A sediment core 7.2 m long from Lake Mirabad, Iran, was examined for loss-on-ignition, mineralogy, oxygen-isotopic composition of authigenic calcite, and trace-element composition of ostracodes to complement earlier pollen and ostracode-assemblage studies. Pollen, ostracode-inferred lake level, and high Sr/Ca ratios indicate that the early Holocene (10000 to 6500 cal yr BP) was drier than the late Holocene. Low δ18O values during this interval are interpreted as resulting from winter-dominated precipitation, characteristic of a Mediterranean climate. Increasing δ18O values after 6500 cal yr BP signal a gradual increase in spring rains, which are present today. A severe 600-yr drought occurred at ca. 5500 cal yr BP, shortly after the transition from pistachio-almond to oak forest. During the late Holocene, two milder droughts occurred at about 1500 and 500 cal yr BP. Within the resolution of the record, no drought is evident during the collapse of the Akkadian empire (4200–3900 cal yr BP). Rather, a decrease in δ18O values to early-Holocene levels may indicate the return to a Mediterranean precipitation regime.
Multiproxy palaeoenvironmental and palaeolimnological analyses of two Holocene-age sediment cores from the margin of Lago Cardiel, a 76 m deep, closed-basin lake in southern Patagonia (latitude 49°S), provide information on lake-level changes that can be related to regional palaeoclimate scenarios. Sedimentol ogic (magnetic susceptibility, organic and inorganic carbon content) and environmental indicators (pollen, dia toms, ostracodes and stable isotopes on ostracodes) show lake levels markedly higher than today during the early Holocene, following a rapid lake-level rise after a desiccation phase prior to 11000 BP. After about 6000 BP, lake levels were generally lower, but underwent repeated fluctuations. These inferred changes support the previously proposed view that the southern westerly stormtracks were focused (zonal) north of latitude 50°S during the early Holocene, allowing for Antarctic cold fronts to bring easterly moisture to southern Patagonia, whereas during the late Holocene the stormtracks shifted seasonally, with an overall more meridional behaviour, resulting in less and more variable moisture at these latitudes.
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