The waters beneath the numerous ice shelves extending from the Antarctic continent into the Southern Ocean are even more hostile to life than the open Southern Ocean. This is especially true in the water layers beneath large ice shelves such as the Ross Ice Shelf. Here, an ice sheet several hundred meters thick floats on top of the ocean and covers an area of about 500,000 square kilometers. In the water beneath this ice shelf, hundreds of kilometers from the open ocean, researchers, in a study led by the University of Otago, New Zealand, have now discovered a diverse microbial community, despite the year-round conditions of complete darkness and nutrient deficiency.
Contrary to what one might suspect, there is surprisingly abundant life beneath the ice shelf even hundreds of kilometers from its edge and open water, as a study of life beneath the Filchner-Ronne Ice Shelf from last year already showed. In the current study, published in the journal Nature Communications, the international team of researchers specifically investigated the phylogenetic and functional diversity of the microbial community beneath the Ross Ice Shelf.
“Ice shelves are extensions of the ice sheet that push out from the continent, floating on the ocean, filling coastal bays and creating unique ice shelf ‘cavity’ environments that are very challenging to explore,” explains Professor Christina Hulbe, glaciologist at the University of Otago. “These unique environments, the combination of big picture questions and fine scientific details, and the diverse team of experts that it takes to make sense of everything we measure makes this work exciting, rewarding and important.”
In order to be able to take samples of the water layer lying beneath the ice shelf, experts from Victoria University of Wellington drilled through the 300-meter-thick ice in the center of the Ross Ice Shelf, about 300 kilometers from the shelf ice edge, using a hot water drilling system. The researchers used a pump to transport water samples to the surface of the ice, which they then analyzed using various genetic methods to determine the composition of the microbial community.
The results surprised the researchers: they found similar diversity and abundance of microorganisms under the ice shelf as in the deep sea of the open ocean, albeit with a different species composition. While light is absent in both habitats, microbes under the ice shelf, unlike those in the deep sea, do not have nutrients available that trickle down from the light-filled surface layer.
“These communities existing below the ice shelf must therefore rely on other energy sources to survive but we didn’t know what those were until now,” says Sergio Morales, a professor in the University of Otago’s Department of Microbiology and Immunology and co-author of the study. “The activity of microbial communities like this are the foundation for all of Earth’s ecosystems, so understanding life in this remote system helps make sense of life everywhere on Earth.”
That is, the microorganisms meet their energy needs from inorganic substances such as ammonium, nitrite and sulfur compounds released from dead biomass, but also from organic sources, as Morales explains. In part, these presumably get under the ice shelf through horizontal ocean currents, which provide nutrient replenishment much more slowly than the “marine snow” that trickles in the open ocean from the surface into the deep sea.
“These organic compounds are themselves likely to be produced using energy from inorganic materials instead of the sun since it can take years for water to complete its passage underneath the ice shelf,” Morales adds. “The really cool thing is that these under ice communities are distinct to those in the open ocean, meaning it’s a hidden living world persisting in the absence of sunlight.”
Julia Hager, PolarJournal
Link to the study: Martínez-Pérez, C., Greening, C., Bay, S.K. et al. Phylogenetically and functionally diverse microorganisms reside under the Ross Ice Shelf. Nat Commun 13, 117 (2022). https://doi.org/10.1038/s41467-021-27769-5
More on the subject: