CONICET | Buscador de Institutos y Recursos Humanos

Changes in the ostracod assemblages from two sediment cores collected from Lago Cardiel in southeastern Patagonia (49° S) reflect the main regional abrupt climatic changes over the last 15.6 cal. ka BP. Shifts in species abundance and switches in dominances suggest that these were mainly driven by variable salinity. During the Late Pleistocene, Limnocythere rionegroensis was abundant and dominant, indicating waters with high salinity and prevalence of evaporative processes.Between 12.6 and 10.8 cal. ka BP Lago Cardiel expanded markedly and reached an Early Holocene highstand of +55 m above present lake level. A major change in ostracod assemblage in which Limnocythere patagonica appears as the dominating species in parallel with the disappearance of L. rionegroensis and Eucypris aff. cecryphalium mirrored this transitional period between the cold and dry Late Pleistocene and the humid and warm Early Holocene. Over the last 4 cal. ka BP, L.rionegroensis returned to the species assemblage and R. whatleyi increased its abundance pointingtowards increasing salinities. The variations in size, shape and ornamentation of L. rionegroensis and R. whatleyi fossil valves were examined using geometric morphometric techniques and further compared to those of modern Patagonian sites. Limnocythere rionegroensis specimens displayed high morphological variability during the Lago Cardiel evolution. More specifically, the switch in reproductive mode - from sexually to parthenogenetic - and the increase in valve ornamentationaround 12.7 cal. ka BP suggest that these changes were promoted by the hydrological alteration that occurred at Late Pleistocene. This exercise provides a robust range of morphological variation for these proxies which will be useful in further taxonomic and palaeoenviromental studies adding more information about different factors influencing the observed morphological trends.