On the Antarctic seafloor, life thrives in surprising abundance.
Andrew Thurber is a self-described connoisseur of worms. He’s fascinated by these wriggling, sinuous creatures, many with jaws and enough legs to propel an army. In the Antarctic, where he dives through the ice in the name of science, a type of worm known as a nemertean can reach 7 feet long.
Giant worms aren’t the only extreme feature of the seafloor next to the Ross Ice Shelf. Voracious sea stars and sponges the size of a person dot a muddy, rock-strewn landscape.
Here, where darkness prevails for much of the year, the density of some species is higher than anywhere else on the planet. In attempting to understand what’s going on in this remote habitat, Thurber is revealing fundamental processes that fuel deep-sea ecosystems worldwide. His work could also refine estimates of how carbon is sequestered in the deep sea, a critical question in climate change.
Over the last decade, Thurber has made the often turbulent trip to the frozen continent four times. Near the United States base at McMurdo, he and his team drill a hole through as much as 10 to 15 feet of ice to reach the water. They place a warming hut over the opening, as though they were preparing for a day of ice fishing.
Despite merciless underwater temperatures, for Thurber, the sea is actually a relief from the bitter Antarctic wind. “The water is so much more pleasant than the air; it’s wonderful,” he says.
Once underwater, Thurber collects samples of seafloor sediment to take back to his lab. In 2012, he and Rory Welsh, an Oregon State graduate student in microbiology, investigated the 100-foot face of a glacier that ended in the Ross Sea.
Thurber’s dives aim to understand the relationship between microorganisms and marine animals. “There’s an idea that bacteria don’t do well in the cold and play a minor role in these ecosystems compared to animals,” he says. “The general idea is that the worms bury their food in the mud and eat it throughout the year, sort of like putting their food in a refrigerator.”
By “food,” Thurber means the algae that grow on the bottom and edges of the sea ice for a brief period during the Antarctic summer, then drop to the seafloor after they die. Thurber is testing the possibility that worms and microorganisms feast on this abundance of organic matter. “By the end of the winter, the easily available food is gone, and the worms switch to eating their competitors. They are living off bacteria as a food source,” Thurber says.
To find out which idea — whether the worms store their food in the mud or feed on microorganisms — is closer to the truth, Thurber collects tubes of sediment during his dives.
In one experiment on the seafloor, Thurber placed transparent tubes, some covered with electrical tape to simulate darkness, vertically into the sediment. He was testing to see if organisms on the seafloor were actually producing food through photosynthesis. He found the diatoms were producing about 25 percent of the daily energy for the community. That additional food source during the light time of the year, Thurber explains, could mean worms experience a greater swing between feast and famine over the course of a year.
Thurber says Ecologists have spent a lot of time studying how large animals interact — wolves and moose, for example, or lions and gazelle. In contrast, science has largely ignored how animals compete with and prey on microorganisms.
“Since bacteria and archaea perform most of the important chemical reactions on the planet, that’s a real shortcoming in our understanding of the globe,” he says.
Thurber’s trying to change that. One dive at a time.