A near field study of sediment plumes for a pre-prototype nodule collector trial in the abyssal Pacific Ocean

Abstract

Observations from multi-platform monitoring of the sediment plume created during a pre-prototype deep-seabed nodule mining collector trial in the Pacific Ocean are presented and discussed. A combination of fundamental and geophysical fluid dynamics theory, as well as built-for-purpose numerical modeling, is used to interpret the observations. In turn, the implications of the interpreted observations for both monitoring and modeling of deep-seabed mining sediment plumes are considered. The observations occurred over a wide range of spatial and temporal scales, obtained through collector-mounted instruments within the mining area, instrumented moorings hundreds of meters away from the mining activity, and instrumented AUV operations at distances of hundreds to thousands of meters away from the test site. At each scale, interpreting plume observations is non-trivial because of the complexity of plume dynamics. Through interpretation of the observations, we exemplify the challenge of using plume monitoring or modeling alone in order to create a complete, non-ambiguous representation of the plume that is spatio-temporally resolved. Our analysis shows that an effective strategy that encompasses monitoring technology, deployment configuration, data interpretation, modeling approach, model parametrization, and model validation must be informed by plume physics at all levels. Furthermore, non-hydrostatic physics are instrumental to the evolution of plumes, and thus plume modeling for deep-sea mining sediment plumes needs to resolve non-hydrostatic processes.