INVESTIGATING THE HOLOCENE HYDROLOGIC RECORD OF AN EXTANT DESERT SPRING AND PLAYA SYSTEM: SODA LAKE, MOJAVE DESERT, CA

Springs on the western margin of Soda Lake playa, in the central Mojave Desert, provide a record of hydrologic variation through the Holocene. The active springs are part of an aquifer system that provides critical habitat for both flora and fauna in this arid ecotone. These ecosystems responded sensitively to rapid climatic fluctuations elsewhere in the southern Great Basin and Mojave Deserts during the middle and late Pleistocene, so a series of sediment cores were obtained to determine if changes in the water budget in this region appear in the Holocene geologic record as well. Variations in the mineral grain size, organic content, redox state of deposition, and microfaunal assemblages provide evidence of considerable changes in the areal extent of the spring-wetland environments throughout the Holocene. The data further suggest that wetland systems lingered after the precursor to Soda Lake, Lake Mojave, regressed, roughly 9,000 years ago. In addition to the sediment cores, a series of soil pits were dug into playa sediments surrounding one of the largest springs. We found at least two distinct black mats that yielded radiocarbon ages ranging from 1217 AD to 1748 AD, which suggest the vegetated wetlands surrounding the springs expanded areally when effective precipitation increased before and during the Little Ice Age in this part of the Mojave Desert. Finally, sediment cores were retrieved from the center of Soda Lake, including a 20-m core that recorded numerous fining-upward sequences of flood deposits that occurred after termination of the Lake Mojave sedimentary sequence. Sediments from all three sample sets were dated using techniques aimed at extracting and concentrating organic matter for radiocarbon dating in an attempt to further understand the hydrologic budget of the central Mojave since the end of the last pluvial.