The South Pacific Gyre (SPG) is the most barren, inaccessible place on Earth, especially in the deepest reaches of the ocean. The SPG is over a thousand miles from Australia to the west and South America to the east, and equally separated north and south from the Equatorial and Antarctic Circumpolar currents.
Far isolated from land, there is very little dust and other nutrients in this region of the Pacific. In the deep ocean, marine snow is the idyllic name given to the organic debris, scraps of all the dead things, drifting down and settling as a fine sediment on the ocean floor. Marine snow feeds the few sluggish and often freakish creatures that live in those hadean depths.
In the SPG, marine snow accumulates at the lowest rates of anywhere on the planet, at about 0.1 to 1 meter of accumulation per million years.
Morono and his team came to this marine desert to see what kind of microbial life can exist under such poor conditions.
Yuki Morono, Ph.D., is a senior researcher with JAMSTEC (Japan Agency for Marine-Earth Science and Technology), and lead author on the paper describing what they found. In the fall of 2010, the team embarked on the JOIDES Resolution drillship to drill in waters up to 19,000 feet deep in stormy oceans as far from land as it is possible to be, and pulled up plugs of clay, of this marine snow that had accumulated over hundreds of millions of years.
The project was given the uninspiring name Integrated Ocean Drilling Program (IODP) Expedition 329, and the goal was to retrieve sediments from the abyssal plains of the SPG and see what could possibly live in the subseafloor in such barren conditions. One almost hopes they pulled up biopsies of a slumbering Godzilla. But the real story is even better.
Morono and the team found a community of microbes that may have remained in a kind of suspended animation for over 100 million years.
One hundred million years. The oldest hominid fossil might be just over 4 million years old. The dinosaurs became extinct 65 million years ago when a huge space rock blasted a hole in the ocean floor, the Chicxulub crater, in Yucatan, Mexico. The first flowers may have evolved about 100 million years ago.
Morono and his team believe the microbes they found were trapped in a quiet slumber for over 100 million years, in a place with insufficient nutrient energy for them to grow and divide.
Previous work by the same team showed microbes present through the whole depth of the ancient mud, all the way to the basement rock, but sparsely. Microbiologists detected on the order of a few hundreds to millions of cells per cubic centimeter in these ancient SPG muds. In other more nutrient-rich areas of the ocean, researchers can find tens of billions of cells per cubic centimeter.
The sediments housing these microbes also contained essentials and nutrients: dissolved oxygen, nitrates, phosphates, and dissolved inorganic carbon were detected through the entire depth of the mud from the surface down to the basement rock. But the amounts were incredibly small, and calculations showed the rate of consumption and amount of energy the microbes could extract was extremely low.
Because the layers of materials in the sediments included a dense, hard rock called porcellanite lying above the oldest sediments, Morono and team felt the cells they detected had not migrated to the oldest and deepest layers, but had been trapped there.
In order to test the condition of these cells, Morono incubated them with stable isotope-labeled food so if the microbes ingested the material, the scientists could detect the isotopes within the cells. Morono was able to show that these cells were alive and that they quickly revived and began to grow and divide.
Morono also showed there were very few (less than 1%) spore-forming microbes. Some microbes can form a very hardy spore able to withstand tremendous environmental and nutritional stresses for extended times. The cell goes dormant and shells up into a nearly indestructible form. The microbes Morono found were not spore-forming cells.
The rapidity with which the bacteria responded to food showed they were not in a spore form, and were merely dormant and waiting for the right conditions to perk up and start dividing.
This all suggested to Morono and the team that the microbial community in the deepest and poorest muds of the SPG all the way to the basement rock were quietly slumbering for over 100 million years.
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