![]() The third hypothesis is thus considered the most likely one. The second hypothesis might explain the oxygen isotope values but not the gas content measurements. Glacial-geological data are sparse but do not appear to support the first hypothesis, while the uplift data have been interpreted in two widely different ways. (3) The Wisconsin ice originated near the main Greenland ice divide whereas the Holocene ice originates within 50 km of the station. (2) The Wisconsin flow pattern was similar to the present one but ice was much thicker and the ice margin considerably in advance of its present position. Three hypotheses are considered: (1) The Wisconsin ice originated near the crest of a high ridge connecting the Greenland ice sheet with an ice sheet on Ellesmere Island. These results are inconsistent with the present ice flow pattern. Total gas content measurements on the core suggest that the elevation difference was about 1300 m. ![]() A more likely interpretation is that the Wisconsin ice originated at an elevation of at least 500 m above the present station. In the Camp Century core, the difference in oxygen isotope ratio between Wisconsin and Holocene ice seems too large to be purely a climatic effect. California thus was an Ice Age refugium for animals and cold-sensitive plants. The persistence of a Mediterranean climate in California during the last glaciation contrasts with dramatic climatic changes experienced in glaciated parts of North America. The paleoecologic record shows that the late Quaternary climate of coastal California was characterized by regimes similar to those prevailing today. Well-defined wet and dry trends in the precipitation pattern characterized this time span, and provide a possible analog to the earlier Holocene and Pleistocene precipitation regime. The historical precipitation record overlaps a late Holocene tree-ring record permitting extrapolation of the precipitation curve back nearly 600 years. Fossil pollen in the Sierra Nevada indicates the influence of the North Pacific high. Fossil plants indicate that sclerophyllous vegetation and forest stands of conifers, adapted to a Mediterranean climate, were widely distributed during late Quaternary time. Charcoal in buried dunes and soils shows that fire was environmentally important throughout the Quaternary, just as it is today. Precipitation then, like the present rainfall regime, was not enough to leach the carbonates from the soils. These sand dunes contain buried, datable, carbonate-rich soils. ![]() Late Quaternary coastal dunes preserve former wind directions and show that prevailing late Quaternary winds were directionally equivalent to modern winds, which are controlled by the North Pacific anticyclone and by interactions between the North Pacific high and the interior basin low. The thick accumulations of sediments in basins of offshore California indicate that while variable sedimentation regimes reflect changing climatic and oceanographic conditions, the Quaternary climate was probably semiarid as now, even during glacial maxima. These synoptic climatic controls, key parts of the global air-sea circulation, were probably operative throughout late Quaternary time as shown by paleoecologic evidence. The present Mediterranean climate of coastal California is unique in North America and reflects the interaction of several important synoptic controls, principally the North Pacific semipermanent anticyclone, and to a lesser extent the Aleutian low-pressure system and the cool California oceanic current. ![]()
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