What is deep-sea mining?

When people talk about deep-sea mining, they are referring to the process of retrieving metal-rich ores from the seabed at depths of over 200 m, but usually 2-5 km.

There are three main types of deep-sea mining deposits:

• Polymetallic manganese nodules – found on large flat areas of the deep sea floor where metals can slowly precipitate around a nucleus like a shark tooth (4 – 6 km)

• Seabed massive sulfide deposits – formed around hydrothermal vents (1 – 4 km)

• Cobalt-rich crusts – form on areas of elevated bathymetry with no sediment covering (600m – 7 km)
  
  

My research focuses on the polymetallic manganese nodule mining, which seems likely to be the first type of deep-sea mining to occur commercially.

Why do people want to mine these nodules?

These potato-sized nodules are rich in cobalt, nickel, copper, rare earth elements (REEs) and other valuable metals. The electric vehicle market is booming, and expected to increase continually over the coming years.

As well as electric vehicles, there is a geopolictical aspect to the growing demand for deep-sea mining. "Critical Minerals" strategies from countries such as the United States and Canada list REE as a priority. However, currently China has the main processing pipeline for these metals which is seen as a threat or political lever by countries that are reliant on their supplies.

What are the environmental worries?

To collect the nodules, a remotely operated vehicle (ROV) picks up and sifts through the top 2–5 cm of sediment, producing clouds of fine-grained clay particles. 

These clouds (also known as collector "plumes") increase suspended sediment concentrations in the water column, which affects filter feeders, and can bury and smother sessile seafloor organisms.

As well as environmental stresses caused by suspended and redeposited sediment, the clouds may increase local concentrations of heavy metals including copper, cadmium, lead, and zinc. 

Both the sediment and dissolved metals will be transported by ocean currents, and the extent of their environmental stresses are not yet well-characterized.

How does my research relate to deep-sea mining?

If we want to know how deep-sea mining will affect the oceans and ocean life, we need to understand how the clouds produced at collection sites will change the local environment, and how they spread from the site.

My research uses laboratory experiments to replicate deep-sea mining sites and investigate how fine particles will travel from the mining vehicles and how they will settle. 

We can use this physical information of cloud behaviour to learn about how environmental stresses will spread under different conditions, to aid ecologists in predicting how deep-sea life will respond.

In-situ studies of plume behaviour are incredibly expensive and difficult to monitor. Laboratory studies allow us to isolate specific plume source terms and release behaviours in a controlled environment in order to investigate the physics that controls these flows. In turn, these physical insights are implemented in numerical models that predict sediment dispersion.