The overall goal of this millimeter scale sediment extrusion method, is to fully characterize events recorded in the sedimentary record by improving sampling resolution. This method can help answer key questions in the fields of oceanography and limnology, such as which events are recorded in the sedimentary record at the annual, to sub-annual scale, and how those events are manifested. The main advantage of this technique is the improvement of sample resolution.
Research technicians from my lab, Bryan O'Malley, and Erika Fridrik, will be demonstrating the procedure. Collect a sediment core that is a meter or less. Insert a plastic puck with the same diameter as the tube into the bottom of the core.
Now either immediately proceed with extrusion, or pack up the core. To pack it, insert a second puck into the other end of the tube, and gently press down, until the puck is just above the sediment interface. Next, cap the ends of the tube, and seal the caps with electrical tape.
Then, label the top cap with the sampling information, and store the core frozen, or at room temperature, depending on the analysis. Begin with preparing labeled sub-sample vessels. Select appropriate vessels based on the type of analysis.
Also have sterilized protective gear at the ready. Then, assemble and sterilize all the necessary cutting implements. If the core has been stored or preserved, remove the bottom cap first using a blade.
Then, transfer the core to the extruder using the vacuum in the tube to hold the core in place. Gently set the core tube onto the piston, and fasten down the core using the clamps. Now, ensure that there is at least five centimeters of core tube above the uppermost clamp to fit the sampling collar.
Next, remove the top cap and place the sampling collar on top of the core tube. Make the collar flush with the uppermost extent of the tube, or the sample may be lost. Proceed by removing the water above the sediment by aspiration.
Keep a sample if desired. Next, turn the piston to align the surface of the sediment with the surface of the sampling collar. Now, set the sample size, a full piston rotation moves the collar two millimeters.
The rig is outfitted with an acrylic plate that has an inner diameter of the sampling collar. Use this plate to make the initial sample cut. Then, slowly move the sub-sample towards the edge of the sampling collar, and get a collection vessel ready.
Then, push the sediment into the sampling vessel. Next, clean up the remaining sediment around the collar, plate, and any other surfaces, and transfer it to the collection vessel. The most difficult aspect of the procedure is ensuring that you sample the entire mass of the sediment from each sample.
So care must be taken using the different implements to ensure that all of the sediment is transferred from the sediment core to the container. Before proceeding, use deionized water to clean off the sampling tools and sampling collar, and then sanitize these implements. After sealing the vessel, continue collecting all the required sub-samples in the same manner.
After all the samples are collected, reset the extruder. Place a rubber band around the piston near its base for the most stability. Then, stretch the rubber band around the head of a drill.
Now, rotate the piston using a low drill speed until it reaches the desired height above the base of the extruder. Aquatic sediment cores were collected in December 2010 and sampled in two millimeter increments for the surficial 15 centimeters. The timing of the Deepwater Horizon Event was determined using a paired, short-lived radio isotope geochronology.
Several parameters were analyzed in the sub-samples. With the Deepwater Horizon Event, there were dramatic increases in the total aliphatic concentration, and decreases in the total benthic foraminiferal density. There were also changes in redox sensitive metal concentrations, suggesting less surface oxygen.
The same factors were also analyzed at the centimeter scale. At this scale, the changes in the aliphatic concentrations, the changes in redox sensitive metals, and the changes in benthic foraminiferal density were all diminished by coarser sampling. After watching this video, you should have a good understanding of how to extrude aquatic sediment cores at millimeter resolution.
Once mastered, this technique can be done in about two to four hours, depending on the sampling resolution and the length of the core. Following this procedure, many physical, chemical, and biological analyses can be performed on the sediment sub-samples, and after its development, this technique paved the way for researchers in the Gulf of Mexico to fully document sedimentary oil deposition and its subsequent effects following the Deepwater Horizon Event. While this procedure has primarily been applied in a marine oil spill context, it has brought applications throughout the fields of oceanography and limnology.
