Scientists Use Drilling Vessel to Uncover Secrets of Life Under Ocean Floor

IODP expedition 370 involved the scientific deep-sea drilling vessel Chikyu. (Credit: JAMSTEC)

(CN) — A new study conducted by an international team of researchers tackles a question that has vexed marine biologists and experts for decades: How hot is too hot for the clusters of microbial life that reside underneath the ocean floor?

Researchers have long understood that of all the habitats around the planet, few are as harsh and unforgiving as the area directly below the ocean floor. As one ventures deeper into the ocean sediment, temperatures and pressure gradually but significantly increase as you inch closer to the immense heat trapped within Earth’s core. 

For years, researchers believed that this dense and dangerous environment underneath the ocean was void of any form of life and that the intense temperatures and low energy supply made it all but impossible for life to find a foothold.

That was, however, until roughly three decades ago when researchers made a startling discovery: despite these seemingly inhospitable conditions, microorganisms such as bacteria do in fact live below the ocean floor and can continue to thrive at depths of at least a few miles below the seabed.

Despite this discovery, relatively little is known about the microbial life that lives below the ocean. This led experts to conduct a research endeavor between the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) and MARUM Center for Marine Environmental Sciences at the University of Bremen in Germany that sought to learn more about this complex biosphere buried in the planet.

In a study published Thursday in the journal Science, researchers announced their findings after conducting a massive drilling operation off the coast of Japan where they used a deep-sea drilling vessel known as Chikyu to obtain sediment samples from miles beneath the ocean, the only vessel in the world currently capable of pulling off such a task.

Using these resources, researchers were able to explore how far down into the Earth they could go before the temperatures became so intense that even the evidently heat-loving microbial life forms could no longer withstand it.

Fumio Inagaki of JAMSTEC and co-chief scientist on the project, reports that the results of the experiment were somewhat unexpected.

“Surprisingly, the microbial population density collapsed at a temperature of only about 45 degrees,” Inagaki said with the release of the study. “It is fascinating — in the high-temperature ocean floor there are broad depth intervals that are almost lifeless. But then we were able to detect cells and microbial activity again in deeper, even hotter zones — up to a temperature of 120 degrees.”

Researchers report that while populations of vegetative cells, a type of bacteria that grows on its own instead of creating spores, rapidly declined at temperatures of around 122 degrees Fahrenheit, endospore populations greatly increased at temperatures of around 185 degrees Fahrenheit — temperatures that far exceed the highest recorded temperature on the surface of Earth.

Researchers note that this unexpected discovery likely comes from the fact that endospores, which are typically dormant cells that live inside certain bacteria, have a unique ability to activate themselves and enter a live state when they find themselves in conditions they prefer.

The study reports that the findings would not have been made possible were it not for the tremendous advancements made recently in life detection technology and that preventing contamination of the sediment samples was a top priority. 

Researchers say they were so concerned about potentially contaminating some of the more crucial samples that some were given special transport by helicopter to special laboratories in Kochi, Japan where they could be safely examined under the strictest of conditions.

Verena Heuer of the MARUM Center for Marine Environmental Sciences at the University of Bremen and co-chief scientist of the project says that while the revelations of the study itself are intriguing, such results would also not have be possible were it not for the dedicated researchers around the world, comprised of 43 authors from 29 different institutes representing nine countries, who came together to attempt such an exhaustive research effort.

“With every expedition, advances are made in technical and analytical methods; researchers with diverse backgrounds and new ideas come together each time in order to answer a scientific question,” Heuer said. “And that is fascinating. Every new hole opens a window to new knowledge.”

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