02.10.2015 – Forschung

How deep-sea hot vents affect our climate

  • This so-called black smoker on the Mid-Atlantic Ridge in a depth of almost 3000 meters has been one the sampling sites of the current study. Source: MARUM – Center for Marine Environmental Sciences, University of Bremen

How does our planet manage to keep a steady climate? Thorsten Dittmar, leader of the Marine Geochemistry Research Group that connects the Max Planck Institute for Marine Microbiology (MPI) in Bremen and the Institute for Chemistry and Biology of the Marine Environment (ICBM) in Oldenburg, and an international team of scientists have just moved one step closer towards an answer to this question. The scientists discovered that volcanism in the deep sea plays a crucial role for our long-term climate. Learn more in their publication in the latest edition of “Nature Geoscience”.

Ever since, the oceans have contributed to keeping the earth’s climate stable. They contain significantly more carbon than the atmosphere (as carbon dioxide, CO2). Amongst others, the ocean stores this carbon in the form of dissolved organic matter (DOM), which is usually preserved for thousands of years. Thus, the ocean serves as an enormous long-term carbon storage.

Thorsten Dittmar and his colleagues now investigated the fate of this DOM if it ends up in hot vents in the deep sea. The seawater around these hot vents can reach temperatures of more than 400 degrees Celsius. With the help of diving robots (so called ROVs, Remotely Operated Vehicles) the scientists were able to collect samples at depths of several thousand meters from various locations in the Atlantic and Pacific Ocean. They wanted to find out whether the high temperatures destroy the present DOM or rather generate new DOM. The clear answer after six years of research: The DOM’s lifetime is limited. At most, it can reach 40 million years, as that is the time it would take to cycle the entire ocean through the hot, geothermal vents.

The present study thus also explains how the ocean manages to keep its share of carbon balanced even for very long periods of time. “Whatever the ocean takes up, it needs to release again sooner or later – that’s one prerequisite of a stable climate”, explains Dittmar.

Dittmar and his colleagues are not concerned that the destruction of DOM in the deep sea could reduce the ocean’s capacity to store CO2, as the investigated processes act on a very long timescale of millions of years. „The CO2 itself is nothing bad. Bad are only the current, rapid changes”, says Dittmar. Rather, CO2 is vital to life on earth. Without it, plants, animals and humans couldn’t exist. Mars, for example, has very little CO2 and is thus inhabitable. Venus contains too much of the greenhouse gas. On earth, the CO2-levels are optimal for life as we know it. The newly discovered role of deep-sea hot vents affects the climate and CO2-levels at very long timescales but does not influence the current climate changes.

Participating Institutes:

Max-Planck-Institut für Marine Mikrobiologie Bremen

ICBM - Institut für Chemie und Biologie des Meeres (ICBM) der Universität Oldenburg

MARUM − Zentrum für Marine Umweltwissenschaften an der Universität Bremen

Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung Bremerhaven

GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel

Jacobs University Bremen

Skidaway Institute of Oceanography, USA

University of Washington, USA

University of Southampton, UK

 

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.