LACUSTRINE OSTRACOD RECORD FROM THE CENTRAL MOJAVE DESERT DESCRIBES LINK BETWEEN LAKE LEVEL AND WINTER INSOLATION

The effect of future warming on water availability in arid and semi-arid regions is a key uncertainty in climate projections. To better constrain hydroclimate models requires geologic records of past changes in the water cycle, which provide critical information about the processes that control surface water abundance. The Mojave Desert is an ideal region to study how climate change affects surface water distribution, as it is currently dry and arid, but experienced wet climates and contained large lakes periodically throughout the past 25 kyr. Here, we investigate a sediment core from Glacial Lake Mojave (GLM): the terminal basin of the Mojave River, which drains the eastern San Bernadino Mountains. We present a high-resolution (~94 yr) oxygen and carbon isotope record measured in lacustrine ostracods deposited between 24 ka and 8 ka. During the deglaciation, GLM ostracods exhibit two periods of dramatic change in their oxygen and carbon values. Beginning at 18 ka during Henrich Stadial 1, ostracod δ¹⁸O and δ¹³C values gradually decrease for ca. 2 kyr, implying enhanced water input to the lake relative to evaporative loss. Indeed, the percent sand in the core also decreases during this interval due to rising lake levels. Ostracod δ¹⁸O and δ¹³C values remain unchanged until 10 ka, after which they gradually increase, suggesting a period of evaporation as the climate becomes drier at the beginning of the Holocene. This pattern in lake hydrography is directly correlated with winter insolation at 30˚N latitude, consistent with insolation playing a primary role in surface water abundance in the Mojave by controlling the amount of winter storms that reach the Southwestern US. Additionally, Pacific sea surface temperatures track the general trend in ostracod δ¹⁸O and δ¹³C compositions, indicating that higher North Pacific Ocean temperatures may also affect surface water balance in the Southern Great Basin by causing wetter winters.