Hydroclimate variability in the low-elevation Atacama Desert overthe last 2500 yr
E. M. Gayo1,2, C. Latorre1,2, C. M. Santoro3,4, A. Maldonado5,6, and R. De Pol-Holz7,8
1Center for Advanced Studies in Ecology and Biodiversity (CASEB) and Departamento de Ecologıa, Pontificia UniversidadCatolica de Chile, Casilla 114-D, Santiago, Chile2Institute of Ecology and Biodiversity (IEB), Las Palmeras 3425,Nunoa, Santiago, Chile3Instituto Alta Investigacion (IAI), Universidad de Tarapaca, Casilla 6-D, Arica, Chile4Centro de Investigaciones del Hombre del Desierto (CIHDE), Avda. Gral. Velasquez 1775, Oficina 18, Arica, Chile5Laboratorio de Paleoambientes, Centro de Estudios Avanzados en Zonas Aridas (CEAZA), Colina del Pino s/n,La Serena, Chile6Direccion de Investigacion, Universidad de La Serena, Benavente 980, La Serena, Chile7Earth System Science Department, University of California, Irvine, California, USA8Departamento de Oceanografıa, Universidad de Concepcion, Casilla 160-C, Barrio Universitario s/n, Concepcion, Chile
Received: 9 September 2011 – Published in Clim. Past Discuss.: 5 October 2011Revised: 6 January 2012 – Accepted: 6 January 2012 – Published: 21 February 2012
Abstract. Paleoclimate reconstructions reveal that Earth sys-tem has experienced sub-millennial scale climate changesover the past two millennia in response to internal/externalforcing. Although sub-millennial hydroclimate fluctuationshave been detected in the central Andes during this inter-val, the timing, magnitude, extent and direction of changeof these events remain poorly defined. Here, we presenta reconstruction of hydroclimate variations on the Pacificslope of the central Andes based on exceptionally well-preserved plant macrofossils and associated archaeologicalremains from a hyperarid drainage (Quebrada Manı, ∼21◦ S,1000 m a.s.l.) in the Atacama Desert. During the lateHolocene, riparian ecosystems and farming social groupsflourished in the hyperarid Atacama core as surface wateravailability increased throughout this presently sterile land-scape. Twenty-six radiocarbon dates indicate that theseevents occurred between 1050–680, 1615–1350 and 2500–2040 cal yr BP. Regional comparisons with rodent middensand other records suggest that these events were synchronouswith pluvial stages detected at higher-elevations in the cen-tral Andes over the last 2500 yr. These hydroclimate changesalso coincide with periods of pronounced SST gradients inthe Tropical Pacific (La Nina-like mode), conditions that areconducive to significantly increased rainfall in the centralAndean highlands and flood events in the low-elevation wa-tersheds at inter-annual timescales. Our findings indicate thatthe positive anomalies in the hyperarid Atacama over the past
2500 yr represent a regional response of the central Andeanclimate system to changes in the global hydrological cycleat centennial timescales. Furthermore, our results providesupport for the role of tropical Pacific sea surface tempera-ture gradient changes as the primary mechanism responsiblefor climate fluctuations in the central Andes. Finally, our re-sults constitute independent evidence for comprehending themajor trends in cultural evolution of prehistoric peoples thatinhabited the region.
1 Introduction
Records of climate fluctuations over the last two millen-nia have increased significantly over the last few years asthey offer the appropriate context to evaluate the relativerole of natural versus anthropogenic factors in generatingclimate shifts at centennial time-scales. Paleoclimate evi-dence for the past centuries is now reaching a certain levelof consensus regarding the temperature and/or hydroclimaticanomalies that were global in extent. In particular, dur-ing those intervals often included within broad definitionsof the Roman Warm Period (RWP; 2200–1500 cal yr BP),Dark Ages Cool Period (DACP; 1500–1000 cal yr BP), Me-dieval Climate Anomaly (MCA; 1050–600 cal yr BP) andLittle Ice Age (LIA; 600–100 cal yr BP) (Ljungqvist, 2010;
Published by Copernicus Publications on behalf of the European Geosciences Union.
288 E. M. Gayo et al.: Hydroclimate variability in the low-elevation Atacama Desert
Pages-News, 2011; Graham et al., 2010; Wanner et al., 2008;De Jong et al., 2006; Mann et al., 2008).
Paleo-records from around the globe and model simula-tions suggest that these rapid climate changes involved reor-ganisations of major components of the Earth’s climate sys-tem as these respond to internal/external climate forcings,such as the North Atlantic and Tropical Pacific (Helama etal., 2009; Reale and Shukla, 2000; Jones and Mann, 2004).Hence, large-scale temperature and/or hydroclimatic changesduring the MCA have been associated with persistent shiftsof the El Nino Southern Oscillation (ENSO) into a La Nina-like state in the tropical Pacific and the locking of the NorthAtlantic Oscillation (NAO) circulation into its positive mode(Mann et al., 2009; Graham et al., 2007, 2010; Pages-News,2011; Seager et al., 2007; Trouet et al., 2009).
Although considerable efforts have been made to iden-tify the spatial extent/expression, global impacts and under-lying drivers, many aspects of southern hemisphere climatefluctuations over the past two millennia remain poorly de-fined. This is particularly true for the central Andes, whichspan from 10◦ to 30◦ S, where the causes, imprint, magni-tude and timing of climate fluctuations during this periodare hampered by the lack of sufficient data and imprecisechronologies. Exploring the past 2500 yr of climate variabil-ity in the central Andes could help elucidate shifts involvedin the hemispheric circulation dynamics and associated pat-terns. Moreover, paleoclimate reconstructions from this areacould provide insights into the centennial-scale climate vari-ability at tropical and subtropical latitudes of South Amer-ica. Potentially, these would encompass highly contrastingbioclimates that extend from the hyperarid to semi-arid en-vironments of the western Andean slope to the forests andsavannas of the eastern slope.
Here, we establish the hydroclimate conditions of thelow-elevation northern Atacama Desert for the last 2500 yrto infer the timing, magnitude, extent and causes of sub-millennial or centennial-scale climate changes in the cen-tral Andes. Our reconstruction was compiled using the re-sponse of the hydrological, ecological and cultural systemswithin the endorheic basin of Pampa del Tamarugal (PdT)to changes in local hydroclimatic conditions over the lasttwo and a half millennia. We compare our results to otherregional reconstructions and conclude that tropical Pacificforcing is likely the most important driver of the climate ofthe Central Andes during the late Holocene.
2 The study site
The PdT basin (19◦17′–21◦45′ S) is located in the CentralValley (elevation range 1000–1600 m) within the hyperaridcore of the northern Atacama Desert (Fig. 1). The sub-surface sedimentary fill of the pediplain hosts the largestand economically most important aquifer system in north-ern Chile (JICA, 1995; Rojas and Dassargues, 2007). The
western basin margin is bounded by the Coastal Cordillera.The northern portion of the PdT basin (19◦17′–21◦ S) ex-tends along the foothills of the central Andes range. Thesouthernmost portion of the PdT (21◦–21◦45′ S) is flanked tothe east by the Sierra Moreno, a Paleozoic-Mesozoic rangethat is part of the Arequipa-Antofalla craton and rises up to4000 m (Tomlinson et al., 2001; Ramos, 1988).
Rainfall is practically absent in the low-elevation desert(<1 mm yr−1 over the last century; DGA, 2007). PdT aquiferrecharge takes place via surface-water infiltration at the apexof alluvial fans radiating out from perennial and ephemeraltributaries that head at>3500 m along the adjacent Andesand Sierra Moreno where summer rainfall is more frequent(Magaritz et al., 1989; JICA, 1995; Houston, 2002, 2006b).Only a few affluents retain enough surface flow to reach thenorthern PdT, and the dominant surface expression of wateroccurs along the western fringe where surface evaporationforces the outcropping of groundwater brines by capillarity(JICA, 1995).
We studied in situ organic-rich deposits, rodent-burrowsand archaeological archives found at Quebrada Mani (QM)an unvegetated, uninhabited and ephemeral (dry) ravine thatdrains into the southernmost PdT basin (∼21◦ S; Figs. 1, 2).All of these records are exceptionally preserved on the sur-face of two abandoned fluvial terraces (Fig. 3) that aggradedduring the latest Pleistocene along the incised late Miocenefan deposit that forms the natural QM walls (T1). This fluvialfill occurred during major past changes in stream and ground-water discharge (Nester et al., 2007; Gayo et al., 2009) asso-ciated with a major pluvial that occurred throughout the cen-tral Andes during the last global deglaciation, now termed the“Central Andean Pluvial Event” or CAPE (17 500–14 200and 13 800–9700 cal yr BP; Quade et al., 2008; Latorre et al.,2006; Placzek et al., 2009).
The southernmost PdT is completely separated from thehigh Andean basins by the Sierra Moreno. Hence, local hy-droclimatic and ecological patterns are strongly tied to sum-mer rainfall variability along the central Andean highlands.Today, short-lived and occasional pulses in surface-waterflooding and growth of isolated annuals (Gajardo, 1994) havebeen observed to occur along dry tributaries after unusuallyheavy summer storms in the Sierra Moreno and the centralAndean headwaters (Houston, 2006b). Phreatophytes suchProsopis alba, Schinus molleandCaesalpina aphyllacan oc-casionally be found growing within the active drainages. Ex-isting paleoclimate evidence from QM and other nearby inac-tive affluents show that positive headwater moisture anoma-lies promoted unprecedented shifts in the local hydrologicaland ecological systems on millennial time-scales. Indeed, in-creased rainfall during the CAPE led to increased perennialrunoff and local water-tables, as well as enabling riparianecosystems and human cultures to flourish in the presentlysterile landscape of the PdT (Santoro et al., 2011; Nesteret al., 2007; Gayo et al., 2009). Thus, these past traces offossil ecosystems and human activities throughout inactive
E. M. Gayo et al.: Hydroclimate variability in the low-elevation Atacama Desert 289
Fig. 1. (a)Study area indicating localities discussed in the text. Red dot: mean location for the 26 geohistorical archives recovered from QMand reported here. Yellow dot: Ramaditas archaeological site at Quebrada Guatacondo. Black dashed line: PdT basin boundaries. Horizontalwhite line: limit between the northern and southern PdT basin.(b) A topographic cross-section located along the transect labeled from 1 to2 in (a).
ravines of the PdT reflect local hydrological budgets abovethe modern mean triggered by increased rainfall amounts athigher-elevations. Paleoclimate reconstructions for the inac-tive canyons from the southern PdT basin thus represent es-tablished proxies for evaluating the hydrological response ofthe central Andes to global centennial-scale shifts in climate.
3 Materials and methods
Our reconstruction is based on radiocarbon dates and macro-fossil analyses from eight in situ organic-rich deposits andfrom eighteen radiocarbon dated organic remains associated
with archaeological artifacts (Table 1, Fig. 3). In situ organic-rich deposits yielded datable and taxonomically identifiablefossil-plant remains with no signs of tissue decay and dam-age (Figs. 4a, A1 and A2). Most of these are leaf-litter de-posits preserved on the T2.5 surface (Fig. 3, Table 1). Wealso analysed two rodent burrows dug into a well-exposedlate Pleistocene paleowetland deposit comprised of∼1.2 mthick fine-medium sands to fine silts (the deposit itself likelydates to∼11 700–7900 cal yr BP, unpublished data) on theT2.5 terrace (Figs. 3 and A3). These burrows contained hard-ened urine deposits with amalgamated feces, vertebrate re-mains and plant-macrofossils akin to rodent middens (QM-22A and QM-22C; Table 1; Fig. A3).
290 E. M. Gayo et al.: Hydroclimate variability in the low-elevation Atacama Desert
Fig. 2. A panoramic view taken looking northwest across the hyperarid Quebrada Mani (QM). Note the widespread extent of the stone-linedcultivation fields (“melgas” in spanish) on the T2.5 terrace. The valley is approximately 300 m wide and the T1 (late Miocene) terrace isvisible in the near background. The low hill to the centre right is Cerro Challacollo (1503 m a.s.l.).
Modern channel
Legend
Wavy-laminated silts and sands
Cross-laminatedsands and gravels
Cross-laminatedwell-sorted sands
Well-laminated poorlysorted sands and gravels
Unwelded tuff (5.4 Ma)
Latest Pleistocene leaf-litter deposits
T3T2.7
T2.5T2
20m
15,600 cal. yr BP
. 11,400-11,700 cal. yr BP
.
T1
Superficial archeological remains
Leaf-litter deposits reported here
Paleowetland deposit containing rodent-burrows
Fig. 3. A generalized stratigraphy of fluvial terraces found in Quebrada Manı (modified from Nester et al., 2007) showing the relationshipbetween these units and the records reported here. Terraces are labelled in descending order (to the modern channel) as T1, T2, T2.5,T2.7, T3 and “modern”. Fluvial terrace systems T2 and T3 dissect late Miocene alluvial fan deposits (T1) at∼1200 m elevation, spreadingbeyond this point to form alluvial fans. The modern channel is inset by 1–3 m at 1250 m elevation and rests>5 m below T3 and continues as aconfined channel for several kilometres downstream. Late Pleistocene leaf-litter deposits (ages shown in red numbers) and paleohydrologicalimplications were reported in Nester et al. (2007).
Remains of past human activities abound upon the sur-face of QM T2.5 and T2.7 terraces (Figs. 2, 3), includ-ing malachite beads, lithic and shell artifacts, rock engrav-ings (petroglyphs), bones, ceramics, agricultural infrastruc-ture (including terraced crop fields, irrigation channels anddams) and collapsed structures. We strategically surveyed
for organic remains found in association with these artifactsas these could offer datable materials unequivocally derivedfrom when human activities took place at QM. Hence, wesampled underneath rocks placed along floodplain irrigationchannels (Table 1, Fig. 4b) or lying on the ridges of stone-lined cultivation fields (locally termed “melgas”; Fig. 4c).
E. M. Gayo et al.: Hydroclimate variability in the low-elevation Atacama Desert 291
Table 1. AMS dates and depositional context for the 22 records used in this study. Calibrated ages in years BP and corresponding confidenceintervals at 2σ level are illustrated graphically in Fig. 5a.
Sample ID Laboratory code Type of record Dated Material 14C yr BP δ13C (‰) Cal yr BP 2σ cal yr BP
We also recovered remains of crop plants (e.g., maize) foundeither in rodent burrows or on the surface of cultivation fields(Table 1, Fig. A4). Exceptionally, we sampledProsopissp.leaves underneath a lithic shovel lying on the surface (Ta-ble 1). Superficial and subsurface charcoal samples were re-trieved from a stone crop field ridge (Table 1) and underneathstructural-stones that formed a semicircular collapsed struc-ture of 4 m diameter associated with crop fields and irriga-tion channels (Table 1, Fig. A5). We also recovered charcoalat 65 cm of depth from a test pit excavated into a horseshoe-shaped dam structure built out of mud and stones that rises upto 1 m upon the T2.5 terrace (Table 1, Fig. A6). Other sam-ples include semi-carbonized herbaceous remains containedin a mud section dug into a perched channel that runs parallelto the stream-bed in the contact between T2.5–T2.7 terracesand rises 82 cm above the T2.7 surface (Table 1, Fig. A7).These remains were sampled at 12 cm (QM-37A) and 26 cm(QM-37C) of depth along this section. Additionally, we re-coveredProsopissp. leaves from two superficial polygonalleaf-beds of 4 cm thick× 1 m length× 1.5 m width (Table 1,Fig. A8).
Organic deposits were hand-sorted for macrofossils undera dissecting binocular microscope (10–50× magnification).Rodent burrow material was processed following proceduresdescribed in Latorre et al. (2002). Fossil plant remainswere identified to the highest taxonomic level possible ei-ther by comparison with our reference collection of mod-ern flora from northern Chile (housed at the Laboratorio
de Paleoecologıa, PUC) or by using published taxonomickeys (Munoz-Pizarro, 1966; Nicora and Rugolo de Agrasar,1987). Molar teeth from a rodent cranium found within theQM-22C burrow were identified as well based on taxonom-ically relevant characteristics. This specimen was identifiedby directly comparing features of molars M1 and M2 withmodern specimens.
Accelerator mass spectrometry (AMS) radiocarbon datingon short-lived plant tissue was preferred rather than associ-ated woody materials to build our chronologies. Woody tis-sues resist degradation in hyperarid environments and repre-sent minimum dates at best. All radiocarbon ages reportedhere were calibrated using CALIB 6.0 at 2-sigma (withthe Southern Hemisphere Calibration calibration curve-SHCal04, Intercept Method; McCormac et al., 2004) and aregiven in calendar years before 1950 (cal yr BP).
Past hydroclimatic shifts at QM were inferred by consid-ering the water requirements/adaptations and modern dis-tribution ranges described for each taxa resolved taxonom-ically to family level or above that occurs within a plant-macrofossil assemblage (Table 2). This is because the ex-istence of plant communities with distinct functional groupsin the Atacama is determined by water availability (Arroyo etal., 1988), which in turn is tightly linked to the strong precip-itation gradient (0 mm yr−1 at 1000 m a.s.l. to 120 mm yr−1
at 4000 m a.s.l.) that occurs on the western Andean slope(Houston and Hartley, 2003).
292 E. M. Gayo et al.: Hydroclimate variability in the low-elevation Atacama Desert
Fig. 4. (a)QM-16 in situ leaf-litter mound. Dashed line describesthe deposit extension.(b) Floodplain irrigation channel. Detailsfor Prosopissp. leaves underneath a stone dam (QM-38 sample)are shown.(c) A “melga” (stone-lined crop field) built on the T2.5terrace. Circle shows where the QM-35A sample was recovered.
Plant distributions were established by verifying the oc-currence of taxa within five current well-defined plant forma-tions developed from semiarid to hyperarid zones along thewestern central Andean slope between 16◦–22◦ S (Table 2).Among these, hillslope ecosystems contain species occurringat elevations between 2600–3300 m and>3400 m (denotedAndean and Altiplano communities, respectively). Thesetaxa survive on direct rainfall, experiencing annual rain-fall amounts between 23–56 mm yr−1 (2600–3300 m) and>60 mm yr−1 at elevations above 3400 m (Houston and Hart-ley, 2003). The other three associations incorporate taxaadapted to extreme hyperaridity and survive either on fog(the coastalLomas formations), groundwater outcropping(Pampa formations) or on perennial runoff (Riparian forma-tions). Non-endemic taxa from the Atacama Desert wereclassified as exotic.
Functional groups for northern Atacama plants were de-fined based on published descriptions of life-forms (annu-als vs. perennials) and water-use strategies (e.g., Mooney etal., 1980; Munoz-Pizarro, 1966; Luebert and Pliscoff, 2006).
Plants were categorised into the following four hygromor-phisms, distinguishing the degree that these could vary ac-cording to environmental factors (facultative vs. obligate).Hygrophytes are plants growing in moist soils maintained byperennial bodies of water (such as those along ponds, in riverfloodplains and in wetlands). Phreatophytes are deep-rootedshrubs and trees that obtain water from a permanent ground-water supply. They often occur inside active washes in ourstudy area. Mesoxerophyte plants are tolerant to prolongeddroughts but cannot survive without two–three months of di-rect rainfall. Finally, xerophytes are plants that are tolerant toprolonged droughts, but survive by hydraulic-lift uptake andfound in association with hygrophytes or phreatophytes.
4 Results and discussion
4.1 Chronology, paleoecology, archaeology and pasthydroclimate conditions
Apart from the archaeological contexts previously described,we found that organic-rich deposits from QM occur in threedifferent natural depositional contexts. The first of these areleaf-litter/wood mounds that emerge slightly above the T2.5terrace (Fig. 4a). These are contained within fine sandy siltsand represent fossilized understories of vegetation that likelywere growing in situ upon the surface. The second type ofdeposits correspond to subsurface leaf-litter deposits foundat <30 cm below the surface (Fig. A2). These deposits ap-pear as concentrated plant material embedded within a wavy-laminated fine silt or sand matrix, possibly indicating anoverbank depositional environment. Therefore, these repre-sent in situ vegetation growing in areas with periodic pond-ing/flooding. Finally, the third type of deposit incorporatesplant-macrofossils encased within rodent burrows dug into apre-existent older surface. Since plant remains were incor-porated into the midden for consumption and nest buildingfrom within the foraging range of the agent (usually<100 mfor murid rodents), they can provide a discrete record for veg-etation growing upon a limited area of the T2.5 terrace whenthey formed.
Twenty-six radiocarbon dates (Table 1) on samples fromQM exhibit three clusters at 1050–680, 1615–1350 and2245–2230 cal yr BP with important hiatuses at the intervals<680, 1350–1050 and 2230–1615 cal yr BP (Fig. 5a). Weinterpret this discrete clustering of ecological-archaeologicalactivity as episodes of augmented productivity brought aboutby positive local hydrological budgets. That is, once surfacewater becomes available at QM, life invades this extreme hy-perarid landscape creating a fertile oasis for economic humanactivities.
Major gaps in our chronology can be interpreted in twovery different ways. They could reflect periods of loweredgroundwater tables and/or decreased perennial runoff, whichwould lull plant productivity as local hydrological budgets
E. M. Gayo et al.: Hydroclimate variability in the low-elevation Atacama Desert 293
Table 2. List of taxa identified from macrofossil analyses on leaf-litter and rodent deposits from Quebrada Manı. (*) Indicates annualphenology. Functional group for each plant species: (Hy) Hygrophyte, (X) Xerophyte, (Ph) Phreatophyte and (Mx) Mesoxerophyte. Taxadistribution at major Northern Atacama Desert vegetational formations: (R) Riparian, (L) Lomas, (P) Pampa, (A) Andean, (AL) Altiplanoand Exotic (Ex).
Species Family Functional group PresenceTaxadistribution
Plant macrofossils
Atriplex atacamensis Chenopodiaceae Facultative X QM-16 R, P, A, AL(from X to Mx) QM-14
Atriplex glaucescens Chenopodiaceae Facultative X QM-14 R, A, AL(from X to Mx)
Atriplex sp. Chenopodiaceae Facultative X QM-14 R, P, A, AL(from X to Mx)
Baccharis alnifolia Asteraceae Obligate Hy QM-16 RQM-14
Baccharis scandens Asteraceae Obligate Hy QM-14 RChenopodium petiolare(*) Chenopodiaceae Facultative Hy QM-14 R, L, A, AL
(from Hy to X, Mx)Cistanthesp. (*) Portulacaceae Facultative Hy QM-16 R, L, A, AL
(from Hy to X, Mx) QM-14Cortaderia atacamensis Poaceae Obligate Hy QM-16 R, A, ALCryptanthasp. (*) Boraginaceae Facultative Hy QM-16 R, A, AL
(from Hy to Mx)Euphorbia amandi(*) Euphorbiaceae Obligate Mx QM-14 ALJunelliasp. Verbenaceae Obligate Mx QM-14 A, ALMuhlenbergiasp. (*) Poaceae Obligate Hy QM-16 RNicotiana longibracteata Solanaceae Obligate Hy QM-14 RPolypogon interruptus Poaceae Obligate Hy QM-16 RProsopissp. Mimosaceae Obligate Ph QM-2E, QM-3, R, P
QM-14, QM-16,QM-18, QM-22A,QM-22C
Solanaceaesp. Solanaceae No data QM-14 No dataSolanaceaesp. 2 Solanaceae No data QM-14 No dataTarasa operculata Malvaceae Facultative Hy QM-14 R, A, AL
(from Hy to Mx)Tessaria absinthioides Asteraceae Obligate X QM-16 R, L, PZea mays(*) Poaceae Irrigated QM-22E Ex
Animal macrofossils
Auliscomyssp. Cricetidae QM-22C AL
remained equal or below the modern. Hence, no macro-fossils or artifacts would date to this period. Or they couldarise from a sampling effort. Simply put, it is possible thatmore sampling could produce dates that “fill” in these gaps.Clearly, the absence of evidence (a “hiatus”) may not consti-tute fail-safe evidence for absence. We extensively surveyedand dated all samples available in the field over the courseof three field seasons in order to reduce this sampling bias.Yet because the contribution of these factors cannot be to-tally ruled out, we are cautious of any paleoenvironmentalinterpretations based on these hiatuses.
A large cluster of seventeen dates between 1050 and680 cal yr BP argues for a prominent increase in agriculturaland biological activity at QM coeval with the MCA (Fig. 5).Nine 14C-dates on leaf-litter deposits and rodent burrows in-dicate that between 960 and 680 cal yr BP, plants grew in situupon the surface of T2.5 terrace (Table 1) and sustained ro-dent populations (Table 2). Similarly, radiocarbon dates frommaize canes in life-position and organic materials in directassociation with widespread farming vestiges suggest pro-longed and intense agricultural activities within an extensivefarming camp established along QM by 1050–730 cal yr BP
294 E. M. Gayo et al.: Hydroclimate variability in the low-elevation Atacama Desert
500 1,000 1,500 2,000 2,500Calendar years BP
0
4
3
2
1
0
-1
-2
-3
Slowdown in AMOC
Win
ter
NA
O r
eco
nst
ruct
ion
(N
AO
ms)
1
1.5
Wet
den
sity
(g
/ccm
)L
ithic co
ncen
tration
(reversed scale)
MCALIA RWP
No
sca
le
La Niña-like conditions
DACP
. .Ramaditas chronology
La Niña-like conditions
Low
High
A
B
C
D
Fig. 5. Comparison of paleoclimate records:(A) all 14C dates on paleoecological and archaeological samples from Quebrada Manı. Greencircles: relict tree mounds and rodent burrows; red circles: organic materials associated with farming (irrigation) structures. Yellow circles:maize remains (in situ canes and corn cob found in a rodent burrow). Heavy horizontal dark line with circles indicates the chronologyfor Ramaditas archeological site (Rivera, 2005).(B) A 30-yr running average for lithic concentrations derived from sediment core SO147-106KL collected offshore central Peru; low lithic concentrations are interpreted as reduced precipitation runoffs associated to prevailing LaNina-like conditions (red arrow up) over the Tropical Pacific (Rein et al., 2005).(C) Wet sediment density from Laguna Aculeo (Jenny et al.2002); reduced sediment density implies low frequency of flood sediment deposition as sustained La Nina-like conditions (black arrow down)promote reduced winter precipitation across central Chile.(D) Winter NAO reconstruction (further details on the estimation of NAOms, seeTrouet et al., 2009); negative NAOms values are interpreted as a subdued Atlantic meridional overturning circulation (AMOC; green arrowdown). Major global climate events over the last 2500 yr such as Little Ice Age (LIA), Medieval Climate Anomaly (MCA), Dark Ages CoolPeriod (DACP) and the Roman Warm Period (RWP) are indicated at top of figure.
E. M. Gayo et al.: Hydroclimate variability in the low-elevation Atacama Desert 295
(Table 1). A preliminary analysis on ceramic fragments as-sociated with the farming vestiges preserved on the T2.5terrace suggest affinities with the Charcollo-Pica pottery typefrom the Pica-Tarapaca complex. This cultural complexincorporates local farmer societies that inhabited perennialriver canyons in the northern PdT basin between 1000 and500 cal yr BP (Uribe et al., 2007).
Plant-macrofossil analyses from eight paleoecologicalsamples indicate that the vegetation growing on the terracesurface between 960 and 680 cal yr BP had low taxonomicrichness: some 20 taxa included in 10 Families (Table 2).Remains of perennial hygrophyte (obligate and facultative)and facultative-xerophytes abound in both tree-relict moundsand rodent-burrows (Table 2), along with abundant leavesindistinctly attributable to obligate-phreatophytes commonlyfound in the PdT (Prosopis albaor P. tamarugo). By anal-ogy with the taxonomical composition and blend of modernfunctional groups present in northern Atacama ecosystems,we postulate that a riparian formation dominated by phreato-phytes invaded QM between 960 and 680 cal yr BP. This as-semblage is similar to those confined to perennial tributariesin the northern PdT and implies that surface water availabil-ity must have increased significantly during the MCA com-pared to what is now an inactive affluent.
Whether this increase was due to augmented water ta-bles, increased perennial riverflow or anthropogenic chan-nelling of resources from higher elevations for irrigation(a sophisticated irrigation system of channels and dams isclearly present at QM) or even a combination of all threefactors needs to be assessed. Evidence for extensive water-dependent farming practices at QM (e.g., maize cultivation;Aubron and Brunschwig, 2008) support the notion that lo-cal exoreic hydrological patterns prevailed between 960 and680 cal yr BP. Yet this could also explain the widespreadpresence ofProsopissp. in our paleo-ecological archives asthese trees could survive off the spillover/infiltration fromcrop irrigation. At present, all theProsopistrees in the PdTbasin grow in areas with shallow outcropping of ground-water, so it seems reasonable to suggest that local water-tables increased during the MCA within the QM drainage.In natural settings, this obligate-phreatophyte is indicative ofphreatic levels down to∼13.3 m b.g.l. (metres below groundlevel), which represents the critical depth for vitality andpotential-growth inP. tamarugo. QM today exhibits ground-water levels of>70 m b.g.l. (PRAMAR-DICTUC, 2007).These could rise quickly after flood events, however, but lit-tle information exists as to the magnitude of these changes.Observational data from two events of anomalous surfaceflow documented in PdT ephemeral watersheds during thesummers of 1999–2000 and 2001 demonstrated that localphreatic levels were quickly recharged owing to infiltrationfrom floodwaters into the underlying unsaturated aquifer(Houston, 2002, 2006b).
More importantly, artificial irrigation at QM must havebeen limited in extent. QM is an ephemeral canyon that
rapidly grades into a narrow high energy box canyon above1400 m a.s.l., with episodic large flooding events capable ofdestroying any but the most robust irrigation channels. Per-manent river flow can be found in the tributaries of QM, butonly above 3400 m where rainfall is high enough to sustain it.Even today, it would be a major enterprise to bring these re-sources>40 km down to the elevations of the extensive cul-tivation fields that flourished between 960 and 680 cal yr BP.
Nevertheless, there is a clear human factor behind the pres-ence ofProsopis in our deposits. These trees have beenplanted and exploited for centuries by local populations forshade, food resources, fuel and building materials (Habit etal., 1981; Nunez and Santoro, 2011). The gathering and con-sumption ofProsopistrees and maize are considered com-mon practices of the Pica-Tarapaca cultural-complex (Mar-quet et al., 1998; Uribe, 2006). In fact, we found unam-biguous evidence for broad usage ofProsopisby QM in-habitants during the MCA. Over 44 % of farming vestigesdated between 1050 and 730 cal yr BP yielded short-livedProsopistissues (Table 2). Remains ofProsopistree stumpsand buried wooden posts can be found throughout the irri-gation channel complex at QM. Therefore, their presence inQM during the MCA may be related to the presence of afarming society that significantly transformed the watershedlandscape. Based on the above, we argue that this was the re-sult of increased and persistent surface runoff that sustainedthese agriculture practices for hundreds of years at a time.
In contrast, the presence of hillslope mesoxerophytes andthe sigmodontine rodentAuliscomyssp. (Table 2) in our sam-ples could be interpreted as a rise in local rainfall during theMCA at QM. Outstanding local preservation of desert pave-ments and exposure ages on boulders preserved∼150 kmnorth of QM indicate, however, that the PdT has remainedhyperarid (with occasional increases in runoff) over the last14.6 million years (Evenstar et al., 2009). Again, we suspectthat the hillslope taxa present in our record are linked to hu-man activities for two reasons. Firstly, modern Andean hu-man communities forage for and useEuphorbia amandiandJunellia sp. (Villagran et al., 1999, 2003), so these speciescould have been introduced deliberately for these purposesby QM inhabitants. Secondly, sigmodontines frequently in-vade grain-crops (Nowak, 1999). Therefore, the presence ofAuliscomyssp. can be explained by passive human transportas corn production thrived locally. In fact, one of our ro-dent burrows contained both a well-preserved maize cob andAuliscomyssp. remains, all dated to 850 cal yr BP and sur-rounded by abandoned cultivation fields.
Evidence for earlier human occupation at QM comes fromnine14C dates taken on buried charcoal and plant fragmentsfrom a section dug into a perched irrigation channel and otherarchaeological remains, including a dam and other structuresfound near the apex of the QM fan (see Sect. 3, Materialsand methods). These dates reveal two distinct periods of in-creased activities dated at∼2200 and 1615–1350 cal yr BP(Table 1) that coincide with the RWP onset and RWP-DACP
296 E. M. Gayo et al.: Hydroclimate variability in the low-elevation Atacama Desert
transition (Fig. 5a). As stated above, this evidence representsagricultural practices that rely on the capture and distributionof freshwater flow (Aubron and Brunschwig, 2008). Hence,we propose that these older events were mediated by aug-mented surface-water availability along the QM drainage.
Archaeological irrigation features in the QM drainagedated to∼2240 cal yr BP are contemporaneous with the Ra-maditas site, an extensive farming/village complex datedto 2560–2040 cal yr BP (Fig. 5a; Rivera, 2005) along Que-brada Guatacondo, an ephemeral drainage located∼19 kmnorthwest of our site (Fig. 1). Akin to QM, the coloniza-tion and exploitation of Q. Guatacondo has been interpretedas the result of steady, reliable and low intensity increasedrunoff when compared to today (Bryson, 2005). This im-plies that the amplified hydrological budgets witnessed atQM, at least for the onset of the RWP, involved other inac-tive tributaries from the southernmost PdT basin with similardirection and magnitude. By combining data from both ar-chaeological sites we can obtain a constrained chronology forsuch hydroclimate conditions. In fact, continuous occupationof Ramaditas between 2500 and 2040 cal yr BP argue for a∼500 yr-period of increased surface water availability as wella shorter duration for the ensuing radiocarbon gap, whichspans from 2040 to 1615 cal yr BP (Fig. 5a). The postulatedduration of the positive hydroclimate anomalies documentedhere is certainly testable by future studies that incorporatefurther archaeological and paleoecological archives retrievedfrom the southernmost PdT basin.
4.2 Regional paleoclimate of the last 2500 yr
We argue that the unprecedented positive hydrologicalanomalies inferred for the southernmost PdT basin were at-tributed to increased moisture availability at higher eleva-tions in the Sierra Moreno over the past 2300 yr (Fig. 5a).This could have come about either by direct increases in rain-fall or glacial-melt output and/or reduced evaporation rates(an air-temperature function). All constitute alternative ex-planations for the persistence of perennial riverflow through-out much of the duration of the MCA and at the onset of theRWP and the RWP-DACP transition.
The relative contribution of glacial meltwater in gener-ating increased surface water availability over the last twoand a half millennia can only remain speculative until therecent glacial history of Sierra Moreno (with peaks topping4000 m a.s.l.) is established. In contrast, the contribution ofreduced evaporation by decreased temperatures can be dis-missed because global and regional reconstructions suggestthat the RWP onset and MCA were periods of exceptionalwarmth (Neukom et al., 2010; Ljungqvist, 2010; Mann etal., 2008). More importantly, observational data suggestthat evaporation rates over the central Andes are primarilycontrolled by moisture availability owing to the effects ofcloudiness on net radiation (Vuille et al., 2000; Houston,2006a). Hence, the simplest explanation is that the events of
increased surface water availability detected in QM at 2500–2040; 1615–1350; and 1050–680 cal yr BP can be interpretedas the result of protracted pluvial events in the Sierra Morenoand central Andes during the RWP onset, RWP-DACP tran-sition and MCA.
Many paleoclimate reconstructions from the central An-des, however, do not agree or are inconclusive regarding ourchronology of hydroclimate changes. For example, limno-geological records from the Altiplano indicate that present-day conditions have remained stable over the last 3000 yr(e.g., Baker et al., 2005) or that the centennial-scale vari-ability over the last two millennia was marked predomi-nantly by negative precipitation anomalies (e.g., Grosjean etal., 2001). Peaks in inorganic concentrations and Cyper-aceae pollen analysed in a core retrieved from the Mar-cacocha basin (13◦ S; 3355 m a.s.l.) have been interpretedas evidence for negative rainfall anomalies at 2450; 1850;and 1400 cal yr BP and during the entire interval encompass-ing the MCA and the LIA,∼1050–150 cal yr BP (Chepstow-Lusty et al., 2003). Similar conclusions were reached forthe Titicaca basin record (16◦ S, ∼3810 m a.s.l.) whichshows three dry events at 2400–2200; 1900–1700 and 900–600 cal yr BP, the latter followed by a period of increasedmoisture throughout the LIA (Abbott et al., 1997, 2003;Mourguiart et al., 1998). Contrasting hydroclimate condi-tions have been also inferred from a calcite record recoveredfrom varves at lake Pumacocha (10◦ S, 4300 m a.s.l.) dur-ing the MCA and LIA intervals (Bird et al., 2011). Moderninter-annual precipitation variability at Pumacocha is underthe same climate regime as the QM headwaters (Garreaudet al., 2009), yet increasedδ18Ocalcite in the lacustrine sed-iments suggest that the Peruvian Altiplano experienced dryconditions during the MCA (1050–850 cal yr BP; Bird et al.,2011). In contrast, negative values inδ18Ocalcite by 650–130 cal yr BP argue for maximum precipitation throughoutthe LIA (Bird et al., 2011).
Archaeological evidence from the Titicaca area and itsKatari tributary also point to opposite hydrological and cul-tural patterns between the Altiplano and the QM drainageduring the MCA. Binford et al. (1997) show that reducedstream flow and phreatic levels at Katari were caused by aconspicuous drought that in combination with anthropogenicfactors provoked the collapse of the Tiwanaku States be-tween 800–750 cal yr BP. It is interesting to note that thesewere also farming societies that inhabited and exploited anartificial regional hydrological productive system in the Tit-icaca basin from 2300 cal yr BP (deMenocal, 2001; Kolata,1993, 1991).
That paleoclimate records along the western Andean slopeevince pluvial phases at times associated with prevailingdrier conditions over the Altiplano is hardly new. Indeed,several authors have highlighted the discrepancies betweenthe timing and direction of hydroclimatic changes on theAltiplano versus the western Andean flank over the last21 000 yr (Rech et al., 2002, 2003; Betancourt et al., 2000;
E. M. Gayo et al.: Hydroclimate variability in the low-elevation Atacama Desert 297
Latorre et al., 2002; Grosjean, 2001, 2003; Quade et al.,2001). Different sensitivities to climate change, lags ingroundwater and lacustrine records, and sub-regional vari-ations have all been suggested as possible explanations forthese discrepancies (Betancourt et al., 2000; Latorre et al.,2005).
Our chronology of positive hydrological anomalies overthe southernmost PdT basin and Sierra Moreno is practicallysynchronous with evidence for wetter interludes detected inother records from the upper margin of the Atacama Desert(>2000 m of elevation) during the MCA and by the RWPonset and RWP-DACP transition. Raised shorelines fromthe Aricota basin (17◦22′ S, 2800 m a.s.l.) indicate a mod-erate lake highstand from 1610 to∼1300 cal yr BP broughtabout by increased moisture budgets in the Peruvian An-des (Placzek et al., 2001). Similarly, the extent and verti-cal thickness of paleowetland deposits dated at 2600–1300(Unit D1) and 800–400 cal yr BP (Unit D2) imply elevatedwater tables within incised canyons and springs across thenorthern and central Atacama (18◦–23◦ S; Rech, 2001, 2003,2002). Prevailing wetter conditions at 2300–2000; 1400–1200 and 1020–600 cal yr BP have also been inferred fromrodent-middens collected between 18◦ and 25◦30′ S alongthe western Andean flank (Latorre et al., 2002, 2006, 2003;Holmgren et al., 2008; Maldonado et al., 2005). Rainfallanomalies calculated using the modern relationship betweenrodent fecal pellet diameters (a proxy for body size) andmean annual rainfall argue for a three-fold increment in rain-fall in the Calama and Salar de Atacama basins (∼24◦ S) dur-ing the MCA (Latorre et al., 2010). The presence of steppegrasses (today confined to elevations>3900 m a.s.l.) in ro-dent middens from the Calama basin’s perennial Rıo Salado(∼22◦ S, 3100 m a.s.l.) suggest a large rainfall increase at800 cal yr BP, which rapidly decreased to modern values by700 cal yr BP as indicated by the presence of local taxa (La-torre et al., 2006).
4.3 What has driven the long-term hydrological andecological dynamics of the PdT over the last2500 years?
Today, most of the tropical rainfall that reaches down to∼2000 m a.s.l. along the western Andean flank occurs dur-ing the austral summer as moisture sourced from the SouthAmerican Summer Monsoon (SASM) (Zhou and Lau, 1998)spills over the Andean crest. This seasonal circulation pat-tern is controlled by the position and strength of the BolivianHigh (Garreaud et al., 2003). Intensification and southwarddisplacement of the Bolivian High enhances easterly flowand increases moisture influx from the Amazon basin andGran Chaco into the Altiplano and along the western slope ofthe Andes (Garreaud et al., 2003; Vuille and Keimig, 2004).
At orbital and millennial time-scales, past hydrologicalchange on the Altiplano and western Andean slope over thelast 180 ka has been linked to mechanisms that affect either
SASM moisture availability or the westward transport ofmoist air masses from eastern South America. The first ofthese hypotheses stresses the role of North Atlantic SSTs andconcomitant effects on moisture availability in the Amazonbasin and westward advection of SASM-derived moistureacross the Altiplano and onto the Pacific slope of the An-des. Wet phases are usually interpreted as a propagation ofthe slowdown in the Atlantic Meridional Overturning Circu-lation (AMOC), resulting from strengthened northeast trade-winds and a southward displaced Intertropical ConvergenceZone (ITCZ) during cold events in the North Atlantic (Ek-dahl et al., 2008; Baker et al., 2001a, b; Fritz et al., 2004).
A different hypothesis links past positive hydroclimaticanomalies to ENSO-like variability, in particular to tropi-cal Pacific SST-gradients (Latorre et al., 2006; Quade etal., 2008; Placzek et al., 2009). This causal mechanism isbased on the modern control that Pacific SST gradients ex-ert on the inter-annual and inter-decadal rainfall variabilityover the central Andes by modulating upper level circula-tion (Vuille et al., 2000; Garreaud et al., 2003; Vuille andKeimig, 2004). Enhanced SST gradients during la Nina yearslead to increased influx of humidity through the strengthen-ing and southward displacement of the Bolivian High and asubdued zonal upper level westerly circulation (Garreaud etal., 2003; Vuille and Keimig, 2004). Opposite atmosphericconditions during El Nino years lead to extended summerdrought throughout the Altiplano (Aceituno et al., 2009).
Modern hydrological observations support the role forENSO variability in driving hydrological shifts in the south-ernmost PdT. Houston (2006c) has pointed out that ENSOactivity is the primary factor behind modern inter-annualvariations for the hydrological patterns in the hyperarid At-acama. During La Nina years, increased summer rainfall inthe high-elevation headwaters promote surface floods alongephemeral streams from the southern basin and increaserunoff in perennial streams located at the northern PdT basin(Houston, 2006b, c, 2001, 2002).
Model simulations and diverse proxy records from widelydistributed regions around the world indicate that during theMCA the tropical Pacific was locked into La Nina-like modeand warmer SSTs prevailed in the North Atlantic as well asan enhanced AMOC (Fig. 5b–d; Graham et al., 2007, 2010;Trouet et al., 2009; Makou et al., 2010; Pages-News, 2011;Cobb et al., 2003; Richter et al., 2009; Norgaard-Pedersenand Mikkelsen, 2009; Jenny et al., 2002). This would ex-plain in part why we observe such a large positive hydrocli-matic anomaly in the southernmost PdT basin during a largefraction of the MCA. The implication is that the persistenceof perennial riverflow in the PdT is chiefly a response to cen-tennial scale modulations of the tropical Pacific SST gradientthrough its influence on upper circulation and moisture trans-port across the Altiplano (i.e., Garreaud et al., 2003).
This is harder to judge, however, for the earlier hy-droclimatic anomalies in the southernmost PDT basinobserved between 2500–2040 cal yr BP (RWP onset) and
298 E. M. Gayo et al.: Hydroclimate variability in the low-elevation Atacama Desert
1615–1350 cal yr BP (RWP-DACP transition). Increasedlithic concentrations in a sediment core offshore central Peru(Fig. 5b; Rein et al., 2005) argue for prevailing El Nino-likeconditions in the equatorial Eastern Pacific between 2500and ∼1250 cal yr BP (Fig. 5b). In turn, this would implythat these older hydroclimate anomalies occurred during in-creased El Nino activity, an explanation that is unsupportedby what we know regarding how the modern climate systemworks. In contrast to the lithic concentration record, how-ever, rainfall histories from other regions sensitive to posi-tive ENSO events (El Nino; Aceituno et al., 2009) such ascentral Chile (Laguna Aculeo, Fig. 5c; Jenny et al., 2002)point to significantly drier conditions during both intervals.Indeed, Laguna Aculeo experienced low debris-flow activitydue to reduced local rainfall that have been linked to pro-longed La Nina-like conditions at∼2200–1750 and∼1600–1450 cal yr BP (Fig. 5c).
As observed for the MCA, warmer SSTs in the NorthAtlantic by the onset of the RWP and RWP-DACP alsooccurred during the earlier positive hydroclimate anoma-lies seen in the PdT basin. Diverse SST-reconstructionsevince a warming of North Atlantic between 2300 and1500 cal yr BP (Eiriksson et al., 2006; Andersson et al., 2003;Sicre et al., 2008; Cronin et al., 2003; Norgaard-Pedersenand Mikkelsen, 2009). Planktonic foraminiferal Mg/Ca ra-tios in a marine core from the Feni Drift (NE Atlantic Ocean),however, suggest that such conditions did not end before1390 cal yr BP (Richter et al., 2009). Taken together, theseobservations show that the timing of the positive anoma-lies seen at the PdT (and by extension the western Andeancordillera) cannot be explained through links to a weakenedAMOC and its influence on the ITCZ (sensu Ekdahl et al.,2008; Baker et al., 2001a, b; Fritz et al., 2004).
5 Summary and conclusions
We present evidence for variations in hydrological conditionsin the low-elevation Atacama Desert over the past 2500 yr.Garnered from relict tree mounds, fossil rodent burrowsand archaeological remains preserved in an inactive tribu-tary of the southern Pampa del Tamarugal basin (21◦ S; PdT),we show that positive hydroclimatic anomalies occurred at2500–2040; 1615–1350 and 1050–680 cal yr BP.
The similarity in timing of these hydroclimate changes inthe low-elevation desert with other records from the westernAndean slope argue for the existence of important pluvialevents on regional spatial scales for the past 2500 yr. Thesynchronous and rapid response of biotic and hydrologicalcomponents from the southern PdT basin to positive hydro-logical budgets at higher elevations implies that these rain-fall anomalies quickly impacted the hydrology, productivityand human-landscape relationships in the hyperarid Atacamacore. The remarkable synchronicity displayed between pale-oclimate changes along the western Andean slope over the
past two and a half millennia also reinforces the use of PdTgeohistorical records as feasible proxies for tracing past hy-droclimatic change in the central Andes on multiple differenttime-scales.
Comparisons with a diverse array of proxy records fromaround the world indicate that the positive hydroclimateanomalies observed in the PdT during the MCA and at theRWP onset and RWP-DACP transition were likely forced byprevailing negative SST gradients in the tropical Pacific (LaNina-like conditions). Thus, ENSO-like variability seems tobe the first-order driving force for climate variability in thisregion over the last 2500 yr.
The link between hydroclimate conditions in the low-elevation desert and past ENSO activity documented here hasprofound implications for further evaluations on the sensitiv-ity of the central Andes hydroclimate to equatorial PacificSST-gradients. The fact that a similar mechanism could beoperating on centennial, as well as annual and inter-decadaltimescales, provides additional support for the role of tropi-cal Pacific SST gradients as the primary mechanism respon-sible for centennial/millennial hydroclimate fluctuations inthe Atacama Desert.
Finally, we point out that the existence of wetter condi-tions at different locations in the Atacama matches abruptincreases in the number of sites and total number of culturalradiocarbon dates over the past 13 000 yr. These numbershave been previously interpreted as an intensification of hu-man activities and population size (Williams et al., 2008).The paleoenvironmental implications for understanding thedynamic relation between human societies and environment(Zaro et al., 2008) are promising, and clearly demonstratedby our data. In particular, changes in the cultural history ofthe people that inhabited the PdT and the Atacama Desertin general can be better understood by combining differentkinds of archives.
The Atacama is an extreme environment where changes inwater availability were ingeniously managed by prehistoricpopulations. In the case of QM, this included the openingof extensive farming fields, irrigated by a network of sev-eral kilometres of stone-lined channels cut into the ground.This interaction created a vegetated landscape that can onlybe fully explained by the intervention of natural forces, bothlocal and regional, coupled with human activities.
300 E. M. Gayo et al.: Hydroclimate variability in the low-elevation Atacama Desert
Fig. A3. Northern face of the remnant late Pleistocene paleowetland deposit containing rodent burrows. Arrow indicates where QM-22Crodent burrow was found.
Fig. A4. Maize (Zea mays) litter (QM-2A) found in situ upon the QM-2E subsurface deposit.
E. M. Gayo et al.: Hydroclimate variability in the low-elevation Atacama Desert 303
Acknowledgements.We thank Daniela Osorio, Carolina Salas,Paula Ugalde, Francisca P. Dıaz-Aguirre, Isabel Mujica, Na-talia Villavicencio, Marıa Laura Carrevedo and Juana “Jota” Martelfor their help in the field; Camila Contreras and Eduardo Ascarrunzfor laboratory assistance and rodent identifications, respectively;Paola Salgado and Hector Orellana helped with the illustrations.Funding was provided by CONICYT #24080156 (to E.M.G.),a PhD scholarship from Proyecto-ICM P05-002 (to E.M.G.),FONDECYT #1100916 (to C.L., C.M.S and A.M.). E.M.G.and C.L. also acknowledges the ongoing support from the IEB,PFB-23 to the IEB and FONDAP 1501-2001 to CASEB. CMSacknowledges support from Centro de Investigaciones del Hombreen el Desierto. A.M. acknowledges support from FONDECYT#1080458. Comments by Vera Markgraf, Martin Grosjean and oneanonymous reviewer helped improve the manuscript.
Edited by: M. Grosjean
The publication of this articlewas sponsored by PAGES.
References
Abbott, M. B., Seltzer, G. O., Kelts, K. R., and Southon,J.: Holocene paleohydrology of the tropical Andes from lakerecords, Quaternary Res., 47, 70–80, 1997.
Abbott, M. B., Wolfe, B. B., Wolfe, A. P., Seltzer, G. O., Aravena,R., Mark, B. G., Polissar, P. J., Rodbell, D. T., Rowe, H. D., andVuille, M.: Holocene paleohydrology and glacial history of thecentral Andes using multiproxy lake sediment studies, Palaeo-geogr. Palaeocl., 194, 123–138, 2003.
Aceituno, P., Prieto, M. R., Solari, M. E., Martınez, A., and Poveda,G.: The 1877–1878 El Nino episode: Associated impacts inSouth America, Climatic Change, 92, 389–416, 2009.
Andersson, C., Risebrobakken, B., Jansen, E., and Dahl, S.O.: Late Holocene surface ocean conditions of the Nor-wegian Sea (Vøring Plateau), Paleoceanography, 18, 1044,doi:10.1029/2001PA000654, 2003.
Arroyo, M. T. K., Squeo, F. A., Armesto, J., and Villagran, C.: Ef-fects of aridity on plant diversity in the northern Chilean Andes:Results of a natural experiment, Ann. Mo. Bot. Gard., 75, 55–78,1988.
Aubron, C. and Brunschwig, G.: Practices consistency in dairyfarms of the dry Andes: analysis in a Peruvian peasants com-munity, Livestock Research for Rural Development, 20, avail-able at: http://www.lrrd.org/lrrd20/2/aubr20030.htm, (last ac-cess: 2 September 2011) 2008.
Baker, P. A., Rigsby, C. A., Seltzer, G. O., Fritz, S. C., Lowenstein,T. K., Bacher, N. P., and Veliz, C.: Tropical climate changesat millennial and orbital timescales on the Bolivian Altiplano,Nature, 409, 698–701, 2001a.
Baker, P. A., Seltzer, G. O., Fritz, S. C., Dunbar, R. B., Grove, M.J., Tapia, P. M., Cross, S. L., Rowe, H. D., and Broda, J. P.:The history of South American tropical precipitation for the past25,000 years, Science, 291, 640–643, 2001b.
Baker, P. A., Fritz, S. C., Garland, J., and Ekdahl, E.: Holocenehydrologic variation at Lake Titicaca, Bolivia/Peru, and its rela-
tionship to North Atlantic climate variation, J. Quaternary Sci.,20, 655–662, 2005.
Betancourt, J. L., Latorre, C., Rech, J., Quade, J., and Rylander, K.A.: A 22,000-yr record of monsoonal precipitation from northernChile’s Atacama Desert, Science, 289, 1546–1550, 2000.
Binford, M. W., Kolata, A. L., Brenner, M., Janusek, J. W., Seddon,M. T., Abbott, M., and Curtis, J. H.: Climate variation and therise and fall of an Andean civilization, Quaternary Res., 47, 235–248, 1997.
Bird, B. W., Abbott, M. B., Vuille, M., Rodbell, D. T., Stansell, N.D., and Rosenmeier, M. F.: A 2,300-year-long annually resolvedrecord of the South American summer monsoon from the Peru-vian Andes, P. Natl. Acad. Sci. USA, 108, 8583–8588, 2011.
Bryson, R.: Implications of macrophysical paleoclimatic modelsfor irrigation agriculture at Ramaditas, Northern Chile, in: Ar-queologıa del Desierto de Atacama: La etapa Formativa en elarea de Ramaditas/Guatacondo, edited by: Rivera, M. A., Edito-rial Universidad Bolivariana, 37–62, 2005.
Chepstow-Lusty, A., Frogley, M. R., Bauer, B. S., Bush, M. B.,and Herrera, A. T.: A late Holocene record of arid eventsfrom the Cuzco region, Peru, J. Quaternary Sci., 18, 491–502,doi:10.1002/jqs.770, 2003.
Cobb, K. M., Charles, C. D., Cheng, H., and Edwards, R. L.: ElNino/Southern Oscillation and tropical Pacific climate during thelast millennium, Nature, 424, 271–276, 2003.
Cronin, T. M., Dwyer, G. S., Kamiya, T., Schwede, S., and Willard,D. A.: Medieval Warm Period, Little Ice Age and 20th centurytemperature variability from Chesapeake Bay, Global Planet.Change, 36, 17–29, 2003.
De Jong, R., Bjorck, S., Bjorkman, L., and Clemmensen, L. B.:Storminess variation during the last 6500 years as reconstructedfrom an ombrotrophic peat bog in Halland, southwest Sweden, J.Quaternary Sci., 21, 905–919, 2006.
deMenocal, P. B.: Cultural Responses to Climate Change Duringthe Late Holocene, Science, 292, 667–673, 2001.
DGA: Informe Final: Estimaciones de demanda de agua y proyec-ciones futuras. Zona I Norte. Regiones I a IV, Ministerio de ObrasPublicas, Santiago-Chile, 596 pp., 2007 (in Spanish).
Eiriksson, J., Bartels-Jonsdottir, H. B., Cage, A. G., Gudmunds-dottir, E. R., Klitgaard-Kristensen, D., Marret, F., Rodrigues, T.,Abrantes, F., Austin, W. E. N., Jiang, H., Knutsen, K.-L., and Se-jrup, H.-P.: Variability of the North Atlantic Current during thelast 2000 years based on shelf bottom water and sea surface tem-peratures along an open ocean/shallow marine transect in west-ern Europe, Holocene, 16, 1017–1029, 2006.
Ekdahl, E. J., Fritz, S. C., Baker, P. A., Rigsby, C. A., and Coley, K.:Holocene multidecadal- to millennial-scale hydrologic variabil-ity on the South American Altiplano, Holocene, 18, 867–876,2008.
Evenstar, L. A., Hartley, A. J., Stuart, F. M., Mather, A. E., Rice,C. M., and Chong, G.: Multiphase development of the Atacamaplanation surface recorded by cosmogenic 3He exposure ages:implications for uplift and Cenozoic climate change in westernSouth America, Geology, 37, 27–30, 2009.
Fritz, S. C., Baker, P. A., Lowenstein, T. K., Seltzer, G. O., Rigsby,C. A., Dwyer, G. S., Tapia, P. M., Arnold, K. K., Ku, T.-L., andLuoh, S.: Hydrologic variation during the last 170,000 years inthe southern hemisphere tropics of South America, QuaternaryRes., 61, 95–104, 2004.
304 E. M. Gayo et al.: Hydroclimate variability in the low-elevation Atacama Desert
Gajardo, R.: La vegetacion natural de Chile: clasificacion ydistribucion geografica, Editorial Universitaria, Santiago-Chile,165 pp., 1994 (in Spanish).
Garreaud, R. D., Vuille, M., and Clement, A.: The climate of theAltiplano: observed current conditions and mechanisms of pastchanges, Palaeogeogr. Palaeocl., 194, 5–22, 2003.
Garreaud, R. D., Vuille, M., Compagnucci, R., and Marengo, J.:Present-day South American climate, Palaeogeogr. Palaeocl.,281, 180–195, 2009.
Gayo, E. M., Latorre, C., Jordan, T. E., and Nester, P. L.: Fantasmasde bosques y agua fosil en la Pampa del Tamarugal, norte deChile, XII Congreso Geologico Chileno, Santiago, Chile, 1–4,2009 (in Spanish).
Graham, N. E., Hughes, M. K., Ammann, C. M., Cobb, K. M.,Hoerling, M. P., Kennett, D. J., Kennett, J. P., Rein, B., Stott,L., Wigand, P. E., and Xu, T.: Tropical Pacific – mid-latitudeteleconnections in medieval times, Climatic Change, 83, 241–285, 2007.
Graham, N. E., Ammann, C. M., Fleitmann, D., Cobb, K. M., andLuterbacher, J.: Support for global climate reorganization dur-ing the “Medieval Climate Anomaly”, Clim. Dynam., 37, 1217–1245, 2010.
Grosjean, M.: Mid-Holocene climate in the south-central Andes: humid or dry?, Science, 292, 5526,doi:10.1126/science.292.5526.2391a, 2001.
Grosjean, M., van Leeuwen, J. F. N., van der Knaap, W. O., Geyh,M. A., Ammann, B., Tanner, W., Messerli, B., Nunez, L. A.,Valero-Garces, B. L., and Veit, H.: A 22,00014C year BP sedi-ment and pollen record of climate change from Laguna Miscanti(23◦ S), northern Chile, Global Planet. Change, 28, 35–51, 2001.
Grosjean, M., Cartajena, I., Geyh, M. A., and Nunez, L.: Fromproxy data to paleoclimate interpretation: the mid-Holoceneparadox of the Atacama Desert, northern Chile, Palaeogeogr.Palaeocl., 194, 247–258, 2003.
Habit, M. A., Contreras, T. D., and Gonzalez, R. H.:Prosopistamarugo: fodder tree for arid zones, Plant Production and Pro-tection Paper (FAO), no. 25, edited by: FAO, Roma – Italy,119 pp., 1981.
Helama, S., Merilainen, J., and Tuomenvirta, H.: Multicenten-nial megadrought in northern Europe coincided with a global ElNino-Southern Oscillation drought pattern during the MedievalClimate Anomaly, Geology, 37, 175–178, 2009.
Holmgren, C. A., Rosello, E., Latorre, C., and Betancourt, J. L.:Late-Holocene fossil rodent middens from the Arica region ofnorthernmost Chile, J. Arid. Environ., 72, 677–686, 2008.
Houston, J.: La precipitacion torrencial del ano 2000 en QuebradaChacarilla y el calculo de recarga al acuıfero Pampa Tamarugal,norte de Chile, Rev. Geol. Chile, 28 163–177, 2001 (in Spanish).
Houston, J.: Groundwater recharge through an alluvial fan in theAtacama Desert, northern Chile: mechanisms, magnitudes andcauses, Hydrol. Process., 16, 3019–3035, 2002.
Houston, J.: Evaporation in the Atacama Desert: An empiricalstudy of spatio-temporal variations and their causes, J. Hydrol.,330, 402–412, 2006a.
Houston, J.: The great Atacama flood of 2001 and its implicationsfor andean hydrology, Hydrol. Process., 20, 591–610, 2006b.
Houston, J.: Variability of precipitation in the Atacama Desert: Itscauses and hydrological impact, Int. J. Climatol., 26, 2181–2198,2006c.
Houston, J. and Hartley, A. J.: The central andean west-slope rain-shadow and its potential contribution to the origin of hyper-aridity in the Atacama Desert, Int. J. Climatol., 23, 1453–1464,2003.
Jenny, B., Valero-Garces, B., Urrutia, R., Kelts, K., Veit, H., andGeyh, M.: Moisture changes and fluctuations of the westerliesin Mediterranean Central Chile during the last 2000 years: TheLaguna de Aculeo Record (33◦50′ S), Quatern. Int., 87, 3–18,2002.
JICA: The study on the development of water resources in NorthernChile, Tokyo, Japan, 249 pp., 1995.
Jones, P. D. and Mann, M. E.: Climate over past millennia, Rev.Geophys., 42, RG2002,doi:10.1029/2003RG000143, 2004.
Kolata, A. L.: The Technology and Organization of AgriculturalProduction in the Tiwanaku State, Lat. Am. Antiq., 2, 99–125,1991.
Kolata, A. L.: The Tiwanaku: Portrait of an Andean Civilization,Blackwell, Cambridge, MA, 317 pp., 1993.
Latorre, C., Betancourt, J. L., Rylander, K. A., and Quade, J.: Veg-etation invasions into Absolute Desert: A 45,000-yr rodent mid-den record from the Calama-Salar de Atacama Basins, northernChile (22–24◦ S), Geol. Soc. Am. Bull., 114, 349–366, 2002.
Latorre, C., Betancourt, J. L., Rylander, K. A., Quade, J., andMatthei, O.: A vegetation history from the arid prepuna of north-ern Chile (22–23◦ S) over the last 13,500 years, Palaeogeogr.Palaeocl., 194, 223–246, 2003.
Latorre, C., Betancourt, J. L., Rech, J. A., Quade, J., Holmgren,C., Placzek, C., Maldonado, A., Vuille, M., and Rylander, K. A.:Late Quaternary history of the Atacama Desert, in: 23◦ S: TheArchaeology and Environmental History of the Southern Deserts,edited by: Smith, M. and Hesse, P., National Museum of Aus-tralia Press, Canberra, Australia, 73–90, 2005.
Latorre, C., Betancourt, J. L., and Arroyo, M. T. K.: Late Quater-nary vegetation and climate history of a perennial river canyon inthe Rıo Salado basin (22◦ S) of Northern Chile, Quaternary Res.,65, 450–466, 2006.
Latorre, C., Gonzalez, F. J., Houston, J., Rojas, M., and Mujica, M.I.: Reliable mean annual rainfall estimates using chinchilla rat(Abrocoma) middens from the Atacama Desert during the lateQuaternary, Eos Trans. Am. Geophys. Union, 91, Meeting of theAmericas Supplement, PP23B-05, 2010.
Ljungqvist, F. C.: A new reconstruction of temperature variabilityin the extra-tropical northern hemisphere during the last two mil-lennia, Geogr. Ann. A, 92, 339–351, 2010.
Luebert, F. and Pliscoff, P.: Sinopsis bioclimatica y vegetacional deChile, Editorial Universitaria, Santiago, 318 pp., 2006 (in Span-ish).
Magaritz, M., Aravena, R., Pena, H., Suzuki, O., and Grilli, A.: Wa-ter chemistry and isotope study of streams and springs in north-ern Chile, J. Hydrol., 108, 323–341, 1989.
Makou, M. C., Eglinton, T. I., Oppo, D. W., and Hughen, K. A.:Postglacial changes in El Nino and La Nina behavior, Geology,38, 43–46, 2010.
Maldonado, A., Betancourt, J. L., Latorre, C., and Villagran, C.:Pollen analyses from a 50,000-yr rodent midden series in thesouthern Atacama Desert (25◦30′ S), J. Quaternary Sci., 20, 493–507, 2005.
Mann, M. E., Zhang, Z., Hughes, M. K., Bradley, R. S., Miller, S.K., Rutherford, S., and Ni, F.: Proxy-based reconstructions of
E. M. Gayo et al.: Hydroclimate variability in the low-elevation Atacama Desert 305
hemispheric and global surface temperature variations over thepast two millennia, P. Natl. Acad. Sci USA, 105, 13185–13186,2008.
Mann, M. E., Zhang, Z., Rutherford, S., Bradley, R. S., Hughes, M.K., Shindell, D., Ammann, C., Faluvegi, G., and Ni, F.: Globalsignatures and dynamical origins of the Little Ice Age and Me-dieval Climate Anomaly, Science, 326, 1256–1260, 2009.
Marquet, P. A., Bozinovic, F., Bradshaw, G. A., Cornelius, C., Gon-zalez, H., Gutierrez, J. R., Hajek, E. R., Lagos, J. A., Lopez-Cortes, F., Nunez, L., Rosello, E. F., Santoro, C., Samaniego,H., Standen, V. G., Torres-Mura, J. C., and Jaksic, F. M.: Losecosistemas del Desierto de Atacama yarea andina adyacente enel norte de Chile, Rev. Chil. Hist. Nat., 71, 593–617, 1998 (inSpanish).
McCormac, F. G., Hogg, A. G., Blackwell, P. G., Buck, C. E.,Higham, T. F. G., and Reimer, P. J.: SHCal04 Southern Hemi-sphere Calibration 0–11.0 cal kyr BP, Radiocarbon, 46, 1087–1092, 2004.
Mooney, H. A., Gulmon, S. L., Rundel, P. W., and Ehleringer,J. R.: Further observations on the water relations ofProsopistamarungoof the northern Atacama Desert, Oecologia, 44, 177–180, 1980.
Mourguiart, P., Correge, T., Wirrmann, D., Argollo, J., Montenegro,M. E., Pourchet, M., and Carbonel, P.: Holocene palaeohydrol-ogy of Lake Titicaca estimated from an ostracod-based transferfunction, Palaeogeogr. Palaeocl., 143, 51–72, 1998.
Munoz-Pizarro, C.: Sinopsis de la flora chilena: Claves para la iden-tificacion de familias y generos, second Edn., Ediciones Univer-sidad de Chile, Santiago-Chile, 500 pp., 1966 (in Spanish).
Nester, P. L., Gayo, E., Latorre, C., Jordan, T. E., and Blanco, N.:Perennial stream discharge in the hyperarid Atacama Desert ofnorthern Chile during the latest Pleistocene, P. Natl. Acad. Sci.USA, 104, 19724–19729, 2007.
Neukom, R., Luterbacher, J., Villalba, R., Kuttel, M., Frank, D.,Jones, P., Grosjean, M., Wanner, H., Aravena, J. C., Black, D.,Christie, D., D’Arrigo, R., Lara, A., Morales, M., Soliz-Gamboa,C., Srur, A., Urrutia, R., and von Gunten, L.: Multiproxy sum-mer and winter surface air temperature field reconstructions forsouthern South America covering the past centuries, Clim. Dy-nam., 37, 35–51, 2010.
Nicora, E. G. and Rugolo de Agrasar, Z. E.: Los generos degramıneas de America Austral, Editorial Hemisferio Sur, BuenosAires-Argentina, 611 pp., 1987 (in Spanish).
Norgaard-Pedersen, N. and Mikkelsen, N.: 8000 year marine recordof climate variability and fjord dynamics from Southern Green-land, Mar. Geol., 264, 177–189, 2009.
Nowak, R.: Walker’s Mammals of the World, Sixth edition edn.,The Johns Hopkins University Press, 1999.
Nunez, L. and Santoro, C. M.: El transito Arcaico-Formativo enla circunpuna y valles occidentales del Centro Sur Andino: ha-cia los cambios “neolıticos”, Chungara, 43, 487–531, 2011 (inSpanish).
Pages-News: Medieval Climate Anomaly, edited by: Xoplaki, E.,Fleitmann, D., Diaz, H., von Gumten, L., and Kiefer, T., PAGESInternational Project Office, Bern, Switzerland, 2011.
Placzek, C., Quade, J., and Betancourt, J. L.: Holocene lake levelfluctuations of Lago Aricota, southern Peru, Quaternary Res., 56,181–190, 2001.
Placzek, C., Quade, J., Betancourt, J. L., Patchett, P. J., Rech, J.
A., Latorre, C., Matmon, A., Holmgren, C., and English, N. B.:Climate in the dry central Andes over geologic, millenial, andinterannual timescales, Ann. Mo. Bot. Gard., 96, 386–397, 2009.
Quade, J., Rech, J., Betancourt, J., and Latorre, C.: Mid-Holoceneclimate in the south-central Andes: humid or dry?, Science, 292,2391a,doi:10.1126/science.292.5526.2391a, 2001.
Quade, J., Rech, J. A., Betancourt, J. L., Latorre, C., Quade, B., Ry-lander, K. A., and Fisher, T.: Paleowetlands and regional climatechange in the central Atacama Desert, northern Chile, Quater-nary Res., 69, 343–360, 2008.
Ramos, V. A.: Late Proterozoic-Early Paleozoic of South America:a collisional history, Episodes, 11, 168–174, 1988
Reale, O. and Shukla, J.: Modeling the effects of vegetation onMediterranean climate during the Roman Classical Period: PartII. Model simulation, Global Planet. Change, 25, 185–214, 2000.
Rech, J.: Late Quaternary paleohydrology and surficial processesof the Atacama Desert, Chile: Evidence from wetland depositsand stable isotopes of soil salts, Unpublished PhD Dissertation,Department of Geosciences, University of Arizona, 2001.
Rech, J., Quade, J., and Betancourt, J. L.: Late Quaternary paleohy-drology of the central Atacama Desert (22–24◦ S), Chile, Geol.Soc. Am. Bull., 114, 334–348, 2002.
Rech, J., Pigati, J. S., Quade, J., and Betancourt, J. L.: Re-evaluation of mid-Holocene wetland deposits at QuebradaPuripica, northern Chile, Palaeogeogr. Palaeocl., 194, 207–222,2003.
Rein, B., Luckge, A., Reinhardt, L., Sirocko, F., Wolf,A., and Dullo, W.-C.: El Nino variability off Peru dur-ing the last 20,000 years, Paleoceanography, 20, PA4003,doi:10.1029/2004PA001099, 2005.
Richter, T. O., Peeters, F. J. C., and van Weering, T. C. E.: LateHolocene (0–2.4 ka BP) surface water temperature and salinityvariability, Feni Drift, NE Atlantic Ocean, Quaternary Sci. Rev.,28, 1941–1955, 2009.
Rivera, M. A.: El Formativo en elarea del Desierto de Atacama:El proyecto Ramaditas, in: Arqueologıa del Desierto de Ata-cama: La etapa Formativa en elarea de Ramaditas/Guatacondo,edited by: Rivera, M. A., Editorial Universidad Bolivariana, 7–36, 2005.
Rojas, R. and Dassargues, A.: Groundwater flow modelling of theregional aquifer of the Pampa del Tamarugal, northern Chile, Hy-drogeol. J., 15, 537–551, 2007.
Santoro, C. M., Latorre, C., Salas, C., Osorio, D., Ugalde, P., Jack-son, D., and Gayo, E. M.: Ocupacion Humana pleistocenica enel Desierto de Atacama. Primeros resultados de la aplicacion deun modelo predictivo interdisciplinario, Chungara, 43, 353–366,2011 (in Spanish).
Seager, R., Graham, N., Herweijer, C., Gordon, A. L., Kushnir, Y.,and Cook, E.: Blueprints for Medieval hydroclimate, QuaternarySci. Rev., 26, 2322–2336, 2007.
Sicre, M. A., Jacob, J., Ezat, U., Rousse, S., Kissel, C., Yiou,P., Eiriksson, J., Knudsen, K. L., Jansen, E., and Turon, J.-L.:Decadal variability of sea surface temperatures off North Icelandover the last 2000 years, Earth Planet. Sc. Lett., 268, 137–142,2008.
Tomlinson, A. J., Blanco, N., Maksaev, V., Dilles, J., Grunder, A.L., and Ladino, M.: Geologıa de la Precordillera Andina de Que-
306 E. M. Gayo et al.: Hydroclimate variability in the low-elevation Atacama Desert
brada Blanca-Chuquicamata, Regiones I y II (20◦30′–22◦30′ S),Servicio Nacional de Geologıa y Minerıa, Santiago – Chile, 1–444, 2001 (in Spanish).
Trouet, V., Esper, J., Graham, N. E., Baker, A., Scourse, J. D., andFrank, D. C.: Persistent positive North Atlantic Oscillation modedominated the Medieval Climate Anomaly, Science, 324, 78–80,2009.
Uribe, M.: Acerca de complejidad, desigualdad social y el com-plejo cultural Pica-Tarapaca en los Andes Centro-Sur (1000–1450 DC), Estudios Atacamenos, 31, 91–114, 2006 (in Spanish).
Uribe, M., Sanhueza, L., and Bahamondes, F.: La ceramicaprehispanica tardıa de Tarapaca, sus valles interiores y costadesertica, Norte de Chile (CA: 900–1450 D.C.): Una propuestatipologica y cronologica, Chungara, 39, 143–170, 2007 (in Span-ish).
Villagran, C., Castro, V., Sanchez, G., Hinojosa, F. L., and Latorre,C.: La tradicion altiplanica: estudio etnobotanico en los Andesde Iquique, Primera Region, Chile, Chungara, 31, 81–186, 1999.
Villagran, C., Romo, M., and Castro, V.: Etnobotanica del sur delos Andes de la Primera Region de Chile: un enlace entre lasculturas Altiplanicas y las de Quebradas Altas del Loa Superior,Chungara, 35, 73–124, 2003.
Vuille, M. and Keimig, F.: Interannual variability of summertimeconvective cloudiness and precipitation in the central Andes de-rived from ISCCP-B3 data, J. Climate, 17, 3334–3348, 2004.
Vuille, M., Bradley, R. S., and Keimig, F.: Interannual climate vari-ability in the Central Andes and its relation to tropical Pacific andAtlantic forcing, J. Geophys. Res., 105, 12447–12460, 2000.
Wanner, H., Beer, J., Butikofer, J., Crowley, T. J., Cubasch, U.,Fluckiger, J., Goosse, H., Grosjean, M., Joos, F., Kaplan, J. O.,Kuttel, M., Muller, S. A., Prentice, I. C., Solomina, O., Stocker,T. F., Tarasov, P., Wagner, M., and Widmann, M.: Mid- to LateHolocene climate change: an overview, Quaternary Sci. Rev., 27,1791–1828, 2008.
Williams, A., Santoro, C. M., Smith, M. A., and Latorre, C.: Theimpact of ENSO in the Atacama Desert and Australian arid zone:exploratory time-series analysis of archaeological records, Chun-gara, 40, 245–259, 2008.
Zaro, G., Builth, H., Rivera, C., Roldan, J., and Suvires, G.:Landscape Evolution And Human Agency: Archaeological CaseStudies From Drylands In Western South America And Aus-tralia, Chungara, 40, 261–271, 2008.
Zhou, J. and Lau, K.-M.: Does a monsoon climate exist over SouthAmerica?, J. Climate, 11, 1020–1040, 1998.
