Deep sea "captures" CO2

Researchers report carbon dioxide increases in 3, 000 to 4, 500 meters

The meteor in action: marine researchers from the IFM-GEOMAR collect data in the Atlantic. © A. Körtzinger, IFM-GEOMAR
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Scientists at the Leibniz Institute for Marine Science (IFM-GEOMAR) in the North Atlantic have now noted a significant increase in carbon dioxide from the atmosphere at a depth of 3, 000 to 4, 500 meters. Using a new method developed at IFM-GEOMAR, they were able to show that the increase in greenhouse gases through the use of fossil fuels has led to significantly more CO2 being stored in deeper layers of the ocean than previously assumed.

The findings are important not only for the global carbon cycle, but for other processes such as acidification of the oceans, according to the marine researchers in the current issue of the journal Proceedings of the National Academy of Sciences (PNAS).

Since the beginning of industrialization, the oceans have received an estimated half of the human-emitted greenhouse gas CO2. Thus, the oceans make a decisive contribution to dampening the greenhouse effect and the resulting consequences, such as global warming. However, the oceans' ability to serve as a buffer for the Earth's climate decreases as the concentration of CO2 in the surface layer increases. In order to be able to better assess the role of the ocean in the future development of the climate, marine scientists from Kiel have set themselves the goal of researching the exact location of the greenhouse gas CO2 in the ocean.

In 2004, marine chemists from Kiel undertook an expedition to the Atlantic, funded by the German Research Foundation (DFG) and the European Union. The route tracked a 22-year-old trip by American colleagues. In this way, data that was two decades apart could be directly compared. The method developed in Kiel relies on the statistical comparison of high-precision measurements of dissolved CO2 and other properties of seawater. With this data, the scientists were able to make a kind of CO2 mapping of the ocean. "We were surprised how convincing our method was by showing that CO2 actually gets from the surface to deeper layers and is stored there, " reports Toste Tanhua, first author of the study.

Double-edged sword for the ocean habitat

On the one hand, what appears to be good news for the development of the anthropogenic greenhouse effect turns out to be a double-edged sword for the ocean as a habitat. Due to the increased uptake of CO2, researchers have recently observed increasing acidification of the ocean, with alarming consequences for marine organisms. Calcifiers such as corals, but also some microscopic plankton species have more and more difficulty forming their skeletons. display

Because these are at the beginning of the food chain, the development has far-reaching consequences for entire ecosystems in the sea. The new study shows for the first time how fast this process has progressed. "Our data shows that the depth at which lime dissolves in the ocean has shifted upwards of 400 meters over the last 200 years, " says Professor Douglas Wallace, co-author of the study and marine chemist at IFM-GEOMAR. "We are in the process of changing the chemistry of the ocean in a dramatic way."

In addition to these insights into past changes in the ocean, the new method is especially important for the assessment of future developments. "Continuing measurements will allow us to observe the distribution and concentration of CO2 in the ocean of the future as an indication of whether or not global action to mitigate the greenhouse effect actually works ", Prof. Wallace emphasizes the method as an important result of the research work in Kiel.

(idw - Leibniz Institute for Marine Sciences, 13.02.2007 - DLO)