KEYNOTE: A HALF-MILLION YEARS OF PALEOCLIMATE RECORDED BY LAKE MANIX, MOJAVE DESERT, CALIFORNIA

Lacustrine sediments from the Manix basin, terminus of the Mojave River for a half-million years, preserve a robust record of river discharge and climate change. Sedimentology, ostracode faunas, and stable isotopes from both core and outcrop record lake fluctuations from oxygen-isotope stage (OIS) 12 (~480 ka) through early OIS 2 (25 ka). The ostracode faunal record displays a shift from an unexpectedly warm, summer-dominated lake hydrology during OIS 12, also indicated by larger amounts of carbonate, to a predominantly colder, winter-dominated lake hydrology afterwards. The stable isotope record from ostracode calcite exhibits large intra-sample variability and does not mimic other well-known terrestrial- and marine-based records of climate change. Particle size also shows large variability on 10²-10³-yr timescales. The most negative d¹⁸O values only occurred four to six times, most notably during OIS 7 and OIS 9, and along with sedimentologic properties indicate that deep, stable lakes were uncommon. Similar large variability in lake level during OIS 3 is recorded by at least 8 ¹⁴C-dated highstands of Lake Manix between 45 and 25 cal ka. Evaporation could have buffered the Lake Manix d¹⁸O record from expected isotopic differences between interglacial and glacial-interval discharge. The highest d¹⁸O values occurred after a drainage integration event at about 190 ka and may reflect a consequent increase in surface area and evaporation. The presence of a moderately deep Lake Manix during some parts of both glacial and interglacial intervals suggests that runoff from the Transverse Ranges is not a simple response to displacement of storm tracks by southward migration of the polar jet as proposed for Great Basin pluvial lakes. Rather, runoff may be controlled by Pacific moisture amount and winter storm frequency.