Life found deep beneath an Antarctic ice shelf

February 16, 2021 • 12:15 pm

There are two places on Earth that constitute Vast Unknowns with the potential for finding new species. One, the tropical rain forest, is relatively easy to access, but the area is so vast and difficult of access that there is much to be discovered. And of course the tree canopies, which are rich with life, are not so easy to access.

The other place is the deep sea, particularly around and below the Antarctic continent. A new paper from Frontiers in Marine Science (click on screenshot below, pdf here, full reference at bottom), describes a batch of organisms, some with stalks, clinging to a rock beneath an ice shelf attached to the land.  The interesting part of this study is not only the existence of life deep below ice shelves (that’s been seen before, including observations of fish, worms, anemones and mollusks), but life so far away from the open sea.  What the eight researchers found was a group of stalked and nonstalked sessile organisms, probably sponges, clinging to a small boulder resting on the sea floor. The boulder was 260 km (160 miles) in from the edge of the Ronne Ice Shelf. (A shorter piece in the Guardian is here.)

This means not only are there sessile, filter-feeding organisms living far away from where the food comes from, but, even more striking, the currents that could bring detritus and microorganisms to those sponges are not from the closest open ocean, but from the opposite direction, since that’s where the currents come from. Given these currents, food for the observed species probably comes from between 625 and 1500 km (388-932 miles) away: the nearest open ocean that constitutes the source of photosynthesis that ultimately yields all the food.  The researchers couldn’t collect the species, for they can be observed only through small holes bored with hot water through the thick shelf. Further, the big rock to which the organisms were affixed is 1233 m (4045 feet) below the ice. Given their remoteness, it’s almost certain that these species are new to science.

What’s striking about all this is that the total area explored by many researchers under the vast Antarctic ice shelves, which are so hard to penetrate, is smaller than a tennis court!  Imagine what’s under there! This, however, is the first time that any sessile (immobile) organisms have been found on a substrate below an ice shelf. The remaining organisms involved—and there’s a table of them in the paper—are mobile (i.e., fish) or live on a soft, sea-bottom substrate.

Click to read the paper; I’ve put some videos of what they saw in the tweets below.

Here are the two great Antarctic ice shelves: the Ross and the Ronne (11 o’clock at the top), with the map taken from the paper. The places where the shelves have been penetrated by boring are indicated with dots: filled black dots show sites that yielded observations of organisms, while the sites showing no life have open (white) circles. The one spot below the Ronne shelf that produced the sessile and stalked organisms in this study is marked with a yellow star.

The animals, which are likely to be sponges but could be some other sessile or stalked organisms like ascidians, barnacles, or even worms or cnidarians, were affixed to a “drop boulder” about 1 x 0.75 meters across. How did it get there? The term “drop boulder” is a clue: this was probably a rock from the mountains on the continent itself that found its way into glacial ice, and then moved onto the ice shelf. At some point it fell through the ice and onto the sea floor. It then—only Ceiling Cat knows how—got colonized from another site.

Here’s the figure from the paper showing the boulder and its affixed organisms. They’re not very clear, and they’ve had to outline and highlight the organisms. I’ve added the caption from the paper

Dimensions and close-ups of the boulder, highlighting where life is clearly visible (A–E) and the top of the boulder where no obvious life is visible (F). The taxa visible on the boulder: Red, large stalked sponge; White, sponge; Orange, stalked taxa [possible sponge, ascidians, hydroid, barnacles, cnidaria (e.g., tubularia), and polychetes].
Here are two videos, the first showing one of the scientists involved in the study explaining the find and its significance. The second video shows the organisms:  the blobs on stocks are particularly clear. You can see the difficulties of trying to manipulate a probe and a light in the darkness through a borehole more than 4,000 feet above. But yes, those aren’t artifacts: they’re alive!

Another map shows the holes drilled in the immediate area and the direction of the sub-shelf currents in the vicinity. The hole that yielded the view of the boulder is FSW2.  The black and purple arrows (see caption) indicate the direction of water flow, i.e., where the food comes from. As you see, the currents don’t flow from the nearest edge of the ice shelf but from a far greater distance, so the food particles have taken a circuitous route.

Map showing location of drill sites on Filchner Ice Shelf (FSW1-2, FSE1-2, and FNE2), comparable samples from continental shelf collected during JR275 as well as the major sub-ice shelf circulation. Black arrows show flows derived from High Salinity Shelf Water (HSSW) from the Ronne Depression. Purple arrow shows the flow from HSSW formed over Berkner Bank (Nicholls, 2004). Ice Shelf Water (ISW) exits along the eastern margin of Filchner Trough, with a possible seasonal influx of modified Warm Deep Water (mWDW) (Darelius et al., 2016). Dashed light blue arrows represent the flow of the slope front and coastal currents (Nicholls et al., 2009). Bathymetry is derived from ETOPO1 (NOAA National Geophysical Data Center, 2009).

The upshot: This is only a preliminary observation, and we don’t even know what those bloody creatures hanging onto the boulder are. But even observing them is a hard job: you have to get yourself onto the ice shelf with all your gear (perhaps they flew in), and then use a hot-water boring system to get through the thick shelf ice and then go down nearly a mile. To find out what these species are, they’d have to collect them, and that would involve either devising a boring/collecting device, or getting some kind of submersible below the shelf, most likely from above, which itself is nearly impossible. Going in below the shelf from the sea is theoretically possible, but it’s a big distance!

At any rate, what we know is that there are certainly many unknown species beneath the shelf, and maybe even unknown phyla. And once again we get the lesson that life is extremely tough and tenacious, here living in total darkness in near-freezing waters about a mile down, in an area where food is pretty damn scarce.

h/t: Jez


Griffiths, H. J., P. Anker, K. Linse, J. Maxwell, A. L. Post, C. Stevens, S. Tulaczyk, and J. A. Smith. 2021. Breaking all the rules: The first recorded hard substrate sessile benthic community far beneath an antarctic ice shelf. Frontiers in Marine Science 8.

21 thoughts on “Life found deep beneath an Antarctic ice shelf

  1. I like how 1/4 way through this post, when I started wondering about where the boulder came from, the writing went into discussion about where the boulder came from.

    I’d figure the drop boulder was coated with all sorts of microscopic life before going underwater. Perhaps :

    the organisms are scavenging what remains from that event (for however long)

    the organisms are in a state of very low metabolic rate as the nutrients are scarce

    perhaps stochastic events bring/brought nutrients, and these little guys won”t last many years – e.g. a carcass washing up or fell down around the boulder, picked clean by now, but enough residual to feed them a while.

    1. I’d figure the drop boulder was coated with all sorts of microscopic life before going underwater. Perhaps :

      Between falling off a mountainside and melting out of the bottom of the glacial ice constituting an ice shelf, the boulder spent a considerable period of time inside a glacier. You could make an estimate if you knew the source location and travel path, if the boulder has an unusual mineralogy ; but unusual mineralogies are – who’d a thunk it ? – unusual. But tens of thousands of years doesn’t seem wildly excessive. That’s quite a stretch for an organism to maintain it’s metabolism and repair DNA damage.
      There was a claim about 2000 of someone isolating culturable bacteria from inside salt crystals in an evaporite formation dating back to about 250 million years. While the researchers documented strenuous efforts to prevent contamination with modern bacteria, the preservation of life for so long, without input of nutrients was “very challenging” and the report hasn’t been generally accepted (It’s popular with Creationist idiots, for some reason.). In particular, since the salt deposit includes beds of carnallite (a potassium-magnesium double chloride – it has a distinctive microscopic appearance and a strong signal on gamma ray borehole logs due to the radioactivity of potassium), the bacteria in question had to be able to repair the DNA damage from their radiation environment … and for these (I can’t remember the name of the salt mine ; doesn’t matter [Edit : Salado Formation, near or in Texas. ) bacteria, people really couldn’t get the numbers to match up, to within several orders of magnitude.
      Compared to that, suspending animation in a bacterium for a few tens of millennia isn’t a big deal. But even so, it’s up against a competing hypothesis that the circulation of seawater under the ice shelf (a topic of considerable research, since basal melting is thought to be a major factor in the stability of ice shelves, and hence of the interior ice sheets of Antarctica, and hence the flooding levels in London, the Netherlands and Bangladesh – whichever exercises you most) takes less than tens of thousands of years.
      Caves, particularly deep ones, support sparse ecologies tens of kilometres from surface inputs of nutrients. Sea water is generally a richer a food supply than cave water, so I’m distinctly unsurprised by finding an ecology here. I’d be considerably more surprised if they didn’t find an ecology.
      The surprise the authors express is in finding sessile organisms (fixed in place by a holdfast of some sort, versus “motile”) here. FTFAbstract, “Mobile macro-benthic life and mega-benthic life have been observed as far as 700 km under an ice shelf,” and their estimates of flowlines from open ocean (not capped by enough ice to prevent photosynthesis) for nutrient-containing water is up to 1500km. Very much a case of being at the end of the line (as a friend from Novy Urengoy used to say).
      Actually, their surprise is in finding living sessile organisms. FTFArticle, “[Concerning the Ross Ice Shelf Project (1977-78) ]: no live sessile organisms were recorded (Bruchhausen et al., 1979; Lipps et al., 1979). Sediment samples obtained from the borehole, ∼475 km from the Ross Ice Shelf front, also contained the dead remains of meiofaunal foraminifera, bivalves, gastropods, ostracods, and possible polychete tubes but did not find any living infauna.” (My emphasis.)
      I wonder if the C-14 content of the water is measurable enough to give an estimate for the last equilibration of the water with atmospheric CO2 … There is a noticeable offset in carbon-14 ages for organisms that have marine-dominated diets, so if circulation under the shelves is on the order of centuries of higher, there should be a detectable signal.
      Or maybe not. The report says “The surrounding sediments [around the boulder] show ripples formed by currents but there is no visible evidence of infauna or mobile epifauna.” which says to me that effective current speeds approach the metre-per-second range, which is 80-odd km/day. I’m going to drop the ballpark for nutrient transport time to months only. The maritime C-14 signal is going to be dominated by the residence time of atmospheric CO2 in the ocean, and the circulation factor is unlikely to be major.
      Interesting story. Lots to chew on.

  2. Very cool discovery.
    Coincidentally, less than a week ago the Europa Clipper was given a launch date by NASA; October 2024. It’ll also be looking for organisms deep under a thick layer of ice, albeit a much more remote one…

  3. Europa and the NASA mission Europa Clipper also came to mind. That mission is a flyby mission though so it will not be able to directly look for life. There has been talk of a lander as well but as far as I know that won’t happen.

  4. I love the serendipitous nature of the discovery – first they’re annoyed that a bl**dy rock is in the way of their drill, and then…

  5. I wonder if the base of a “food chain” there could be some form of chemosynthetic bacteria, like at the deep ocean vents. Antarctica DOES have some significant dormant volcanoes, if I understand correctly. Those currents look like they could do a good job of stirring up some interesting chemistry from deeper “inland” and sweeping it outward.

    1. I wonder if the base of a “food chain” there could be some form of chemosynthetic bacteria, like at the deep ocean vents

      The myth is that these are somehow “independent of photosynthesis. Except that all the physiologies which I’ve heard of work by oxidising various mineral solutions with oxygen in the sea water. And that oxygen comes from … photosynthesis.
      There are interesting chemistries that happen in hydrothermal – meteoric systems. But they are linked to surface conditions. If you read the OOL literature, people are reasonably careful to avoid invoking significant oxygen activity (or is it fugacity? I can never remember which it is) in the pore fluids they’re cooking with.

  6. I have seen this movie. It ends with a giant octopus pulling down the Golden Gate bridge because we bothered its pet rock. But, fascinating how resilient life can be.

  7. It’s cool. It reminds of that discovery of that coral reef found at the mouth of the Amazon River which wasn’t expected to be here because of the amount of sediment the river was depositing.

    You would think that they would be a hydrothermal vent underneath, supplying these boulder organisms with some sort of chemosynthetic food source. Maybe the boulder has a specific mineral composition that works for these organisms to thrive there?

  8. Dumb question :

    Did Antarctic ocean (?) water temperature increase and in a time frame that would account for growth in that location?

  9. Beside the point:

    But that ice shelf and roughly the star on the map is where Shackleton’s ship got trapped in the ice ~1915. They were drifting with it, but camped beside it when it began to look dodgy. Then the ship was crushed and sank. Off they went dragging two lifeboats, eventually rescued in one of the greatest adventure stories of the 20th century, from Elephant Island, after a few, led by Shackleton, somehow got over to South Georgia.

    Off topic again!

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