan C. Ashworth)

A diverse Miocene flora of diatoms

The researchers analyzed diatoms in 14 to 15-million-year-old Antarctic lake sediments, deposited just before the great Miocene cooling began. Diatoms are one of the most diverse and ecologically important algal groups in the world and can easily fossilize thanks to their cell wall made of amorphous glass.

To their surprise, the team discovered more than 200 species of diatoms in the sediments. Virtually every species was new to science. For this reason, the researchers further analyzed the lake sediments at genus level, the classification level above the species. The analysis showed that Miocene diatom floras are very similar to the communities found today in the Arctic and, in particular, contained taxa that today are recorded only in temperate regions of the southern hemisphere, specifically South America, Australia and New Zealand. There was very little similarity with the diatoms found in Antarctica today. The researchers postulate that the extremely species-poor modern communities in Antarctica evolved from the few survivors of the Miocene flora and new settlers that are adapted to cold conditions.

Figure 2. The Friis Hills (Antarctic Continent) where some of the sediment cores were collected (photo ©Allan C. Ashworth)

 

Extinction waves due to climate change

The researchers conclude that major climate changes, such as those in Miocene Antarctica, could have dramatic consequences for microorganisms and may lead to large-scale extinction waves. Since micro-organisms play a crucial role in the healthy functioning of ecosystems, it is crucial to better understand the impact of a changing climate and environment on their diversity.
 

The results of this study were published in the journal Science Advances (link: https://www.science.org/doi/full/10.1126/sciaadv.abh3233).