Researchers uncover the secret of the deep sea

More than half of the Earth is covered by water, but even the far side of the moon has been more thoroughly explored than the world's oceans. Researchers have now solved one of the oceans' mysteries: they have discovered how the hot springs in the deep sea help to keep the global climate stable. How does the Earth manage to keep the climate stable? An international team of researchers led by geoecologist Prof Dr Thorsten Dittmar from the Institute of Chemistry and Biology of the Marine Environment (ICBM) at the University of Oldenburg has come a step closer to answering this question. The scientists from ten different Institutes in Europe and the USA have discovered that volcanism in the deep sea plays a decisive role in the long-term climate. The results have been published in the October issue of the scientific journal "Nature Geoscience". The oceans have always played a major role in keeping the Earth's climate stable. They contain a lot of carbon, much more than is bound in the carbon dioxide in the atmosphere. Among other things, the ocean stores carbon in what is known as dissolved organic matter (DOM). A large proportion of DOM survives for many thousands of years in seawater. It therefore acts as a large long-term carbon store. In the current study, the researchers led by ICBM scientist Dr Jeffrey Hawkes wanted to find out what happens to the DOM when it enters the hot springs of the deep sea. With the help of diving robots, they collected samples from depths of several thousand metres at various locations in the Atlantic and Pacific. Not only is the pressure in the deep sea much higher than on the surface, there are also hot springs and volcanoes on the sea floor where the seawater heats up to over 400 degrees Celsius. The researchers' precise question: Does the heat build up new DOM or destroy the existing one? The clear answer after six years of research: it is destroyed. Even the most stable compounds no longer stand a chance at 400 degrees Celsius. And: the DOM has a limited lifespan as a result. It is a maximum of 40 million years. This is because the entire ocean has passed through the geothermal sources once during this time. The researchers have thus found an explanation for how the ocean manages to keep its carbon content in balance even over very long periods of time. Because what it absorbs, it has to get rid of again - an important prerequisite for a stable climate. Despite the current debate about the greenhouse effect, the researchers do not believe that the destruction of the DOM in the deep sea means the loss of a carbon reservoir and therefore ultimately also a CO2 reservoir, as the processes studied are only significant over very long periods of millions of years. "CO2 is not a bad thing in itself. The only bad thing is the rapid changes at the moment," explains Dittmar. In fact, CO2 is essential for life, as plants, animals and humans could not exist without it. On Mars, for example, there is very little CO2, which makes it uninhabitable. Venus has too much of the greenhouse gas. On Earth, on the other hand, the amount of CO2 and the climate are ideal for life. The newly discovered role of hot springs in the deep sea is one of the factors that have an effect on CO2 levels and climate over very long periods of time, but have no influence on current climate changes. In addition to the ICBM, the following institutes were involved in the study: MARUM - Centre for Marine Environmental Sciences at the University of Bremen; Max Planck Institute for Marine Microbiology Bremen; Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research Bremerhaven; GEOMAR Helmholtz Centre for Ocean Research Kiel; Jacobs University Bremen; Skidaway Institute of Oceanography, USA; University of Washington, USA; University of Southampton, UK; Université de Toulouse, France. Original article: "Efficient removal of recalcitrant deep-ocean dissolved organic matter during hydrothermal circulation" by Jeffrey A. Hawkes, Pamela E. Rossel, Aron Stubbins, David Butterfield, Douglas P. Connelly, Eric P. Achterberg, Andrea Koschinsky, Valérie Chavagnac, Christian T. Hansen, Wolfgang Bach and Thorsten Dittmar, Nature Geoscience, doi 10.1038/NGEO2543.