Deep-sea challengers
Friends, I am pleased to announce the publication of another one of my scientific papers today! The paper's release is well-timed because the first author is Andrew Sweetman, my friend and former advisor who recently came to visit.
Regular readers of this blog may recall a research expedition that Andrew invited me on in 2015. We sailed out of San Diego on R/V Thomas Thompson and headed to the Clarion-Clipperton Fracture Zone, a region of the tropical eastern Pacific. The seafloor in the CCZ is covered with manganese nodules, which look like rocks but hold high concentrations of manganese and other minerals that several companies and nations are interested in mining. Our job during the cruise was to conduct baseline research in two mining claim areas in the CCZ to understand what would be lost if the seafloor were disturbed by mining activities.
The short answer? A lot.
Besides the animals that live on and in the nodules themselves, the sediments in the eastern CCZ have high species richness. Most of the animals are concentrated in a thin layer of the sediment surface, where there is exchange of oxygen with the water, but which would also be most disturbed by mining. Animals that live in the deep sea have been exposed to constant conditions for centuries - stable temperatures, slow currents, low deposition of organic material - and they would very likely take centuries to recover from broad-scale mining disturbance, if ever.
On the cruise, Andrew and I were specifically investigating the respiration of organisms that live in the sediments. We used a deep-sea lander to measure how much oxygen the sediment infauna consume, how they respond to sudden pulses of food, and which group used most of the carbon. We deployed the lander to the seafloor 4,000 m below, isolated three small areas of the sediment with chambers, injected artificial food sources into some, measured the oxygen consumption, and then called the lander back 48 hours later.
The cruise was not without its struggles. We had failed deployments. We made repairs to the lander on the fly. We had an entire evening of panicked phone calls to Germany. But in the end, we had a number of successful deployments and got enough data to show some really, really cool things about the world.
First, the bacteria are responsible for the vast majority of carbon cycling in the CCZ. Maybe this sounds unsurprising (I mean, come on, bacteria run the world), but it contrasts with the other other similar study every conducted, in the northeastern Atlantic. The difference? The amount of food reaching the deep seafloor in the northeastern Atlantic is much higher than in the equatorial Pacific. It appears that when there's very little food, the bacteria take over.
The second major finding of the paper - and by far the most exciting - is that the bacteria weren't just using carbon from the algae we gave them. They were using inorganic carbon. From the beginning of time until now, everyone has believed that organisms in deep-sea sediments are entirely dependent on food falling from the surface - dead algae and things like that. Chemosynthesis, the production of organic food from inorganic materials, supposedly only happens at hydrothermal vents and cold seeps. But our results show that's not the case. Inorganic carbon is being used to make food by bacteria in the sediment in the eastern CCZ, and not just a little bit. If you scale our findings up to the area of the whole deep sea, you get a number that is 10% of the whole carbon budget. Holy carbon, Batman.
Andrew's willingness to interpret his data honestly, even if it challenges the scientific status quo, is one of the many reasons I admire him. He will go down in history as the man who made deep-sea biologists rethink all of their carbon budgets. I'm grateful that I got to be a part of this study, and I hope many of you will give the paper a read. It appears in the journal Limnology and Oceanography:
https://aslopubs.onlinelibrary.wiley.com/doi/10.1002/lno.11069
Update: Our paper has been covered by The National, Newsweek, and the Daily Mail.
Regular readers of this blog may recall a research expedition that Andrew invited me on in 2015. We sailed out of San Diego on R/V Thomas Thompson and headed to the Clarion-Clipperton Fracture Zone, a region of the tropical eastern Pacific. The seafloor in the CCZ is covered with manganese nodules, which look like rocks but hold high concentrations of manganese and other minerals that several companies and nations are interested in mining. Our job during the cruise was to conduct baseline research in two mining claim areas in the CCZ to understand what would be lost if the seafloor were disturbed by mining activities.
The short answer? A lot.
Besides the animals that live on and in the nodules themselves, the sediments in the eastern CCZ have high species richness. Most of the animals are concentrated in a thin layer of the sediment surface, where there is exchange of oxygen with the water, but which would also be most disturbed by mining. Animals that live in the deep sea have been exposed to constant conditions for centuries - stable temperatures, slow currents, low deposition of organic material - and they would very likely take centuries to recover from broad-scale mining disturbance, if ever.
On the cruise, Andrew and I were specifically investigating the respiration of organisms that live in the sediments. We used a deep-sea lander to measure how much oxygen the sediment infauna consume, how they respond to sudden pulses of food, and which group used most of the carbon. We deployed the lander to the seafloor 4,000 m below, isolated three small areas of the sediment with chambers, injected artificial food sources into some, measured the oxygen consumption, and then called the lander back 48 hours later.
The cruise was not without its struggles. We had failed deployments. We made repairs to the lander on the fly. We had an entire evening of panicked phone calls to Germany. But in the end, we had a number of successful deployments and got enough data to show some really, really cool things about the world.
First, the bacteria are responsible for the vast majority of carbon cycling in the CCZ. Maybe this sounds unsurprising (I mean, come on, bacteria run the world), but it contrasts with the other other similar study every conducted, in the northeastern Atlantic. The difference? The amount of food reaching the deep seafloor in the northeastern Atlantic is much higher than in the equatorial Pacific. It appears that when there's very little food, the bacteria take over.
The second major finding of the paper - and by far the most exciting - is that the bacteria weren't just using carbon from the algae we gave them. They were using inorganic carbon. From the beginning of time until now, everyone has believed that organisms in deep-sea sediments are entirely dependent on food falling from the surface - dead algae and things like that. Chemosynthesis, the production of organic food from inorganic materials, supposedly only happens at hydrothermal vents and cold seeps. But our results show that's not the case. Inorganic carbon is being used to make food by bacteria in the sediment in the eastern CCZ, and not just a little bit. If you scale our findings up to the area of the whole deep sea, you get a number that is 10% of the whole carbon budget. Holy carbon, Batman.
Andrew's willingness to interpret his data honestly, even if it challenges the scientific status quo, is one of the many reasons I admire him. He will go down in history as the man who made deep-sea biologists rethink all of their carbon budgets. I'm grateful that I got to be a part of this study, and I hope many of you will give the paper a read. It appears in the journal Limnology and Oceanography:
https://aslopubs.onlinelibrary.wiley.com/doi/10.1002/lno.11069
Update: Our paper has been covered by The National, Newsweek, and the Daily Mail.
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