The WEVF shows 7 open maar lakes, which reach water depths below 20 m. These are Pulvermaar, Meefelder Maar, Holzmaar, Weinfelder Maar, Gemündener Maar, Schalkenmehrener Maar and Ulmener Maar. 3 other maar structures are covered with shallow ponds from anthropogenic activity; these are Jungferweiher, Immerather Maar and Eichholzmaar. The ELSA Project has focused its drilling on Holzmaar, Schalkenmehrener Maar and Ulmener Maar. Sediment cores are taken from a platform with an UWITEC drilling equipment, operated by Klaus Schwibus and Frank Dreher from Mainz University. The sediments of the last millennium have been drilled with a freeze coring system.
Cores to cover the Holocene are drilled with the UWITEC system in 2 m segments from the same platform as the freeze cores. The Holocene sediment is often compacted by the drilling processes, which explains that a core from 0-2 sediment depth is not entirely 2 m long, see core photo from Holzmaar. The next 2 m segment is then taken at the same borehole from 2-4 sediment depth. It remains an open question if sediment loss occurred between individual segments. Respective proxy time series have to take these drilling disturbances into consideration. We thus cored for ELSA-20 always overlapping cores to check for sediment loss – and sampled the most complete core.
The ELSA-20 section from today back to 1000 AD is perfectly varved in two freeze cores from Schalkenmehrener Maar. The uppermost meter is dated with 210Pb and 137Cs; the second meter shows the 1342 flood layer as a 10 cm-thick layer. This layer is usually the thickest of all medieval flood layers, but in particular well distinguishable by a high amount of debris from plants, which were analyzed in detail by Herbig & Sirocko (2012). The well visible flood layers are documented also in all cores from Holzmaar and used to continue the ELSA-20 record from SMfreeze into HM4. This core has a twin record drilled with a 1 m offset at the same location, to document that HM4 is indeed continuous. HM4 reveals the distinct Laacher See Tephra layer with its established age of 12,880 yr b2k and reaches further back to the late glacial initial warming at 14,690 yr b2k. This warming is documented in the lake sediments by an increase of Corg and phosphorus at the same level where first pollen of juniper and grasses occur. The same environmental change is observed in the late Pleistocene sections of cores AU3 and AU4 and is thus used to extent the ELSA-20 record without any gap into the last glacial maximum times.