Key components of marine mineral-related characterization studies learned from collaborative research on mineral systems in the Southern California Borderland

Interest in independent marine mineral-related ecological studies has recently risen significantly as attention to the resource potential of marine minerals has increased and activities in some regions are forecast to transition from exploration to exploitation. To design studies relevant to marine mineral systems that may be targeted for exploitation, both geological and biological expertise is needed to write proposals, choose study regions of interest, and design experiments. On two recent expeditions to the Southern California Borderland, researchers from Scripps Institution of Oceanography and the U.S. Geological Survey collaborated on such a study using ROVs to investigate fauna associated with ferromanganese crusts and phosphorites. The project experimental design will determine correlation of multiple size classes of fauna and microbes with each of the mineral substrates to inform potential biological associations with mineral textures, surface area, mineralogy, and chemistry. The primary challenges for this work, that are consistent with other studies where marine mineral deposits are not well characterized, are mineral distribution and the ability to collect representative samples. Most regions of interest for mineral occurrences are defined either 1) based on dated research with spatial resolution that may not be relevant to biological distributions and ROV operations or 2) based on oceanographic and geographic criteria but that has usually not been ground-truthed. Thus, mineral occurrences may be sparser than expected or unlocatable (phosphorites), or mineral distributions may be thinner than the deposits of economic interest globally (crusts). In addition, collection by ROV biased sampling to rocks that were loose and of collectable size that did not represent pavements and large in-place features that can host thicker ferromanganese crusts. The small number of samples accommodated on ROVs can also lead to sample bias toward rocks with more visible fauna based on the desire to sample biodiversity, which may not be representative of all rocks in the region. While challenges remain for the study of biological and geological baselines in marine mineral-rich regions, collaborative studies such as these help determine best practices for future marine mineral characterization studies. Interest in independent marine mineral-related ecological studies has recently risen significantly as attention to the resource potential of marine minerals has increased and activities in some regions are forecast to transition from exploration to exploitation. To design studies that are relevant to marine mineral systems that may be targeted for exploitation, both geological and biological expertise is needed to write proposals, choose regions of interest for study sites, and design experiments. On two recent expeditions to the Southern California Borderland, researchers from Scripps Institution of Oceanography and the U.S. Geological Survey collaborated on such a study using ROVs to investigate fauna associated with ferromanganese crusts and phosphorites. The project experimental design will determine correlation of multiple size classes of fauna and microbes with each of the mineral substrates to inform potential biological associations with mineral textures, surface area, mineralogy, and chemistry. The primary challenges for this work, that are consistent with other studies where marine mineral deposits are not well characterized, are mineral distribution and the ability to collect representative samples. Few regions of the global ocean are well-characterized in terms of mineral density and composition, such as the Clarion-Clipperton Zone, whereas most regions of interest for mineral occurrences are defined either 1) based on dated research with spatial resolution that may not be relevant to biological distributions and ROV operations or 2) based on oceanographic and geographic criteria but that has usually not been ground-truthed. Thus, mineral occurrences may be sparser than expected or unlocatable, as was the case for phosphorites in the Southern California Borderland; or, mineral distributions may be thinner than the deposits of economic interest globally, which was the case for ferromanganese crusts collected on these expeditions. In addition, collection by ROV biased sampling of rocks that were loose and of collectable size that did not represent pavements and larger in-place features that can host thicker ferromanganese crusts. The small number of samples accommodated on most ROVs can also lead to sample bias toward rocks with more visible fauna based on the desire to sample biodiversity, which may not be representative of all rocks in the region. While challenges remain for the study of biological and geological baselines in marine mineral-rich regions, collaborative studies such as these are helping to determine best practices and maximize knowledge gain for future marine mineral characterization studies.