The hydraulic piston corer as a tool for the sampling of unconsolidated sediments: its history, applications, limitations, and potential

Abstract

Seafloor sediment samples have been collected since antiquity, but techniques for deep-water sediment coring were not developed until the twentieth century. Gravity-driven coring devices were the state of the art until the hydraulic piston corer (HPC) was introduced by the NSF-sponsored Deep Sea Drilling Project. Since its operational debut in 1979, the HPC has provided a new dimension in the study of soft marine sediments. Core recovery and quality in the uppermost tens to hundreds of meters of the marine sediment section are vastly superior to the rotary-drilled equivalent. High-resolution stratigraphy has come of age with the availability of continuous and undisturbed core samples, and it has grown to be a discipline of great importance in marine geology and paleoceanography. A "hybrid" system, the HPC utilizes the principles of the oceanographic piston corer and temporarily converts the drill string to a hydraulic accumulator and source of energy to drive the core barrel into the sediment at the bottom of the borehole. The system is compatible with the wireline retrieval system of its predecessor, the rotary core barrel system. As a specialized sampling system, the modern HPC (known as the APC) is subject to limitations imposed by sediment properties and environmental conditions. In general, the boundaries are recognized, and satisfactory results beyond those limits can be sustained with alternative coring systems. Resolution of some inherent mechanical limitations still is needed to reduce flow-in core disturbance and to enhance penetration and depth capabilities. Complete stratigraphic sections currently are collected only by coring multiple holes with overlapping depth intervals. More work is needed to minimize factors causing systematic loss of section and axial expansion of cored material. The considerable advantages of HPC coring in soft subaqueous sediments currently are unavailable to investigations outside the Ocean Drilling Program because of high costs associated with fabricating and deploying the coring system. A case can be made for a coordinated effort to make an APC system available for use on lighter drilling platforms. Potential applications exist in the fields of paleolimnology, EEZ assessment, coastal environmental monitoring, limited-depth paleoceanography, and others.