Living On the Edge: Life Under the Ice (Part 1)

After drilling through the 800-meter-thick ice sheet that covers subglacial lake Whillans in western Antarctica, a US research team discovered a thriving microbial ecosystem on the lake floor that hasn't been reached by sunlight possibly for up to a million years. The image shows the view down the bore hole as the drill melted its way through the ice. Image Credit: Reed Scherer/Northern Illinois University — After drilling through the 800-meter-thick ice sheet that covers subglacial Lake Whillans in western Antarctica, a U.S. research team discovered a thriving microbial ecosystem on the lake floor that hasn’t been reached by sunlight possibly for up to a million years. The image shows the view down the bore hole as the drill melted its way through the ice. Image Credit: Reed Scherer/Northern Illinois University

Is there life elsewhere in the Universe? Attempts at answering that age-old question have been increasingly linked in recent years with the continuing discoveries of ecosystems in places on Earth that were previously thought of as overtly inhospitable to any forms of life. The growing realisation during the last few decades that a new category of microorganisms, called extremophiles, thrive in environments that would be detrimental to any other life forms on Earth has led to a paradigm shift in our view of life, forcing us to reconsider the definition of habitable environments on Earth as well as in other places in the Universe. A new fascinating study, published earlier this month detailing the surprising discovery of a whole new microbial ecosystem in the waters and sediments of the subglacial Lake Whillans in Antarctica, further showcases the tenacity of life on Earth, while offering valuable insights into the possibility of life on other similar environments in the outer Solar System, like the ice-covered oceans that are thought to exist on Jupiter’s moon Europa and Saturn’s moon Enceladus.

Buried in the deep

Locations of some of the major subglacial Antarctic lakes. Image Credit: Subglacial Lake Ellsworth Consortium

Being the coldest and driest continent on Earth, the Antarctic mainland was long regarded as a barren wasteland that was devoid of any life. Yet, during the last 50 years, a series of astonishing discoveries have revealed a fascinating microbial biology which thrives in the inhospitable environments that are present there, from the extremely arid McMurdo Dry Valleys of continental Antarctica to the frozen and highly acidic neighboring Lake Vida. In addition, the advent of radioglaciology in the 1960s allowed scientists to probe Antarctica’s ice sheet using ice-penetrating radar in order to measure its thickness with great accuracy, leading to a series of ground-breaking discoveries of entire mountain ranges and hundreds of subglacial lakes buried beneath several kilometers of ice.

One of these, named Lake Whillans, was discovered in 2007 by Helen Fricker, a glaciologist at the Scripps Institution of Oceanography in California, following an analysis of laser altimeter data from NASA’s ICESat Earth observing satellite. A subglacial, 23-square-mile-wide lake lying under 800 meters of ice on the lower portion of the Whillans Ice Stream in West Antarctica, Lake Whillams was found to be part of a wider network of several interconnected subglacial lakes which constantly fill and drain during the course of a five-year period, exchanging their waters with one another due to the pressure of the overlaying ice. The pressure of the ice also helps to lower the freezing point of water by up to several degrees, thus keeping it at a liquid state, while acting as a thermal blanket that traps the geothermal heat radiated away by the Earth, constantly melting the ice at the base of the ice sheet. Could this site be home to any microbial life?

The answer to this question was one of the overarching goals of the Whillans Ice Stream Subglacial Access Research Drilling project, or WISSARD, a unique research project aimed to return the first pristine samples of water and sediment from an Antarctic subglacial lake. Although a Russian research team was able to identify traces of more complex multicellular life in samples that had been previously retrieved from the bottom of the much deeper ice sheet that sits atop Lake Vostok, their findings have since been questioned by many members of the scientific community as being the result of contamination from the drilling equipment used.

First view of the bottom of Antarctic subglacial Lake Whillans, captured by the high-resolution imaging system aboard the Micro-Submersible Lake Exploration Device. The imagery and other data from the mini-sub were used to survey the lake floor and help the WISSARD team verify that the rest of their instruments could be safely deployed into the lake. Image Credit: NASA/JPL-Caltech

The relatively thin ice sheet covering Lake Whillans, on the other hand, coupled with its close proximity to the U.S. McMurdo Research Station, made it an ideal target for the WISSARD research team. Funded by the National Science Foundation in 2009, with contributions from NOAA, the Gordon and Betty Moore Foundation, and NASA’s Cryospheric Sciences and Astrobiology programs, WISSARD consisted of 13 research groups from eight different universities across the U.S., with additional collaboration from two international institutions. Following years of intensive preparation and planning, the WISSARD team set out in January 2013 with the aim of drilling into the 800-meter-thick ice sheet over Lake Whillans in a race against time, as the 2013/2014 field season was coming to a close. The scientists used a specially designed hot water drilling system to break through the ice and reach the lake bed. Extreme care was also taken in order to ensure that the equipment would not contaminate the pristine environment of the lake waters. To that end, a total of four sterilisation techniques were used in order to kill any invasive microorganisms that might have been present on the drilling equipment during its descent into the ice, including filtration, ultraviolet irradiation, pasteurization, and disinfection with hydrogen peroxide.

Colonies of bacteria cultured from samples of the water column from subglacial Lake Whillans. Image Credit: Brent C. Christner, Louisiana State University

With all sterilization procedures in place, the drilling system started melting its way through the ice on 23 January 2013. On its way down, the drill opened a 60-cm-wide bore hole that allowed the WISSARD team to lower a specialised micro submarine called the Micro-Submersible Lake Exploration Device, or MSLED, which was equipped with a high-resolution camera and hydrological chemical sensors and was developed by a team of students at the Arizona State University under the direction of Dr. Alberto Behar from NASA’s Jet Propulsion Laboratory in Pasadena, Calif. With excitement steadily mounting among the research team in the days that followed, the drill finally came to a stop in the morning hours of 27 January, signaling its long-awaited rest on the floor of Lake Whillans, with the MSLED offering scientists shortly thereafter their historic first views of a site that hasn’t been reached by sunlight for possibly hundreds of thousands of years. “This is the first instrument ever to explore a subglacial lake outside of a bore hole,” says Behar. “It’s able to take us places that are inaccessible by any other instruments in existence.”

Sample retrieval operations soon followed, before the bore hole could freeze shut again by the extreme cold, with the WISSARD team successfully getting their hands on three distinct samples of water and sediment from Lake Whillans in the following days, totaling approximately 30 liters of lake water and eight sediment cores—the first ever to be retrieved from a subglacial Antarctic lake. The very exciting results of the sample analysis, which were presented in a recent study published in the 21 August issue of Nature, revealed the surprising presence of an entire microbial ecosystem thriving in Lake Whillans, that may have been isolated and buried under the ice for up to a million years. Scientists were able to discover, with the use of DNA sequencing, 3,931 species of archaea and bacteria, which are the simplest forms of life on Earth. Furthermore, it was found that in the absence of sunlight these microorganisms were based on chemosynthesis instead to power their metabolic processes, getting their energy from the scarce amounts of elements like ammonium, iron, and sulfide compounds present in the lake water and sediment samples.

Morphological diversity of microbial cells in the water sampled from Lake Whillans. a) An epifluorescensce micrograph showing a variety of cell morphotypes, which was confirmed by scanning electron microscopy (images b to d). The yellow arrows indicate cells with rod (b), curved rod (c) and cocoid morphologies (d). The scale bar on the bottom right is 2 micrometres. Image Credit: Christner, B. C. et al. Nature 512, 310–313 (2014). — Morphological diversity of microbial cells in the water sampled from Lake Whillans: a) An epifluorescensce micrograph showing a variety of cell morphotypes, which was confirmed by scanning electron microscopy (images b to d). The yellow arrows indicate cells with rod (b), curved rod (c), and cocoid morphologies (d). The scale bar on the bottom right is 2 micrometres. Image Credit: Christner, B. C. et al. Nature 512, 310–313 (2014).

The possibility of life in the nutrient-poor and frigid environments of the subglacial Antarctic lakes has been pondered for decades, yet the results from the WISSARD team are the first to unequivocally show that life in Lake Whillans not only has earned a foothold but it is thriving as well, while feeding off the ammonium produced by the decomposition of dead organic matter that has been accumulating on the lake floor for millions of years and from the iron and sulfide compounds that are present in the lake sediments. “Our data show that Lake Whillans supports a metabolically active and phylogenetically diverse ecosystem, that functions in the dark, at sub-zero temperatures, confirming more than a decade of circumstantial evidence regarding the presence of life beneath Antarctica’s ice sheet,” conclude the researchers in their study. “Hidden beneath a half-mile of ice in Antarctica is an unexplored part of our biosphere,” says Dr. Brent Christner, associate professor at the Louisiana State University’s Department of Biological Sciences and lead author of the study. “WISSARD has provided a glimpse of the nature of microbial life that may lurk under more than 5 million square miles of ice sheet.”

Life elsewhere?

These findings by the WISSARD team are the latest in a long series of discoveries of microorganisms that have been found to thrive on extremely inhospitable terrestrial environments which would be detrimental to most other life forms on Earth. These extremophiles have helped to revolutionize the science of biology, as well as the search for other habitable environments elsewhere in the Universe. The fascinating and important discovery of life thriving on cold and dark aquatic environments deep beneath the Antarctic ice, a place previously considered to be too hostile for life, hints at the possibility of life existing on other similar environments in the Solar System as well, like the oceans of liquid water that are thought to exist on many outer Solar System moons, like Europa and Enceladus. “I think that [the WISSARD findings] do nothing but strengthen the case for life on other icy bodies in our Solar System and beyond,” said Christner during an interview for Nature. “The first time we’ve gone to Antarctica, the first place we selected to drill a hole to the bottom and look for life, we found it … It’s really not that much of a stretch to suggest that similar conditions [exist] on a place like Jupiter’s icy moon Europa, that has an ocean underneath a 50-to-100-km thick ice shell. Why can’t life exist there?”

Could life indeed be flourishing on those distant alien landscapes in the outer Solar System? This question will be examined in the second part of this article.