We have been extracting different types of minerals from the ocean for thousands of years.  Over the last one hundred years technological advances have allowed us to access resources which are more difficult to extract.  We began tapping shallow oil and gas deposits around the turn of the 20th century and moved into deeper water later.  We have been dredging sand and aggregates at industrial scale for decades all over the world and we continue the practice every day. We have also dredged for diamonds in shallow waters for decades.

There are a wide variety of mineral deposits on the seabed.  The deposit types are highly distinct from one another in terms of geology and location.  Because of these differences, the impacts from extracting these minerals are unique to each type of deposit.  

The deposits that society has focused on to this point mainly sit in shallow waters—waters that are less than 1,000 meters in depth.  Because shallow water is fed by sunlight, there is plentiful food at these depths and this naturally leads to high levels of biomass.  Shallow ocean waters are also very high in biodiversity.  Coral reefs, for instance, are thought to hold as many as one million distinct species. (EPA, 2023) Shallow mineral deposits generally occur on the continental shelf, not far from shore, so their extraction has more potential to impact humans (vs. deep water operations) – both because the waters are intensively fished, and because currents can push waters around the deposits onto beaches, mangroves, and marshes where human activity is high.  Minerals found in shallow waters include various mineral sands and aggregates, precious stones, and oil and gas. We extract these minerals today with care to avoid harming people and doing too much damage to the ecosystem.     

The critical ocean minerals upon which COMRC focuses are found in deep ocean waters—waters that are over 1,000 meters in depth.  These deposits are distinct from shallow water minerals. The ocean environment changes as depth increases due to the absence of sunlight, the growing pressure, and the dropping temperatures. There is generally less food available at greater depth and thus often much less biomass. There is biodiversity even in the deepest depths of the ocean, but the biodiversity present is dominated by very small microbes—many of which are not visible to the naked eye. And the biodiversity present is modest relative to that which is found in shallow environments such as coral reefs.

When COMRC references critical ocean minerals, we are normally referring to four different types of mineral formation found in deep waters: polymetallic nodules, seafloor massive sulfides, cobalt crusts, and seafloor muds (we exclude methane hydrates which are a gas).  These resources are each highly unique.  They differ in mineral composition and grade, they are located in vastly different environments, and they are created in different geologic processes. 

• Polymetallic Nodules – found in very deep water of 4,500 to 5,500 meters, minerals precipitate out of the water or from the sediment in a chemical reaction to form a small rock-like accretion around a “seed.” Seeds are typically a piece of bone or shark tooth. Nodules usually host nickel, cobalt, copper, manganese, and rare earths in addition to other minerals. They occur as loose, spherical rocks which are about the size of a potato.
• Seafloor Massive Sulphides –  Produced by hydrothermal vents, these tower-like structures usually contain gold, copper, silver, and zinc.  The hot water emanating from the vents and the variation of the topography associated with the towers create a highly unique and fragile ecosystem that hosts unique organisms.   The vents are normally found at depths of 1,000 to 4,000 meters.  
• Cobalt Crusts – the richest crusts are found at depths of 800 to 2,500 meters on the side of underwater mountain ranges.  These crusts contain high concentrations of cobalt, rare earth metals, platinum, and manganese.  Because these crusts are found on seamounts they often experience upwelling ocean currents that bring nutrient-filled water to shallower depths where most pelagic life exists.  Sponges and corals are often found on seamounts.   
• Seafloor Muds – similar to shallow water mineral sands, the deeper water variety sometimes hold relatively high concentrations of rare earth minerals and yttrium.  

The Critical Ocean Minerals Research Center is most focused on polymetallic nodules because research and data have demonstrated that these nodules are located in an area that is less densely inhabited than the other mineral formations (due to lower depth and less varied terrain), and the minerals can be extracted with less damage to the environment than in the case of crusts or sulfides which are attached to the ocean bottom and need to be dug or cut out of the surface for extraction.

Some environmental organizations try to group each of these very distinct resources together because doing so allows them to attribute the most sensitive environments and the most invasive of the extraction methods to all of the resources as a group.  This helps to obscure the relatively light touch needed to extract polymetallic nodules which sit unattached in the deep ocean.

What is Nodule Harvesting 

Why call it harvesting and not mining?  

Nodule extraction involves picking up small rock-like accretions that sit loose on the bottom of the deep ocean – on the abyssal plains.  The abyssal plains are located at depths of around 15,000 feet, almost three miles below the surface of the ocean.  There is no sunlight or plant life at this depth.  The dominant form of life on the abyssal plains are microbes – most too small to see with the naked eye.

Harvesting nodules is a fairly straightforward operation, though the technology involved is advanced.  A harvester or crawler is lowered to the seabed (an exercise that can take 3-6 hours) and that machine then crawls over the ocean floor, collecting some of the nodules in its path, while leaving other nodules behind.  Those nodules are then sent to a ship above through either a long pipe, or using a system of large buckets called skips.   

There are several different technologies that can be used on the collector head to capture nodules and feed them into the harvester.  The one that seems to have the most momentum and is also one of the least disruptive to the seafloor, uses a fluid dynamics concept termed the Coanda Effect.  This technology works by shooting a jet of water over the nodules which creates a pressure difference that lifts the nodules off the floor and into the body of the harvester as the machine moves past.  This system avoids putting metal into the sediment, which is part of the reason it is viewed as light touch. The nodules can then be sent into the riser pipe with some sediment and seawater, or the sediment can be separated from the nodules as the nodules are sent to a skip to await being lifted by winch.      

The extraction of nodules from the seafloor is similar in process and in impacts to those we see when a farmer runs his or her harvester over a field.  That farm harvester disturbs the soil, it compacts the soil in some places, and it creates a plume which can be blown by the wind over a wide area (wider than the plume from a seabed harvester).  Each time that harvester rolls over the field it kills some microbes and insects.  Nodule crawlers work similarly to harvesters and have similar impacts, and that is why we call nodule extraction harvesting.  Note that neither of these activities are similar to mining, which requires digging, blasting, boring, and cutting deep into the earth.  The invasiveness of mining is clearly on a different scale from that of harvesting in a farm field or a nodule field.  

In some ways the impacts of nodule crawlers are less extensive than farm harvesters.  A crawler rolls over the terrain on a set of tracks, but the impact from the heavy equipment is much less than one would expect because the buoyancy of the vehicle can be set so that it is very light at the bottom of the ocean.  Even though a crawler is heavier than a farming harvester, it may actually compress the surface less meaningfully.  Just like a farmer’s harvester rolling over a field, the underwater harvester creates a plume of sediment that is suspended for a time and will flow with the current.  But unlike the plume created by farming equipment, the bottom-water plume from a harvester doesn’t travel great distances upward or along the surface because of friction.  Water is denser than air, so it creates more friction drag on sediment particles in the water than is created on land.  In addition, sediment particles on the bottom of the ocean have a tendency to flocculate, or clump together, so that they settle rapidly.  Environmental groups focus a lot of attention on the plume created by a harvester, but the reality is that plumes created by terrestrial mining operations such as digging and blasting are far more threatening to the environment than are bottom water harvester plumes. (Fugiel, 2017) Not only do they travel further, but they contain dangerous components such as particulate matter, nitrous oxide, sulfur dioxide, and others, which can cause disease in human and animal populations that live nearby and can contaminate food sources.   Empirical data from studies on nodule harvesting have shown little impact on biodiversity or biomass in the plume zone. (O’Malley, 2023)