HR: 1340h
AN: PP43A-0591    [Abstracts]
TI: Seasonal Climate Dynamics Inferred From High Resolution Modern Diatom Data
AU: * Hausmann, S
EM: Sonja.Hausmann@cen.ulaval.ca
AF: Center of nordic studies, Laval University, Quebec, G1K 7P4 Canada
AU: Pientiz, R
EM: Reinhard.Pienitz@cen.ulaval.ca
AF: Center of nordic studies, Laval University, Quebec, G1K 7P4 Canada
AB: keywords: seasonal, sediment-traps, diatoms, lakes To understand and predict future climatic changes, we study past climate dynamics, using subfossil diatoms deposited in lake sediments. A training set consisting of surface lake sediments integrating diatom assemblages over recent years is the classical approach to reconstruct past environmental conditions in palaeolimnological research. However, not only annual temperatures and average limnological conditions are relevant but also seasonal thermal and limnological variability, as evidenced by spring and autumn diatom blooms. As high temporal resolution plays an important role in understanding the diatom ecology and its use in palaeolimnological reconstructions, we investigated diatom succession and seasonal limnological variability on a bi-weekly basis using sediment traps. In order to better understand the impact of climate on the seasonality of diatoms we studied 6 lakes distributed over an altitudinal gradient from 330 to 950 m a.s.l., in the Laurentides Provincial Park region north of Quebec-City, Canada. Multivariate statistics was applied to explore the main biological and limnological patterns in the modern data, revealing that the climatic gradient explained most of the biological variance. One advantage of sediment traps is that, compared to surface sediment samples, the time of deposition is exactly known, thus changes in environmental variables can be better related to shifts in the biological assemblages. From one of the study lakes, at 830 m altitude, a sediment core was taken. Fossil diatoms of the past 9500 years were analysed at high resolution (about 15 years/sample) and modern seasonal diatom distribution was used to interpret changes in fossil diatom assemblages. From ca. 9.5 until ca. 8 ka cal. BP, spring bloom species that are presently found in the low altitude lakes occurred with ca. 30%, whereas an autumn bloom species typical of autumnal diatom communities in the highest elevation lake occurred with 50%. In the more recent sediments of the core, autumn bloom taxa typical of the lowest altitude lakes increased upcore to 20%. These patterns could be related to a cooling of spring temperatures and warming of autumn temperatures during the Holocene, which are in agreement with changes in spring and autumn solar insolation patterns of the Milankovitch orbital cycles. Contrary to the surface sediment sample technique, our novel approach using sediment traps with high temporal resolution of modern data may allow inferences about past seasonal climate dynamics.
UR: http://www.cen.ulaval.ca/paleo/Sonja/Hausmann.html
DE: 1845 Limnology
DE: 1620 Climate dynamics (3309)
DE: 0315 Biosphere/atmosphere interactions
DE: 0400 Biogeosciences
DE: 0644 Numerical methods
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting