A research connects deep-sea bioluminescence with dense water formation in the Mediterranean Sea
Permanent deep-seaʼs darkness is sometimes lightened by biogenic light blooms, a phenomenon so-called ʻdeep-sea bioluminescenceʼ. It is the ability of numerous marine organisms to emit light by chemical processes. According to an article published on the journal PLOS ONE, based on an inter-disciplinary research carried out with ANTARES telescope —the first underwater equipment to detect high energy neutrinos—, deep-sea bioluminescence blooms are connected with dense water formation. The article, signed by an international group composed by more than 150 experts, was coordinated by Miquel Canals, professor from the Department of Stratigraphy, Paleontology and Marine Geosciences at the Faculty of Geology of the UB, affliliated centre with the campus of international excellence BKC, and the experts Christian Tamburini and Stéphanie Escoffier, from Aix-Marseille University, and Xavier Durrieu de Madron, from the University of Perpignan.
Permanent deep-seaʼs darkness is sometimes lightened by biogenic light blooms, a phenomenon so-called ʻdeep-sea bioluminescenceʼ. It is the ability of numerous marine organisms to emit light by chemical processes. According to an article published on the journal PLOS ONE, based on an inter-disciplinary research carried out with ANTARES telescope —the first underwater equipment to detect high energy neutrinos—, deep-sea bioluminescence blooms are connected with dense water formation. The article, signed by an international group composed by more than 150 experts, was coordinated by Miquel Canals, professor from the Department of Stratigraphy, Paleontology and Marine Geosciences at the Faculty of Geology of the UB, affliliated centre with the campus of international excellence BKC, and the experts Christian Tamburini and Stéphanie Escoffier, from Aix-Marseille University, and Xavier Durrieu de Madron, from the University of Perpignan.
The North-West Mediterranean Sea is the best region to study dense water formation, a process originated by the cooling of surface waters which provides nutrients and oxygen to marine communities. From March to July in 2009 and 2010, the undersea telescope ANTARES, located close to Nice coast, detected a great increase of abyssal pelagic organism bioluminescence in the Gulf of Lion; it constitutes a unique data set, never recorded before.
Marine organism bioluminescence is a well-known phenomenon. About 90 % of abyssal organisms are able to emit light; this ability responds to defence, food or reproduction needs, and some behaviour guidelines. However, the origins of this process remain unknown. Miquel Canals, head of the Research Group on Marine Geosciences of the UB and first author of an article, published on Nature (2006), which described the phenomenon of dense water cascading in North-Western Mediterranean Sea, explains that “the process is produced by dense water formation. The research proves quick connections among the atmosphere, the ocean —even in deep waters— and marine biological communities. Data show a quick response of deep water pelagic ecosystem to external stimuli. In short, all these processes are correlated”.
In 2009 and 2010, the values detected by ANTARES light sensors —between 40 and 100 kHz— went up to 9,000 kHz, an extreme value which enabled to relate bioluminescence to salinity and temperature changes in Gulf of Lion waters. This extreme value is due to the vertical mixing of deep water and the sinking of surface water. “The observed area —adds Canals—, located at a depth of about 2.4 kilometres, has suffered for some years the phenomenon so-called ʻopen-sea convectionʼ, a process similar to dense water cascading”. Convection results in the formation of deep water owing to the combination of atmospheric forcing and regional circulation that lead the water column to overturn. Dense deep water formation occurs during late winter and early spring due to cold, strong and persistent northern winds, Mistral and Tramontane.
Canals, who was associated research director of the Training and Research Centre on Marine Environment (CEFREM) of the University of Perpignan, points out that “these periods, which match the end of winter, spring and the beginning of summer, show surface watersʼ cooling. The phenomenon responds to the cooling and subsequent sinking of saltier water currents; and, consequently, salinity is increased.
The research group suggests that the measurement of bioluminescence should be considered a priority method to continuously assess deep water biological activity. The objective is to better understand how marine ecosystems work and their relation to atmospheric and oceanic circulation and, in the last resort, to global climate change.
Finally, it is important to remember that, within the Mediterranean Sea, the group led by Miquel Canals has recently published an article about the trawling effect on the seabed (Nature, 2012), a publication honoured with an editorial on The New York Times.