Coring Guidelines for Chronological Dating Profiles
If you are first timer, the below tips may be of use to you!
Choosing a water basin and coring
1. Select a water body that has a single basin. Bigger lakes tend to have better sediment records but lower sedimentation rates. Small lakes can have excellent sediment records that track changes very well and reasonably higher sedimentation rates. Shallow lakes are prone to mixing. Big long narrow lakes have a large fetch and this may cause sediment mixing. Site selection is crucial, do you homework before heading out.
2. Background research: get hold of a bathymetric map. Determine if others have done sediment coring on the lake so you can gauge the sedimentation rate and ultimately determine how long your core should be for 210Pb dating. Make sure you keep some deep sediments for determining background for dating. We can only date back 150 years using 210Pb. For example a core from a mid sized lake with a sedimentation rate of 0.015 g/cm^3/yr would require a 30 cm long for dating; rates of 0.04 g/cm^3/year would require a core of 50 cm for dating. However, always err of the side of caution and add an extra 10cm so as to make sure you meet the background requirements for 210Pb dating.
3. Always core in the deepest location in the basin, if possible. If you have no bathymetry, then try to core in the centre of the water body. Be sure to examine the shorelines, do they drop off quickly on one side and very shallow in other areas? Adjust your coring location accordingly.
4. Do not core in areas near the inflow and outflow of the water body, the sediment record will be mixed in these areas.
5. Ensure your boat is not drifting while coring, the corer should go in straight. Always anchor and wait for the craft to stop drifting.
6. Always try to take a long core and keep the whole core.
7. Do not “lump” together intervals, for instance 0-5, 6-10, 11-15 and so on … this cannot be dated.
8. Please try not to combine cores. For instance, 0-10 cm from 1 core and then 10 - bottom from another core. This is not ideal and the 2 cores can have very different sediment focusing factors. If you must, please align your cores using elemental analysis, LOI, or XRF. ATTENTION: Chronos Scientific will not make this alignment for you.
9. Record the inner diameter of your core tube, date of coring, latitude and longitude, length of core and the depth of the lake where you cored.
10. Sectioning the core, typical sections are 0.5 or 1 cm thick. Please record the total interval wet weight for each slice and determine the % water for your intervals. We require this data along with the parameters listed in # 9.
If you are working on very large lakes, remote locations like Antarctica, or above the Arctic Circle, your cores will have very low sediment accumulation rates and thus your core should be sectioned at 0.5 or 0.25 cm thickness for obtaining a good profile.
Peat tends to accumulate faster than lake sediments, you need a very long core to date peat. Intervals tend to be 1 cm each when sectioned due to the higher accumulation rates. When submitting peat cores, keep the top active layer of the peat as this represents the current atmospheric concentration of 210Pb and is the starting point for our calculations. This sample should be treated as all the others, freeze-dried and homogenized. Please record the collection date, inner diameter of core tube, total interval wet weight, % water, latitude and longitude. Do not label as plant material, we do not have plant import permits.