Silver Lake is the modern terminal playa of the Mojave River. As a result, it is well
located to record both influences from the winter precipitation dominated San Bernardino
Mountains the source of the Mojave River as well as the late-summer to early-fall
North American monsoon. Here, we present various physical and geochemical data from
a new 8.2 m sediment core taken from Silver Lake, CA that spans modern through 14.8
kcal yrs BP. Age control is based on six bulk organic C radiocarbon dates processed with
Bacon v2.2 to generate an age model. Texturally, the core varies between a clayey sand and
a silty sand, often with abrupt sedimentological transitions. Our working hypothesis
states that high percent clay values indicate persistent standing water wherein the
deposition, accumulation, and preservation of fine grain sediment exceeds some
undefined thickness that inhibits deflation during succeeding desiccation events or
ephemeral lake environments. Based on this clay lake status hypothesis, the sediment
core is divided into five lake status intervals. Clay values are highest between 14.4 13.6
kcal yrs BP, coeval to Lake Mojave II. Clay values decrease abruptly at 13.6 kcal yrs BP
(encapsulating the Younger Dryas) indicating a return to an ephemeral lake. At 11.6 kcal
yrs BP, clay values rise abruptly indicating a return to a perennial lake; this early
Holocene pluvial ended abruptly at 7.4 kcal yrs BP. From 7.4 4.2 kcal yrs BP, clay is
low, but variable and mudcracks are common. At 4.2 kcal yrs BP, clay values increase
but only moderately indicating a return to more frequent sustained perennial lakes. The
early Holocene pluvial is likely a result of higher summer insolation, which generated a
more intense and spatially expansive North American monsoon. Coupled with lower
winter insolation and thus more winter storms across the region, Silver Lake flourished.
A comparison to stable carbon isotope data from Leviathan Cave (NV), support our
interpretation as indicated by more productive soils (i.e., wetter) (Lachniet et al., 2014).
The resurgence of a wet Mojave ca. 4.2 kcal yrs BP is also supported by the NV cave
data. We attribute this late Holocene pluvial to the strengthening of El Niño.
Matthew kirby obtained his A.B. from Hamilton College. He is an Associate Professor at Cal State Fullerton. He studies past climate using lake and wetland sediments.
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