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How do the interactions between land, earth and atmosphere determine or influence climate change? This workshop will consider this question in relation to dry lands – areas generally characterised by limited soil moisture, low precipitation, high evaporation, as well as aeolian and episodic fluvial processes.

The world is currently experiencing the highest levels of carbon dioxide ever. Over the last eight hundred thousand years, the carbon dioxide levels have been fluctuating between about 170 and 300 parts per million. It is more important than ever to understand how climate changes and what impacts this might have.

The fluctuations in carbon dioxide levels correspond to glacial and interglacial conditions. Measurements of historic carbon dioxide levels are made using ice cores – ice that has been preserved over thousands of years and that can be found in the Antarctic continental plate. If you look at where the ice has accumulated and you drill back down, the conditions of the ice below function as records of what the atmosphere was like at the time.

As of 2010, the levels of carbon dioxide have been about 386 parts per million, which is really high. Since these values are greater than what we’ve ever experienced as far as we know, we don’t know how the planet will respond to them or if we’ll ever return to a glacial period, which has in the past been a key part of the earth’s climate cycles.

While we have records of how climate has changed based on poles largely in the global north, using measurement techniques such as drilling ice cores, we have less information about what climate change has meant to other parts of the world – what does it mean to Africa?

Oxford University is currently carrying out research on palaeolakes, former or shrunken lakes, in the Kalahari basin. These palaeolakes are also known as salt pans.

 

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Salt pans form in arid and semi-arid regions where evaporation rates are high and precipitation is low. When water from rain or underground sources accumulates in a basin, it slowly evaporates, leaving behind salts and minerals that were dissolved in the water. Over time, these salts accumulate and create a salt crust.

African salt pans include the Makgadikgadi system of pans, which covers a large part of Botswana, as well as Etosha pan, which is located in Northern Namibia. The Etosha pan, in the Etosha National Park, is very vast and dry. It spans approximately 4,800 square kilometres and is one of the largest salt pans in Africa. Oxford University’s research focuses on arid environments or the dry lands of Africa because their climate processes might be different to the ones represented at the poles in Antarctica or in the Arctic.

It is quite challenging to work in deserts. Alongside harsh conditions, it’s generally very windy and dry and that means that a lot of the material is highly migratory and often degraded. But places such as Etosha give us hope to reconstruct these deserts’ climate histories.

Oxford is researching climate dynamics of Etosha over the long term: how has Etosha been in the last 23,000 years, what was the climate like, how did it change and why did it change, what can we learn from that and how can that inform how we predict future climate? For example, there is an 800 year drought cycle that comes in Namibia. This is something we wouldn’t be able to notice if we were looking at past climate records for a shorter time span.

Here are some more details on what makes a pan, and why they are important:

Pans are important in southern Africa to research long-term climate dynamics.

A salt pan is a dry lake bed also known as a palaeolake.

It is a basin or depression in the landscape that formerly contained a standing water body which might have disappeared or reduced when evaporation processes exceeded the water’s recharge.

Pans are mostly found in semi-arid areas and deserts around the world.

Sediments found in salt pans act as archives, containing evidence of past environmental and climatic change.

There are lots of theories about how Etosha was formed. One of them speaks about the contribution of the Kunene river into Etosha. It is believed that in the Pleistocene era (which began around 2.6 million years ago and ended 11,700 years ago) the Kunino river used to flow into Etosha pan and give it a large component of its water. However, river capture happened, which is a geomorphological change in the landscape, that then diverted the river and made it start flowing westwards towards the Atlantic ocean. When this happened it is believed that Etosha was then deprived of its main source of water, and therefore the pan reduced in size up until where it is today, which is a much smaller artefact.

Etosha is located in what we call a summer rainfall zone – it gets much of its rainfall in the summer and that’s when it floods, then in the winter it’s completely dry, so we are able to drive on the pan and study it.

So why choose to study Etosha? Etosha is a key study in southwestern Africa because it is located at the confluence of various atmospheric circulation systems. There is the Congo air boundary, where air masses from the Atlantic and Indian oceans meet. We also have what used to be called the ITCZ, which has now been coined the African tropical rain belt, which a band of low pressure around the Earth, near the equator, where the trade winds of the northern and southern hemispheres come together, leading to the development of frequent thunderstorms and heavy rain. We believe that in the past the climate of Etosha was probably influenced by how these systems were expressed or how they interacted. They would have determined where or when humidity, periods of higher rainfall, drought and greater wind-related processes happened.

Regarding the formation of Etosha, there’s been two main schools of thought around how the pan was formed. These have been often mutually exclusive:

• There was one school of thought, the ‘Deflation only hypothesis’, where the scientists believed that Etosha is an erosional landform. That means that it is getting continuously eroded and exposed over time through the seasonal wetting and drying, and therefore results in overall deflation from the pan.
• The other theory, the ‘Fluctuating Quaternary hydrology hypothesis’, is the one mentioned earlier – arguing that Etosha is a desiccated palaeolake that got much smaller after the main source of water that Kunene river was diverted back.

Some methods used when researching the Etosha Pan include:

• Radiocarbon dating, which uses the decay of a radioactive isotope of carbon to measure the time and date of objects containing carbon-bearing material. This is a useful way of determining the age of very old objects.
• Luminescence dating, which determines how long ago mineral grains were last exposed to sunlight or heating.

Collecting sediment cores. For the Etosha Pan, you research the mud cores rather than the ice cores studied in Antarctica.

Macrofossils – specifically eggshell fragments – have been found in the Etosha Pan mud cores. The exact nature of these eggs have not yet been identified. Initially they looked like ostrich eggs. Ostriches live in dry areas and do not lay their eggs in water. The mud cores were carbon dated to have been deposited between 14,000 and 10,000 years BP (which means before 1950, when carbon dating originated).  This suggests that, 10,000 years ago, the pan was very dry. This would mean that something must have changed in the environment in that period, as now we know that rainfall comes every summer. Ostriches get all of their water from the plants they eat. If we could reconstruct the diet of these ostriches, then we could infer from their shells what kind of vegetation existed on the pan all those years ago. However, that hypothesis fell away when other scientists revealed that the fragments were not from ostrich shells.

So what are they? The current hypothesis is that they are flamingo shells . Flamingos thrive in different environmental conditions from ostriches, so this changes what we think about the conditions of the Etosha pan over 10,000 years ago. Flamingos lay their eggs in muddy conditions, so there must have been rainfall. You would not find flamingos in freshwater or ice conditions, so that suggests that there were salty conditions. The question is, what happened in the climate of the time to make the area able to support the life of those flamingos?

As you can see, therefore, tiny pieces of evidence such as fragments of eggshells can be used to tell us a lot about the wider features of an environment. Using our knowledge about what an animal needs to survive, we can work out the necessary conditions of an ancient landscape. Forms of research such as this are very important to understanding the way in which the climate has changed over time in a variety of different landscapes.

Further Reading

Click here to learn about Namibia from the WWF.

You can look at Nasa’s satellite images of the Etosha pan during different seasons here. Also click here to read about them. You can explore the Etosha National Park website here.