Simple Technique for Fine-Scale, Vertical Sectioning of Fresh Sediment Cores

摘要

Biogeochemical processes occurring at the sediment-water interface and within the very near-surface sediments are known to affect or control what occurs above or below the sediment surface. Studies of these phenomena often require vertical sampling of the variables of interest over very fine (e.g., millimeter) spatial scales. Existing techniques for such fine-scale vertical sectioning of fresh sediment cores were developed primarily for studies of porewater chemistry and of the distributions of meiofauna or microbes, where only very small samples (cores < or = 3.0 cm in diameter) are required. In most cases, the vertical sectioning technique requires subcoring a much larger sediment sample (e.g., a box core) after it is taken. This potentially introduces error (contamination between layers) when sectioning at millimeter intervals, because near-surface sediments within the sample may mix vertically or horizontally on transit to the water surface. We here describe a technique for fine-scale vertical sectioning of fresh sediment cores that operates on the same general principle as many previously described core extruders but that can be used on larger cores. We also describe a technique for subcoring a box core while it is taking a sample, to avoid errors which may be introduced by subsampling on deck. The precision (in terms of vertical positioning, contamination between adjacent layers, and smearing) of this extruding technique is discussed, based on results of laboratory calibration experiments using muddy sediments. Reprints. (AW)