Übertragung von Klimasignalen in saisonal geschichtete Sedimente des Tiefen Sees bei Klocksin - Monitoring, Transferfunktionen, quantitative Rekonstruktionen
Final Report Abstract
Monitoring of Lake Tiefer See started in March 2012. The database comprises weather and lake conditions, which are uploaded to a website. Potential lake proxies were sampled in sediment traps from production in Epi- and Metalimnion (manually) and deposition in the Hypolimnion (automated trap with 12 rotated containers) and analysed (contents of organic and inorganic matter (OM, IOM) and CaCO3, stable isotopes of OM (δ13C, δ15N) and CaCO3 (δ13C, δ18O), plankton assemblage composition (diatoms, Phacotus10). Based on this data set we found new relations between monitored conditions and lake proxies. Based on process understanding of these proxy relations, they are tested using instrumental or modelled past conditions and evaluated sediment proxies. The latter are derived from the recent subannually laminated (varved) record, which currently covers varves until 2010 and proxy analyses until 2008. The tests build on an exact chronological classification (varve counting), which is supported by the recently compiled 10Be record. The record matches the expected amplitude variations throughout solar cycles 22 and 23 and underlines the large potential of 10Be in varved lake sediments for tracking the atmospheric radionuclide production signal. The observation of an inverse relation of diatom bloom and lake mixing duration in spring was tested in a defined strategy and reached the most advanced step with two novel transfer functions linking diatom silica deposition inversely with the duration of lake mixing in spring, determined by the spring temperature gradient. The transfer functions are valid for the periods 1924 - 1951 - 2008, except for the period of high nutrient load (1987 – 2004), where diatoms and silica deposition are low. The high nutrient input (1987-2004) can be related to manuring. High sediment δ15N is synchronous with high NO3 concentrations in the lake water. In context with the high δ15NNO3 of epilimnion water, the δ15N signatures of soil, trapped organic matter, and recent sediments hint at manure as the main nitrogen source of the lake. The small δ15Norg change indicates nitrification and denotes the potential to indicate human impact. In relation with that, Cyanobacteria blooms are promoted, which enrich 13C in the organic matter produced. In Lake Tiefer See, such blooms were favored during extended periods of low wind and shallow mixing and this relation became stronger with increased nutrient availability from 1970 onwards. This hints at an increased susceptibility of plankton to effects of warming. Water temperature is archived in δ18O values of the calcite sublayers of varves as indicated by a marked inverse relation of calcite δ18O with temperature, which is mediated by the mode of calcite precipitation (bio-induced by algal blooms and biogenic as Phacotus). The respective vital effects cause negative offsets from temperature-equilibrium precipitation. Resuspension during the cold season is indicated by the presence of Phacotus as it forms only at T>15°C.
Publications
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(2013) Modification of climate signals by human activities recorded in varved sediments (AD 1608-1942) of Lake Holzmaar (Germany). J Paleolimnol 50:561-575
Kienel U, Vos H, Lücke A, Dulski P, Schwab MJ, Nowaczyk NR
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(2013) Recently induced anoxia leading to the preservation of seasonal laminae in two NE-German lakes. J Paleolimnol 50:535-544
Kienel U, Dulski P, Ott F, Lorenz S, Brauer A
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(2015) Effects of changes in land management practices on pollen productivity of open vegetation during the last century derived from varved lake sediments. The Holocene 25:733-744
Theuerkauf M, Dräger N, Kienel U, Kuparinen A, Brauer A
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(2015) Solar cycles and depositional processes in annual 10Be from two varved lake sediment records. Earth and Planetary Science Letters 428:44-51
Czymzik M, Muscheler R, Brauer A, Adolphi F, Ott F, Kienel U, Dräger N, Slowinski M, Aldahan A, Possnert G
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(2016) Varve microfacies and varve preservation record of climate change and human impact for the last 6000 years at Lake Tiefer See (NE Germany). The Holocene
Dräger N, Theuerkauf M, Szeroczyńska K, Wulf S, Tjallingii R, Plessen B, Kienel U, Brauer A
