Late Holocene lake level dynamics inferred from magnetic susceptibility and stable oxygen isotope data: Lake Elsinore, southern California (USA)

Abstract

Southern California faces an imminent freshwater shortage. To better assess the future impact of this water crisis, it is essential that we develop continental archives of past hydrological variability. Using four sediment cores from Lake Elsinore in Southern California, we reconstruct late Holocene ($3800 calendar years B.P.) hydrological change using a twentieth-century calibrated, proxy methodology. We compared magnetic susceptibility from Lake Elsinore deep basin sediments, lake level from Lake Elsinore, and regional winter precipitation data over the twentieth century to calibrate the late Holocene lake sediment record. The comparison revealed a strong positive, first-order relationship between the three variables. As a working hypothesis, we suggest that periods of greater precipitation produce higher lake levels. Greater precipitation also increases the supply of detritus (i.e., magnetic-rich minerals) from the lake's surrounding drainage basin into the lake environment. As a result, magnetic susceptibility values increase during periods of high lake level. We apply this modern calibration to late Holocene sediments from the lake's littoral zone. As an independent verification of this hypothesis, we analyzed 18 O (calcite) , interpreted as a proxy for variations in the precipitation:evaporation ratio, which reflect first order hydrological variability. The results of this verification support our hypothesis that magnetic susceptibility records regional hydrological change as related to precipitation and lake level. Using both proxy data, we analyzed the past 3800 calendar years of hydrological variability. Our analyses indicate a long period of dry, less variable climate between 3800 and 2000 calendar years B.P. followed by a wet, more variable climate to the present. These results suggest that droughts of greater magnitude and duration than those observed in the modern record have occurred in the recent geological past. This conclusion presents insight to the potential impact of future droughts on the over-populated, water-poor region of Southern California.

A Holocene record of Pacific Decadal Oscillation (PDO)-related hydrologic variability in Southern California (Lake Elsinore, CA)

“…An examination of the relationship between twentieth century lake level at Lake Elsinore and regional precipitation indicates a strong positive correlation (Kirby et al 2004(Kirby et al , 2007. A similar comparison using the PDO also shows a positive relationship to lake level (Kirby et al 2007).…”

“…The Lake Elsinore Basin is 11 km long, 3.5 km wide, and less than 2 million years old (Hull 1990). As of March 2007, water occupies only 5.7 km 9 2.8 km of the total basin surface area, though the lake's surface area can change dramatically from year to year (Kirby et al 2004(Kirby et al , 2007. The lake is surrounded by a combination of predominantly igneous and metamorphic rocks (Hull 1990).…”

“…It is constrained along its southern edge by the steep, deeply incised Elsinore Mountains that rise to more than 900 m above lake level. The Elsinore Mountains likely provide a local sediment source during heavy precipitation years and/or wet climates (Kirby et al 2004(Kirby et al , 2007. The lake's drainage basin is relatively small (\1,240 km 2 ) from which the San Jacinto River flows (semi-annually) into and terminates within the lake's basin ( Fig.…”

“…The lake's drainage basin is relatively small (\1,240 km 2 ) from which the San Jacinto River flows (semi-annually) into and terminates within the lake's basin ( Fig. 1) (Kirby et al 2004). Lake Elsinore has overflowed to the northwest through Walker Canyon very rarely, only three times in the twentieth century and 20 times since AD 1769, according to mission diaries (Kirby et al 2004(Kirby et al , 2007.…”

“…The prehistoric record ([150 years) of climate variability in Southern California is sparsely documented, and limited to Mission diaries, tree-ring studies, some palynology, and a few lake studies (see Kirby et al 2007 for reference summary). Building on these previous studies, there is an on-going project that focuses specifically on the rare, but valuable lacustrine archives of Southern California (Kirby et al 2004(Kirby et al , 2005(Kirby et al , 2006(Kirby et al , 2007Bird et al 2010).…”