| ABSTRACT | High resolution multiproxy data (pollen, sedimentology, geochemistry and chironomids) from the Basa de la Mora (BSM) lake sequence (42º32’ N, 0º19’ E, 1914 m a.s.l.) show marked climate variability in the central southern Pyrenees throughout the Holocene. A very high sedimentation rate and a robust age model based on 15 AMS radiocarbon dates reveal the first precise reconstruction of rapid climate changes during the Holocene from this area. Additionally, the Holocene palynological record from Lake Estanya (EST) (670 m a.s.l., 42°02’N, 0°32’E) provides the first Holocene vegetation reconstruction from the basal belt of the southern Pyrenees. The comparison of the EST and BSM sequences illustrates the role of temperature and precipitation changes as main drivers of the altitudinal vegetation shifts in the southern Pyrenees during the Holocene.
The onset of the Holocene (11.7-9.8 cal Ka BP) was characterized by the occurrence of high seasonality and low water availability that led to the expansion of steppe communities dominated by Juniperus and Artemisia in the lowlands.
The second part of the Early Holocene (9.8-8.2 cal Ka BP) was characterized by still high continentality but increased water availability and milder winter temperatures that allowed the expansion of the arboreal taxa in the lowlands and favored the rise of the forest upwards. Superimposed on these long-term climate conditions the BSM sequence shows the existence of at least four short-living and abrupt climate shifts centered at 9.7, 9.3, 8.8 and 8.3 cal ka BP and characterized by dry conditions.
The Mid Holocene (8.2-6 cal Ka BP) was characterized by an increase in winter temperatures and a change in the precipitation characterized by high rates of rainfall and absence of a dry season (Atlantic-like precipitation pattern) that led to the upward migration of the deciduous forest.
At ca 6 cal Ka BP, it took place a change toward drier and similar-to-present conditions. This change took place in two main steps. Between 6 and 4.8 cal Ka BP, it established a Mediterranean-like pattern with the occurrence of a dry season that resulted in the substitution of the deciduous forest by a pine forest. From 4.8 cal Ka BP, it took place a progressive decline in the total amount of annual rainfall that led to a reduction in the presence of mesophytes and an expansion of semi-deciduous and evergreen Quercus. |