Deep-Sea Sediment Sampler for Hadal Depths

Sediment cores are gathered to collect data on seabed chemical and mineral composition. This paper reviews the process of designing and testing a purely mechanical sediment sampler for use at hadal depths. These samples are important in determining the health of the surrounding environment and give us insight into what organisms currently live or have lived on or under the seabed. Sediment samples are relevant to many fields of research, including marine archaeology, biology, ecology, geology, and climate science. Over the last few decades, 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]. The environmental history and trajectory of our ocean floors are not well understood, and deep sea sediment cores are crucial in filling this gap. 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 at ambient pressures of 110.32 MPa [3]. The first phase of this project was to design and fabricate a prototype sediment core sampling device. This prototype had to fulfill several design requirements that resulted from environmental conditions, lander constraints, and sample condition specifications. 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. The extreme pressure in the Mariana Trench imposed restrictions on the materials we could use and led our design to incorporate low-precision interfaces. Additionally, the sediment core sampling system is limited in size and weight to avoid interfering with the functionality of seafloor landers. Most importantly, the layers of the sediment core samples must be preserved and secured as the lander ascends to preserve relative time scales within the sample. Our purely mechanical sediment collection system consists of the collection tube subsystem, re-sponsible for collecting and retaining the sediment, and the frame subsystem, whose objective is to facilitate insertion and retraction of the tube from the seafloor. 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 in 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. Additionally, we tested the frame subsystem and evaluated the performance of the spring pulley system based on reliability and consistency. 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 on a number of marine research areas.