Ancient pollens help scientists understand climate change

The Drakensberg holds a number of clues about how climate once
affected South Africa and will affect the country in the future. (Luke Patterson, Gallo)

The Drakensberg holds a number of clues about how climate once affected South Africa and will affect the country in the future. (Luke Patterson, Gallo)

About 450-million years ago, the first plants sprung to life, releasing into the air pollen that floated over oceans and islands, and skipped through valleys and above mountains along the wind. The fine powder spread across the Earth like skin covering a body and, as the wind died down, the pollen fell to the ground and rested in the soil, holding within it important secrets about the environment. Now, these ancient pollen “finger prints” tell an old story of how the Earth’s climate and vegetation have changed over time. 

Our team at the University of KwaZulu-Natal in the department of geography is trying to uncover these lost “finger prints” hiding in the soil to answer questions about ancient and future climate change.

By applying palynology — which comes from the Greek word palun, “to scatter or strew”, and is the study of pollen and spores — to ancient rocks and ground samples, we can say what plants were living where thousands of years ago. Through carbon dating, we can determine the age of the living and fossilised pollen we find. 

Each vegetation type has unique pollen morphology, and this acts as a “finger print”, identifying the different plant species that made up an ecosystem.

Pollen is invisible to the human eye and can only be seen under a microscope. Yet through its lens researchers can see a whole other world, in which pollen grains come in beautiful shapes and sizes, with interesting patterns on their surface. Some look like stars with tiny spikes jutting out of their surface and others look similar to Mickey Mouse’s head and ears. There are some that look like tubes with gills running down the sides and others that resemble beans.

Each unique grain shape indicates a species of plant, and each species of plant suggests the climate conditions it survived in. The more pollen grains you can identify, the more you can say about plant biodiversity and therefore the more you can say about the climate where they were found. It also allows us to make inferences about how that vegetation responded to climatic variation. By understanding how historic vegetation communities changed because of climate, scientists can make reasonable and logical deductions about how they expect the environment to change in the future. 

The windswept Drakensberg mountain range has enormous ecological significance for South Africa, especially from a botanical point of view because of its great biodiversity. This makes the Drakensberg extremely important in terms of pollen research as it holds a number of clues about how climate once affected South Africa and will affect the country in the future. 

While palynology allows us to pinpoint the sources, it does not explain how pollen got to a certain place thousands of years ago. This means that scientists are restricted in their reconstructions of what past vegetation communities looked like. Computer modelling is one way to piece together what might have happened. Researchers at the University of KwaZulu-Natal, in association with colleagues at the University of Hull in England, are using specialised computer software called HUMPOL to model pollen dispersal and deposition characteristics in the Drakensberg’s Cathedral Peak region. 

Using characteristics such pollen, grain size, wind speed and proximity to vegetation, researchers have modelled the pollen dispersal and deposition pathways of the region and created a picture of vegetation composition. 

Improving our knowledge of how vegetation changed with climate in the past is fundamental to being able to accurately predict what will happen to us in the future as our climate continues to change.

Tristan Duthie is a MSc candidate at the University of KwaZulu-NatalTristan Duthie – MSc – University of KwaZulu-Natal.

This publication is the culmination of a six-month-long Mail & Guardian project, called Science Voices, to teach postgraduate science students how to turn their academic writing into something the public can read and enjoy.