Der Ozean gehört zu den größten Senken der Erde, um Kohlenstoff aus landbasierten (terrestrischen) Ökosystemen zu speichern. Trotz seiner entscheidenden Rolle im globalen Kohlenstoffkreislauf ist jedoch noch immer nicht klar, woher dieser Kohlenstoff stammt. Forschende des Alfred-Wegener-Instituts haben mit neuartigen Methoden Sedimentkerne aus dem Pazifik untersucht und können anhand von alter Pflanzen-DNA nun zum ersten Mal detaillierte Aussagen über die genaue Herkunft und die Dynamik terrestrischen Kohlenstoffs in Ozeanen machen. Das kann helfen, die Wechselwirkungen zwischen Land und Meer sowie die Rolle der Ozeane als Kohlenstoffsenken besser zu verstehen. Ihre Ergebnisse veröffentlichten die Forschenden in der Fachzeitschrift Communications Earth & Environment.
Studies suggest that around a third of the carbon in marine sediments comes from the biosphere or the soil ashore. Which plant species make up this carbon and where they come from is a puzzle that has yet to be solved because it is difficult to reconstruct how its distribution and composition has changed over long time periods. A look into the past might be of help: Researchers at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) have examined ancient plant DNA to find out from which plant sources the carbon in the oceans of our age originated. “We examined six sediment cores from different regions in the Pacific, all of which cover the transition from the Pleistocene to today's Holocene, that is 40,000 years,” says AWI biologist Prof Ulrike Herzschuh. During this time, the terrestrial and marine carbon cycle changed significantly in response to climate signals, a phenomenon that we have been able to observe again in recent years. “Understanding what the carbon in the ocean from this period consists of, helps us to understand how the ocean might develop as a carbon sink in the future and how we can protect it.”
For the analysis, the researchers filtered the old plant DNA from the sediment cores and then assigned small fragments of this old DNA to the appropriate different species (shotgun sequencing). This way, they were able to determine the proportion of different plant species in sediments from the sea floor for the first time and to understand how carbon from terrestrial sources enters the ocean. The results show that more organic material from the land surface found its way into the sea during the transition from the Pleistocene to the Holocene. Sediments from the high northern latitudes, for example, contain a high amount of DNA of willow plants, which most likely reflects the expansion of riparian forests. These were able to spread at this time because they had more water available, as a rise in temperature caused glaciers to melt. The scientists were also able to find a large number of grasses that were adapted to a dry, cold climate, which indicates an increased input from the widespread glacial steppes of the northern hemisphere.
The low-latitude cores also show a significant change during the transition, characterized by DNA from tree and shrub species. There appears to have been a change from coastal submerged plants to regional land plants associated with a rise in sea level during this time. Traces of birch plants show the massive spread of this species far from their typical distribution areas, probably in response to the warming in the early Holocene. Five of the six cores show larger DNA traces of fern and moss species, which have been steadily increasing since the beginning of the Holocene. The strong increase in moss and grass input signals in the Southern Ocean during the Holocene could indicate that a terrestrial biosphere was established earlier and faster than previously expected. In general, the composition of the plant DNA of the individual sediment cores is largely characterized by species that have spread primarily from neighboring continents and could have led to a far-reaching redistribution of carbon sources in the oceans.
“Our study helps to determine the global carbon balance more precisely and to better understand the role of the oceans as a carbon sink,” summarizes Ulrike Herzschuh. “The results are important for climate research as they improve our understanding of the interactions between land and sea. In this way, we can help to develop more effective protective measures for marine ecosystems.”
Original publication
Herzschuh, U., Weiß, J.F., Stoof-Leichsenring, K.R. et al. Dynamic land-plant carbon sources in marine sediments inferred from ancient DNA. Commun Earth Environ 6, 78 (2025). https://doi.org/10.1038/s43247-025-02014-9