National and international scientists, led by the University of Granada, have discovered that the deep ocean (below 200 meters deep, where sunlight does not penetrate) houses fluorescent organic matter that resists degradation between 400 and 600 years, and that supposes a reduced organic carbon storage.
This work provides new data on organic matter in the deep ocean, an enigma for many researchers due to its high chemical complexity, made up of thousands of substances that persist for hundreds or thousands of years.
The researchers from the University of Granada Teresa S. Catalá and Isabel Reche, main authors together with their colleagues from the Malaspina 2010 expedition, have advanced in the knowledge of this organic matter thanks to its spectrofluorimetric characterization.
The results deepen the knowledge of the so-called "microbial carbon pump", a process that consists in that the microorganisms of the deep ocean, during the mineralization of organic matter, generate reduced compounds that are persistent and can be stored in depth. This storage prevents them from being returned to the atmosphere in the form of CO2 and, thus, mitigating its increase in the atmosphere.
Scientists have focused on organic molecules that have the peculiarity of absorbing light and re-emitting it in the form of fluorescence and that represent persistent compounds. They have discovered that these molecules persist for 400 to 600 years in the deep ocean, below 200 meters deep, where sunlight does not penetrate. A life span that is longer than the time it takes for the deep ocean to renew itself: about 350 years.
"This means that fluorescent organic molecules, which represent between 1 and 15 percent of dissolved organic matter, have the potential to sequester carbon in the deep ocean and thereby contribute to reducing the greenhouse effect," he explains. Isabel Reche Cañabate, from the Department of Ecology of the University of Granada and co-author of the work.
800 SAMPLES OF OCEANS
The circumnavigation carried out by the ship Hespérides in 2010 and 2011, within the framework of the Malaspina 2010 expedition, represented "a unique opportunity" to obtain samples from the three great oceans, the Atlantic, the Indian Ocean and the Pacific and from depths that reached 4000 meters.
"We have carried out a census of fluorescent organic molecules in 800 samples present in 24 different water masses collected from all oceans" explains UGR researcher Teresa S. Catalá.
The 800 samples collected were analyzed on board, immediately after being taken, so that their properties were not altered. To do this, the scientists used a spectrofluorimeter, with which they recorded the fluorescence emission of each water sample in response to light of different wavelengths (colors).
"This instrument worked for 270 hours and provided us with 2.5 million data. Never before had a similar effort been made, nor had so much data been collected to determine the fluorescence of the deep ocean", highlights Catalá.
The scientists hope with their work to contribute to continue advancing in the knowledge of the "microbial carbon bomb", a mechanism that could be used in the future to produce a greater quantity of persistent dissolved organic matter and thus to partially counteract the effects of increase of CO2 in the atmosphere.
The Malaspina 2010 expedition is a Consolider-Ingenio 2010 project that, managed by the CSIC and financed by the Ministry of Economy and Competitiveness, comprises some 50 research groups, including that of the University of Granada led by Isabel Reche.