A late Wisconsin (32–10k cal a BP) history of pluvials, droughts and vegetation in the Pacific south‐west United States (Lake Elsinore, CA)

Abstract

Continuous, sub‐centennially resolved, paleo terrestrial records are rare from arid environments such as the Pacific south‐west United States. Here, we present a multi‐decadal to centennial resolution sediment core (Lake Elsinore, CA) to reconstruct late Wisconsin pluvials, droughts and vegetation. In general, the late Wisconsin is characterized by a wetter and colder climate than during the Holocene. Specifically, conditions between 32.3 and 24.9k cal a BP are characterized by large‐amplitude hydrologic and ecologic variability. Highlighting this period is a ∼2000‐year glacial mega‐drought (27.6–25.7k cal a BP) during which the lake shallowed (3.2–4.5 m depth). This period is approximately coeval with a Lake Manix regression and an increase in xeric vegetation in the San Bernardino Mountains (Baldwin Lake). The Local Last Glacial Maximum (LLGM) is bracketed between 23.3 and 19.7k cal a BP − a ∼3000‐year interval characterized by reduced run‐off (relative to the glacial), colder conditions and vegetative stability. Maximum sustained wetness follows the LLGM, beginning at 19.7 and peaking by 14.4k cal a BP. A two‐step decrease in runoff characterizes the Lateglacial to Holocene transition; however, the vegetation change is more complex, particularly at the beginning of the Younger Dryas chronozone. By 12.6–12.4k cal a BP, the climate achieved near Holocene conditions.

Deglacial water-table decline in Southern California recorded by noble gas isotopes

“…Two wells with outlier reconstructed WTDs have apparent 14 C-based recharge ages of ~24 ka and 12 ka, which may be temporally consistent with other studies that have proposed evidence for a local glacial megadrought and wet Younger Dryas stadial, respectively. Measurements of various physical, geochemical, and biological proxies from Lake Elsinore, roughly 100 km north of our SD study area, independently suggest extreme aridity persisting from ~27.5 to 25.5 ka 26–28 , which is within the dating uncertainty of the ~24 ka groundwater sample. A record of groundwater-discharge deposits from southeastern Arizona suggests the persistence of a shallow, near-surface regional water table from ~50 ka to 15 ka, after which the water-table lowered, except for a brief rebound to wet conditions during the Younger Dryas stadial ~12.5 ka 29 .…”

Pacific Southwest United States Holocene Droughts and Pluvials Inferred From Sediment δ18O(calcite) and Grain Size Data (Lake Elsinore, California)

“…Furthermore, ecological inertia limits the functional response of the vegetation to environmental stresses. The hydrology of Lake Elsinore, however, experiences change on a variety of timescales (Figures 4, 5, 8), that are unlikely recorded in the San Jacinto pollen-temperature record (Kirby et al, 2018).…”

“…The preservation of warm season precipitated CaCO 3 is also favored by a warmer water column and the associated decrease in CaCO 3 solubility at higher water temperatures. The latter relationship is apparent in Lake Elsinore via the presence and near absence of CaCO 3 during the warmer Holocene versus the colder Glacial, respectively (Kirby et al, 2007(Kirby et al, , 2013(Kirby et al, , 2018.…”

“…Simplified, Lake Elsinore's net annual hydrologic budget is a combination of two seasonal end members -winter precipitation (P) and summer-to-early fall evaporation (E), hereafter referred to as the P:E ratio. The winter end member is documented in several papers using changes in grain size and other physical or chemical parameters to infer precipitation-related runoff dynamics (Kirby et al, 2007(Kirby et al, , 2010(Kirby et al, , 2013(Kirby et al, , 2018. However, a direct summer-to-early fall evaporation indicator was not available for Lake Elsinore, thereby limiting our knowledge of Holocene precipitation seasonality trends in the PSW.…”

Southern California Vegetation, Wildfire, and Erosion Had Nonlinear Responses to Climatic Forcing During Marine Isotope Stages 5–2 (120–15 ka)

“…Allochthonous sources dominated deposition in Baldwin Lake during MIS 2, while charcoal and pollen concentrations declined to their lowest sustained levels in the record. Arboreal pollen still signaled rapid forest expansion ~24 ka, coeval with wetter conditions at Lake Elsinore (Kirby et al, ), and other paleorecords in Southern California (Oster et al, ).…”