Paleohydrological fluctuations and steppe vegetation during the last glacial maximum in the central Ebro valley (NE Spain)

摘要

Combined analysis of sedimentary fades, geochemistry and pollen from lake sediment records, and sedimentological and palynological studies from slope deposits allow the characterization of vegetation and lake level status during the Last Glacial (LGM) in the central Ebro valley (NE Spain). These records show the presence of phases of increased effective moisture, while regional vegetation was dominated by steppe species. The longest lake record comes from La Salineta, one of the saline lakes in the Los Monegros area; the other lake sequence comes from a sinkhole in the Gallego River floodplain. The slope deposit from Valmadrid is the only periglacial deposit found in the central Ebro valley. Our data indicate that, at least for some intervals during full glacial times, when cold steppe vegetation dominated the region, some lakes experienced more positive water balance than today, and run-off was also high. The data are coherent with the hypothesis that, at least for some periods, the ice-age climate of the western Mediterranean was characterized by cold winters, with relatively higher effective moisture (precipitation minus evaporation ratio) and summer droughts. Increased flow from the Pyrenean rivers during the early deglaciation could also have played a significant role in the paleohydrological cycle in the central Ebro valley. However, La Salineta records also show evidence for arid periods during glacial times, indicating the complex evolution of hydrology and moisture availability in the central Ebro valley during the LGM.