Design and Testing of a Hadal Sediment Sampling System

Abstract

Sediment cores are conventionally gathered to collect data on seabed chemical and mineral composition. These samples are important in determining the health of the surrounding environment and, if sediment layers are preserved, assessing the environmental history and trajectory of our ocean floors. Over the last few decades, some attempts to collect sediment core samples have been made from as deep as the Mariana Trench, which contains the deepest known point on Earth’s surface at 11,000 meters [1] [2]. However, the hadal region remains one of the most underexplored areas of our oceans [3]. Working in conjunction with Inkfish, a submersible technology company, we developed a deep-sea sediment core sampler that will travel to the Mariana Trench aboard one of Inkfish’s submersible landers and will collect four inches of sediment in ambient pressures of 110.32 MPa [4]. The first phase of this project was to design and fabricate a prototype sediment core sampling device. We designed an entirely mechanical sampler because underwater actuators suitable for use in hadal conditions are difficult to source and require additional communication and power resources. Furthermore, our device aims to preserve the layers of the sediment core samples as the lander ascends to preserve relative time scales within the sample. The next phase involved testing the functionality of different subsystems of our device. In this paper, we considered two different sediment collection apparatuses and one-way valves for our collection tube. We performed field testing at the Charles River in Cambridge, MA to assess which apparatus and valve combination would provide the best results based on the volume of sediment collected and retained. Building on our mechanical proof-of-concept, we improved the design and fabricated a second iteration prototype for 2-3 km depths. In this version, we addressed the two main weaknesses of the initial proof of concept design: substantial friction during sliding and the complexity of assembly and maintenance due to the numerous parts. Lastly, we engineered a deployment system that made our device compatible with Inkfish’s lander deployment procedure. The deployment system was designed to lower the sediment sampler device from within the bay to below the lander once the lander was submerged in water. In early October, the improved sediment sampler and the deployment system were tested during an engineering expedition near the shores of Tonga. Ultimately, we believe that our sediment sampler presents a viable purely mechanical solution to collecting deep-sea sediment from profoundly unexplored areas at hadal depths like the Mariana Trench. Our sampler can easily be mounted onto any surface where it would touch the ocean floor, requiring no electronics or controls. Though we were constrained by the particular seafloor lander used by Inkfish, the size of the sampler is scalable, allowing both the sample diameter and depth to be adjusted for a given mission. By making these sediment samples more accessible, we believe we will have an impact across a number of marine research areas.