Marine sediments – valuable climate archives from the seafloor

Prof. Dr Gesine Mollenhauer, geochemist and  scientific head of MICADAS 14C dating laboratory at the Alfred Wegener Institute and Professor at the University of Bremen.

Radiocarbon dating


Sediment transport


The seafloor is a gigantic repository. Every particle that is not consumed by marine animals, including dead marine microorganisms, material transported to the oceans by rivers –the particles that trickle down are deposited layer by layer at depth. Ultimately, a unique archive is created, one that we can ‘read’ in using e.g. chemical analysis of sediment samples. With the information encoded, e.g., by chemical components, in each individual layer, we can reconstruct the climate and other environmental conditions from the respective period. What is crucial here is that the sediment is precisely dated. To do so, we can use what is known as the radiocarbon dating or 14C method. One of the aims of the various analyses is to determine how much carbon the ocean removed from the atmosphere and stored in its depths in the past.

The permanently frozen soils of the Arctic store tremendous amounts of carbon in the form of plant and animal remains. However, as a result of climate change, the soils are thawing to increasing depths and for longer periods. When this happens, microbes break down the thawed material, and rain, streams and rivers then carry the components away. At some point, a portion of this transported material is deposited on the seafloor, leaving clues that enable the AWI geoscientists not only to reconstruct the Arctic’s climate history, but also to understand the role of thawing permafrost in past climate changes. Based on this knowledge, they can make more accurate predictions about Earth’s climate future.