Animal graveyard found in deeply buried Antarctic lake | Science News for Students

Animal graveyard found in deeply buried Antarctic lake

Mud from Lake Mercer revealed tiny squashed creatures that resemble spiders and worms
Feb 27, 2019 — 6:45 am EST
a photo showing a drill into the ice above Lake Mercer in Antarctica

Researchers drilled through a kilometer of ice above Lake Mercer in Antarctica. They found mud that contained carcasses of tiny animals resembling spiders, crustaceans, worms and water bears.

Billy Collins/SALSA Science Team

Scientists have uncovered a big surprise from Antarctica’s Lake Mercer: the remains of tiny animals. Some looked like “squished spiders and crustacean-type things with legs,” says David Harwood. “Some other things … looked like they could be worms.”

Harwood is a micropaleontologist. He studies fossils of microscopic creatures at the University of Nebraska–Lincoln. He was describing animal carcasses retrieved from Lake Mercer, some 600 kilometers (370 miles) from the South Pole.

A thick layer of ice has topped this lake for thousands of years. In late December, researchers drilled through about a kilometer (0.6 mile) of that ice to reach the lake. The mud they dredged up from its bottom contained the animal remains. They found the tiny carcasses by examining the water and mud under a microscope.

Harwood was part of an expedition known as SALSA, which stands for Subglacial Antarctic Lakes Scientific Access. Its researchers were the first to sample this deeply buried lake. In addition to the other animal carcasses, they spotted what appeared to be remnants of a water bear. Water bears, or tardigrades, are durable microscopic critters. Examining DNA from the remains will help researchers ID them.

An announcement of the SALSA team's discovery of Lake Mercer's animal graveyard appeared in a news report published online January 18 in Nature.

Were they lake dwellers or just drop-ins?

Until now, scientists hadn’t considered that Antarctic lakes like Mercer could host organisms larger than microbes. That’s why this find “is really intriguing,” says Slawek Tulaczyk. Not part of the SALSA team, he studies glaciers for the University of California, Santa Cruz.

In 2013, scientists sampled another buried lake in Antarctica — Lake Whillans. “We didn’t uncover any evidence of anything more complex than a microbe,” says SALSA team member Brent Christner. He is a microbiologist at the University of Florida in Gainesville. “We had a similar expectation” for Lake Mercer, he says.

a map of Antarctica showing the location of Laker Mercer and Lake Whillans
Scientists were surprised by Lake Mercer’s animal graveyard. Samples taken from neighboring Lake Whillans turned up only microbes.
E. Otwell

It’s unclear if animals that once lived in Lake Mercer left behind the newly unearthed carcasses, Tulaczyk says. Ice or water may have carried these fragments in from the ocean. Or the remains could have washed in from nearby lakes in the Transantarctic Mountains.

The SALSA team could use radiocarbon dating to help pinpoint the samples’ ages. This technique works by comparing the relative amounts of two forms of carbon. One of them, carbon-14, is radioactive. That means it is unstable and sheds energy. As carbon-14 loses energy, it turns into carbon-12. This conversion occurs at a known rate. The ratio of carbon-12 to carbon-14 in material from a once-living object can be used to determine its age. And that, Tulaczyk says, may provide a clue as to how and when these minuscule carcasses arrived in Lake Mercer.

If any of these animals once called Lake Mercer home, some of them may still be alive down there, Harwood says. “It’s interesting to think that life can exist in really extreme environments,” he says. Lake Mercer is a great example.

The lake has been cut off from both the ocean and atmosphere for thousands of years. Indeed, Harwood says, “If life is still persisting there, that’s important for our thoughts about what we might find out in space.”

Power Words

(more about Power Words)

Antarctica     A continent mostly covered in ice, which sits in the southernmost part of the world.

atmosphere     The envelope of gases surrounding Earth or another planet.

carbon     The chemical element having the atomic number 6. It is the physical basis of all life on Earth. Carbon exists freely as graphite and diamond. It is an important part of coal, limestone and petroleum, and is capable of self-bonding, chemically, to form an enormous number of chemically, biologically and commercially important molecules.

colleague     Someone who works with another; a co-worker or team member.

DNA     (short for deoxyribonucleic acid) A long, double-stranded and spiral-shaped molecule inside most living cells that carries genetic instructions. It is built on a backbone of phosphorus, oxygen, and carbon atoms. In all living things, from plants and animals to microbes, these instructions tell cells which molecules to make.

environment     The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of things in the vicinity of an item of interest).

expedition     A journey (usually relatively long or over a great distance) that a group of people take for some defined purpose, such as to map a region’s plant life or to study the local microclimate.

fossil     Any preserved remains or traces of ancient life. There are many different types of fossils: The bones and other body parts of dinosaurs are called “body fossils.” Things like footprints are called “trace fossils.” Even specimens of dinosaur poop are fossils. The process of forming fossils is called fossilization.

glacier     A slow-moving river of ice hundreds or thousands of meters deep. Glaciers are found in mountain valleys and also form parts of ice sheets.

microbe     Short for microorganism. A living thing that is too small to see with the unaided eye, including bacteria, some fungi and many other organisms such as amoebas. Most consist of a single cell.

microbiology     The study of microorganisms, principally bacteria, fungi and viruses. Scientists who study microbes and the infections they can cause or ways that they can interact with their environment are known as microbiologists.

microscope     An instrument used to view objects, like bacteria, or the single cells of plants or animals, that are too small to be visible to the unaided eye.

microscopic     An adjective for things too small to be seen by the unaided eye. It takes a microscope to view objects this small, such as bacteria or other one-celled organisms.

online     (n.) On the internet. (adj.) A term for what can be found or accessed on the internet.

organism     Any living thing, from elephants and plants to bacteria and other types of single-celled life.

radioactive     An adjective that describes unstable elements, such as certain forms (isotopes) of uranium and plutonium. Such elements are said to be unstable because their nucleus sheds energy that is carried away by photons and/or and often one or more subatomic particles. This emission of energy is by a process known as radioactive decay.

radiocarbon dating     A process to determine the age of material from a once-living object. It is based on comparing the relative proportion, or share, of the carbon-12 to carbon-14. This ratio changes as radioactive carbon-14 decays and is not replaced.

ratio     The relationship between two numbers or amounts. When written out, the numbers usually are separated by a colon, such as a 50:50. That would mean that for every 50 units of one thing (on the left) there would also be 50 units of another thing (represented by the number on the right).

tardigrade     An eight-legged creature not much larger than the period at the end of a sentence. Tardigrades live in many places, including ponds, the sea floor and parts of Antarctica where rock sticks above the ice.

Citation

News Report:​ D. Fox.​ Tiny animal carcasses found in buried Antarctic lake. Nature. Vol. 565, January 24, 2019, p. 405. doi: 10.1038/d41586-019-00106-z.