An international team of scientists has discovered a surprisingly huge and active bacterial community living on the sea floor at the deepest site on Earth, the Mariana Trench.
Photo of the sediment surface at Challenger Deep – 6.77 miles water depth (Ronnie N. Glud et al)
According to their study, published in the journal Nature Geoscience, a highly active bacteria community exists in the sediment of the trench – even though the environment is under extreme pressure almost 1,100 times higher than at sea level.
“Deep sea trenches act as hot spots for microbial activity because they receive an unusually high flux of organic matter, made up of dead animals, algae and other microbes, sourced from the surrounding much shallower sea-bottom. It is likely that some of this material becomes dislodged from the shallower depths during earthquakes, which are common in the area,” said lead author Prof Ronnie Glud from the Nordic Center for Earth Evolution at the University of Southern Denmark.
“So, even though deep sea trenches like the Mariana Trench only amount to about two percent of the World Ocean area, they have a relatively larger impact on marine carbon balance – and thus on the global carbon cycle.”
The team measured the distribution of oxygen in trench sediments (6.77 miles) and at a reference site (3.75 miles) to get accurate data on bacterial activity, and took sediment cores with an autonomous device. The results show that the trench sediments house almost 10 times more bacteria than the sediments of the surrounding abyssal plain at much shallower water depth of around 4 miles.
“If we retrieve samples from the seabed to investigate them in the laboratory, many of the microorganisms that have adapted to life at these extreme conditions will die, due to the changes in temperature and pressure. Therefore, we have developed instruments that can autonomously perform preprogrammed measuring routines directly on the seabed at the extreme pressure of the Marianas Trench”, Prof Glud said.
“We have also made videos from the bottom of the Mariana Trench, and they confirm that there are very few large animals at these depths. Rather, we find a world dominated by microbes that are adapted to function effectively at conditions highly inhospitable to higher organisms”, he said.
“The deep sea trenches are some of the last remaining ‘white spots’ on the world map. We know very little about what is going on down there or which impact the deep sea trenches have on the global carbon cycle as well as climate regulation. Furthermore, we are very interested in describing and understanding the unique bacterial communities that thrive in these exceptional environments.”
Data from multiple deep sea trenches will allow us to find out how the general conditions are at extreme depths, but also the specific conditions for each particular trench – that may experience very different deposition regimes. This will contribute to our general understanding of Earth and its development,” Prof Glud concluded.
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Bibliographic information: Ronnie N. Glud et al. High rates of microbial carbon turnover in sediments in the deepest oceanic trench on Earth. Nature Geoscience, published online March 17, 2013; doi: 10.1038/ngeo1773
