OOS 21-3 - Tracing deep-sea mining waste into mesopelagic fauna in the eastern tropical North Pacific using amino acid isotope analyses

Interest in deep-sea mining for abyssal polymetallic nodules containing cobalt, copper, manganese and nickel—elements used to produce batteries that power electric vehicles—has risen dramatically in the last decade. Over 1.5 million km2 of the seabed are currently under exploration licenses by mining companies. Deep-sea mining could pose significant risks to deep midwater (mesopelagic) organisms. These ecosystems represent >90% of the biosphere, contain enormous biomass, and play key roles in carbon export and nutrient regeneration. However, the ecology of mesopelagic organisms in areas of mining interest remain poorly understood. Although mining strategies vary, many involve a seafloor collector vehicle with a vertical pipe that transports ore and sediment to a surface vessel, shipboard separation of ore from sediment and discharge of that sediment at midwater depths. The goal of this work is to use amino acid compound specific isotope analyses (AA CSIA) to track organic particles in mine tailings into mesopelagic fauna. We have analyzed the isotopic compositions of amino acids in size fractionated particles and zooplankton collected throughout the upper 1500 m of the water column during baseline cruises in Spring and Fall 2021 and of particles collected during a mining test cruise in Fall 2022. All cruises were in a potential mining region in the Clarion-Clipperton Zone of the eastern tropical North Pacific Ocean. Comparison of source and essential amino acid isotopic values of particles and zooplankton can identify the particle sizes forming the base of the food web. Results of AA CSIA of particles and zooplankton collected at midwater depths show that all particle sizes may be important in forming the base of mesopelagic zooplankton foodwebs. However, the δ13C values of lysine of the 2.0-5.0 mm size class of zooplankton strongly overlap with that of the 0.7-6 µm particle size emphasizing the importance of this particle size class to these larger zooplankton. Preliminary AA CSIA of particles in discharged sediments show that some essential amino acid δ13C values are different from natural particles and may be used to trace these anthropogenic particles into mesopelagic zooplankton; nitrogen isotope analyses are ongoing. The International Seabed Authority (ISA) is developing mineral exploitation regulations to manage deep-sea mining. The ISA is required to ensure effective protection of marine environments, including deep midwater ecosystems, from harmful effects of mining-related activities. Our work is helping develop guidelines to minimize environmental impacts from discharged mine waste on mesopelagic metazoan communities.