What are Isotopes?
Isotopes are hugely important in geochemistry. I explain what they are, using oxygen as an example.
I am both a geologist and an oceanographer. I go to sea on research ships for weeks or months at a time, and drill into the seafloor to get long cylinders of mud (sediment cores), which I can then study to find what the environment looked like thousands or millions of years ago.
My next expedition will be in January and February 2022, when I’ll go to Antarctica on the German research ship Polarstern.
We’ll set sail from Cape Town in South Africa and steam south for over a week until we reach Neumeyer III, the main German Antarctic research base. We’ll resupply the station and then work our way along the coast of East Antarctica, surveying and drilling around the clock. After over 40 days, we’ll head back north to South Africa.
Oceanographic research ships are fitted out with well-equipped laboratories, which means we can do some preliminary analysis of the sediment cores we get while we’re still at sea. The rest needs to be done back on land, in our specialist labs at the University of Southampton.
I am investigating whether the ice sheet that covers West Antarctica has disappeared in the last few million years. If it has, the effects of climate change mean it might be at risk of collapsing again, raising global sea levels by up to 5 metres – and inundating coastal cities including New York, Shanghai, and Mumbai.
The sediments on the seafloor contain many clues about ancient climates, and if you read them correctly, you can paint quite an accurate picture of what the Earth looked like millions of years ago – including what was happening to Antarctica’s ice.
The chalky shells of single-celled organisms called foraminifera contain various isotopes of oxygen, which can tell me how much ice was around and how warm the water was at the time they were alive.
I also look at pieces of rock broken off from Antarctica by glaciers and carried out to sea by icebergs. When they melt, they drop the rocks, which become part of the seafloor sediment. Using lead isotopes, I can trace where the rocks came from.
If West Antarctica had no ice, there would be a new sea since parts of West Antarctica are below sea level. Suddenly, East Antarctic icebergs could float across to West Antarctica when they couldn’t before.
So, if I find rocks from East Antarctica, it probably means West Antarctica had lost its huge ice cap. Then I can look at other clues to chart the changes in the climate that came before it.
Adding this into today’s climate models would make them much more accurate – particularly for sea level projections – and governments everywhere would have a much stronger foundation to plan effective defences and policies to save lives and property.