The quality of forecasts and models for global warming depends to a large extent on how well we can understand past climate change. In his PhD, Matthias Sinnesael (VUB-UGent) studied astronomical cycles for the geological period of the Ordovician, some 450 million years ago, when the climate looked completely different. He developed new methods in collaboration with signal processing engineers. The result is timescales of unprecedented precision that allow a better understanding of the causes, timing, and duration of climate change during the Ordovixian period. "Because astronomical cycles are very regular in nature, we were able to reconstruct very precise geological timescales unique to such ancient rocks", says Sinnesael.
The sun is an important driver of our climate. The Earth’s orbit and orientation in relation to the sun varies very regularly. These natural variations – astronomical cycles – determine the intensity and distribution of the sun’s rays on Earth, and are therefore largely responsible for variations in the climate over long periods of time. Led by Professor Philippe Claeys of the VUB research group Analytical, Environmental and Geo-Chemistry (AMGC), Matthias Sinnesael studied the role of astronomical cycles in the Ordovician climate system.
The Ordovician, which covers the period between 485 million years and 444 million years ago, is of particular interest because it contains important information on rapid and profound climate changes. Carbon dioxide concentrations in the atmosphere were many times higher than they are today, and there was virtually no vegetation on the continents. Most of the developed life was still in the oceans. Almost all land masses were in the southern hemisphere and one giant ocean covered the northern hemisphere. Another fascinating feature of the Ordovician is the evolution from a very warm climate to a very cold climate characterised by ice ages. Nevertheless, mapping the climate in such an early period remains a challenge.
Reconstructing timescales with unique precision
Of all the natural ‘archives’ that allow us to study the climate of the past, such as trees, ice, peat deposits and stalagmites, it is only rock deposits that make it possible to go back many millions of years. “Because we work with such old rocks, we have to be very careful in our approaches. That’s why much of this work revolves around this crucial question: How can we identify and reconstruct these astronomical cycles as faithfully as possible?” says Sinnesael. “Our study has used existing methods for this purpose, but above all it has developed new ones.”
This was done in close collaboration with the VUB research group Fundamental Electricity and Instrumentation (ELEC) led by Professor Johan Schoukens. Algorithms originally developed to analyse music signals were adapted to the geological context. Sinnesael: “Basically, both astronomical cycles and music consist of combinations of frequencies and amplitudes. In collaboration with the Universidad Pública de Navarra, Pamplona, we are now going to further refine this research.”