A 180,000-year pollen record from Owens Lake, CA: terrestrial vegetation change on orbital scales

A 180,000-year pollen record from Owens Lake, CA:terrestrial vegetation change on orbital scales

Wallace B. WoolfendenMountain Heritage Associates, USDA Forest Service, P.O. Box 429, Lee Vining, CA 93541, USA

Received 9 January 2003

Abstract

Pollen from the upper 90 m of core OL-92 from Owens Lake is a climatically sensitive record of vegetation change that indicates shiftsin the plant associations representing warm and cold desertscrub, pinyon–juniper woodland, and pine–fir forest during the past 180,000years. These changes are synchronized with glacial–interglacial cycles. During glacial and stadial climates, juniper woodland expandeddownslope and replaced warm desert shrubs while upper montane and subalpine forests in the arid Inyo Mountains also expanded, and thosein the Sierra Nevada were displaced by the ice cap and periglacial conditions. Conversely, during interglacial and interstadial climates, warmdesert plants expanded their range in the lowlands, juniper and sagebrush retreated upslope, and montane and subalpine forests expandedin the Sierra Nevada. The reconstructed vegetation history demonstrates a regional climatic response, and the congruence of the pollensequence with marine and ice cap oxygen isotope stratigraphies suggests a link between regional vegetation and global climate change atorbital scales.© 2003 Elsevier Science (USA). All rights reserved.

Keywords: Vegetation dynamics; Pollen records; Paleocology; Climate change; Glacial cycles; Owens Valley; California

Introduction

Multimillennial terrestrial pollen records are becomingmore common in the far western United States, includingthose at Clear Lake (Adam, 1988; Adam et al., 1989),Humptulips (Heusser and Heusser, 1990), Santa BarbaraBasin (Heusser, 1995), Carp Lake (Whitlock et al., 2000),and Searles Lake (Litwin et al., 1999). The primary value ofthese records is the long-term vegetation history relative toclimate dynamics and orbital effects by correlation withmarine isotope chronostratigraphies. In the eastern SierraNevada pollen sequences and plant macrofossils from pack-rat middens from Mono Lake, Black Lake, the White Moun-tains, and Owens Valley illustrate the shorter-term variationof desert vegetation since about 35,000 yr ago (Batchelder,1970; Koehler and Anderson, 1994, 1995; Jennings andElliot-Fisk, 1993; Davis, 1999; Mensing, 2001). They pro-

vide evidence that the characteristic lowland vegetation typeof the last glacial was a pygmy conifer woodland, domi-nated by Utah juniper, with an understory of sagebrush.During the last glacial maximum (20,000 yr ago) in OwensValley the lower forest border of pinyon–juniper woodlandwas depressed about 500–600 m. Between about 19,000and 9500 yr ago xeric shrub species appeared followed bythe departure of Utah juniper and the establishment ofmodern desert vegetation.

In the summer of 1992, the United States GeologicalSurvey retrieved a nearly continuous 323-m core dated to anestimated 800,000 yr ago from Owens Dry Lake in south-eastern California (lat 36° 22.85�N, long 117° 57.95�W,1067 m in elevation; Fig. 1) (Smith and Bischoff, 1997).The upper 90 m was sampled for a pollen record to study theresponse of desert vegetation to climate changes that ex-tended in time from the late Holocene to the penultimateglaciation at 180,000–130,000 yr.

Throughout most of the Holocene and late Pleistocene,Owens Lake was the terminus for the 8500-km2 OwensRiver watershed that drains the Sierra Nevada via 30 trib-E-mail address: [email protected] (W.B. Woolfenden).

R

Available online at www.sciencedirect.com

Quaternary Research 59 (2003) 430–444 www.elsevier.com/locate/yqres

0033-5894/03/$ – see front matter © 2003 Elsevier Science (USA). All rights reserved.doi:10.1016/S0033-5894(03)00033-4

utary streams. Before water diversions desiccated the lakeafter the Los Angeles Aqueduct became operational in1913, it was about 10 m deep with a surface area of 290 km2

(Smith and Street-Perrott, 1983). Under an arid climate,with an average annual precipitation of 100–150 mm, theimpermeable bedrock substrate and the lake sill preventedoutflow from the valley. During the last glaciation OwensLake had an area of 330 km2 (Snyder et al., 1964), a stablesurface level of 1140 m, and extended upvalley about 16 kmnorth of Lone Pine (Smith and Street-Perrott, 1983) (Fig. 2).Currently the primary precipitation maximum is deliveredin the winter by extratropical Pacific cyclones tracked by thepolar jet stream, supplemented by anomalous cold storms

from the north and anomalous warm storms from the westor southwest. A secondary late spring maximum arrivesfrom the northeast, and a secondary convective summermaximum originates from tropical moisture in the Gulf ofCalifornia, the Pacific, and, to some extent, the Gulf ofMexico (Pyke, 1972; Hales, 1974).

Owens Lake sediments reveal that cycles of saline/closedand fresh/overflowing lake conditions are broadly correlatedwith interglaciations and glaciations, respectively (Bischoffet al., 1997a, 1997b; Menking et al., 1997; Bradbury, 1997;Carter, 1997). Although glaciations occurred for most of thepast 500,000 yr, the lake was closed about 66% of the timepunctuated by seven brief intervals of overflow.

Fig. 1. DEM map showing the location and surrounding topography of Owens Lake and the site of Core OL-92. The Sierra Nevada on the west and the InyoMountains on the east flank the deep Owens Valley.

431W.B. Woolfenden / Quaternary Research 59 (2003) 430–444

The latitudinal extent of Owens Valley, the north tosouth decrease in base level, the extreme valley–mountainrelief, and the orographic influence of the Sierra Nevadawith its rain shadow produces a well-developed bioclimaticzonation with altitude and latitude. A climatically sensitivetransition between the southern hot Mojave Desert FloristicProvince—characterized by creosote bush, bursage, andsaltbush associations—and the northern cold Great Basin

Floristic Province—characterized by big sagebrush and bit-terbrush associations—centers on Owens Lake (Fig. 3).

Natural vegetation of the southern Owens Valley floor isdesert saltbush scrub dominated by Atriplex spp. (saltbush)and Sarcobatus vermiculatus (greasewood), alkali meadowsand seeps, and riparian and bottomland associations ofPopulus fremontii (Fremont cottonwood) and Salix spp.(willow). Above the valley floor along the flanking Sierra

Fig. 2. DEM map indicating the approximate full-glacial extents of the Sierra Nevada ice cap and Owens Lake following Wahrhaftig and Birman (1965) andSmith and Street-Perrott (1983). The contours of the ice cap are generalized. The map suggests the area of land excluded from vegetation habitat.

432 W.B. Woolfenden / Quaternary Research 59 (2003) 430–444

Nevada and Inyo Mountains, the alluvial fans provide hab-itats for several shrub associations characterized by shad-scale (Atriplex confertifolia), other saltbush species, Larreatridentata (creosote bush), Ambrosia dumosa (white bur-sage), and Yucca brevifolia (Joshua tree) southeast ofOwens Lake.

This vegetation intergrades upward on the Sierra Nevadabajadas into a mixed shrub association dominated by Co-leogyne ramosissima (blackbush), above which lies bigsagebrush (Artemisia tridentata)/bitterbrush (Purshia tri-dentata) scrub. Pinus monophylla (singleleaf pinyon) and

Cercocarpus ledifolius (mountain mahogany) form wood-land on the mountain front and in the canyons. The drain-ages emitting from the Sierra Nevada canyons containwillow, Betula occidentalis (water birch), Fremont cotton-wood, Populus balsamifera spp. trichocarpa (black cotton-wood), Populus tremuloides (aspen), Quercus kelloggii(black oak), and Quercus chrysolepis (canyon live oak).Between 2590 and 2740 m are relatively pure stands ofPinus Jeffreyi (Jeffrey pine), and Pinus contorta ssp. mur-rayana (lodgepole pine) and Juniperus occidentalis ssp.australis (mountain juniper) are found at higher elevations

Fig. 3. Generalized vegetation map of the Owens Valley area showing the present distribution of vegetation associations.


along with extensive thickets of montane chaparral. A sub-alpine forest of Tsuga mertensiana (mountain hemlock),Pinus albicaulis (whitebark pine), Pinus flexilis (limberpine), Pinus balfouriana (foxtail pine), and Pinus monticola(western white pine) grows above 2900 m. The typicaltree-line species of P. albicaulis (whitebark pine) formsstands of krummholz (shrub form), and alpine associationsof sedges, grasses, forbs, and dwarf shrubs grow abovetimberline.

In the xeric Inyo Mountains the saltbush, shadscale, andcreosote bush scrub shifts to big sagebrush and pinyon–juniper (Juniperus osteosperma) woodland at about 2000 m.Above 2900 m a mosaic of low sagebrush scrub, mountainmahogany, and open conifer woodland composed of P.flexilis (limber pine) and the long-lived Pinus longaeva(bristlecone pine) forms the subalpine zone. Riparian wood-land with shrubs of black and Fremont cottonwood as wellas willow occurs along the watered drainages and wetlandson the escarpment.

Lithology and chronology

The top 38 cm of core OL-92 consists of salts precipi-tated by the historic desiccation of the former saline lake.Beneath these salts is a 3.84 m unit of aragonite oolitesresulting from an earlier period of drying. Below an appar-ent erosional surface, the rest of the lacustrine sediments arebedded clays, silty clays, and coarse sand (Smith, 1997).

Palynomorph samples were taken at depths from 5.52 to90 m, which have been given ages of approximately 10,200cal yr ago to 180,300 yr ago, respectively. Chronologicalcontrol for this study is provided by using a cubic spline fitto interpolate ages for each sample point from age-depthvalues that are based on a revised chronology derived fromthe 230Th ages and palynostratigraphy of Searles Lake(Litwin et al. 1999) (Fig. 4). Revised ages are assumed forcitations of research based on the original average massaccumulation rates (MAR) calculated for core OL-92(Bischoff et al., 1997c). Two problems disrupt the chronol-ogy of the upper 60 m of the core. First, no core wasextracted between 19.06 and 20.09 m, 27.78 and 30.86 m,48.02 and 49.15 m, and 50.69 and 52.20 m. Second, radio-carbon dates (Benson et al., 1998), sediment characteristics,and anomalies of the pollen sequence identified five seg-ments of core that apparently liquified and slumped duringdrilling from an interval higher up in the drill hole. Internallitho and biostratigraphic coherence permitted a rearrange-ment of two of the disturbed intervals (10.75–12.68 and14.02–16.60 m) sampled for pollen, but the chronology iscompromised (Woolfenden, 1996).

Methods and interpretation issues

A total of 413 2- to 5-cm3 samples were processed forpollen and spores via standard methods (Faegri and Iversen,1985; O.K. Davis, personal communication, 1992). Lyco-

Fig. 4. Age–depth curve for the upper 90 m of OL-92. Ages of the samples (plotted as circles) are interpolated by a cubic spline fit of 11 age–depth pointscalculated by Litwin et al., 1999. Ages for the top 31.13 m of the core are constrained by 25 AMS radiocarbon dates (Bischoff, 1996). The intervals of thesample points between 123,000 and 134,400 yr are compressed as compared to the original sample intervals based on Bischoff’s model of mass accumulationrates (Bischoff et al., 1997c; Woolfenden, 1996).


podium spores were added as a tracer to determine pollenconcentration (grains/cm3). Of the total, 159 samples werecounted. Palynomorphs were identified to the lowest taxo-nomic level possible and counted at magnifications of 450and 1000�. Published keys, microphotographs, and slidereference collections assisted identification. Unknown taxawere described and photographed for future reference, andunknown, deteriorated or obscured palynomorphs were cat-egorized as indeterminate. A minimum of 300 nonaquaticpollen grains were counted for each sample, and no less than100 non-Pinus or non-Juniperus grains were counted. Atotal of 95 terrestrial and aquatic pollen taxa, two species ofBotryococcus sp., and four species of Pediastrum sp. wereidentified. Only terrestrial and riparian pollen are consid-ered in this study. Tilia software (Grimm, 1992) was used toenter the data, calculate percentages, determine pollen ac-cumulation rates, and plot the diagrams (Figs. 5 and 6).Calculations of pollen percentages were based on the sum ofterrestrial and riparian pollen. Pollen accumulation ratessupport the percentage sequences throughout the record.The pollen sequence was divided into six assemblage zonesof 16 pollen types by use of the Constrained IncrementalSum of Squares Cluster Analysis (CONISS) program(Grimm, 1987).

The coarse sampling interval not only fails to adequatelyresolve finer-scale temporal variations in pollen but alsointroduces the potential for creating low-frequency artifactsby randomly selecting and merging high-frequency compo-nents. Short of more intense sampling this error can bepartially controlled by correlating the pollen variations withthose of other sedimentary variables as given below.

Reconstructed vegetation associations and their past dis-tribution are inferences based on multiple variables. Closeobservation of the vegetation patterns in the eastern SierraNevada and an attempt to understand the ecological contextare critical. Data on modern pollen deposition were pro-vided by two surface samples taken by the author from theshores of Mono and Owens Lakes and an air sample transectfrom the Sierra Nevada montane forest (2850 m) to the crestof the Inyo Mountains (2530 m) (Solomon and Silkworth,1986). In addition, 13 pollen types from the Mono Basinand Owens Valley samples, along with 8 pollen-based veg-etation types of the western United States (Davis, 1995),were plotted to compare proportions of modern pollen taxaamong different climatic areas (Fig. 7, Table 1). In order toshow the biogeographic relations between the OL-92 pollensequence and modern surface samples a detrended corre-spondance analysis was done (Fig. 8).

The influence of mountain–valley topography with itscomplex vegetation patterns and mesoscale wind patternsprobably affected pollen dispersal. The northwest–southeastorientation of Owens Valley channeled and intensified sur-face winds along its axis and may have amplified the lati-tudinal movement of warm and cold desert taxa duringclimate changes, while diurnal changes in insulation pro-

duced daytime upslope and nightly downslope flows, mix-ing pollen along an elevation gradient (Flohn 1969; So-lomon and Silkworth, 1986). The presence of thermal bar-riers or inversion layers may have modified elevation flows,however, and isolated pollen within mountain and valleyatmospheric layers. A linear or exponential function is notappropriate for downwind pollen deposition in a mountainregion. Rather, pollen seems to be deposited in a stepwisemanner with abrupt decreases in frequency from the sourceand constant low frequencies thereafter, irrespective of dis-tance (Markgraf, 1980; Solomon and Silkworth, 1986).Transportation of extralocal pollen by tributary streams andthe Owens River supplement the pollen airfall to the lakealthough it is assumed to be a minor source of error becausethe area of Owens Lake is large and most of the pollenreaches the lake by atmospheric fallout.

Results

Zone OL-I

The very high abundances of Juniperus pollen indicatethat extensive juniper woodland associated with single-leafpinyon and a shrub understory of sagebrush, bitterbrush,and grass, lowered from its present range by 950–1000 m,was the prevailing vegetation type on the alluvial fans ofOwens Valley (Table 2). Utah juniper (J. osteosperma) isassumed to be the primary species represented by the pollenas based on macrofossils of that species in late Pleistocenepackrat middens from the Owens Valley area (Koehler andAnderson, 1994, 1995; Jennings and Elliott-Fisk, 1993).Western juniper (J. occidentalis) may also have contributedpollen.

An ecologically compatible explanation for the pollenassemblage is that the prevailing climate during this periodwas cold and semi-arid with cool, dry summers and in-creased precipitation and runoff delivered by Pacific stormsembedded in the westerlies between October and April(Neilson, 1987). This climatic condition is associated withthe penultimate glaciation in the Sierra Nevada, locallytermed Tahoe II or Older Tahoe, Mono Basin, and Rovana,and variously dated between about 130,000 and 200,000 yrago (Fullerton, 1986; Bursik and Gillespie, 1993; Bach etal., 1992). The Rock flour maxima from Owens Lake indi-cate overflowing conditions at this time (Bischoff et al.,1997c, Bischoff and Cummins, 2001). The Sierra Nevadaicecap, regional lowering of the equilibrium line altitude byabout 1 km (Porter et al., 1983) (Fig. 2), and periglacialconditions must have restricted the habitat of montane andsubalpine forests to the lower mountain slopes. Therefore,most of the Pinus pollen was probably derived from thebristlecone pine and limber pine forests of the unglaciatedInyo Mountains and southern Sierra Nevada.


Fig. 5. Pollen percentage diagram (selected taxa) for OL-92 during the past 180,000 yr. The shaded portions of the curves are a 10� exaggeration of the pollenabundances that are plotted in black. The blank horizontal bands represent missing core sections. Pollen zones were calculated from a constrained cluster analysis.

436W

.B.

Woolfenden

/Q

uaternaryR

esearch59

(2003)430

–444

Fig. 6. Pollen percentage diagram for OL-92 detailing the time interval 120,000 to 134,000 yr ago The interval encompasses the compressed sample interval referredto in Fig. 3.

437W

.B.

Woolfenden

/Q

uaternaryR

esearch59

(2003)430

–444

Zone OL-II

A major change in vegetation is indicated with a dimin-ishing of Juniperus pollen about 130,000 yr ago along withrapidly expanding thermophilous taxa (i.e., Ambrosia(white bursage), Chenopodiaceae (saltbush), Cercocarpusand Purshia (mountain mahogany and bitterbrush), otherAsteraceae, Ephedra (Mormon tea), and Fabaceae (le-gumes) at the expense of sagebrush and other cold desertplants. During this transition the lower treeline of juniperwoodland apparently retreated upslope while riparian wood-lands of oak and cottonwood expanded. In addition, the

subsidence of Owens Lake to closed lake conditions ex-posed sediments to the colonization of saltbush species andgreasewood (Bischoff et al., 1997a, 1997b; Menking et al.,1997; Bradbury, 1997; Carter, 1997; Bischoff and Cum-mings, 2001). During the transition, at the end of ZoneOL-1, birch increases and then declines after about 1000 yr.

Rapid increase of the pollen representative of white bur-sage implies either rapid immigration of the plants fromglacial-age distributions in the southwest or immigrationfrom glacial refugia in favorable habitats near Owens Lake.Pollen of creosote bush, the defining plant of the MojaveDesert, was not identified in the Owens Lake core. It is notdispersed widely and so would be rare in lake sediments ifit were present at that time.

The vegetation reconstruction suggests a warm, arid cli-mate in Owens Valley with a high surface water budget. Asinferred from the pollen the greater abundance of juniperand oaks compared to the Holocene implies more wateravailability in the mountains. Winter precipitation from lowpressure anomalies over the eastern Pacific and more fre-quent summer and fall rainfall with increased cloud coverfrom warm, humid, unstable air masses brought in by anexpanded southerly flow and southern cyclonic storms mayhave contributed to this increased moisture (Neilson, 1987;Pyke, 1972; Thompson et al., 1993). More water may havebalanced the interglacial warmth and allowed for the en-hanced recruitment of juniper that would otherwise not be

Fig. 7. Pollen percentage diagram of 13 pollen taxa for Owens Valley and Mono Basin surface samples collected by the author and 8 pollen-based vegetationtypes of the western United States (Davis, 1995). Abbreviations used: OV, Owens Valley; MB, Mono Basin; CAXF, California Xeric Forest; RMXF, RockyMountains Xeric Forest; GBST, Great Basin Steppe; GBDS, Great Basin Desert Grassland; UMDS, Upper Mojave Desert Grassland; LMDS Lower MojaveDesert Grassland; USDS, Upper Sonoran Desert Grassland; LSDS, Lower Sonoran Desert Grassland. Table 1 summarizes the temperature and precipitationvariables for each vegetation type.

Table 1Summary climatic data for vegetation types of the southwestern UnitedStates (in part, after Davis 1995)

Sample ID MAT (C°) MAP (mm)

Mono Basin (MB) 8.6 302Owens Valley (OV) 15.4 133California Xeric Forest (CAXF) 12 409Rocky Mountains Xeric Forest (RMXF) 11 236Great Basic Steppe (GBST) 11 235Great Basin Desert Grassland (GBDS) 12 236Upper Mojave Desert Grassland (UMDS) 18 135Lower Mojave Desert Grassland (LMDS) 21 81Upper Sonoran Desert Grassland (USDS) 18 215Lower Sonoran Desert Grassland (LSDS) 21 141


attainable and intensified the warm season runoff for theriparian woodland.

Zone OL-III

An increase in Juniperus and Artemisia pollen from theprevious zone and a concurrent decrease in Cercocarpus/Purshia-type and Ambrosia pollen is interpreted as a drop inthe elevation range of juniper woodland on the westernslopes of the Inyo Mountains, the contraction of mountainmahogany, and the local die off and receding range of warmdesertscrub, signaling a shift to cooler temperatures. Theplant associations on the lower elevation sites were proba-bly a mixed association of sagebrush, shadscale, and othercold-desert species.

Pinus pollen, including pinyon pine, variably increasesthroughout the zone from a significant rise about 126,600 yrago to a peak 116,100 yr ago. Abies has a similar, but moreirregular, rise in abundance during this interval, peakinglater at 109,600 yr ago. Most of the trend probably repre-sents the expansion of Sierra Nevada montane forests sincethe previous glaciation. Riparian woodland is representedby the occasional appearance of Betula and Shepherdia(buffalo berry) pollen as Salix and Populus decrease in

average abundance. The range or abundance of oak wasapparently drastically reduced after 126,600 yr ago.

After 124,000 yr ago, pinyon became emergent in thewoodland, indicated by the first significant rise in its pollen.The increase of Pinus monophylla pollen relative to Juni-perus pollen is interpreted as a shift in dominance of pinyonin the Inyo Mountains as the lower treeline of juniperretreated. There also seems to have been a general balanceamong warm and cold desertscrub and saltbush associa-tions.

A third vegetation change began after 110,000 yr ago,with another rapid increase of Juniperus pollen accompa-nied by a more moderate increase in Artemisia and a de-crease in Ambrosia and Chenopodiaceae/Amaranthus. Thisreflects mutual adjustments in abundances and ranges be-tween species associated with pinyon–juniper woodland,sagebrush scrub, and warm desertscrub, implying adjust-ments to cooling temperatures. Pinus also decreases duringthis interval. Although the lake remained closed (Bischoff etal., 1997b; Bischoff and Cummings, 2001), pollen dataindicate that temperatures were probably lower than andprecipitation higher than the previous cool period. Increasedwinter precipitation and runoff probably provided a suffi-

Fig. 8. Scatter diagram of a detrended correspondence analysis (Hammer et al., 2001) showing the percentages of 13 pollen taxa (Pinus, Juniperus, Quercus,Ephedra, Chenopodiaceae–Amaranthus, Sarcobatus, Artemisia, Ambrosia, Eriogonum, Brassicaceae, Fabaceae, Asteraceae, and Poaceae) associated with thevegetation types (Davis, 1995) and surface samples of the Owens Valley and Mono Basin given in Fig. 6 and the OL-92 samples. The vegetation types andsurface samples are numbered and indicate where they correspond to the subfossil assemblages of the OL-92 stratigraphy: 1, Owens Valley; 2, Mono Basin;3, California Xeric Forest; 4, Rocky Mountains Xeric Forest; 5, Great Basin Steppe; 6, Great Basin Desert Grassland; 7, Upper Mojave Desert Grassland;8, Lower Mojave Desert Grassland; 9, Upper Sonoran Desert Grassland; 10, Lower Sonoran Desert Grassland. The points are grouped by ellipses accordingto the pollen zones, from glacial conditions on the left of Axis 1 to interglacial conditions on the right. Owens Valley, Great Basin Grassland, and UpperMojave vegetation types are within the Last Interglacial Zone OL-II; Mono Lake, Great Basin Steppe, and Rocky Mountain Xeric Forest are on the edgeof Zone OL-III; and California Xeric Grassland, Lower Mojave Desert Grassland, and Upper and Lower Sonoran Desert Grassland are outside the pointscatter. There are apparently no modern analogs for glacial and interstadial vegetation associations.


ciently high water table to allow greasewood scrub to ex-pand in the available bottomlands.

Finally, again responding to warm temperatures afterabout 93,000 yr ago, the elevation range of juniper retracted,there was little or no change in the abundance of pinyon, therange of Ambrosia expanded slightly, and there was a sec-ondary expansion of montane forest in the Sierra Nevada asindicated by an increase in pine pollen. An increase inArtemisia pollen at this time can be attributed to the localdie off of the juniper overstory and opening of the formerwoodlands. Riparian woodland was augmented with thereestablishment or expansion of buffalo berry, birch, andwillow, but greasewood dramatically decreased with low-ering of water tables, as indicated by a closed lake and anincrease in saline diatoms (Bischoff et al., 1997b; Menkinget al., 1997; Bradbury 1997).

Zone OL-IV

The pollen record for this interval is interpreted as an-other expansion of juniper–pinyon woodland and sage-

brush–bitterbrush scrub and a decline of warm desertscrub,as responses to cooler and wetter conditions after about79,000 yr ago. The climate, however, was dry enough toprevent juniper from expanding to its full glacial extent orabundance. Corresponding Owens Valley packrat middenfloristic assemblages contain the anomalous Joshua tree,and the plant associations have affinities with both cold andhot deserts (Koehler and Anderson, 1994, 1995). The riseand fall of Owens Lake carbonates (Bischoff et al., 1997a,Menking et al., 1997), brief fluctuations of saline and fresh-water diatoms, and seven maxima in the rock flour record(Bischoff and Cummings, 2001) seem to reflect climaticvariability during this period (Bradbury, 1997). The in-crease in rock flour 79,000 yr ago is interpreted as thebeginning of glacial advances in the Sierra Nevada(Bischoff and Cummings, 2001). A decrease in Pinus andAbies pollen is again interpreted as a contraction of SierraNevada subalpine and montane forests as the Sierra Nevadaice cap and glacier complex grew while the balance of Pinuspollen probably came from the expansion of bristlecone andlimber pine subalpine forests in the Inyo Mountains. A

Table 2Description of Owens Lake (OL-92) pollen percentage diagram and modern abundancesa

Pollen zone Depth (m) Age (14C yr ago) Description

n/a Surface Modern Pinus dominates modern pollen at 74.6 Juniperus is a low 0.6% as is Quercus (1%). ChenoAmb

(25.2%), Poaceae (5.1%), and Salix (20.1%) are abundant, but Artemisia (1.9%), Cercocarpus/Purshia(0.6%), Fabaceae (1%), other Asteraceae (0.6%), Ephedra (0.3%), and Sarcobatus (1%) are low.

OL-VI 5.5–10 10,200–17,700 This zone is characterized by a decrease in terrestrial tree pollen and an increase in terrestrial shrub andherb pollen. Juniperus decreases to �5% and Pinus (45.9%), Abies (2.3%), Ambrosia (8.8%), ChenoAm(13.3%), Cercocarpus/Purshia (5.6%), and Ephedra (2.5%) increase. Artemisia increases to 19.8%before decreasing to 10.5%. All the riparian taxa except Salix, which decreases to �1%, areoccasionally present in variable percentages.

OL-V 10–17 17,700–25,700 Juniperus dominates at 57% and rapidly declines to 20.1%. Pinus decreases to 27% and increases to amaximum of 38.2% at the top of the zone. Abies and all of the dominant shrub taxa—Artemisia,Cercocarpus/Purshia type, ChenoAm, Sarcobatus, and Ambrosia—and Asteraceae similarly decrease tolow abundances after which they increase. Poaceae continues to be abundant. Salix increases bimodallyto �5.6% and the other riparian taxa are present.

OL-IV 17–41 25,700–80,100 This zone is characterized by an increase of Juniperus and Artemisia (�23.7%) and a decrease ofPinus. Ambrosia has low percentages (�2.8%); ChenoAm and Asteraceae vary around 5 and 4%,respectively. Poaceae also attains higher but variable percentages. Salix increases to �3.5% and theother riparian taxa are represented in low (�1%) abundances.

OL-III 41–68 80,100–126,500 This zone is distinguished by a fluctuating increase in the frequencies of Pinus (75.5–25.9%) and Abies(�2.5%), both achieving the highest percentages within the entire 90-m record. Pinus cf. monophyllabegins to have high accumulation rates. Juniperus increases to two periods of higher percentages (mean18.8%) and two periods of lower percentages (mean 10.2%). Artemisia also defines a bimodal curve at17.6 and 18.4%. Ambrosia does not exceed 7.9%. Chenopodianceae/Amaranthus fluctuates between aminimum of 2.2% and a maximum of 14.5% and Poaceae and Quercus decrease to trace frequencies.Terrestrial shrubs and herbs declined to �40% while terrestrial trees increased to �60%.

OL-II 68–75 126,500–130,200 This zone is defined by a rapid decline in Juniperus (9.9%) and a rapid increase in Ambrosia (21.2%),ChenoAm (16.3%), and Cercocarpus/Purshia (�8%). Pinus (�20%), Artemisia (�8%), Asteraceae(�8%), Sarcobatus, Salix (�5.6%), Populus (�3%), and Poaceae are relatively frequent. Ephedraviridis, Fabaceae, and especially Quercus (�3.8%) become relatively abundant in this zone.

OL-I 75–90 130,200–180,000 Juniperus pollen (34.7–71.2 %) dominates with lesser amounts of Pinus (max 38.8%), Artemisia (max13.9%), Asteraceae (�6.5%), ChenoAm (�4.6), Ambrosia, and Cercocarpus/Purshia-type (�2%).Sarcobatus, Shepherdia, Populus, Salix, and Poaceae are frequent. Betula (1.9%) peaks at the top of thezone.

a Note that variations in pollen abundance are given with reference to time going forward from Zones OL-I to OL-VI.b ChenoAm � Chenopodiaceae/Amaranthus.


well-watered Owens Valley and a rising lake are expressedby increased values of Poaceae, Sarcobatus, and Salix pol-len.

Zones OL-V and VI

The pollen record for these two zones reflects vegetationresponses to the onset of a cold and wet full-glacial climate(Tioga glaciation), followed by a trend of warming anddrying. The packrat midden macrofossil sequence providesfloristic detail to complement the pollen record (Koehlerand Anderson, 1994, 1995). As in Zone OL-I, juniper wood-land with a sagebrush–bitterbrush–grass understory appearsto have been the dominant vegetation type in the OwensValley between 25,000 and 20,000 yr ago. Juniperus pollenrapidly increased, and the low pollen percentages of Am-brosia indicate that bursage became locally extirpated. An-other decrease in Pinus pollen and the temporary disappear-ance of Abies pollen from the record reflect thediminishment of Sierra Nevada forests due to the expandingTioga ice cap and periglacial environment, similar to ZonesI and IV. Riparian vegetation was primarily a willow–grassassociation with buffalo berry and either cottonwood oraspen. Owens Lake was cold, fresh, and overflowing (Carter1997; Bischoff et al., 1997a, 1997b; Bradbury, 1997;Bischoff and Cummings, 2001)). Inception of the last gla-cial advance, also found in the Owens Lake rock flourrecord, was ca 30,000–32,000 yr ago (Phillips et al., 1996,Bischoff et al., 1997b, Bischoff and Cummings, 2001). Thefirst pulse of the Tioga glaciation has been dated between26,400 and 24,300 yr ago (Atwater et al., 1986; Bursik andGillespie, 1993; Phillips et al., 1996) and the maximumbetween 19,000 and 21,000 yr ago (Fullerton, 1986; Phillipset al., 1996; Bach et al., 1992; Bursik and Gillespie, 1993).The last glacial maximum in the Sierra Nevada was anextreme climatic phase but it seems to have been shorter andless intense than the penultimate glaciation. The Tioga-ageglaciers did not advance quite as far as did the Tahoe-ageglaciers, and the maximum Juniperus pollen percentage at21,200 yr is 10% lower than that at 149,000 yr ago.

Deglaciation marks a significant change in vegetationfrom a biome dominated by cold pinyon–juniper woodlandto one dominated by a hot desertscrub (see also Mensing,2001). The principal pollen taxa of Zone VI show a series ofrapid oscillations from the height of the Tioga Glaciationinto the early Holocene. This is reflected by the multiplelake transgressions of Owens Lake (Benson et al., 1998;Bischoff et al., 1997a, 1997c; Menking et al., 1997; Brad-bury, 1997). The reversal began after about 21,000 yr agowhen juniper and pinyon began to thin and retreat upslopeleaving sagebrush–bitterbrush scrub as a dominant associ-ation. Sagebrush–bitterbrush scrub also retracted after14,000 yr ago with the completion of deglaciation (Clark etal., 1995) when warm desertscrub expanded. Pine and firforests also expanded in the Sierra Nevada. Birch and oak,which are not present in the pollen spectra throughout most

of Zone OL-V, became an increasingly significant part ofthe riparian woodland.

Discussion and conclusions

The vegetation history interpreted from the Owens Lakepollen sequence was placed in an ecological context accord-ing to known biogeographic distributions of the representedplants and correlated with regional climatic conditions in-ferred from Owens Lake sediments and the Sierra Nevadaglacial chronology. It is apparent that desert and montanevegetation responded to large-scale variation in climate.Pinyon–juniper woodland and warm desertscrub were po-larized between glacial and interglacial conditions wherebyone or the other dominated the vegetation associations inconcert with cold and hot climatic phases and varied withclimatic fluctuations in between these extremities. The de-trended correspondence analysis (Fig. 8) positions modernvegetation types within the OL-92 pollen assemblages. Theformer and recent interglaciations of OL-II, -III, and -VIwere similar to the present lower Owens Valley and UpperMojave Deserts at their warmest, and similar to the GreatBasin Desert, Mono Basin Desert, Great Basin Steppe, andRocky Mountain Xeric Forest during cooler periods but didnot approach the warmer and more southerly Lower Mojaveand Sonoran Deserts. The glaciations of OL-I, -V, and -IVconverge on the Mono Basin Desert, Great Basin Steppe,and Rocky Mountain Xeric Forest in their warmer fluctua-tions but there is no known analog for the coldest periods.

Further analysis suggests that low frequency variation inthe most abundant pollen taxa contains a regional climatesignal expressing global orbital variations. Empirical corre-lations were made between the 180,000-yr Owens Lakepollen sequences and the �18 O marine chronostratigraphy(SPECMAP) of Martinson et al. (1987) by visually match-ing the most abundant pollen types with the �18 O curve.The juniper curve was found to be the most useful match.From this comparison and the climatic characteristics in-ferred for the pollen assemblage zones, a possible assign-ment of each zone to the marine isotope stages (MIS) wasmade such that OL-I � MIS stage 6, OL-II and III � MIS5, OL-IV � MIS 3 and 4, OL-V � MIS 2, and OL-VI �MIS 1 (Fig. 9). The revised OL-92 chronology resolved the� 15,000-yr discrepancy between the OL-92 chronologyand SPECMAP, most evident at Termination II, (Wool-fenden, 1996; Smith et al., 1997; Menking et al., 1997),although the increase in juniper pollen now precedes the �18

O increase after 130,000 yr. Accounting for error, the sim-ilarities in pattern but differences in timing of the variationsof the biological and physical sedimentary records amongOL-92, SPECMAP, Devil’s Hole, and Vostok records andother pollen records (Winograd et al., 1992; Petit et al.,1999; Adam, 1988; Heusser and Heusser, 1990; Heusser,1995; Whitlock et al. 2000) seem to reflect common but


complex responses of various proxies to climate change atdifferent times (Karner and Muller, 2000).

Initiation of vegetation change in the southern OwensValley region during the last two glacial terminations wasrelatively coherent with the precipitous rise in temperatureand carbon dioxide, along with the abrupt retreat of conti-nental ice sheets, and appears coherent with MIS 3, 4, and5. The glacial to interglacial pollen transitions are also asabrupt as the lake CaCO3 record, but do not compare withthe earlier and more gradual increases of lake �18 O(Bischoff et al., 1997c; Menking et al., 1997). This suggeststhat transitions in the lake environment and vegetation re-sponded to similar climate drivers but have different re-sponse thresholds. On the scale at which the pollen recordwas analyzed desert vegetation, represented by the sequenceof pollen types through time, appears to track the climati-cally forced glacial–interglacial cycles of the Sierra Nevadaand fluctuations of Owens Lake and to coincide with orbitalvariations.

Acknowledgments

I thank G.I. Smith and the US Geological Survey for theopportunity to do the research on the Owens Lake Core and

Owen Davis for the use of the pollen laboratory at theUniversity of Arizona and for his assistance. Commentsfrom Kirsten Menking and an anonymous reviewer greatlyimproved the manuscript. Financial support for this researchwas provided in part by the Cranwell Award (University ofArizona) and the USDA Forest Service.

References

Adam, D.P., 1988. U.S. Geological Society Professional Paper 1363, LakeCounty, California.

Adam, D.P., Sarna-Wojeicki, A.M., Rieck, H.J., Bradbury, J.P., Dean,W.E., Forester, R.M., 1989. Tulelake, California: The last 3 millionyears. Palaegeography, Palaeoclimatology. Palaeoecology 72, 89–103.

Atwater, B.F., Adam, D.P., Bradbury, J.P., Forester, R.M., Mark, R.M.,Lettis, W.R., Fisher, G.R., Gobalet, K.W., Robinson, S.W., 1986. A fandam for Tulare Lake, California, and implications for the Wisconsinglacial history of the Sierra Nevada. Geological Society of AmericaBulletin 97, 97–109.

Bach, A.J., Dorn, R.I., Elliott-Fisk, D.L., Phillips, F.M., 1992. Paleohy-drological and paleoclimatological implications of glacial morainecomplexes from Pine Creek, Bloody Canyon, and Bishop Creek, East-ern Sierra Nevada, in: Hall, C.A., Doyle-Jones, V., Widawski, B.(Eds.), The History of Water: Eastern Sierra Nevada, Owens Valley,White-Inyo Mountains White Mountain Research Station Symposium,Vol. 4, University of California, Los Angeles, pp. 440–441.

Fig. 9. Comparison of the juniper pollen sequence and the marine oxygen isotope chronostratigraphy (from Martinson et al., 1987) for the past 180,000 yr,with suggested correlation of the oxygen isotope stages (MIS). The juniper pollen curve is inverted in order to show the correspondence in direction betweenthe two curves.


Batchelder, G.L., 1970. Post-glacial Ecology at Black Lake, Mono County,California. Unpublished Ph.D. thesis, Northern Arizona University,Flagstaff, AZ.

Benson, L.V., May, H.M., Antweiler, R.C., Brinton, T.I., Kashgarian, M.,Smoot, J.P., Lund, S.P., 1998. Continuous lake-sediment records ofglaciation in the Sierra Nevada between 52,000 and 12,500 14C yr B.P.Quaternary Research 50, 113–127.

Bischoff, J.L., Cummings, K., 2001. Wisconsin glaciation of the SierraNevada (79,000-15,000 yr ago) as recorded by rock flour in sedimentsof Owens Lake, California. Quaternary Research 55, 14–24.

Bischoff, J.L., Fitts, J.P., Fitzpatrick, J.A., 1997a. Responses of sedimentgeochemistry to climate change in Owens Lake sediment: and 800-k.y.record of saline/fresh cycles in core OL-92, in: Smith, G.I. Bishoff, J.L.(Eds.), An 800,000-Year Paleoclimatic Record from Core OL-92,Owens Lake, Southeast California, pp. 37–47.

Bischoff, J.L., Menking, K.M., Fitts, J.P., Fitzpatrick, J.A., 1997b. Cli-matic oscillations 10,000–155,000 yr ago at Owens Lake, Californiareflected in glacial rock flour abundance and lake salinity in CoreOL-92. Quaternary Research 48, 313–325.

Bischoff, J.L., Stafford, T.W. Rubin, M., (1997c). A time-depth scale forOwens Lake sediments of core OL-92: radiocarbon dates and constantmass-accumulation rate, in: G.I. Smith Bishoff, J.L., (Eds.), An800,000-Year Paleoclimatic Record from Core OL-92, Owens Lake,Southeast California” pp. 91–98.

Bradbury, J.P. (1997). A diatom-based paleohydrologic record of climatechange for the past 800 k.y. from Owens Lake, California, in: SmithG.I. Bishoff, J.L., (Eds.), An 800,000-Year Paleoclimatic Record fromCore OL-92, Owens Lake, Southeast California, Geological Society ofAmerica Special Paper 317, pp. 99–112.

Bursik, M.I., Gillespie, A.R., 1993. Late Pleistocene glaciation of MonoBasin, California. Quaternary Research 39, 24–35.

Carter, C., 1997. Ostracodes in Owens Lake core OL-92: Alternation ofsaline and freshwater forms through time, in: Smith G.I. Bishoff, J.L.(Eds.), An 800,000-Year Paleoclimatic Record from Core OL-92,Owens Lake, Southeast California, pp. 113–119.

Clark, D.H., Bierman, P.R., Larsen, P., 1995. Correlation of late Pleisto-cene glaciation in the western United States with north Atlantic Hein-rich events. Geology 23, 483–486.

Davis, O.K., 1995. Climate and vegetation patterns in surface samples fromarid western U.S.A.: application to Holocene climatic reconstructions.Palynology 19, 95–117.

Davis, O.K., 1999. Pollen analysis of a Holocene–late-Glacial sedimentcore from Mono Lake, Mono County, California. Quaternary Research52, 243–249.

Faegri, K., Iversen, J., 1985. Textbook of Pollen Analysis, 4th ed. Hafner,New York.

Flohn, H., 1969. Local wind systems, in: Flohn, H. (Ed.), World Survey ofClimatology, Vol. 2. General Climatology, Amsterdam.

Fullerton, D.S., 1986. Chronology and correlation of glacial deposits in theSierra Nevada, California. Quaternary Science Review 5, 161–169.

Grimm, E.C., 1987. CONISS: a FORTRAN 77 program for stratigraphi-cally constrained cluster analysis by the method of incremental sum ofsquares. Computers and Geoscience 13, 13–35.

Grimm, E.C., 1992. Tilia and Tilia-graph: pollen spreadsheet and graphicsprograms, Programs and Abstracts, 8th International PalynologicalCongress, Aix-en-Provence, September 6–12, p. 56.

Hales Jr., J.E., 1974. Southwestern United States summer monsoonsource—Gulf of Mexico or Pacific Ocean? Journal of Applied Mete-orology 13, 331–342.

Hammer, O., Harper, D.A.T., Ryan, P.D., 2001. PAST: paleontologicalstatistics software package for education and data analysis. Palaeontol.Electron. 4, 1–9 http://palaeoelectronica.org/2001_1/past/issuel_01.htm.

Heusser, C.J., Heusser, L.E., 1990. Long continental pollen sequence fromWashington State (U.S.A.): correlation of upper levels with marinepollen-oxygen isotope stratigraphy through substage 5e. Palaeogeog-raphy, Palaeoclimatology, Palaeoecology 79, 63–71.

Heusser, L.E. (1995). Pollen stratigraphy and paleoecologic interpretationof the 160-K.Y. record from Santa Barbara Basin, Hole 893A, in:Kennett, J.P. Baldauf, J.G. Lyle, M., (Eds.), Proceedings of the OceanDrilling Program, Scientific Results, Vol. 146 (Pt. 2), pp. 265–277.

Jennings, S.A., Elliott-Fisk, D.L., 1993. Packrat midden evidence of lateQuaternary vegetation change in the White Mountains, California-Nevada. Quaternary Research 39, 214–221.

Karner, D.B., Muller, R.A., 2000. A causality problem for Milankovitch.Science 288, 2143–2144.

Koehler, P.A., Anderson, R.S., 1994. Full-glacial shoreline vegetationduring the maximum highstand at Owens Lake, California. Great BasinNaturali 54, 142–149.

Koehler, P.A., Anderson, R.S., 1995. Thirty thousand years of vegetationchanges in the Alabama Hills, Owens Valley, California. QuaternaryResearch 43, 238–248.

Litwin, R.J., Smoot, J.P., Durika, N.J., Smith, G.I., 1999. Calibrating LateQuaternary terrestrial climate signals: radiometerically dated pollenevidence from the southern Sierra Nevada, USA. Quaternary ScienceReviews 18, 1151–1171.

Markgraf, V., 1980. Pollen dispersal in a mountain area. Grana 19, 127–146.

Martinson, D.G., Pisias, N.G., Hays, J.D., Imbrie, J., Moore, T.C., Shack-leton, N.J., 1987. Age dating and the orbital theory of the ice ages:Development of a high-resolution 0 to 3,000,000-year chronostatigra-phy. Quaternary Research 27, 1–29.

Menking, K.M., Bischoff, J.L., Fitzpatrick, J.A., Burdette, J.W., Rye, R.O.,1997. Climatic/hydrologic oscillations since 155,000 yr ago at OwensLake, California reflected in abundance and stable isotope compositionof sediment carbon. Quaternary Research 48, 58–68.

Mensing, S.A., 2001. Late-glacial and early Holocene vegetation andclimate change near Owens Lake, eastern California. Quaternary Re-search 55, 57–65.

Neilson, R.P., 1987. On the interface between current ecological studiesand the paleobotany of pinon-juniper woodlands. in: Everett, R.L.(Ed.), Proceedings—Pinyon-Juniper Conference. General TechnicalReport INT-215, Intermountain Research Station, Reno, Nevada, pp.93–98.

Petit, J.R., Jouzel, J., Raynaud, D., Barkov, N.I., Basile, I., Bender, M.,Chapellaz, J., Davis, J., Delaygue, G., Delmotte, M., Kotlyakov, V.M.,Legrand, M., Lipenkov, V., Lorious, C., Pepin, L., Ritz, C., Saltzman,E., Stievanard, M., 1999. 420,000 years of climate and atmospherichistory revealed by the Vostok deep antarctic ice core. Nature 399,429–436.

Phillips, F., Zreda, M.G., Benson, L.V., Plummer, M.A., Elmore, D.,Sharma, P., 1996. Chronology for fluctuations in Lake PleistoceneSierra Nevada glaciers and lakes. Science 274, 749–751.

Porter, S.C., Pierce, K.L., Hamilton, T.D., 1983. Late Wisconsin mountainglaciation in the Western United States, in: Wright Jr., H.E. (Ed.),Late-Quaternary Environments of the United States: Volume 1, TheLate Pleistocene, University of Minnesota Press, Minneapolis, pp.71–111.

Pyke, C.B., 1972. Some Meteorological Aspects of the Seasonal Distribu-tion of Precipitation in the Western United States and Baja California.University of California Water Resources Center, Contribution No.139, Los Angeles.

Smith, G.I., 1997. Stratigraphy, lithologies, and sedimentary structures ofOwens Lake core OL-92, in: Smith, G.I., Bischoff, J.L. (Eds.), An800-000-Year Paleoclimatic Record from Core OL-92, Geological So-ciety of America Special Paper 317, Owens Lake, Southeast California,pp. 9–23.

Smith, G.I., Bischoff, J.L., 1997. An 800,000-Year Paleoclimatic Recordfrom Core OL-92. Geological Society of America Special Paper 317,Owens Lake, Southeast California.

Smith, G.I., Bischoff, J.L., and Bradbury, J.P., 1997. Synthesis of the


paleoclimatic record from Owens Lake core OL-92, in Smith G.I.Bischoff, J.L. (Eds.), An 800,000-Year Paleoclimatic Record fromCore OL-92, Owens Lake, Southeast California. Geological Society ofAmerica Special Paper 317, pp. 143–160.

Smith, G.I., Street-Perrott, F.A., 1983. Pluvial lakes of the Western UnitedStates, in: Wright Jr., H.E. (Ed.), Late-Quaternary Environments of theUnited States, Volume 1, University of Minnesota Press, Minneapolis,pp. 190–212.

Snyder, C.T., Hardman, G., Zdenek, F.F., 1964. Pleistocene Lakes in theGreat Basin, U.S. Geological Survey, Washington, DC.

Solomon, A.M., Silkworth, A.B., 1986. Spatial patterns of atmospheric pollentransport in a montane region. Quaternary Research 25, 150–162.

Thompson, R.S., Whitlock, C., Bartlein, P.J., Harrison, S.P., Spaulding,W.G., 1993. Climatic changes in the Western United States since18,000 yr B.P, in: Wright Jr., H.E., Kutzbach, J.E., Webb III, T.,Runddiman, W.F., Street-Perrott, F.A., Bartlein, P.J. (Eds.), Global

Climates since the Last Glacial Maximum, University of MinnestotaPress, Minneapolis, pp. 468–513.

Wahrhaftig, C., Birman, J.H., 1965. The Quaternary of the Pacific Moun-tain System in California, in: Wright, H.E., Frey, D.G. (Eds.), TheQuaternary of the United States, Vol. 1, The Late Pleistocene, Prince-ton University Press, Princeton, pp. 299–340.

Whitlock, C., Sarna-Wojcicki, A.M., Bartlein, P.J., Nickmann, R.J., 2000.Environmental history and tephrostratigraphy at Carp Lake, southwest-ern Columbia Basin, Washington, USA. Paleogeography, Palaeoclima-tology, Palaeoecology 155, 7–29.

Winograd, I., Coplen, T.B., Landwehr, J.M., Riggs, A.C., Ludwig, K.R.,Szabo, B.J., 1992. Continuous 500,000-year climate record from veincalcite in Devils Hole, Nevada. Science 258, 255–260.

Woolfenden, W.B., 1996. Late-Quaternary Vegetation History of theSouthern Owens Valley Region, Inyo County, California, UnpublishedPh.D. thesis, The University of Arizona, Tucson, AZ.


Documents

A 180,000-year pollen record from Owens Lake, CA: terrestrial vegetation change on orbital scales