ENSO tropical–extratropical climate teleconnections and mechanisms for Holocene debris flows along the hyperarid coast of western South America (17°–24°S

tters 249 (2006) 467–483www.elsevier.com/locate/epsl

Earth and Planetary Science Le

ENSO tropical–extratropical climate teleconnections andmechanisms for Holocene debris flows along the hyperarid

coast of western South America (17°–24°S)

Gabriel Vargas a,⁎, José Rutllant b, Luc Ortlieb c

a Departamento de Geología, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Plaza Ercilla 803, Santiago, Chileb Departamento de Geofísica, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Blanco Encalada 2002, Santiago, Chile

c PALÉOTROPIQUE, Institut de Recherche pour le Développement (IRD), 32 Avenue Henri Varagnat, F-93143, Bondy Cedex, France

Received 28 March 2006; received in revised form 3 July 2006; accepted 12 July 2006Available online 30 August 2006

Editor: R.D. van der Hilst

Abstract

El Niño, the warm phase of the ENSO cycle, involves ocean-climate anomalies in the tropical Pacific Ocean and in theextratropics, which frequently result in heavy rainfall episodes along the equatorial and subtropical regions of western SouthAmerica. Here, we investigate meteorological mechanisms producing heavy rains, floods and debris flows along the less-knownhyperarid coasts of southern Peru and northern Chile, to evaluate the paleoclimate significance of Holocene debris flow deposits.

Our results reveal that heavy rainfall over the coast of southernmost Peru occurs either during austral summer, at the mature stage of ElNiño in connection with warmer sea surface temperatures and anomalous jet streams off northern Chile, or during the previous australwinter–spring associated with equatorward-shifted Pacific South America (PSA) atmospheric teleconnection patterns. At Antofagasta, innorthern Chile, such events occur almost exclusively in the latter season when deeper PSA-related anomaly poles extend their influenceequatorwards beyond central Chile. During non-El Niño conditions short-lived heavy rainfall episodes in southernmost Peru can beassociatedwith similar, albeit weaker or less persistent, circulation anomalies. In addition to that, a seasonally-enhanced low-level southerlyflow provides orographic uplift (rainfall-favourable conditions) by the Andes at the 18 °S coastal bend. Ultimately, the trigger for rainfallevents in all seasons and phases of the ENSO cycle was invariably connected with mid-troposphere wave disturbances frommid-latitudes.

The chronostratigraphy of debris flow deposits from both areas and its comparison with other paleoclimate records at thewestern side of the Andes, suggests that the ENSO-related teleconnection patterns operated only during the second half of theHolocene, supporting an onset of modern El Niño manifestations at 5300–5500 cal BP and increased frequency of major eventsduring recent times. We suggest that several debris flows dated between 12,900 and 8400 cal BP in southernmost Peru, previouslyinterpreted as an indication of strong El Niño events, were associated with short and intense heavy rainfall episodes similar to thosedescribed here during the late winter–spring season in non-El Niño conditions, concomitant with stronger low-level southerlies,strengthened South-Eastern Pacific Subtropical Anticyclone and intensified coastal upwelling.© 2006 Elsevier B.V. All rights reserved.

Keywords: debris flow; El Niño; tropical–extratropical teleconnections; heavy rainfall; Holocene; western South America

⁎ Corresponding author. Fax: +56 2 6963050.E-mail address: [email protected] (G. Vargas).

0012-821X/$ - see front matter © 2006 Elsevier B.V. All rights reserved.doi:10.1016/j.epsl.2006.07.022

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468 G. Vargas et al. / Earth and Planetary Science Letters 249 (2006) 467–483

1. Introduction

ENSO (El Niño-Southern Oscillation) is an oscillatorymode of interannual climate variability inherent to the

Fig. 1. Regional geomorphologic setting of northern Chile and southernmost PDesert for the period 1960–1990. The amount of total monthly rainfall stronglycoast located between Antofagasta (23°S) and Ilo-Tacna region (17°S). The co

tropical Pacific Ocean involving large ocean-climateanomalies in its warm/El Niño and cold/La Niña extremephases, with vast socio-economic impacts in many regionsof the Earth. Given that, the relevant physical mechanisms

eru and monthly rainfall in coastal stations along the hyperarid Atacamadiminishes from the semiarid climate at La Serena (30°S) to the hyperaridre of the hyperarid coastal Atacama Desert is situated near 20°S.

469G. Vargas et al. / Earth and Planetary Science Letters 249 (2006) 467–483

of the ENSO-related climate variability, their pastevolution and projection into the greenhouse future receivemuch attention and is a matter of current discussion [1,2].As the tropical Pacific Ocean is the source region forENSO-related climate instability, the coasts of Ecuadorand northern Peru experience particularly severe impactsduring the mature phase of El Niño events [3–5]. There,heavy rainfall episodes related to a weakened subsidingbranch of the Pacific Walker circulation and strong posi-tive sea surface temperature (SST) anomalies lead toinundations, flooding and debris flows that have been usedfor historic reconstructions [5–7]. During the developmentphase of El Niño in austral winter–spring, tropical–extra-tropical climate teleconnections produce positive rainfallanomalies in subtropical central Chile [8]which, at historictimescales, seem to have been more effective from thebeginning of the nineteenth century and during the glob-ally warmer twentieth century than in the previous colderseveral hundreds of years [6,7].

At millennial timescales results from geologicalrecords suggest persistent ENSO variability throughoutthe entire last glacial–interglacial cycle, but weaker fre-quency and amplitude of major El Niño events seem tohave characterized the latest Pleistocene and the first halfof the Holocene, with respect to the late Holocene [9–11].A similar pattern of evolution of orbitally-driven changesin the frequency and amplitude ofmajor ENSO events hasbeen suggested also through model results [12,13].However, inferences from alluvial sequences in thecoastal region of Ilo-Tacna (17–18.4°S) in southernPeru, at the northern extremity of the core of the hyperaridAtacama Desert (Fig. 1), point to strong El Niño manifes-tations at the Pleistocene–Holocene transition [14,15].Together with the hyperarid coast of the Antofagastaregion in northern Chile (22–23.7°S), these areas con-stitute transitional climatic zones between the equatorialand subtropical regions experiencing large, albeit out ofphase, seasonal rainfall impacts during El Niño events,and constitute key areas to study extreme manifestationsof modern and past ENSO climate teleconnections.

2. ENSOanddebris flows during the twentieth century

The hyperarid climate along the coast of northernChile and southern Peru is mainly controlled by theeastern rim of the South-Eastern Pacific SubtropicalAnticyclone (SEPSA) and the steep, narrow and coast-parallel Andes which rise to elevations in excess of6000 m a.s.l. in this area. Their combined effects resultinto complex air–sea–land interactions including theChile–Peru coastal current, coastal upwelling and anextensive stratus cloud deck that sustain a cactus belt in

northern Chile, or give rise to relatively dense vege-tation zones (“lomas”), in southern and central Peru.Equatorward from north-central Chile, coastal rainfalldecreases from about 100 mm y−1 at 30°S to less than1 mm y−1 at the core of the hyperarid coastal AtacamaDesert, located roughly at about 20°S (Fig. 1). Seasonalrainfall maxima concentrate around austral winter as theresult of a few mid-latitude disturbances that succeed inreaching the area, most commonly during the develop-ment of El Niño events, concomitantly with a weakenedSEPSA and/or enhanced blocking of the westerlies athigh latitudes [8,16,17]. During these ENSO-related wetyears most of the annual rainfall concentrates into a fewisolated events occurring when the favourable phase oflarge intraseasonal oscillations reinforce the El Niñoconditions [18].

The relationship between modern debris flows in theAntofagasta region of northern Chile (23°S) and El Niñoevents was studied through the revision of local news-papers, rainfall data and the characterization of geologicsections [19]. During the twentieth century, all the debrisflow episodes were associated with heavy rainfalls (20–40 mm/3 h) during the austral winter of the developmentphase of strong to moderate El Niño events: in August1930, June 1940, May, 1982 July 1987 and June 1991(Fig. 2). The two strongest debris flow events whichoccurred in June-13-1940 (39 mm) and June-18-1991(42 mm) caused serious damage in the city. Relativelystrong and sudden rainfalls of convective nature alsooccurred in July 1925 and 1940, generating inundationsin Antofagasta city and important debris flows farthernorth. Meteorological conditions for the development ofheavy rains on June-18-1991 have been described [20],but further verification and search for additional meteo-rological mechanisms should lead to improved ENSOreconstructions from Holocene alluvial sequences in thisregion.

A similar historical revision was performed for theTacna-Ilo coastal area in southern Peru [21]. Eightflooding events since 1960 were associated with heavyrainfall episodes during El Niño events: January 1983,December 1997 and January 1998; July 1963 and 1972,September 1963, 1965 and 1997. Major debris flowsoccurred in January 1983 and September 1997, andminorevents in July 1972 and January 1998 (Fig. 2). However,the floods and roof collapses reported in September 1960,1961 and 1962 are not related to El Niño [21], suggestingthat other mechanisms not previously reported may bealso involved in the generation of sudden and strongrainfalls in this region during early austral spring.Previous authors suggested the occurrence of floodingand debris flows also in 1992–1993 [15, and references

Fig. 2. Comparison of total annual rainfall at Antofagasta (northern Chile) and Tacna (southern Peru) with the Southern Oscillation Index (SOI) andthe Pacific Decadal Oscillation Index (PDO); [22]. Black and white arrows represent debris flow and flooding events, respectively [19,21].


therein], but these events are not reported in the localhistorical analysis [21] and could be associated withrainfalls on the western Andean slopes of southern Peru.

Here we investigate meteorological mechanisms pro-ducing heavy rains in coastal northern Chile and south-ern Peru and their relationship with present ENSO-related atmospheric circulation anomalies, to interpretthe climate significance of debris flow deposits, as wellas the Holocene evolution of ENSO manifestationsalong the western coast of South America.

3. Methods

The analysis of meteorological mechanisms associ-ated with the occurrence of heavy rainfalls in northernChile and southern Peru [19,21], was based on dailyweather charts obtained from the NCEP/NCAR reanal-ysis (http://www.cdc.noaa.gov/Composites/Day).The

selected anomalies (A) charts, based on 1968–1996long-term means, are:

a) Mid-troposphere circulation from geopotential heightsat 500 hPa (AH500),

b) Upper-troposphere vector wind charts at 250 hPa(AVW250),

c) Vertical p-velocity (omega) in the lower-troposphereover the study area at 850 hPa (AOM850).

Composites for each storm have been constructedfrom these daily weather anomaly charts, correspondingto daily mean values substracted from the long-termmean. Since the 2.5×2.5 degrees resolution of theNCEP/NCAR Reanalysis smoothes out the steep Andesorography, the model coastline lies a few hundred kilo-meters offshore the actual coastline, resulting in a cor-responding offset of the topographically-induced low-

http://www.cdc.noaa.gov/Composites/Day

Table 1Radiochronological data from sites Las Conchas and Coloso-Garumas in the Antofagasta area and Punta Guanillos, located in coastal Atacama Desertof Northern Chile

Unit Material 14C Lab# 14C age y. BPTh/U, ESR age

DR⁎

(yr)Mean cal.age BP

1σ rangecal. BP⁎

Reference

Antofagasta, Las Conchas alluvial sequence and archaeological site Chimba13: 23°34′15″S 70°21′58″WAlluvial terrace Terrestrial snails Pa1860 16,527±300 19,670 19,216–20,124 This workAlluvial terrace Terrestrial snails Pa2054 19,915±400 23,558 22,993–24,123 This work

Chimba 13-cuadrantsA-top Otolith TO-5631 9170±80 496±304 9245 8868–9621 This workA-middle Charcoal P-2702 9400±160 10,568 10,377–10,759 This workA-bottom Charcoal P-2702b 9680±160 10,860 10,751–10,969 This workB-top Charcoal TO-6526 9460±90 10,655 10,547–10,762 This workB-top Mollusc shell UQ-2156 9088 ±120 496±304 9124 8756–9491 This workB-middle Charcoal TO-6528 9910±90 11,264 11,183–11,345 This workB-middle Mollusc shell UQ-2157 9163±140 496±304 9238 8849–9626 This workB-bottom Charcoal Beta94994 10,120±70 11,652 11,549–11,755 This workC-top Charcoal TO-6527 9260±90 10,428 10,359–10,496 This workC-top Mollusc shell TO-6320 9800±80 496±304 9947 9577–10,316 This workC-top Mollusc shell Beta134136 9900±40 496±304 10,052 9755–10,349 This workC-middle Charcoal TO-6530 7100±80 This work,

wrong dataC-middle Mollusc shell TO-6319 10,030±90 496±304 10,229 9819–10,639 This workC-bottom Shell TO-6325 10,280±90 496±304 10,550 10,244–10,856 This work

Antofagasta, Coloso litoral-alluvial sequence: 23°45′24″S 70°27′29″WLast 5 debris

flow depositsAnthropicremains

Newspaper,rainfall data

AD 1930, 1940,1982, 1987, 1991

[19]

+6 m-littoraldeposits

Molluscshells

ESR 106,000 LIM: 125,000 [23]

112,000103,000106,000109,000

+6 m-littoral deposits Mollusc shells U/Th 154,700 LIM: 125,000 [23]110,000

Antofagasta, Garumas Holocene debris flow deposits: 23°42′36″S 70°24′27″WDeposits #41–45 Anthropic

remainsNewspaper,rainfall data

AD 1930, 1940,1982, 1987, 1991

This work

Deposit #22 Charcoal Pa1920 971±40 846 (AD 1105) 828–863 This workDeposit #7 Charcoal Pa1918

Pa1925 N43,100N45,430 This work,

fossil woodDeposit #2 Mollusc shell Pa1859a 5157±60 175±101 5331 5187–5475 This workDeposit #2 Mollusc shell Pa1859b 5569±60 175±101 5764 5648–5879 This work

Pta. Guanillo, Holocene debris flow deposits and archaeological levels: 21°58′12″70°10′53″WDep./Level-3 Mollusc shells Pa 1027±40 320±145 360 (AD 1591) 223–496 This workDep./Level-2 Mollusc shells Pa 2930±70 175±101 2493 2340–2645 This workDep./Level-2 Mollusc shells Pa 3100±40 175±101 2657 2520–2794 This workDep./Level-1 Mollusc shell Pa1929 5289±115 175±101 5453 5291–5615 This workDep./Level-1 Mollusc shells Pa1936 5369±65 175±101 5559 5431–5687 This workDep./Level-1 Charcoal Pa1923 6088±140 6887 6743–7030 This work

Conventional 14C ages are corrected for δ13C with respect to PDB (−25‰). Calibrated ages are calculated through Calib4.3-Method B [32], withMarine-98 data set for shells and otolith samples, Intcal 98-Southern Hemisphere data set, after subtraction of 24 yr, for terrestrial samples. Samplesindicated in italics yielded anomalous values which are not trusted. Calibration of marine materials considers the mean ΔR value calculated from thecomparison of terrestrial and marine samples for the entire Holocene period in the Northern Chile–Southern Peru area [31].



level upward motion at the Perú–Chile coastal bend(18°S).

The chronostratigraphy of debris flow sequences inthe Antofagasta region was determined considering theirmorphostratigraphic relationship with the marine terraceassociated with the Last Interglacial Maximum (LIM)[23–25], 14C determinations and the recognition oftwentieth century anthropogenic remains.

The application of the 14C method in this hyperaridcoastal region presents complications for both marineand continental materials. In the first case, mainlymollusk shell fragments, conventional ages can beanomalously increased due to the Regional ReservoirEffect (ΔR), which results from the advection, duringupwelling events, of deep waters with depleted [14C]CO2toward the surface of the ocean. The difficulty toestimate the ΔR value for each sample of marine ori-gin in this region has been discussed in previous works[26–30]. New estimations of ΔR throughout theHolocene period have been recently provided [31],suggesting meanΔR values of 496±304 yr, 175±101 yr,320±145 yr and 250±207 yr for the periods comprisedbetween 9587–6925 cal BP, 5249–1224 cal BP, 682–465 cal BP and 41–15 cal BP, respectively. We used thesevalues to calibrate the marine conventional ages.Additionally, charcoal remains may not provide precisedating, since old wood fragments well preserved in thehyperarid environment, possibly during centuries, weresometimes used as fuel by the early inhabitants [28–30].Therefore, when radiocarbon data from both marine shelland charcoal samples were available, we considered thefirst data. Calibrated ages were obtained using Calib4.3[32]. Table 1 summarizes geochronological data fromsites in northern Chile.

4. Meteorological mechanisms associated with modernheavy rainfall events

4.1. Southern Peru

The historically-documented debris flows and floodsalong the coast of the Ilo-Tacna region in southern Peruhave occurred in different seasons and phases of theENSO cycle. During the mature phase of El Niño(austral summer) such events have been reported inJanuary 1983 and 1998, while in austral winter–springthey have occurred in July 1972, August–September1965 and August–September 1997. During La Niña andin near neutral conditions, debris flow and flood eventshave been reported only in early austral spring (Septem-ber 1961 and 1962, respectively). This suggests thatstrong rainfall events in southern Peru, regardless of

their intensity, tend to occur during El Niño in australsummer and in austral winter–spring; although in thelatter season they may occur in any phase of the ENSOcycle. This feature is consistent with a September peakin the average seasonal rainfall at Tacna.

Two heavy rainfall episodes occurred in January 1983(7–15 and 24–26) and in January 1998 (4–6 and 13–14)at the peak of the major 1982–1983 and 1997–1998 ElNiño events. The culmination of these extraordinaryepisodes in austral summer featured a large eastwardshift of the convective clusters along the equatorialPacific, resulting in an enhanced Hadley circulation inthe eastern tropical Pacific with a strengthened andequatorward-displaced subtropical jet stream. Therefore,although the strength of the subtropical anticyclone fea-tures seasonal and interannual minima along southernPeru/northern Chile in austral summer at this phase (ElNiño) of the Southern Oscillation, a weak subsidenceinversion consistent with the enhanced Hadley-cellcirculation must have been instrumental, together withlarge SST positive anomalies (4–5 °C) along the coast, ingenerating potential instability. The release of this po-tential instability occurs when the lower troposphere islifted, resulting often in severe convective activity. Thelifting mechanism was provided here by mid-tropo-sphere, mid-latitude wave disturbances enhanced by theeastward drift of the South Pacific Convergence Zone(SPCZ; [33,34]) and the equatorward-shifted subtropicaljet. Persistent anticyclonic anomalies over and off australChile during the first storms in January 1983 and 1998,respectively, were accompanied by enhanced subtropicaltroughing and positive speed anomalies in the jet streamat lower latitudes (25–30°S) (Fig. 3-Ib), resulting inenhanced upward motion along the topography insouthern Peru (Fig. 3-Ic). In the two second storms ofJanuary 1983 and 1997, a deep trough extended all theway from southern latitudes into the subtropics, withsimilar results along the coastal area of southern Peru.

During the developing stage of the El Niño 1965event, heavy rainfall was reported in the Tacna areabetween August 29 and September 4. Here a per-sistent high-latitude positive anticyclonic anomaly(AH500 N0), consistent with a Pacific–South-America(PSA+) teleconnection pattern [35], was centred atabout 90°W (Fig. 3-IIa), farther north than thosepreviously reported for similar events in central Chile[8], resulting in the equatorward shift of the corres-ponding subtropical cyclonic anomaly (AH500 b0).The general anticyclonic wind shear equatorward of astrong northwesterly jet over northern Chile and theassociated secondary ageostrophic circulations around ajet streak (Fig. 3-IIb), favoured a localized rising motion

Fig. 3. Composites of atmospheric circulation anomaly patterns from NCEP/NCAR reanalysis: (a) 500 hPa geopotential heights, which is equivalent to the atmospheric pressure at ca. 5000 m a.s.l., (b)250 hPa (ca. 10,000 m a.s.l.) vector winds, and (c) 850 hPa (ca. 1500 m a.s.l.) p-velocities. From left to right, composites correspond to the first storms of (I) January 1983 and 1998 (El Niño/australsummer); (II) August–September 1965 (El Niño/austral late winter; also valid for the storms occurred on July 1972 and September 1997); (III) September 1961 and September 1962 (non El Niño/austral late winter–spring); (IV) July 1987 and June 1991 (El Niño/austral winter; also valid for the storm occurred on May 1982). Events represented in (I), (II) and (III) affected southern Peru, whilethose in (IV) affected northern Chile. In (a) positive/negative anomalies can be interpreted as anticyclonic/cyclonic anomalies or rainfall unfavourable/favourable conditions.

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anomaly over southern Peru (Fig. 3-IIc). During theextended rainfall period between August 12 andSeptember 28, 1997, at the first peak of the 1997–

Fig. 4. Generalized stratigraphic columns of debris flow sequences in northernStratigraphic column of late Pleistocene–Holocene alluvial sequences disposedsouthern extremity ofAntofagasta [37]. b: Stratigraphic section of the upper segmcorrelated with the Chimba-13 archaeological site, at Quebrada Las Conchas, locin this last deposit suggests dominant southwesterly winds at the time of its genestratigraphic column of debris flow deposits in the Holocene alluvial fans at the Cthe base of this unit is correlated with the aeolian accumulation of the Chimba-1early Holocene debris flow deposits at Quebrada Tacahuay andMiraflores, in theorganic-rich sediment. e: General stratigraphic columnof lateHolocene debris flo(#4) units [14,15,21]. f: Stratigraphic column of twentieth century debris flow d

1998 large El Niño event, the mean positive pole of thePSA+ pattern was centred at 55–60°S, west of 90°W. Adeeper subtropical trough (negative pole of the PSA+

Chile (Antofagasta region) and southernmost Peru (Ilo-Tacna region). a:over a +6 m a.s.l. marine terrace assigned to the LIM [23], located at theent of a late Pleistocene alluvial terrace overlain by anaeolian accumulationated in the northern extremity of Antofagasta. Dip direction of laminationsration. Black sections in the scale bar indicate aeolian deposits. c: Generaloloso-Garumas areas, located south of Antofagasta. An aeolian deposit at3 archaeological site. d: General stratigraphic column of late Pleistocene–Ilo-Tacna region of southernmost Peru [14,15,21]. Grey deposit indicateswdeposits in the Ilo-Tacna region, including theMiraflores (#3) andChuzaeposits in the Ilo-Tacna region, southernmost Peru [21].


pattern) at 90°W produced strong northwesterly flowover northern Chile, resulting in persistent upward flowanomalies over southern Peru and also northern Chile.The two heavy rainfall events in July 1972 (3–7 and 20–23) featured a deep negative anomaly (trough) at highlatitudes and a mid-latitude ridge in the 500 hPageopotential anomalies (AH500 N0) centred at 35°S(not shown), both consistent with a PSA- teleconnectionpattern [35], intersecting the deep trough into anequatorward (cutoff low) and a poleward side, againwith a strong northwesterly jet over northern Chile.

One-day heavy rainfall episodes in the Tacna areaoccurred on September 4, 1961, at the onset of a weakLa Niña, and on September 18, 1962, under near neutralENSO conditions. Both cases were associated withAH500 circulation patterns (Fig. 3-IIIa), jet streamanomalies (Fig. 3-IIIb) and enhanced upward motionover southern Peru (Fig. 3-IIIc), qualitatively very simi-lar to those found in the 1965 rainfall episode (Fig. 3-II).This is consistent with previous results which show thatthe PSA+ teleconnection pattern, featuring a blockinghigh to the southwest of South America, is only morefrequent and long-lasting during El Niño [8]. However,some additional mechanism compatible with a strongsubtropical anticyclone must be present to explain anearly spring maximum in the Tacna rainfall climatologyand the short-lived strong rainfall episodes during non-El Niño conditions discussed here.

4.2. Northern Chile

Along the coast of the Antofagasta region in northernChile, debris flows associated with heavy rains occurredduring the austral winter season of 1982 (May 23–24),1987 (July 26–30) and 1991 (June 18–19). Besides thefact that all these events coincided with the developmentphase of El Niño, several features are common to thosediscussed in the previous section. At high latitudes deeppositive (anticyclonic) AH500 poles, corresponding tothe PSA+ pattern, were present in July 1987 and June

Fig. 5. Panoramic view and stratigraphy of latest Pleistocene–early Holocene(17°S), in southernmost Peru. A late Holocene vertical incision in the quebr

1991 [20] with their centres located south of 60°S(Fig. 3-IVa: June 1991). In May 1982 anomalousridging at 85°W, 37°S, intersected the Chilean coast at40°S, generating a cutoff low centred at 27°S. In allthese cases, associated jet streak anomalies were locatedon the coast at about 20–23°S (Fig. 3-IVb: June 1991),producing coast-aligned upward velocity anomalies offnorthern Chile (Fig. 3-IVc: June 1991).

5. Paleoclimate implications of debris flow sequences

5.1. Debris flow sequences in coastal southern Peru

Complex alluvial fan systems at the foot of the Andesin southern Peru include late Pleistocene and Holoceneunits formed by sporadic alluvial flows. These flowshave been produced by rainfalls which affect either thecoastal region itself, in exceptional cases, or, morefrequently, the piedmont area at elevation over 1600 ma.s.l. The main drainage basins in this region are theOsmore, Locumba, Sama and Caplina hydrologic sys-tems, which receive discharges from the high Andes ortheir foothills. Previous work on paleoclimate implica-tions of latest Pleistocene–Holocene alluvial depositsfocused in the coastal alluvial fans and provided com-plete descriptions about the morpho-stratigraphic con-text, sedimentological properties and chronostratigraphyof those geological records [14,15,21,36].

The chronostratigraphy of major debris flow andflood events in coastal sites of the Ilo-Tacna region hasbeen recently obtained [15,21] (Fig. 4). The most com-plete sequence can be observed at Quebrada Tacahuay(Fig. 5), where debris flow and flood deposits have beeninterpreted as the result of heavy rainfall episodes as-sociated with El Niño events during the late Pleisto-cene–Holocene period [14,15]. A radiocarbon date of38,200±4300 yr BP provides the oldest age for the latePleistocene–Holocene alluvial sequence at this queb-rada Tacahuay [15]. A total number of 10 major alluvialevents are inferred between this date and 12,880 cal BP

debris flow deposits in the alluvial fan system at Quebrada Tacahuayada axis is evident.


[15]. Between 12,880 cal BP and 8400 cal BP, six debrisflow and flood events were inferred at QuebradaTacahuay and Quebrada Miraflores [15]. These 16 latePleistocene–early Holocene major events correlate withthe 18 and 16 pre-mid Holocene debris flow depositsdescribed at El Ahogado and Quebrada El Cañon,respectively [21]. In this last quebrada, located 1 kmsouth of Quebrada Los Burros [36], a several meterthick aeolian dune produced a natural hydrologic damduring the Pleistocene–Holocene transition [21,36]. Theinternal laminations in this dune, together with otherconspicuous aeolian accumulations observed betweenthe debris flow and flood deposits of the period 12,880–8400 cal BP at Quebrada Tacahuay and in otherlocalities [14,15,21], suggest intensified southwesterlywinds, since there was no other source of aeolian sand inthe area than the sand from the exposed coastal platformat that time. All the stratigraphic sections studied in thisregion point to a period of quiescence without majordebris flows or flood events between 8400 and 5298 calBP [14,15,21,36]. Thick remnants of a single debrisflow deposit at Quebrada Tacahuay, dated ca. 5300 calBP, are interpreted as a manifestation of the onset of theHolocene hydrologic system involving vertical incisionin this quebrada and regressive erosion following a midHolocene high sea level stand.

During the second half of the Holocene four majordebris flow events were inferred in the region. Beside theca. 5300 cal BP episode at Quebrada Tacahuay, otherevents occurred between 4200 and 3100 cal BP atQuebrada Yara [15]. The most recent pre-historic events,named Miraflores and Chuza units [38–40], were datedbetween AD 1300–1400 and AD 1607–1608, respec-tively [15]. These last four episodes are well correlatedwith conspicuous debris flow deposits observed at ElAhogado and Playa Muerta in the same region [21].Finally, three debris flow events which provoked seriousdamages and important vertical erosion within thequebradas are well documented by local rainfall andnewspaper chronicles since 1960 [21]. Among theseepisodes, the outstanding debris flows and associateddeposits generated on September 1997 are related to themost intense El Niño event of the twentieth century.

5.2. New data from northern Chile

Along the coast of the Antofagasta region in northernChile, alluvial fans are disposed over uplifted Pleisto-cene marine terraces at the foot of the western side of thecoastal range, characterized by elevations of 1000–2000 m a.s.l.. Holocene alluvial fans in this coastalregion prograded westwards according to a climatic-

induced pattern produced by the strengthening of thehyperaridity during the Holocene [19,37]. This contrib-uted to the vertical incision induced after a high sea levelstand most probably dated between 7000 and 6000 calBP [38,39].

The Quebrada Las Conchas is located at the northernextremity of the Antofagasta city (23.6°S) and drains25.6 km2 of Jurassic volcanic rocks in the coastalcordillera. Radiocarbon dates obtained from terrestrialgastropods within massive debris flow deposits in a latePleistocene alluvial terrace (19,670 and 23,558 cal BP),suggest the occurrence of sporadic heavy rains during theLast Glacial Maximum (LGM). A conspicuous andwidespread, 1–2 m thick, aeolian sand deposit overliesthe late Pleistocene alluvial terrace and marks the end ofthe constructive phase of this last unit (Fig. 4). Theabsence of alluvial deposits within the aeolian accumu-lation, located in the axis of this quebrada, suggestspersistent drought conditions at that time, concomitantlywith dominant intensified southwesterly winds assuggested by dip direction measurements of laminationsin this deposit (N45±15/24±7; n=40). The thick sandcover is well exposed, overlying a mid-Pleistocene dune,at the archaeological site Chimba-13 [40–42], wheremollusc remains, lithic artefacts, hearth remnants andother archaeological material related to the Huentelau-quén culture were preserved [42]. Several radiocarbondates obtained from marine shells in this deposit suggestan age range of 10,550–9124 cal BP as the most pro-bable depositional period of this aeolian sand accumu-lation [40,41].

At the southern end of the Antofagasta city (23.7°S), aseries of quebradas discharge sporadic debris flows onthe narrow coastal fringe. The restricted area of thewatersheds (between b1 km2 and 2.7 km2) favours arapid response of the drainage basins during heavyrainfall episodes and the deposition of debris flows at thebase of the coastal escarpment [19]. The erosion ofreddish cretaceous continental rocks induced the accu-mulation of brown-reddish late Pleistocene–Holocenealluvial sequences which are directly lying over a marineterrace assigned to the Last Interglacial Maximum[23,37]. Brownish and massive Holocene debris flowdeposits prograded with respect to the late Pleistocenebetter-sorted reddish alluvial deposits. A several deci-metre thick aeolian sand layer at the base of the Holocenesequence is correlated with the aeolian accumulation ofthe Chimba-13 archaeological site (Fig. 4). Artificialoutcrops in several alluvial fans in this area allowed aprecise counting of 45 Holocene debris flow deposits(Fig. 6). Two radiocarbon measurements on marinemollusc shells (Fissurella sp.), probably carried there by

Fig. 6. Panoramic view of a late Holocene alluvial fan located at the southern extremity of Antofagasta (23.7°S). Several artificial outcrops allowdetailed characterization and cuantification of debris flow deposits in this unit.


early inhabitants and found at the base of this unit(deposit #2), yielded ages of 5764 and 5331 cal BP forthe onset of this alluvial sequence. A single radiocarbondate obtained from a charcoal fragment in the debris flowdeposit #22, within its middle segment, provides an ageof 846 cal BP. Anthropogenic remains at the base of thedeposits #41 and 42 support their correlation with theheavy rainfall episodes of 1930 and 1940 [19]. Similarly,the deposits #43 and 44 are correlated with the heavyrainfalls of 1982 and 1987 [19]. Finally the deposit #45can be precisely attributed to the major event, whichoccurred on June 1991. The last two historic episodesassociated with strong to moderate El Niño events,produced vertical erosion in the proximal area of theHolocene alluvial fans and generated conspicuous debrisflow deposits. Other field observations in the regionconfirm this morphostratigraphical evolution. At PuntaGuanillo (22°S), for instance, radiocarbon dates obtainedfrom archaeological remains underlying a large debrisflow deposit widely distributed over a late Pleistocenealluvial fan surface, suggest that the vertical incision inthis quebrada began after 5559–5453 cal BP. Later on,radiocarbon dates from other archaeological layersunderlying debris flow deposits led to infer importantevents after 2657–2493 cal BP, and also after 360 cal BP(AD 1591), which, in the last case, can be closelycorrelated with the Chuza event recognised in southernPeru.

6. Discussion

6.1. Modern meteorological mechanisms, teleconnec-tion patterns and debris flows

During austral summers coinciding with the maturephase of El Niño, heavy rainfall events have beendocumented in southern Peru, but not in northern Chile.For southern Peru, several lifting mechanisms of thelower troposphere contribute to reach the thresholdneeded to trigger summer rainfalls, including the con-

spicuous warmer SST in the Ilo–Arica–Iquique triangle[43] and the strong convergence and subsequent upliftwhen nearshore winds meet the orography along thecoastal bend in southern Peru. In fact, nearshore oceansurface winds along northern Chile tend to peak insummer afternoons since reduced cloudiness at this timeenhances the land–sea thermal contrast [44]. Then,localized wind divergence along the nearshore striptends to occur as the southerlies speed-up while flowingfrom colder to warmer waters along northern Chilebefore reaching the coastal bend where flow conver-gence occurs. Therefore, a sharp contrast in the like-lihood of the buildup (warm SST) and subsequentrelease (flow convergence) of potential instability be-tween northern Chile and southern Peru would explainthe gap in the occurrence of El Niño-related australsummer heavy rainfall events along the coast of northernChile.

In austral spring the seasonal peak in the trade-windregime associated with the maximum intensity of thesubtropical anticyclone should enhance a widespreadorographic low-level flow convergence along southernPeru. In fact an “orographic blocking” of the southerlyflow along southern Peru has been documented in amodelling study related to the diurnal cycle of strato-cumulus clouds [45]. This effect should be enhancedduring the cold phase of the ENSO cycle when theSEPSA is strongest. A comparison of the NCEP/NCARreanalysed September anomalies in the pressure–velocity (AOM850) fields between El Niño's 1997/1987 and La Niña's 1998/1988 (not shown) reveals alarger area of upward motion anomalies concentratedalong this coastal area. However, the associated strongsubsidence temperature inversion should prevent wide-spread rainfall events, allowing only sporadic and short-lived episodes, depending heavily on the strength of themid-latitude weather disturbance reaching the area,which in turn depends on the position and strength of theassociated PSA teleconnection patterns. So, it is pro-posed here that during cold interannual ENSO events


(La Niña) and longer-scale cold ENSO-like periods (LaNiña-like) [46,47], the southern coast of Peru is moreprone to experience sporadic heavy rainfalls with re-spect to the northern Chile coastal region. This inter-pretation is supported by the common occurrence ofinundations before 1976 in the first area, concomitantlywith near absolute drought in the second region (Fig. 2).Furthermore, an intensified SEPSA and colder watersalong the coast during these cold periods would favourlow-level stability, fostering low-level coastal fogs(“camanchacas”).

The effects of the tropical–extratropical PSA atmo-spheric teleconnection patterns discussed here are betterdocumented in subtropical Central Chile, where a strongpositive correlation between heavy rains/drought and ElNiño/La Niña occurs during austral winter and earlyspring [8,16]. Then, only exceptional heavy rainfall eventsduringmoderate tomajorElNiño episodes affect SouthernPeru and Northern Chile, consistently with the limitedprobability of occurrence of local atmospheric anomaliesthat induce the development of heavy rains [20], and withthe limited number of debris flows relative to the numberof El Niño events registered in the sedimentary seriesduring the twentieth century [15,19,21], probably inconnection with longer-term El Niño-like conditions[46,47].

The unusual northward extension of the anomaloussubtropical trough results either from an equatorward-shifted blocking anticyclone to the southwest of thecontinent (PSA+) or from a mid-latitude ridge embed-ded in a deep trough (PSA-) that generates a cutoff lowoff northern Chile as the ridge progresses eastwardthrough southern Chile. The opposite polarity in theanomalies associated with these circulation schemesmay arise from sequences of PSA+ and PSA-teleconnection patterns forced by intraseasonal variabil-ity in near-equatorial Pacific convection [35].

6.2. Debris flows and ENSO during the Holocene

Our comparison of previous and new geologic datafrom southernmost Peru and northern Chile shows thatdebris flows occurred in both areas at the time of the LGMand during the late Holocene, but different manifestationscharacterized the latest Pleistocene and early Holocene(Fig. 7). While six debris flows and flood events are welldocumented between 12,900 and 8400 cal BP in coastalsouthern Peru [14,15,21], the geological record in coastalnorthern Chile suggests a lack of alluvial events,particularly during the accumulation of the aeolian depositin the Antofagasta area, between 10,550 and 9120 cal BP.The geological records from both regions coincide in a

period of quiescence without evidences of major alluvialepisodes from 8400 cal BP onward. Debris flow activitybegan simultaneously in both areas at ca. 5500–5300 calBP and similar tendencies in the frequency of majorevents can be observed afterward. In fact, rough estimatesof recurrence intervals of 1 event per 2350 yr and 1 eventper 210 yr can be calculated for the periods comprisedbetween 5300 and 605 cal BP and between 5330 and850 cal BP, in southern Peru and northern Chile,respectively. In the last thousand years or so the wellcorrelated Miraflores and Chuza events suggest a meaninterval of recurrence of 1 event per 310 yr in southernPeru, while 1 event per 40 yr can be inferred from sites innorthern Chile. The total number of debris flow episodesper century becomes even greater and similar in bothregions during the well constrained twentieth century.These common tendencies as well as the close temporalmatching in the onset of the debris flow activity in bothregions, ca. 5500–5300 cal BP, confirm that of the ElNiño climate teleconnection patterns, in their modernsense, was onset in the mid Holocene.

The last interpretation supports previous inferencesfrom the analysis of the sedimentary record at LagunaPallcacocha, located in the southern high Andes ofEcuador (02°46′S; 4060 m a.s.l.), which suggest that theinfluence of ENSO was absent from ca. 15,000 cal BPand during the early Holocene, appeared around7000 cal BP, and that modern El Niño manifestationswere well-established at ca. 5000 cal BP when a sig-nificant band of 2–8.5 yr in clastic torrential sedimen-tation became dominant in the spectral analyses [9,10].Consistently, increased influence of El Niño-relatedflooding events in the input of lithic particles toward thecontinental margin off Lima (12°S) in central Peru hasbeen inferred from 5600 cal BP and dominantly after5200 cal BP [48]. In subtropical central Chile, theanalysis of the sedimentary record at Laguna de Aculeo(33°50′S; 350 m a.s.l.) suggests the formation of afreshwater lake at 5700 cal BP and increased clastictorrential sedimentation afterward, following a period ofstrong aridity during the early to mid Holocene [49,50].As this region shows a strong positive correlation be-tween rainfall anomalies and ENSO [8], these tenden-cies can be interpreted as due to an increasing influenceof El Niño events from the mid Holocene [49,50], whichis also coherent with previous work that suggest morevariable and humid conditions from 5700–4200 on-ward, with respect to an extremely dry early tomid Holocene period in semiarid and central Chile(27–35°S) [51–57]. Intensified advection of warmsubtropical water masses toward central Chile from3000 cal BP onward [58], is also consistent with an


increased influence of El Niño off Chile during thesecond half of the Holocene.

Therefore, the general agreement in the chronology ofthe reconstructed regimes of heavy rainfall activity inwestern equatorial, tropical and subtropical South Amer-ica, including our compilation of previous and new datafrom the hyperarid Atacama Desert, supports the hypoth-esis that the tropical–extratropical climate teleconnectionthat characterizes modern El Niño events operated during,and only during, the second half of the Holocene. Resultsfrom a coupled ocean-atmosphere model [59], suggestthat ENSO variability was weak during the early to midHolocene and that it increased from the mid Holoceneonward, closely related to orbitally-driven changes in theseasonal cycle of the solar radiation in the tropics whichdominated extratropical influences [60]. In modern times,the climate teleconnection occurs during the borealsummer–autumn, when the Bjerknes positive feedbackfavours the growing of the El Niño-related anomalies that

Fig. 7. Comparison of the number of major debris flow and flood events per ceChile, based on previous [14,15,19,21,36,37] and new data. Numbers at the rthe corresponding periods. Lower and upper limits of periods characterized bradiocarbon data (squares) or from extrapolated age estimates (crosses).

peak around the end of the calendar year (austral summer),when the Intertropical Convergence Zone (ITCZ) moveson to the equatorial zone [1]. This last observation mayexplain why, comparatively to the northern Chile coastalregion and with respect to previous periods in the lateHolocene, the southern Peru coast suffers the effect ofwarm ENSO episodes more frequently during moderntimes, when maximum austral summer insolation occurs,concomitantly with more intense El Niño events as sug-gested by inferences from coral records in the westerntropical Pacific Ocean [11].

6.3. Climatic scenario during the latest Pleistocene andearly Holocene

Geological records in the study area suggest thatintensified southwesterly winds occurred during thelatest Pleistocene and early Holocene, when six debrisflow and flood events are well documented between

ntury inferred from alluvial deposits in southernmost Peru and northernight side of each curve indicate the total debris flow events inferred fory different periodicities were determined according to direct available


12,900 and 8400 cal BP in the southern Peru coastalregion [14,15,21]. This occurred concomitantly withpersistent drought conditions in northern Chile, partic-ularly at the time of the occupation of the Chimba-13archaeological site, between 10,550 and 9120 cal BP(Fig. 7). Stable isotope oxygen measurements onmollusc shells from several occupational layers of thisarchaeological site provided valuable, although prelim-inary, information for the reconstruction of paleo-SST atthat time [41]. δ18O values from fossil and modern shellsof Concholepas concholepas, suggest that sea surfaceconditions were characterized by mean SST valuescolder than nowadays and probably similar to what theyare now at 33°S (Fig. 8). Paleo-SST reconstruction fromalkenones analyses from sediment cores off central Chile(33°S) also suggests cool to near neutral conditions

Fig 8. a: Comparison between serial δ18O measurements from modernC. concholepas shells collected at 23°S (black squares) and 33°S (greysquare), with fossil C. concholepas shells from the archaeological siteChimba-13 (23°S; black circles; grey circles correspond to two fossilshell samples which provided unreliable δ18O measurements).Numbers at the right side of each sample indicate the total number ofisotopic analyses performed from each mollusc shell. Original isotopicdata from [41]. b: Modern monthly mean SST values at Antofagasta(23.6°S) and Valparaíso (33°S).

during the Pleistocene–Holocene transition to earlyHolocene, probably as the result of intensified northwardadvection of Subantarctic Waters [61]. Particularly coolSST occurred between ca. 11,900 and 9800 cal BP [61],and probably between 10,400 and 9300 cal BP accordingto a new chronological model proposed for the sedimentcore GIK17748-2, which takes into account extrapolatedΔR values [31]. SST similar to nowadays off centralChile persisted until ca. 7100 cal BP increased rapidlyafterward and decreased slowly during the mid Holo-cene, reaching modern values during the last thousandyears [31,61]. The overall data are coherent with aclimate scenario characterized by intensified coastalatmospheric circulation that induced higher ΔR valuesduring the early Holocene related to strong upwellingprocesses in coastal northern Chile and southernmostPeru [31]. The enhancement of upwelling most probablyresulted from a strengthened SEPSA, as suggested bystrong regional aridity and coastal humidity in semiaridand central Chile (27–35°S; [51–57]).

In this context, the former occurrences of sporadicrainfall events able to produce debris flows in the coastalregion of southern Peru, simultaneously with persistentdrought along the coast of northern Chile, could belinked to climate mechanisms similar to those developednowadays during cold to neutral conditions in the latewinter–spring season: a strengthening and/or equator-ward shift of the SEPSA resulting in enhanced cold-water upwelling, atmospheric subsidence and coastalcloudiness. This climate condition is also consistent witha significant northward shift of the ITCZ resulting in thecutoff of the equatorial waveguide limiting the fulldevelopment of El Niño conditions. Consequently thelatest Pleistocene–early Holocene debris flow and flooddeposits in southern Peru, probably reflect local short-lived rainfall events associated with the release ofpotential instability favoured by stronger southerlywinds topographic convergence, and not necessarilythrough El Niño episodes, as proposed previously[14,15]. A combination of reinforced costal subsidenceand alongshore winds for the latest Pleistocene–earlyHolocene transition is also consistent with higher thanpresent summer rainfall in subandean basins of thecentral Atacama Desert, between 16,200 cal BP and10,500 cal BP [62–64] or until 9500 cal BP [65,66],through a mechanism that, in its modern analogue, hasbeen recently shown [67]. Recent work suggests therelevancy of ENSO-induced precipitation variability athigh elevation in the Central Andes, where the relation-ship between summer rainfall and ENSO is equallystrong but reversed [68,69]. In fact, as the cordillera isvery close to the coast in the southernmost Peru region, it


has been documented that the precipitation anomalies athigh altitude over this area may either show a coastalsignal (e.g. wet during the 1997/98 ENSO), or anAltiplano signal (e.g. wet during 1983/84) [70]. Aninvestigation on monthly rainfall data and reports of twolocal Tacna newspapers (“Correo” and “Caplina”,January and February 2000 and 2001), during the verylong June 1998–March 2001 La Niña episode, revealedlarge impacts of summer rainfalls in the high Andesincluding floods and debris flows. However the spill-over precipitation events were too weak to producedebris flows in the coastal watersheds that are consideredhere (e.g. January 12 and 22, 2000: 3.4 mm over Tacna inthe second event; January 27, 2001: 0.8 mm over Tacna,“Correo”). Additionally, the same investigation showedthat the Moquegua river and other basins draining higherareas in the Andes experienced large debris flow andflood events during this major cold-ENSO episode,which tends to stress the use of debris flow and flooddeposits in these large river basins as indicators of past ElNiño events.

Thus, we suggest that the study region was char-acterized by La Niña-like conditions, particularly be-tween 10,550 and 9120 cal BP and probably between12,900 and 8400 cal BP, which favoured the occurrenceof spring-time debris flows in coastal southernmost Perutriggered by atmospheric mid-latitude circulation anom-alies concomitant with a strengthened coastal low-levelatmospheric equatorial flow impinging over the orogra-phy north of 18°S. These events may have occurredconcomitantly with excess of summer rainfalls in thehigh Central Andes. Later on, the onset of El Niño-related heavy rainfall anomalies along the western slopeof the Andes during the mid Holocene, closely matchesorbitally-driven variations in the frequency and ampli-tude of major El Niño events [12,13,60], which occurredfollowing important oceanographic changes in the southeastern Pacific Ocean [61,71] and in Antarctica [72].

7. Conclusions

Meteorological mechanisms explaining the occurrenceof heavy rains in coastal southern Peru and northern Chilein the last 50 yr are generically associated with El Niño-related atmospheric circulation anomalies derived fromtropical–extratropical teleconnections referred to as PSAteleconnection patterns [35]. These patterns are morefrequent or intense during the developing stage of thewarm phase of ENSO (austral winter–spring), when theanomalous convection is located around the central equa-torial Pacific. The subtropical atmospheric circulationanomalies associated with these teleconnection patterns

(subtropical troughing off western South America) appearin northern Chile and southern Peru when the PSAteleconnection poles get stronger or are locatedmore to thenorth than their usual position. In austral summer, duringthemature stage of El Niño, heavy rains tend to occur onlyin southern Peru, in connection to the buildup of potentialinstability due to positive SSTanomalies inArica's coastalbend and weak subsidence above theMBL. The release ofthis potential instability is triggered by mid-troposphere,mid-latitude weather disturbances that might becomestrengthened by the eastern and equatorward displacementof the SPCZ during strong El Niño events.

During La Niña or neutral conditions in australspring, short-lived heavy rainfall events tend also tooccur exclusively along the southern Peru coast, wherethe effects of comparatively higher SST within the Ilo–Arica–Iquique triangle and low-level southerly flowconvergence induced by the topography at the Perú–Chile coastal bend, reinforce the marine boundary layerlifting produced by weak mid-latitude weather dis-turbances in connection with transient PSA atmosphericcirculation anomalies.

Our comparison of the geological records from thesouthern Peru and northern Chile coastal zones supportsthe hypothesis of an onset of the modern ENSO tropical–extratropical climate teleconnections system during themid Holocene, ca. 5300–5500 cal BP, consistently with aseries of other proxies of ENSO variability from thewestern slope of the Andes. Before that, different mani-festations during the latest Pleistocene and early Holocenesuggest that these climate teleconnection patterns did notfully operate. For the La Niña-like conditions in thatperiod, we suggest the alternative climate mechanismproposed in the precedent paragraph that could explain theoccurrence of debris flows in southern Peru concomitantlywith the lack of heavy rainfall in a cooler and cloudiernorthern Chile. These results contradict previous inter-pretations of former occurrences of El Niño events in thesouthernmost Peru area, that were based upon extrapola-tion of present-day conditions and, more generally,encourage careful analyses of possible modifications ofthe climate patterns in a relatively recent past.

Acknowledgements

Field work and subsequent sedimentological andgeochronological analyses were performed in the frame-work of several collaborative projects between the IRDand the Universidad de Chile (PRODAC), the Universi-dad de Antofagasta, and the Instituto Geofisico del Peru.Other financing agencies to be acknowledged areCONICYT (Proyecto FONDECYT # 1950036, A.


Llagostera PI), the Fonds Canadien d'Aide à la Rechercheet CNRSNG (C. Hillaire Marcel). Special thanks areexpressed to C. Hillaire-Marcel and G. Bilodeau, J.F.Saliege and M. Mandeng Yogo, N. Guzman, Z. Salinas,C. Arriagada and S. Rome-Gaspaldy for geochemical andradiocarbon analyses, field support, figures and somerainfall data. R. Armijo and one anonymous reviewerprovided useful comments to the manuscript.

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http://dx.doi.org/10.1029/2001PA000727

http://dx.doi.org/10.1029/2002JD003357

http://dx.doi.org/10.1029/2004PA001099

Documents

ENSO tropical–extratropical climate teleconnections and mechanisms for Holocene debris flows along the hyperarid coast of western South America (17°–24°S