Accurate And Precise Alkenone Records Of Atmospheric CO2 For The Pliocene And Beyond To Inform The Future

Human activity is changing the composition of the Earth's atmosphere at a rate not seen for millions of years. The burning of fossil fuels for energy production releases carbon dioxide, which, once in the atmosphere increases the trapping of heat near to the planet's surface. While the physical basis of this process (known as the greenhouse effect) is well established by the scientific community the sensitivity, in terms of rate and magnitude of responses, of the Earth's surface environment to changes in CO2 is associated with some uncertainty.
Given the climate crisis that we face, one of the most important things that we can learn from the past is how the Earth's climate system operates under a range of different atmospheric compositions in order to understand, to mitigate, and to act to prevent negative impacts of human activity. The geological record of Earth history allows us to insight into the climate system by studying the vast array of natural experiments which it records, and by viewing the action of the actual (and whole) system, we can develop and test the climate models which are the best way to predict our climate future. To this end, this project aims to reduce uncertainty in our understanding of the Earth System, both by improving one of the main ways by which we measure ancient atmospheric CO2 concentrations, and by producing a record of CO2 in unprecedented detail over a critical interval in Earth history, the Pliocene.
The Pliocene (an interval of time 5.33 to 2.58 million years ago) has long interested climate scientists. It was warmer than present, and previous work (including some by us) has shown that it is the most recent time when CO2 was as high or higher than it is today. In the context of all of Earth history it is relatively recent meaning that many of the factors that influence climate change on very long timescales, like the position of the continents and the composition and distribution of ecosystems, are very similar to today. This means that the Pliocene is an ideal time interval to test exactly how the climate system works, and how it responds to changing CO2 in a warm world. This sets it aside from the more recent, great Pleistocene ice ages when the world was generally cooler.
As the Pliocene was before the great ice ages, we cannot rely on ice core records to determine atmospheric greenhouse gases. We must instead estimate past carbon dioxide concentrations by measuring chemical signatures found in molecules (called alkenones) preserved in deep-sea sediments, which were made by plankton which lived in the oceans millions of years ago. Whilst this method has been applied for over twenty years, recent concerns have been raised over the accuracy and precision of the technique (including in work by the PI). In this project we will develop improved ways of measuring the chemical signatures of the alkenones, and, building on further recent work by the PI, cross-check and calibrate the alkenone technique against Pleistocene ice core CO2 records. This will build a new framework for confidently applying the alkenone system for interrogating the Pliocene (by us) and throughout the full 66 million years of the Cenozoic (in future projects) opening up even more natural experiments for study.
The substantial global community effort to document in great detail the temperature changes within the Pliocene (in projects such as PRISM, PlioVAR and PlioMIP) mean that fantastic records of global surface temperature already exist. These are crying out for atmospheric carbon dioxide records of similar quality, which we will provide. Together, these temperature and carbon dioxide records will provide a critical new understanding of how our climate system works in a warm, future-relevant world.