It’s Friday in Providence. Our crate just came in and I’m very excited. Inside are 45 two-inch diameter pipes, one meter long. Each pipe contains sediment from the bottom of an Alaskan lake and clues to the climatic and ecologic history of northern Alaska.
Sponsored by the National Geographic Society, Will Longo, myself, and our Brown University advisors, Yongsong Huang and Jim Russell spent about two weeks this spring doing Livingstone coring, through lake ice, to retrieve these sediment cores. The idea behind livingstone coring is to collect the full sediment record by incrementally collecting 1 meter of mud from the same hole. The idea of doing this when there is still ice on the lake is that we have a stable platform to work from (as opposed to a conglomoration of rafts, canoes, and anchor systems).
Livingstone coring requires a few steps:
1) Locate the coring location. Auger a hole in the ice.
2) Insert the casing. We used 4″-diameter PVC with threaded couplers. Casing helps keep core rods from bending when we push into the mud and also ensures we core into the same hole for each 1-meter section.
3) Prepare core tube, pistons, piston cable. The start of each core drive needs to be carefully measured so we know how deep in the mud each section is. The livingstone device uses a special square rod to keep the piston at the front nose of the core barrel while we push the device through slop in the hole.
4) Push it into the mud. Strong threaded rods, each ~6 feet in length, are added to the device to reach the appropriate depth. When the mud is stiff, it takes some serious muscle to push the corer down, and even more serious muscle to pull it back up.
5) Pull it up. Extrude the mud. We used a metal core barrel, so each 1 meter section needed to be pushed out into a PVC sleeve for storage and transportation.
6) Clean and repeat for the next 1 meter section. Do this until you can’t push anymore. In some cases, we stopped when we hit the ‘junk layer’ at the bottom of the sediment column, and in others, we may have been stopped by permafrost.
We have a lot of work to do now that the cores are here. The next steps are to create an age-depth model for each core and to measure a suite of organic biomarkers and other traditional paleolimnologic proxies that are indicative of past climate and ecosystems.