Prof. Dr. Gert-Jan Reichart

Marine geologist professor Gert-Jan Reichart studies ongoing and past climate change via various animals in the ocean that deposit calcium carbonate. ‘Calcium carbonate is an important part of the carbon bookkeeping of “System Earth”. As oceans are by far the biggest reservoir of free carbon in the global carbon cycle, research into calcium-carbonate-producing animals is important in the current climate issue. Such animals include shellfish and corals but also the so-called foraminifera. The latter are single-celled animals that build a calcium carbonate skeleton around themselves. That skeleton contains tiny holes called “foramen” in Latin, and that is where the name comes from.’

Fossilised calcium carbonate

‘Fossils of organisms that deposit calcium carbonate, which are found in a certain layer of sediment, tell us something about the climate in the period this sediment was deposited. I try to extract as much detailed information as possible from these. The presence of a certain type of fossil says something about the temperature that species best thrives under, whereas the amount of calcium carbonate says something about the carbon content of the water. Broadly speaking: the greater the amount of CO₂ dissolved in the water, the more difficult it may be for shellfish, coral polyp or foraminifera to deposit calcium carbonate.’

Modern calcium carbonate

‘I study how various organisms now deposit calcium carbonate to learn precisely which information I can extract from fossil calcium carbonate. If we know how a certain temperature, salt level or pH level influences modern calcium carbonate skeletons, then we can derive which ocean temperature or pH the ocean was when these organisms formed. This approach gives us an increasingly better idea about the climate in earlier times, and thereby helps to better predict our future.’

Solution from the ocean

‘One picture that arises from our calcium carbonate reconstructions is the influence of humans on the climate. Due to our emissions of CO₂ and other greenhouse gases, the earth is becoming measurably warmer. Another important lesson is the role of ocean systems in climate. No less than 98% of all CO₂ in the carbon cycle is dissolved in the oceans. If only the C in CO₂ is considered, then we still find 95% of the free carbon, in other words, carbon not contained in rocks, in the ocean waters. Only 5% is found in the air, soil or as biomass in plants and animals. This means that sooner or later, we may have to look at the oceans to find a solution for the climate crisis that we have now caused ourselves.