"Typical" vibracores. A typical vibrocore, if there is such a thing, is a layered column of various natural sediment types, possibly including silt, sand, gravel, clay, shells and organic matter. Contaminated sediments, as found in many industrialized harbors, can include a broad range of man-made substances as well. The detailed structure and contents of the core will be apparent only after the core is cut open and the interior is exposed. Here's a good example of a core containing polluted and natural substrates.
Intact vs. disturbed cores. Most vibracores can be characterized as relatively "undisturbed" cores, except for a narrow zone along the core tube wall and the upper few watery inches of silty cores, which is resuspended by the vibration. In the firmer sediment layers below that, the natural core structure is largely intact. Exceptions to this can occur when sediments are full of gas bubbles, some of which escape the core tube, causing some layers to be compressed. Rodding can also occur in very soft or oily sediments, when the core tube stops collecting material as it continues penetrating. Finally, the core may be disturbed during withdrawal if the lowest material in the tube is very slippery or cohesive, and flows back out through the catcher. In order to detect these sorts of problems, the length of tube penetration can be recorded and then compared to the actual length of the core.
Replicate core samples. In large deep bodies of water, sediment quality may vary little over great distances. However, in coastal or inland waters sediment profiles can be highly variable. When multiple cores are collected at the same location, surprising differences in structure are sometimes observed. In high-energy environments like rivers and streams, sediment character can change abruptly due to natural sorting of different materials. In disturbed environments like dredged harbors, sediment strata may be reshuffled any number of times. Not surprisingly, adjacent core samples can look significantly different. When studying levels of contaminants in these sediments, it is important to realize that most of the measured differences between duplicate samples are due to sample variability, not analytical error.
Vizualizing core data. When vibracores are collected at multiple sites and sub-sampled for analysis at multiple intervals, the result can be a three-dimensional data set. There are various ways to represent such 3-D data in order to visualize how constituents of the sediment are distributed in space. For example, if the goal is to show how different pollutant concentrations vary in a core from one site, a tandem bar graph is one simple way to represent that. On the other hand, an icon bar graph can be used to represent profiles of a single pollutant at multiple stations, as located on an accompanying map. A simpler version of that uses color coded dots, instead of bars, to represent different ranges of concentration at several locations on a map. With enough data of this sort, a color-coded contour map can be generated with contouring and mapping software. Concentration contours can be depicted for different levels or zones in the cores. If the data density is adequate, 3-D data models can be produced. Some versions of these visualization models can be manipulated on computers to explore different scenarios of pollutant remediation through dredging or other means.
