Uncovering a Deep Sea Microbial World
In the “muck” of the ocean floor is a strange sort of life — thriving communities of single-cell organisms, feeding on carbon and minerals that filter down from the world above. This alien ecosystem may seem distant from our life on the surface, but a recent paper in Nature Communications recently brought attention to why these organisms are so critical for maintaining the very climate and atmosphere that make life above the ocean possible.
In September, the Hertz Foundation talked to one of the authors of this paper about this research and his other work. Arthur Spivack (Hertz Fellow ’81) is Professor of Oceanography at the University of Rhode Island, where he specializes on the chemistry of the oceans, focusing particularly on understanding how biology, geology, and chemistry interact in Earth’s systems. Working in the lab and on ships drilling into the seafloor for samples, he’s leading research that’s deepening our understanding of the microbial life deep under the sea floor.
Q: Dr. Spivack, your recent paper brings attention to something most of us don’t even realize exists: that deep beneath the ocean floor, there are communities of microbes that not only have an extremely unique life, it’s a life uniquely vital to our own. Could you explain?
A: I’d say we owe the majority of the oxygen we breathe to these microbes. This isn’t because they’re producing all the oxygen we breathe — forests and algae correctly get credit for that. In fact, it’s because these microbes are inefficient. There’s a lot of carbon on the sea floor, in the form of biomass that has sunk to the bottom of the ocean over millions of years. All of this is microbial food so if these microbes actually ate all of it—by oxidizing it—they would take up the majority of the oxygen in our atmosphere. So we should be glad they behave as they do.
Q: By eating inefficiently, and allowing this carbon to remain on the seafloor, these microbes also affect two of the most important chemical metrics for our world: the amount of CO2 in the atmosphere, and the acidity of the ocean. Both of these are increasing rapidly thanks to human activity, to the detriment of our climate and oceans. Could the subseafloor microbes help us reverse that?
A: Unfortunately, no. These microbes grow and eat on timescales vastly longer than a human lifetime. It can take thousands of years for one cell to divide into two. So from the standpoint of the changes we’re making, it’s better to think of these ecosystems as setting the baseline for these measures, and our activity perturbs that baseline.
“We owe the majority of the oxygen we breathe to these microbes.”
Q: How do cells manage to grow so slowly?
A: We’re trying to understand this now. It’s important for understanding the past and future evolution of the Earth’s biosphere: after all, these microbes are vital to the air, water, and climate!
So how many of these cells are simply growing extremely slowly, and how many are going into stasis and waking up only when there are nutrients around? This requires working out exactly what they eat and how they eat it, which itself can be very unusual from our perspective. We’re not necessarily looking at the photosynthesis and respiration reactions we’re familiar with, reducing CO2 into sugar and oxidizing it back into CO2. Some of these microbes use the oxygen in, say, sulfate salts to reduce compounds like hydrogen and methane — and some of them even harness radioactive decay to make the hydrogen food.
Q: I understand that the research itself is also catalyzing technologies that are having tremendous benefits not only to scientists, but cities and even nations.
A: Absolutely. Key to exploring these seafloor microbial communities is drilling down very deep—remember, these microbes can be as far as a kilometer below the seafloor — and extracting samples with very, very little contamination. We can’t have drilling fluid or surface microbes messing with our biochemical data!
It turns out there are other places where drills that can extract a sample with very little contamination is useful, and one of these is testing groundwater—the lower the contamination of your sample from the drilling fluid, the better you’re able to detect the more dangerous sort of contamination in the sample itself. So a while back, I was brought on board this team led by scientists at Columbia University who were working on testing groundwater in Bangladesh. I was happy to help, and it turns out there’s also a lot of interesting microbiology in the rocks that matter, so I’m glad to say that my work today is helping keep water safe throughout Bangladesh and beyond.
Q: I also heard the Rhode Island police turned to your team to investigate the cause of a mysterious blast on a public beach – one that actually hurled someone off her chair and through the air.
A: It’s another example of how the skills and understanding we develop doing very curiosity-driven science allow us to solve very applied problems – and in this case, a unique one. There was an explosion on a Rhode Island beach, and when the bomb squad had ruled out terrorism or old munitions, they came to me and my colleagues at the University of Rhode Island to ask whether something in the sand might be causing a build-up of methane that caused the explosion.
The culprit turned out to be something else entirely. A colleague analyzed samples taken from around the site and found that the sand contained really remarkable levels of hydrogen gas. We then saw a corrosion pattern on an electric cable under the explosion that would have created the hydrogen gas, like running a hydrogen fuel cell in reverse. So after determining hydrogen was the culprit, and that the explosion had released all the gas, we were able to determine that the beach was safe.
Q: Looking back, what spawned your interest in these deep-sea microbial communities?
A: In the 1990s, I joined an international research team interested in the ways chemicals move between the sea and the rock underneath, since this is a major, poorly understood part of the various nutrient cycles on Earth. It’s common to hear of the carbon cycle and the nitrogen cycle, but we were also studying things like the chlorine cycle and sulfur cycle. This team was led by the US, Japan, and Germany, and we studied an undersea trench off the south coast of Japan, where the Philippine Sea Plate is pushing under Japan. This subduction zone, called the Nankai Trough, is geologically interesting because it’s the source of some of the most destructive earthquakes and tsunamis to have hit Japan, and there may also be significant hydrocarbon fuel sources trapped in the ice at the bottom of the trench.
At that time, we were just studying the geochemistry, how the chemicals moved through the sediment and water, with no consideration for any of the life that might live under the sea floor. But we kept bringing up samples from deep beneath the sea floor with rich communities of bacteria, archaea, and viruses. As scientists do, I wanted to learn more. Since then, I’ve ended up spending much of the next two decades studying this tenuous but important form of life.
“[T]he way life survives under the ocean can tell us how life might exist on planets like Mars or moons covered in icy seas like Europa.”
Q: Your research is also funded and applied in ways that might surprise people.
A: A lot of my research is funded by NASA, because the way life grows under the ocean can tell us how life might form on planets like Mars or moons covered in icy seas like Europa.
Q: And in fact, you’re teaching a class in astrobiology?
A: Yes. And it’s a focus that has been deeply informed by my work, since life at the extremes – far away from the surface, growing at time scales so different from ours, and using many different energy sources and chemical reactions – can tell us how life elsewhere might exist.
But I also think classes like astrobiology are a great way to get non-scientists excited about science. There are so many related topics — from evolution and climate to the cosmological history of our universe — it’s a great way to introduce people to a broad range of scientific ideas, by capturing their imagination.