Research Fellows Directory
Dr Helen Coxall
I am a geologist and I try to understand the workings of Earth’s past climate. I do this by deciphering chemical clues locked-up in the shells of microscopic marine fossils that have accumulated in thick piles on the sea floor over millions of years. These sediment piles are the only archives long and detailed enough to see what happens to climate when big changes in carbon dioxide or plant and animal life, on the scale of modern man-made changes, occur. Intervals of particular interest are:
Cretaceous/Paleogene transition: The catastrophic meteorite impact believed to have killed off the dinosaurs also wiped out 70-90% of many microscopic ocean plants and animals at the base of marine food chains. Chemical reconstructions indicate that the extinctions, which severed food chains, disrupted biologically-driven ‘pumping' of carbon from the surface ocean into the deep sea and seafloor sediments for 1-2 million years. This is important information because this carbon pumping is one of the key processes that naturally minimizes global warming by hiding carbon away from the atmosphere. The results confirm the vital role of tiny creatures in the ocean carbon-system balance and warns against human activities that might interfere or disrupt this balance.
The Eocene-Oligocene transition ~34 million years ago, represents a climatic tipping point when the Earth cooled rapidly from the last natural high-carbon dioxide ‘greenhouse climate’, a large ice-cap formed on Antarctica for the first time and the oceans become well-stirred. Understanding the drivers of this major switch, and the extent to which the different hemispheres of the Earth responded to the changes is important for understanding the sensitivity of the modern system to threats of future greenhouse warming.
The results of my research are helpful for informing debate on the likely effects of increased man-made carbon dioxide, and developing and testing computer models that try to predict future climate change.
Interests and expertise (Subject groups)