LATE PLEISTOCENE SHORELINE FLUCTUATIONS OF LAKE MANIX, MOJAVE DESERT: PALEOCLIMATE IMPLICATIONS

Marine and ice cores provide highly detailed proxy records of past climate conditions and suggest global teleconnections. However, recent records from cave speleothems in the western U.S. compared with lake-level proxies suggest that continental interiors may respond to multiple drivers that influence climate conditions at the scale of the geographic region. Previously published work on pluvial lake levels in the western U.S. during marine isotope stage (MIS) 3 suggests that lakes rise in response to warm phases of the Dansgaard-Oeschger (D-O) cycles, in agreement with wetter warmer periods in the Santa Barbara Basin marine record. In contrast, two speleothem records in south-central Arizona and southeastern New Mexico record cool wet periods coincident with cool D-O phases. These conflicting records may be reconciled by an hypothesis that regional climate was influenced by the Pacific Ocean for the more western parts of the western U.S., and by the Atlantic Ocean, as mediated by the Gulf of Mexico, for the more eastern regions of the Sonoran and Chihuahuan desert area. Lake Manix, the main terminal lake for the Mojave River in south-central California until about 25 cal ka, lies between the speleothem locations and the Santa Barbara Basin. This lake, which was likely shallow due to previous sediment loading, achieved multiple highstands during MIS 3 and early MIS 2. Our preliminary lake-level curve, constrained by >40 calibrated ¹⁴C ages on Anodonta shells, indicates rapid fluctuations between 45 and 25 ka and at least 8 highstands within 10 m of the 543-m upper threshold for Lake Manix. Correlations of Manix highstands with ice, marine, and speleothem records suggest that some highstands coincide with colder D-O phases, whereas others coincide with warmer phases. Thus Lake Manix, and hence runoff from the Transverse Ranges, may have responded alternately to southerly displacement of Pacific winter storm tracks during colder D-O phases and to increased moisture transport from the North Pacific off southern California during the warm D-O phases.