Geochemical evidence for holocene palaeodischarge variations in lacustrinerecords from the Westeifel Volcanic Field, Germany: Schalkenmehrener Maar and Meerfelder Maar

Various chemical elements (Fe, Mn, U, Mo) can be transported in both dissol ved and solid form and then deposited into lakes. Geochemical profiles of t hese elements in lacustrine records;re therefore potential palaeoclimatic p roxies since there should be a positive correlation between discharge from the catchment and dissolved element input. Flux rates for the dissolved inp ut of uranium Ul(t) and the total allochthonous minerogenic deposit were ca lculated for an annually laminated sediment record from the Lake Schalkenme hrener Maar (SMM). Calculated UI(t) values were critically examined with th e help of monitoring data (hydrochemistry, soil chemistry) from the modem M eerfelder Maar (MFM) catchment. The calculated Ul(t)-profile and the variat ion of varve thickness show a corresponding pattern. The palaeoproductivity of Lake SMM with respect to diatomaceous matter was clearly controlled by the discharge from the catchment. The deposition rate of allochthonous mine rogenic matter, which received significant aeolian contributions from a rem ote source during the early Holocene, has been found to correlate with the Ul(t) values. The deposit of dust on the lake surface is undoubtedly influe nced by rainfall events during which fine particles are washed out from the atmosphere. A higher discharge of groundwater from the lake's catchment is indicated at around 10 200 (D1), 8500 (D2), 7150 (D3), 6000 (D4) and betwe en about 4050 and 3300 varve years BP (D5), Significantly lower discharge w as obtained for periods around 11 000, 9500, 5000 and after about 3050 varv e years BP. There are several indications of a lowering of the SMM lake lev el between 8100 and 7300 varve years BP. A drier climate can, therefore, be suggested as likely far this period. In addition to three early Holocene p eriods, which display an increase in element input into Lake MFM (thus supp orting the positive discharge indications D1, D2, D3 from the SMM sediment profile), a general increase of discharge since the Neolithic period due to anthropogenic forest clearance can be inferred from the MFM sediment recor d.