Environmental and climate change in Sierra Nevada (S Spain) during the latest Pleistocene and Holocene

In this study, we studied palynomorphs from the alpine record from Laguna Seca in Sierra Nevada, southern Spain to investigate the response of forests and lake environments in the western Mediterranean area to climate changes and to human impact during the latest Pleistocene and Holocene. Xerophyte herbs such as Artemisia, Ephedra, and Amaranthaceae are highest during the late Bölling-Allerod (BA) and Younger Dryas (YD) indicating aridity. Poaceae (grasses) are maximum in the BA and Early Holocene, probably indicating expansion in the barren areas left by glaciers after deglaciation. Forest abundance and composition, in particular of deciduous Quercus and Pinus species indicates maximum humidity during the Early Holocene and aridification in the Middle and Late Holocene. Microcharcoal analysis done on the palynological preparations agrees with the vegetation changes, showing maxima in the Early and Middle Holocene and a decrease in the Late Holocene when the Mediterranean vegetation, and thus fuel availability, diminished. The record of Laguna Seca is particularly interesting with respect to the algae and other aquatic microscopic remains. Pediastrum algae only occurred and showed very high abundances during the end of Heinrich Stadial 1 and beginning of the BA, probably indicating deepest lake conditions with deglaciation. Botryococcus, Debarya, Spirogyra and Zygnema algae also peaked at that climate transition, also supporting lake conditions. Botryococcus increased during the Early Holocene, while the rest of the algae almost vanished, which could indicate that the lake became shallower but very productive until 8200 cal yr BP. From then on, the lake level lowered and became a seasonal lake in the Middle-Late Holocene transition.