Climatic changes vs. catastrophic events in lacustrine systems: A geochemical approach

摘要

A geochemical study of oligotrophic Lake Sanabria (NW Iberian Peninsula) allows us to distinguish the geochemical response of a lacustrine system to catastrophic events and climatic events. The main major elements analysed were: K, Na, Mg, Ca, Ti, Al, Fe, Mn, P and S. The organic matter content in the sediment of Lake Sanabria is determined by the rainfall regime of the region. Periods when sediments were enriched in Ti, Mg, K, and Al are indicative of relatively wet paleoenvironmental conditions, whereas intervals when sediments were enriched in S and P (associated with organic matter) are indicative of dry conditions. A factor analysis of the geochemical data shows a progressive temporal displacements from organic rich conditions (relatively high values of S and P) to inorganic rich conditions (relatively high values of Ti, Mg, K, Al, and Na). Maximal inorganic content occurred at the beginning of two discrete sedimentary levels: the LOL2 (cal. 1160-1230 yr AD) and the LOL1 (cal. 1510-1680 yr AD) horizons. The LOL2 and LOL1 horizons constitute two discrete events related to climatic changes during the beginning and end of the Little Ice Age, respectively. In contrast, the geochemical analysis provides evidence that the samples associated with the 1959 catastrophic event that occurred in the catchment area of Lake Sanabria do not follow the long-term geochemical evolution paths of the climate driven system.