Small fish, shrimps, and squids (micronekton) at midwater depths form deep ocean sound scattering layers that can undergo diel vertical migration (DVM), a coordinated movement up into shallow waters to feed at night and descending down several hundred meters during the day. These animals provide critical ecosystem services as a forage base for commercially important top predators and charismatic marine mammals and contribute to carbon sequestration through their active vertical migrations. Yet, many of these animals remain understudied and it’s unclear how the patterns and behaviors of midwater populations will change in response to environmental disturbances like deep-sea polymetallic nodule mining. This activity may commence as early as 2022 in the Clarion-Clipperton Fracture Zone (CCZ)- an area in the central North Pacific Ocean that spans a width equal to the continental United States. How might deep scattering layers be affected by mining-related sediment plumes in the water column? How do these layers vary naturally across the CCZ prior to mining? This poses a major gap to our knowledge considering the significant ecological value of midwater populations.
The CCZ currently holds mining exploration claims by 17 countries, regulated by the International Seabed Authority (ISA).
The mining process for polymetallic nodules involves large machines that will effectively scrape the seafloor, lifting nodules and fine clay mud up through a pipe to a platform at the surface. The excess seawater and sediments will then be expelled back into the deep ocean. This will generate sediment plumes that could extend up to 200 km away from each mining site, affecting midwater organisms, possibly for years, as particles slowly settle back to the seafloor. Seafloor studies are underway, but no one has evaluated the potential impacts of extensive sediment plumes to water column communities.
In August 2018 we held an international workshop at the University of Hawai’i, which brought together scientists and mining contractors to discuss the potential midwater impacts of deep-sea mining and propose strategies to mitigate harmful effects. This workshop highlighted the clear necessity for baseline biological information across the region, including knowledge about the biodiversity, abundance, and migratory behaviors of midwater communities. Our research is currently working to describe the vertical dynamics of midwater organisms across the vast region of the CCZ.
Using active bioacoustic data collected from the CCZ we are monitoring the activity of midwater communities. This technique offers a reliable method to track depths and intensities of organisms in the water column before, during, and after mining operations. We hope to fill gaps in our spatial coverage of the region with additional bioacoustic data collected by Saildrone, a new cutting-edge technology for high resolution ocean data.
Our goal is to provide scientifically based recommendations to ISA policy makers regarding the natural environmental drivers of DVM, the potential alteration of these behaviors by mining activities, and the structure of mining operations (such as discharge depth).
Contrary to environmental catastrophes like the Deepwater Horizon oil spill in the Gulf of Mexico in 2010, we have the rare opportunity here to study these baseline conditions and potential impacts BEFORE a major disturbance event.
Check out some of our lab's recent work on seafloor ecosystems in the CCZ featured in Nature News: