HR: 1330h
AN: B12B-0786    [PDF]
TI: Trace Elements in Diatom Frustules as a Paleochemical Proxy
AU: * Jaccard, T
EM: tomjaccard@urbanet.ch
AU: Ariztegui, D
EM: daniel.ariztegui@terre.unige.ch
AB: The calibration in modern environments of the different proxies used in any paleoenvironmental study is a critical aspect leading to more realistic reconstructions of past conditions. Diatoms are among the main contributors to phytoplankton blooms in both lakes and oceans. They have been widely used as ecological and biogeochemical indicators of present and former environmental conditions. During the formation of highly ornamented cell walls or frustules, these algae take up dissolved silicic acid from the water to precipitate it as opaline silica that is further preserved in the sediments. Recent investigations have shown that diatoms can also incorporate trace elements in the opal. The causes and mechanisms of this incorporation, however, remain elusive. Thus, understanding the processes leading and regulating the uptake of different trace elements by diatoms will potentially furnish a new proxy for past water conditions. This indicator would be independent of the mobility of the elements and/or of diagenetic effects within the sediments. We tested the potential of this approach by determining the elemental composition of recent diatom frustules from Lake Geneva (Switzerland). The studied samples were further placed in a well defined chronological framework and compared with the most recent environmental history of the lake. Our preliminary results imply that the incorporation of different trace elements into the frustule has substantially changed throughout the studied time interval. A similar trend characterize most of the analyzed metals (Al, Ca, Ti, V, Cr, Mn, Fe, Ga, Rb, Sr, Ba, Pb) with comparatively higher concentrations for the last half of the twentieth century. Some other elements such as Sc seems to follow a rather opposite trend whereas Zn concentrations show a more scatter distribution. The calibration of these results with the well-known environmental history of Lake Geneva and its catchment area will allow us to evaluate the use of this technique as proxy for former environmental conditions. Furthermore, the combination of ongoing laboratory and field studies will provide crucial information concerning the interaction of known concentrations of dissolved trace elements in the water and diatoms, as well as the mechanism leading to their incorporation in the frustule.
DE: 1065 Trace elements (3670)
DE: 1845 Limnology
DE: 4267 Paleoceanography
DE: 4808 Chemical tracers
DE: 4845 Nutrients and nutrient cycling
SC: Biogeosciences [B]
MN: 2003 Fall Meeting