CoolRhythms: the impact of ice volume and ocean circulation on Earth's Coolhouse climate beat

Earth's changing climate is inexorably linked to the energy it receives from the Sun, which varies rhythmically, driven by the eccentricity, obliquity and precession of Earth's orbit. Earth redistributes this solar energy, sustaining warmer and cooler climate states that last for millions of years (Myr). The shifts between Earth's long-term climate states are caused by large changes in polar ice and greenhouse gasses.

Over the last 40 million years, ice volume has played an important role in influencing Earth's climate. One of these climate states - the Coolhouse - captures when large ice sheets first formed at Earth's poles. The solar energy also drives a faster climate response, which beats in tune with these orbital variations.

Even though the rhythmic energy that drives Earth's climate response has not changed, Earth's climate beat itself has not been stable through time. We currently do not understand what causes this. Through the CoolRhythms proposal, I will establish when and why these different beats in Earth's climate occur and explore if global warming could cause another change of climate beat in the future.

Two major ice growth events coincide with big transitions at the beginning and the middle of the Coolhouse word. Surprisingly, Earth's climate beat responded differently during these two important climatic transitions. About 34 Myr ago in the early Coolhouse, ice first formed on Antarctic ice as Earth shifted from a warm to cool climate transition and eccentricity was unchanged as the main driver of Earth's climate beat.

The Earth cooled again in the mid-Coolhouse and gained more ice between 15 and 5 Myr ago, yet this time the climate beat changed from eccentricity to obliquity. Why Earth's climate changed its beat is an enigma, which I will investigate by: 1. Establishing Earth's exact climate beat during the early and mid-Coolhouse transitions;

2. Determining which processes caused Earth's climate beat to switch from eccentricity to obliquity; 3. Exploring if future warming could reverse this switch.

CoolRhythms will be hosted at UCL in collaboration with a network of world experts. To achieve my aims, I will combine data science with a novel targeted sampling approach that integrates stratigraphy and geochemistry to optimise information recovery. I will establish Earth's climate beat across the key transitions by filling gaps in our knowledge with new data from deep-sea microfossils and by resolving conflicting interpretations of existing records.

I will develop software to characterise the climatic beat in the different records and then combine them to acquire a global view of climate. I will analyse the stable oxygen and carbon isotope and trace element composition of microfossils from deep-sea sediments, collected during IODP ocean drilling expeditions in all ocean basins. I will combine this geochemistry with the sedimentary composition to reconstruct high-resolution ice volume and ocean circulation patterns at the same scale as Earth's climate beat.

I will also use modelling to test how the location of the ice growth affects the climate beat and whether an eccentricity driven beat could return in the future.

My approach will enable me to determine which Earth system feedback caused the differing climate beats during these transitions. Refining our understanding of how Earth's climate beat varied during warmer and cooler climate states will ultimately help understand how a warmer Earth may affect the variability of future climate.