Man-made global heating has long been presented as a relatively simple chain of cause and effect: humans disrupt the carbon cycle by burning fossil fuels, thereby increase the concentration of CO2 in the atmosphere, which in turn leads to higher temperatures around the globe. “However, it becomes increasingly clear that this is not the end of the story. Forest fires become more frequent all over the world, release additional CO2 into the atmosphere, and further reinforce the global warming that enhanced forest fire risk in the first place. This is a textbook example of what climate scientists call a positive feedback mechanism,” stresses David De Vleeschouwer, a postdoctoral researcher at MARUM – Center for Marine Environmental Sciences at the University of Bremen.

To reveal these kind of climate-carbon cycle feed­back mechanisms under natural circumstances, David De Vleeschouwer and colleagues exploited isotopic data from deepocean sediment cores. “Some of these cores contain sediments of up to 35 million years old. Despite their respectable age, these sediments carry a clear imprint of socalled Milanković cycles. Milanković cycles relate to rhythmic changes in the shape of the Earth’s orbit (eccentricity), as well as to the tilt (obliquity) and orientation (precession) of the Earth’s rotational axis. Like an astronomical clockwork, Milanković cycles generate changes in the distribution of solar insolation over the planet, and thus provoke cadenced climate change”, explains David De Vleeschouwer. “We looked at the carbon and oxygen isotope composition of microfossils within the sediment and first used the eccentricity, obliquity and precession cadences as geological chronometers. Then, we applied a statistical method to determine whether changes in one isotope system lead or lag variability in the other isotope.”

Read more at: MARUM - Center for Marine Environmental Sciences, University of Bremen

The research vessel JOIDES Resolution in Fremantle (Australia) the morning before the ship sailed on Expedition 356. The results are based on samples taken from this drilling vessel as part of the International Ocean Discovery Program IODP. (Photo Credit: The research vessel JOIDES Resolution in Fremantle (Australia) the morning before the ship sailed on Expedition 356. The results are based on samples taken from this drilling vessel as part of the International Ocean Discovery Program IODP.)