LATE PLEISTOCENE RECORD OF MOJAVE RIVER DISCHARGE INTEGRATED ACROSS MULTIPLE BASINS

The Mojave River is the only basin-integrated river of the Mojave Desert, stretching nearly 200 km ENE across the desert from its source in the episodically-glaciated Transverse Ranges to Silver Lake. Many of the basins it traverses are only partly integrated, and the river can terminate in as many as three basins today depending on local avulsions and volume of water. We have investigated lake records in all basins in order to address the river’s late Pleistocene discharge and report here on the last 50 ka. The record before ~25 ka is provided by combined Lake Manix and Lake Harper deposits. Lake Manix’s threshold eroded about 25 ka, after which the records of upstream Coyote and Harper basins along with downstream Lake Mojave constitute the river discharge history. Our dating and stratigraphic studies in combination with previous studies (Wells and others, 2003; Meek, 2004; Garcia and others, in press) indicate that between 50 and 37 ka, discharge created significant lakes in Manix three times (at ~46, 43, 40 ka), and one that is poorly age-constrained in Harper. After 37 ka, fairly deep lakes with fluctuating levels persisted. Protracted highstands occurred 32-30 ka and starting at 27 ka. After Lake Manix failed, large lakes were sustained consistently in either Coyote or Mojave lakes until ~13.5 ka, except for the period 23-22 ka. Lakes of variable size continued from 13.5 ka to ~10 ka. In contrast, during the remainder of the Holocene, only three short-lived lakes left sediment records ( ~3 ka, AD ~1250, and AD ~1650). Most Marine Isotope Stage (MIS) 3 highstands coincide with colder Dansgaard-Oeschger phases and Heinrich events 3 and 4. The MIS 2 highstands coincide in large part with the last glacial maximum but also the Bølling-Allerød, a time of northern hemisphere warming. The integrated record shows nearly continuous big lakes over a protracted period 37 to 13 ka (parts or all of MIS 3 and 2), a record that is much longer than for lakes farther north in the Great Basin. Southerly deflection of storm tracks by ice sheets is not a viable solution; extratropical moisture sources may have played a strong role in Mojave River discharge.