Quantifying phytoplankton evolution through Cretaceous Oceanic Anoxic Event 2

The geological record contains fossil shells and shell chemistry that allow us to reconstruct ancient Earth environments. This shows us that Earth has seen a wide range of different climates, including times when it was much colder or warmer than it is now. This research project aims to better understand how life responds to these changing climates by using the geological record of a specific warming event. We are especially interested in finding out what drives biological evolution and how much of a part climate plays in this. It is important to understand how life responds to changing environments, because our modern climate is warming rapidly and we need to find out what the impact of these changes will be. Will we see more extinction? Will life in the oceans become less abundant and so provide less food and absorb less carbon dioxide (which would make climate become warmer even faster)? To answer these questions, we will study a climate-warming event that occurred 93 million years ago, in the Cretaceous, when dinosaurs dominated on land. This greenhouse climate interval saw subtropical forests on Antarctica, crocodile-like animals in the Arctic, no ice-caps and sea-levels that were 70m higher than today. This event is known as Oceanic Anoxic Event 2 (OAE2) because it was first recognised by abundant black shale sediments that indicate that the ocean floors had little or no oxygen, allowing the accumulation of large amounts of carbon from plants and animals. As well as all that carbon burial, this event also saw rapid and extreme climate warming with increases of 6-9C within a few tens of thousands of years. Peak temperatures were at least 36C, compared with modern annual mean temperatures that rarely exceed 30C. So this looks like an ideal event for studying the response of life to warming, but there are some problems. The black shales that occurred during this event do not preserve the fossils that we use to measure evolution. The best fossils for this purpose are the shells of microscopic, single-celled plankton, which are produced in their billions and which are normally preserved in sea-floor sediments, worldwide. However, these shells are made from calcium carbonate and in black shales the shells are usually dissolved away because of acidic fluids in the sediment. To overcome this problem, we have searched the world to find rocks in which the fossils are preserved perfectly. We have found two such places where unusual conditions have preserved plankton fossils of the correct age very well, one in Tanzania (eastern Africa) and one in Morocco (NW Africa). Because these rocks are rich in clay and have never been buried deep in the Earth, the fossils have been protected from damage, and though they are over 90 million years old, they look like modern examples. We will use these fossils to collect information that will tell us how the plankton responded through the OAE2 climate warming. We particularly want to find out whether the rate of evolutionary change increased as the environment changed, and whether more species evolved or became extinct. We will also use these fossils to investigate whether certain types of species were more affected than others. For example, were warm-water-loving species more affected than cool-water types, or were species that produced heavier, thicker shells more affected than types that formed small, delicate shells? By looking at these details of evolution, we can find out which kinds of environmental change were most influential, for example, was it water temperature, food supply, or ocean chemistry (acidification) changes. More broadly, these records of plankton evolution will help us understand how these warm climate events operated and how Earth returned to more normal conditions. With a better understanding of how life responded to these past climate events, we will be better able to make predictions of how Earth's biosphere will respond through the coming decades.