They were among the first responders to the Deepwater Horizon oil spill in the Gulf of Mexico; have helped restore coral reefs in stressed ecosystems around the world; treat cancer and cure infections; form the basis of deep ocean food webs; sequester carbon and fix nitrogen; and produce about 20 percent of the oxygen in the atmosphere, making it possible for humans (and most other life forms) to live on this planet.
They are marine microbes, and they are some of Earth’s most important yet understudied residents that live throughout the global ocean.
Now, as industrial developments move into even deeper and more remote regions of the ocean, activities such as deep-sea mining could put many marine microbial communities and their critical ecosystem functions at risk. This is especially worrisome given the vast repository of knowledge and information they hold, and ocean ecosystem services they provide.
Scanning electron micrograph of a deep-sea microbe fondly named “Snot Bug” from the underwater volcano Axial Seamount, located about 300 miles (482 kilometers) off the coast of Oregon. (Photo courtesy of Julie Huber, © Woods Hole Oceanographic Institution)
“Microbes are the hidden heroes of our planet,” said Julie Huber, an oceanographer at Woods Hole Oceanographic Institution who studies marine chemistry and geochemistry, and was an author on a paper about the impacts of deep-sea mining on microbial ecosystem services. “They are doing all of these important things to keep the planet healthy, and when we think about these types of disruptions, we’re not just talking about killing microbes, we are removing their ability to do their job.”
Critical ecosystem services
One of these jobs is nutrient cycling. In the deep, there’s no sunlight and thus no opportunity for photosynthesis, so microbes instead feed themselves with leftover organic carbon raining down from the surface or dissolved minerals in the water, building body mass and extracting energy from carbon dioxide, sulfur, nitrogen, or other nutrients. As a result of their hard work, the food web can start to build up with fresh organic matter that protists can eat, and things grow from there.
“These systems are hotspots of fauna because you have primary producers,” said Maria Pachiadaki, a microbial ecologist at WHOI, who was a co-author on the microbial ecosystem services paper. “In such dark environments, they cannot produce as much organic matter as photosynthesis, but in comparison with the majority of the ocean floor they are very, very productive ecosystems.”
This nutrient cycling is not just crucial to the food web; it may also play an important role in carbon sequestration. Estimates vary on whether the microbes themselves capture a lot of carbon, but even if they don’t, they are the foundation of the marine processes, like photosynthesis, that store much of the excess carbon dioxide that human activities have released into the atmosphere. The global ocean has absorbed about 40 percent of all excess greenhouse gas emissions from burning fossil fuels and about 90 percent of the excess heat.
Schematic of a ship-based deep-sea mining operation. (Illustration by G. Mannaerts)
If deep-sea mining takes place, it could interrupt the carbon sequestration cycle and it would not be limited to just one part of the global ocean. There are four main types of significant mineral deposits that are being considered or explored for mining on ocean floors around the world: polymetallic nodule fields, active hydrothermal vents, inactive vents, and cobalt crusts. The different types of metals vary from site to site, but in general, they contain elements such as cobalt, copper, and nickel that are currently required for the transition from a fossil fuel-powered world to an electrified one. These metals, along with rare earth materials, are currently necessary for lithium-ion batteries, which power everything from electric car batteries to smartphones.
Unknown consequences
Dr. Huber said she is concerned about the prospect of large-scale and intensive mining operations taking place in the deep before scientists know what these ecosystems need to function or fully understand the many and complex services these organisms provide the deep ocean, and, by extension, all of us.
As deep-sea mining edges from the realm of science fiction towards reality, scientists have warned about the possible consequences to marine animals: how sediment plumes might smother them; how mining waste dumped at the surface level might interrupt photosynthesis; and how ocean noise might deafen and disturb larger marine animals like whales and dolphins that rely on echolocation.
Despite their importance to a healthy ocean, the threats posed to microbes by mining have been less well studied and less fretted over by those expressing concern about ocean industrialization.
The race for resources
Seabed mining in international waters is governed by the International Seabed Authority (ISA), a little-known United Nations agency based in Jamaica, that was established as part of the U.N. Convention on the Law of the Sea in 1982. The agency, composed of 167-member states plus the European Union (but not the United States), is responsible for establishing a code for mining, and protecting the marine environment from any of the harmful effects that may ensue. So far, the ISA has granted a total of 31 exploration contracts for mining in the deep sea, with nineteen of them in the polymetallic nodule fields in the Clarion Clipperton Zone (CCZ), an expanse of the Pacific Ocean stretching from near Hawaii towards the coast of Mexico, and spanning about 1.7 million square miles.
