Variations on a theme of gravity coring: K-B, Glew and TechOps corers with core extrusion and high-resolution vertical sectioning of shallow aquatic sediments

Abstract

The goals of gravity coring for environmental limnological studies are to obtain an undisturbed sample of bottom sediments, preserve the sediment-water interface, maintain the original water content, and maintain the original vertical distributions of chemical, mineralogical, and biological constituents. Gravity coring devices are designed to drive core tubes or cylinders vertically into the sediments and withdraw them back to surface intact. Examples of open-barrel or gravity corers that are used within the Northern Canada Division of the Geological Survey of Canada are a modified Kajak-Brinkhurst (K-B) corer, Glew (and modified Glew) corers, and TechOps corer. Although the principles of operation are similar, each device has advantages and disadvantages that should be taken into consideration for the requirements of each specific lake sediment study. Shallow lake cores ( ?1m) taken by gravity coring methods typically require extrusion and sectioning on-site because of the high water content and likelihood of core disturbance during handling and transport. Zorbitrol (a water binding agent) can fix most gravity cores sufficiently to enable gentle transport back to the laboratory; however, it is a source of contamination that would preclude any subsequent geochemical analyses. For high water content cores, vertical extruders are the most effective. There are three components to vertical core extrusion and sectioning: maintenance of the core in a vertical position, advancement of the core material through the core tube so that sections can be expelled, and removal of the extruded section that can be transferred to sample containers. Three examples of vertical core extruding and sectioning devices portable for field use are available: one designed for use with the K-B corer with fixed interval sections and two for which the operator can define the sectioning intervals.