Pollen based vegetation reconstruction
Pollen, deposited in the lake sediments, are the most established tool for paleovegetation reconstruction. The signal can, however, be biased from long distance transport and erosion of fossil pollen from soils. The latter must be regarded indeed as a source for most of the ELSA cores, because most maar lakes receive a part of the sediment from fluvial inflow or local erosion gullies, but most of the pollen appear to be deposited directly from air. The main argument in this direction is the observation that the pollen from all MIS3 cores have an almost identical pollen succession (Albert et al., in prep.)
However, single pollen grains, which does not fit the general picture, must be treated careful before interpretation. This is most problematic if pollen from temperate trees appear in stadial or glacial sections. We regard these single pollen as being reworked from older soils. The Eifel pollen pattern is established for the Holocene since long, but there are no existing information of the typical vegetation succession in the time from the last glacial maximum (MIS2) back to MIS4. This time has seen 15 warm interstadial of a duration from centuries to a few millennia. The first pollen profiles from Auel and Dehner Maar has documented for the first time a MIS3 profile for the Eifel (Sirocko 2009, Sirocko et al., 2016). The early MIS3 is accordingly clearly dominated by a pronounced spruce (Picea) maximum (48.000 – 60.000 yr b2k), a finding now reproduced by 5 other records (Albert et al., in prep.). The presence of spruce continues during GI 12 and GI11, and then disappears. Small amounts of spruce during GI3 could be reworked. A synthesis of all GI3 records with decadal resolution is under preparation.
The interstadials of MIS3 all reveal grass, birch and pine. Stadial sediments are often free of pollen. This could represent a landscape free of vegetation, e.g. during the Heinrich 4 event, or the pollen have been dissolved. This must have occurred for most of the time between 25.000 – 14,700 yr b2k. Pollen are extremely hard and cannot be dissolved by any acid, but they deteriorate as soon as they are exposed to oxygen. This must have been the case in the sediments of the LGM, when temperatures reached below 4°C even in the summer nights and cold, oxygen rich surface water sunk to the lake basin because of its high density. The glacial ELSA pollen and macroremain record (see below) suggest for the Last Glacial Maximum the continuous presence of grass and moss, and some birch during the warmer phases.