Late Pleistocene and Holocene palaeoclimate and glacier fluctuations in Patagonia

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Global and Planetary Change 43 (2004) 79–101

Late Pleistocene and Holocene palaeoclimate and

glacier fluctuations in Patagonia

Neil F. Glassera,*, Stephan Harrisonb, Vanessa Winchesterb, Masamu Aniyac

aCentre for Glaciology, Institute of Geography and Earth Sciences, University of Wales, Aberystwyth, Ceredigion SY23 3DB, Wales UKbSchool of Geography and the Environment, University of Oxford, Mansfield Road, Oxford OX1 3TB, UK

c Institute of Geoscience, University of Tsukuba, Ibaraki 305-8571, Japan

Received 12 March 2004; accepted 24 March 2004

Abstract

This paper presents the evidence for Late Pleistocene and Holocene palaeoclimate and glacier fluctuations of the two major

icefields in Patagonia, the Hielo Patagonico Norte (47j00VS, 73j39VW) and the Hielo Patagonico Sur (between 48j50VS and

51j30VS). The palaeoenvironmental evidence suggests that glaciers still covered large areas of Patagonia at approximately

14,600 14C years BP. Uniform and rapid warming took place after 13,000 14C years BP, with no unequivocal evidence for

climate fluctuations equivalent to those of the Northern Hemisphere Younger Dryas cooling event (the Younger Dryas

Chronozone, dated to 11,000–10,000 14C years BP (12,700–11,500 cal. years BP). During the early Holocene (10,000–500014C years BP) atmospheric temperatures east of the Andes were about 2 jC above modern values in the period 8500–6500 14C

years BP. The period between 6000 and 3600 14C years BP appears to have been colder and wetter than present, followed by an

arid phase from 3600 to 3000 14C years BP. From 3000 14C years BP to the present, there is evidence of a cold phase, with

relatively high precipitation. West of the Andes, the available evidence points to periods of drier than present conditions

between 9400–6300 and 2400–1600 14C years BP. Holocene glacier advances in Patagonia began around 5000 14C years BP,

coincident with a strong climatic cooling around this time (the Neoglacial interval). Glacier advances can be assigned to one of

three time periods following a ‘Mercer-type’ chronology, or one of four time periods following an ‘Aniya-type’ chronology. The

‘Mercer-type’ chronology has glacier advances 4700–4200 14C years BP; 2700–2000 14C years BP and during the Little Ice

Age. The ‘Aniya-type’ chronology has glacier advances at 3600 14C years BP, 2300 14C years BP, 1600–1400 14C years BP

and during the Little Ice Age. These chronologies are best regarded as broad regional trends, since there are also dated examples

of glacier advances outside these time periods. Possible explanations for the observed patterns of glacier fluctuations in

Patagonia include changes related to the internal characteristics of the icefields, changes in the extent of Antarctic sea-ice cover,

atmospheric/oceanic coupling-induced climate variability, systematic changes in synoptic conditions and short-term variations

in atmospheric temperature and precipitation.

D 2004 Elsevier B.V. All rights reserved.

Keywords: Patagonia; Glacier fluctuations; Palaeoclimate; Holocene

0921-8181/$ - see front matter D 2004 Elsevier B.V. All rights reserved.

doi:10.1016/j.gloplacha.2004.03.002

* Corresponding author. Tel.: +44-1970-622785; fax: +44-1970-622659.

E-mail address: [email protected] (N.F. Glasser).

N.F. Glasser et al. / Global and Planetary Change 43 (2004) 79–10180

1. Introduction

1.1. Climatological background

Records of atmospheric circulation across southern

South America show strong interannual, interdecadal

and intercentennial variability. Climatic changes in

South America are associated directly or indirectly

through long-term (Ma) mountain-range uplift (Hart-

ley, 2003); atmospheric teleconnections, with large-

scale atmospheric/oceanic forcing such as the El Nino-

Southern Oscillation (ENSO) (Aceituno, 1988; Allan

et al., 1995; Diaz and Markgraf, 2000); the tempera-

ture gradient between tropical and extratropical region;

the sea-surface temperatures of the South Atlantic and

South Pacific oceans, and the circum-Antarctic ocean

circulation (Villalba et al., 1997).

Understanding the pace and timing of climatic

changes in the Late Pleistocene and Holocene is a

key issue in southern South America for three main

reasons. First, these changes reflect changes in cli-

matic gradients across the region, e.g., the latitudinal

migration of the precipitation-bearing Southern West-

erlies (Heusser, 1995; Veit, 1996; Lamy et al., 2000,

2001). Second, this climatic background provides

constraints on studies of relative sea level, glacioisos-

tasy and glacier fluctuations (Ivins and James, 1999;

Rostami et al., 2000; Rignot et al., 2003). Third, the

timing of glacier expansion and contraction in differ-

ent parts of the region provides information on the

forcing mechanisms of climate change (Aniya and

Enomoto, 1986; van Geel et al., 2000; Markgraf and

Seltzer, 2001). Previous studies have concentrated on

the uncertainty concerning interhemispheric timing of

climatic changes during the last glacial– interglacial

transition (e.g., Lowell et al., 1995; Steig et al., 1998;

Denton et al., 1999) and Holocene (Wasson and

Claussen, 2002). Different hypotheses, relying on

different lines of evidence, point variously to the

Northern Hemisphere leading the Southern Hemi-

sphere and vice versa, or to synchrony between the

hemispheres.

For many years changes in Antarctic climate and

glaciers were assumed to lag the northern hemi-

sphere. Recently, however, ice-core evidence led

Steig et al. (1998) to suggest that climate change

was synchronous in both hemispheres, implying an

atmospheric mechanism of rapid climate change. In

contrast, Blunier et al. (1998) suggested that Antarc-

tic climate change is out of phase with the northern

Hemisphere, perhaps as a result of an oceanic mech-

anism such as the bipolar seesaw (Broecker, 1998).

Other authors (e.g., McCulloch et al., 2000) have

argued from a synthesis of key proxy records that

these comparisons are complicated by the fact that

climate changes were regionally variable. For exam-

ple, in South America there was a sudden rise in

temperature that initiated deglaciation synchronously

over 16j of latitude at 14,600–14,300 14C years BP

(17,500–17,150 cal. years BP). There was a second

step of warming in the Chilean Lake District at

13,000–12,700 14C years BP (15,650–15,350 cal.

years BP), which saw temperatures rise close to

modern values. A third warming step, particularly

clear in the south, occurred at c. 10,000 14C years BP

(11,400 cal. years BP), thus achieving Holocene

levels of warmth. Following the initial warming,

there was a lagged response in precipitation as the

Westerlies, after a delay of c. 1600 years, migrated

from their northern glacial location to their present

latitude, which was attained by 12,300 14C years BP

(14,300 cal. years BP). The latitudinal contrasts in the

timing of maximum precipitation are reflected in

regional contrasts in vegetation change and in glacier

behaviour. Since the delay in the migration of the

Westerlies coincides with the Heinrich 1 iceberg

event in the North Atlantic, McCulloch et al. (2000)

argued that the suppressed global thermohaline cir-

culation at the time may have affected sea-surface

temperatures in the South Pacific, and the return of

the Westerlies to their present southerly latitude only

followed ocean reorganisation to its present intergla-

cial mode.

In Patagonia there is considerable evidence that

glaciers and icefields have expanded and contracted

in the past in response to variations in climate

systems (Fig. 1). The outlet glaciers extend to lower

latitudes than those of any other substantial ice

masses in the world and the icefields are nourished

by midlatitude weather systems characterised by

abundant precipitation, causing high ablation rates,

steep mass-balance gradients and high ice velocities

(Rott et al., 1998; Matsuoka and Naruse, 1999).

These circumstances, together with sharp local topo-

graphic and climatological contrasts, create a dynam-

ic glacier system (Hulton and Sugden, 1997).

Fig. 1. Southern South America showing the location of the major icefields (Hielo Patagonico Norte and Hielo Patagonico Sur), major lakes and

other place names mentioned in the text. Individual outlet glaciers from the two icefields are named on Figs. 2 and 3. The position of the High and

Low atmospheric pressure centres, the oceanic Winter Polar Front and associated precipitation maximum >500 mm are taken from Miller (1976)

and van Geel et al. (2000). Numbers 1 and 2 on the map indicate climatic regimes dominated by (1) humid cool temperate conditions and (2) humid

temperate conditions with no dry season.

N.F. Glasser et al. / Global and Planetary Change 43 (2004) 79–101 81

1.2. Field setting

In this paper we consider in detail the area of

Patagonia south of 46jS and Tierra del Fuego. Two

major ice masses exist in the region:

(1) The Hielo Patagonico Norte or North Patago-

nian Icefield (47j00VS, 73j39VW) is some 120 km

long and 40–60 km wide, capping the Andean Cor-

dillera between altitudes of 700–2500 m a.s.l. (Fig. 2).

The icefield covers some c. 4200 km2. Annual pre-

cipitation on the western side of the icefield increases

from 3700 mm at sea level to an estimated maximum

of 6700 mm at 700 m a.s.l. (Escobar et al., 1992).

Precipitation decreases sharply on the eastern side of

the icefield although few reliable precipitation data are

available (Kobayashi and Saito, 1985; Fukami et al.,

Fig. 2. The major outlet glaciers of the Hielo Patagonico Norte.

N.F. Glasser et al. / Global and Planetary Change 43 (2004) 79–10182

1987). Of the 30 or so outlet glaciers of the Hielo

Patagonico Norte only a few have been studied in any

detail.

(2) The Hielo Patagonico Sur or South Patagonian

Icefield is much larger, running north–south for 360

km between 48j50VS and 51j30VS with a mean

width of c. 40 km (Fig. 3). The Hielo Patagonico

Sur covers an area of c. 13,000 km2. Warren and

Sugden (1993) reviewed recent fluctuations of 28

outlet glaciers of the Hielo Patagonico Sur, but little

is known about the behaviour or characteristics of the

remaining outlet glaciers.

N.F. Glasser et al. / Global and Planetary Change 43 (2004) 79–101 83

1.3. Aims

Whilst there have been reviews of contemporary

and historical Patagonian glacier behaviour (e.g.,

Fig. 3. The major outlet glaciers of the Hielo Patagonico Sur. The

location of satellite glaciers at San Lorenze Este, Narvaez, Dos

Lagos and in the Rio Guanaco are also indicated.

Warren and Sugden, 1993; Aniya et al., 1997; Luck-

man and Villalba, 2001; Heusser, 2002) and the

palaeoecology of the region (e.g., Markgraf, 1989),

the glacier data have never been considered in the

context of Late Pleistocene and Holocene palaeocli-

mate. The aims of this paper are therefore:

1. To outline the rates and timing of climatic changes

during the Late Pleistocene (including the Last

Glacial Maximum) and the Holocene in Patagonia.

2. To describe the geomorphological and geochrono-

logical evidence for the timing of glacier fluctua-

tions in Patagonia during the Holocene.

3. To present correlations of the timing of events in

Patagonia with those in other areas, at both South

American and global scales.

4. To explore possible explanations for the observed

patterns of glacier fluctuations in Patagonia.

The overall approach taken in this paper is to

examine broad trends in palaeoclimatic variability

and glacier behaviour wherever possible, rather than

concentrating on discussions at a site-specific level.

Unless otherwise stated, all dates quoted in this paper

are 14C years BP (i.e., uncalibrated ages) (Stuiver et al.,

1998a,b).

2. Data acquisition

2.1. Terminology

The Holocene is the time-stratigraphic term adop-

ted for the last 10,000 14C years of geological time.

Subdivision of the Holocene is problematic since it

appears that, except for changes in sea level, no events

within this short Epoch have been experienced simul-

taneously worldwide. It is generally agreed that Ho-

locene global temperatures peaked around 6000 14C

years BP, although Holocene sea level in Patagonia

culminated 8000–7000 14C years BP at 6–7 m above

present sea level (Rostami et al., 2000). During the

last 5000 14C years, most mountainous regions of the

world including Patagonia have undergone a series of

glacial resurgences (Porter, 2000). Porter and Denton

(1967) proposed the term ‘‘Neoglaciation’’ for this

interval. In Patagonia, where glaciers appear to have

advanced on more than one occasion during the

N.F. Glasser et al. / Global and Planetary Change 43 (2004) 79–10184

Neoglacial, this interval is conveniently subdivided

into four parts (Neoglacial Advances I–IV).

2.2. Methods

Glacier fluctuations in Patagonia during Neoglacial

Advance IV (the ‘‘Little Ice Age’’) have been recon-

structed using a variety of methods. Historical sources

include scientific reports from expeditions to the

glaciers and icefields (e.g., Steffen, 1947; Lawrence

and Lawrence, 1959) and accounts of early travellers

to the region (e.g., Darwin, 1839; Simpson, 1875). In

the absence of large-scale and accurate maps, aerial

photographs of the glaciers have proved invaluable in

marking their former limits. For instance, the first

vertical aerial photographs of the Hielo Patagonico

Norte were taken in 1974 and these provided the base

for the subsequent 1:50,000 scale maps, which are the

largest scale available. Much of the ground coverage

is obscured by cloud (a perennial problem in this

region). Complete aerial photograph coverage of the

Hielo Patagonico Sur was taken for the first time

between 1979 and 1984 by the Chilean Instituto

Geographico Militar. Lower oblique photographs

were then taken by the Japanese in 1986, 1990 and

1993 (Aniya, 1992; Wada and Aniya, 1995; Aniya et

al., 1996). The latest Instituto Geographico Militar

aerial photographic coverage dates from 1997 to

1998. The ‘‘air force division’’ of the US army took

Trimetrogen oblique photographs (using three cam-

eras to give a 180j field of vision) of the region in

1944/1945. These have allowed Aniya (1988) to

compare the glacier frontal positions of the icefield

between 1944 and 1986 and Winchester and Harrison

(2000) to construct regional lichenometric and den-

drochronological dating schemes.

Lichenometry (using Placopsis patagonica and P.

perrugosa, the most common rock-inhabiting species

in the area) and dendrochronology (using Nothofagus

nitida, N. betuloides, N. pumilio, and N. antarctica)

have been employed at a number of proglacial loca-

tions to date constructional landforms, boulders, and

bedrock surfaces exposed by the receding glaciers

since the peak of the Little Ice Age. However, the

early and mid-Holocene glacier advances in Patagonia

lie outside the limits of dendrochronological and

lichenometric dating methods and earlier Holocene

advances in Patagonia are therefore based almost

exclusively on 14C dating of organic material (e.g.,

wood, peat and limnic sediments) in and around

moraine ridges. Other 14C dates in Patagonia have

been obtained from organic remains in and around

vegetation trimlines (e.g., Aniya, 1996), from tree

remains embedded in moraines and from trees killed

by glacier advances (e.g., Glasser et al., 2002). Some

workers (e.g., Mercer, 1968, 1970) collected samples

for 14C dating from the base of sections excavated in

peat deposits within these moraine ridges. Mercer

(1970, p. 6) fully acknowledged that basal peat ‘‘gives

a minimal age for a feature but not necessarily a close

minimal age, because the interval between the expo-

sure of a surface from beneath ice or water and the

start of peat growth must depend on several factors,

the most important of which are climate, microrelief,

and composition of the surface material’’.

Evidence for Holocene palaeoclimates in Patagonia

comes chiefly from palynological analysis of 14C dated

records of sediments and associated organic remains

obtained from surface exposures and cored deposits.

These palaeoecological archives include peat bogs,

freshwater lakes, playa lakes and dune fields (Bianchi

et al., 1999; Haberle et al., 2000; Gilli et al., 2001).

3. The Late Pleistocene

3.1. The Last Glacial Maximum and Younger Dryas

Caldenius (1932) laid the foundations of Patago-

nian glacial chronologies, establishing the existence of

four main moraines systems east of the Andes, which

are situated at or before the entrances of the Cor-

dilleras, several tens of kilometres or more from the

modern ice fronts. These appear to represent the Last

Glacial Maximum extent in Patagonia (e.g., Porter,

1989; Hulton et al., 1994). However, Caldenius (1932,

p. 148) also observed that behind the four principal

moraine systems are ‘‘still some others, situated far in

the valleys of the Cordilleras and one rather near to

the present glaciation’’. The moraine systems within

these valleys represent the Holocene fluctuations of

the modern glaciers. The moraine systems closest to

the modern glacier margins date from the Little Ice

Age advances (Harrison, 2004).

Palaeoclimatic studies of southern South America

have yielded a variety of results concerning the rates

N.F. Glasser et al. / Global and Planetary Change 43 (2004) 79–101 85

and timing of environmental change (Porter, 1981a;

Markgraf, 1989; Rabassa and Clapperton, 1990; Stine

and Stine, 1990; Heusser et al., 1996; Ariztegui et al.,

1997; Mancini, 1998; Coronato et al., 1999; Paez et

al., 1999; Thompson et al., 2000; McCulloch et al.,

2000; Hodell et al., 2001; Heusser, 2002). According

to McCulloch et al. (2000), glaciers still covered

large areas of southern Chile and a considerable

portion of the eastern section of the southern Andes

at approximately 14,600 14C years BP. By 10,000 14C

years BP, after several warming episodes, the Pata-

gonian Ice Field of the Last Glacial Maximum had

separated into the Hielo Patagonico Norte and Hielo

Patagonico Sur. East of the Andes, the middle and

high latitudes of South America warmed uniformly

and rapidly from 13,000 14C years BP, with no

indication of subsequent climate fluctuations equiva-

lent to those of the Northern Hemisphere Younger

Dryas cooling event (the Younger Dryas Chronozone,

dated to 11,000–10,000 14C years BP (12,700–

11,500 cal. years BP). This chronology agrees broad-

ly with that of Mercer (1968, 1969, 1970, 1976,

1982) who postulated that glaciers in Patagonia had

become smaller than now by 11,000 14C years BP

and remained diminished until the advances of the

last few millennia.

Clapperton (1993) pointed out that Mercer’s hy-

pothesis that glaciers in southernmost South America

receded rapidly after 13,000 14C years BP and did not

readvance until the Neoglacial was based on obser-

vations from compressed peat with a radiocarbon

date of c. 11,070 14C years BP in the basal layer of

two moraine systems: at Punta Bandera on the east

side of ice field, some 22 km east of the Moreno

glacier, and at Tempano Glacier, a sea-terminating

outlet from the northwest part of the Hielo Patago-

co Sur. Mercer (1976, p.156) concluded from this

that the Tempano Glacier had remained at least as

small as it is today from 11,000 14C years BP until

the beginning of the Neoglacial interval. However,

Clapperton (1993) pointed out that because Tempano

Glacier terminates in the sea it may not reliably

reflect small-scale changes in climate and that the

dates obtained from the moraines at Punta Bandera

were interpreted incorrectly on geomorphological

grounds (see also Strelin and Malagnino, 2000).

Furthermore, a significant advance of the Tronador

ice-cap, Argentina, which feeds proglacial Lake Mas-

cardi, occurred during the Younger Dryas Chrono-

zone (Ariztegui et al., 1997; Hajdas et al., 2003).

Data from an ice core retrieved from Huascaran

(Peru) by Thompson et al. (2000) show a sharp

decrease of d18O concentrations at f 10,000 14C

years BP, indicating a change in the warm conditions

in South America before this period. From a site on

the Taitao Peninsula, Massaferro and Brooks (2002)

suggest a cooling around Younger Dryas times. In

contrast, Bennett et al. (2000) contend that conditions

on the Taitao Peninsula, to the west of the Hielo

Patagonico Norte, were as warm as present during the

Younger Dryas. Overall, the palaeoenvironmental

record in Patagonia seems to indicate that the period

13,000–5000 14C years BP was marked by relatively

warm temperatures (Heusser and Streeter, 1980;

Rabassa and Clapperton, 1990). This period may or

may not have been punctuated between 11,000 and

10,000 14C years BP by a Younger Dryas-like cold

epoch. Rabassa and Clapperton (1990) even sug-

gested that the icefields might have been substantially

smaller during the period 13,000–5000 14C years

BP than at present, although this has yet to be

substantiated.

Markgraf (1993) presented a continuous palaeo-

climatic history for the past 14,000 14C years BP in

South America based on palynological records from

south of latitude 50jS. Prior to 12,500 14C years BP,

dry Empetrum heathlands dominated throughout the

high southern latitudes, indicating high winds, annual

precipitation of less than 300 mm, and freezing year-

round temperatures. After 12,500 14C years BP,

steppe replaced the heathlands, suggesting a decrease

in wind intensity, an increase in effective moisture,

and increased temperatures. Low moisture levels

prior to 12,500 14C years BP between latitudes 45jand 55jS suggest that the westerly storm tracks

responsible for precipitation patterns in southern

South America may have been located closer to the

equator than today. The precipitation increase at

12,500 14C years BP, extending only as far south as

50jS, indicates that the stormtracks had shifted

poleward, but did not reach Tierra del Fuego. By

9000 14C years BP, the stormtracks had shifted to the

high southern latitudes.

McCulloch and Davies (2001) described late-gla-

cial and early Holocene palaeoclimate from two sites,

Puerto del Hambre and Estancia Esmeralda II, in the

N.F. Glasser et al. / Global and Planetary Change 43 (2004) 79–10186

central section of the Strait of Magellan, southern

Chile. Climatic warming commenced at 14,470 14C

years BP, although mean annual temperatures contin-

ued to be cooler than present until c. 10,300 14C years

BP. These authors considered that there was a sharp

decrease in effective moisture at c. 12,550 14C years

BP, after which moisture levels fluctuated but

remained relatively low until c.10,300 14C years BP.

After 10,300 14C years BP, a shift to warmer con-

ditions occurred.

3.2. Late Pleistocene (the Last Glacial Maximum and

Younger Dryas) palaeoclimates: summary

Palaeoclimatic studies of southern South America

have yielded a variety of results concerning the rates

and timing of Late Pleistocene environmental change.

It seems likely that glaciers still covered large areas of

southern Chile and a considerable portion of the

eastern section of the southern Andes at approximate-

ly 14,600 14C years BP. After 13,000 14C years BP,

the palaeoenvironmental record in Patagonia seems to

indicate relatively warm temperatures (Heusser and

Streeter, 1980; Rabassa and Clapperton, 1990). This

period may or may not have been punctuated between

11,000 and 10,000 14C years BP by a Younger Dryas-

like cold epoch.

4. Palaeoenvironmental evidence of Holocene

climate change in Patagonia

4.1. Sources of information

Tables 1, 2 and 3 present details of the palae-

oclimatic significance of the palaeoenvironmental

evidence obtained by studies from sites in Patagonia

to the east of the Andes, to the west of the Andes

and in southernmost South America (including Tierra

del Fuego). We quote in these tables only sites in

southern South America below 46jS avoiding those

from further afield, such as the Chilean Lake District

(Heusser, 1984; Heusser and Streeter, 1980) and the

semiarid regions of Norte Chico, central and north-

ern Chile (Veit, 1996; Lamy et al., 2000, 2001;

Jenny et al., 2002; Maldonado and Villagran,

2002), where climatic influences may have been

different.

4.2. Holocene palaeoclimates

The earliest phase of the Holocene is generally

considered an interval of ameliorating climatic con-

ditions with temperatures in the Chilean Lake District,

600 km north of the present icefields, peaking at about

2 jC above modern values either between 8500 and

6500 14C years BP (Heusser, 1974) or between 9410

and 8600 14C years BP (Clapperton, 1990). Other

palaeoclimatic studies of southern South America

(Rabassa and Clapperton, 1990; Mancini, 1998;

Thompson et al., 2000; Hodell et al., 2001) have

identified the existence of a strong cooling episode

at 5000 14C years BP resulting in glacier advances.

For example, Mancini (1998) argued that, based on

palynological records, prior to 8000 14C years BP, a

grass steppe extended east of the Andes, indicating

relatively high precipitation under cold conditions.

Between 8000 and 6000 14C years BP, an increase

in shrub–steppe taxa dominated by Asteraceae tubuli-

florae represents an increase in temperature, whilst

precipitation remained in the previous range of about

200 mm. The mid-Holocene (around 5000 14C years

BP) is reflected by the brief return of steppe taxa,

primarily grasses, indicating either cold conditions

similar to those of the early Holocene or an increase

in precipitation. Certainly by 4500 14C years BP, the

vegetation is represented by grass–shrub steppe dom-

inated by Asteraceae tubuliflorae, with these condi-

tions continuing after 3500 14C years BP and the

development of more extensive late Holocene forest

suggesting greater effective moisture, probably related

to cooler temperatures.

Schabitz (1994) cored 17 playa lakes in Patagonia

between 39j and 47jS with the aim of reconstructing

their vegetational, climatic and geomorphological his-

tory, presenting palynological results from two lakes,

Salina Anzoategui (39j00V23US, 63j46V30UW) and

Salina Piedra (40j34V59US, 62j40V26UW). Both the

sedimentological and the palynological results suggest

prevailing arid climatic conditions with mainly aeo-

lian morphodynamic processes active during the mid-

Holocene. In late Holocene times, the climate changed

to more semiarid conditions, with a higher rainfall

frequency and more frequent fluvial input into the

lake, possibly reflecting greater influence from the

Atlantic high pressure cell leading to more distinct

seasonality.

Table 1

Palaeoclimatic information for the Holocene from selected sites east of the Andes

Location Dates Inferred climatic regime Type of evidence Reference

Parque Nacional Perito

Moreno, Santa Cruz,

Argentina

Before 6500 Arid; colder than present Pollen analysis Mancini et al.,

2002

Parque Nacional Perito

Moreno, Santa Cruz,

Argentina

6500–2700 Increase in summer

temperatures; higher

moisture availability

Pollen analysis Mancini et al.,

2002

Parque Nacional Perito

Moreno, Santa Cruz,

Argentina

2700–2000 Decrease in temperature;

increase in precipitation

Pollen analysis Mancini et al.,

2002

Parque Nacional Perito

Moreno, Santa Cruz,

Argentina

1200–250 Increase in temperature;

precipitation similar to

present

Pollen analysis Mancini et al.,

2002

Cerro Verlika, Santa Cruz,

Argentina

4500–3600 Colder and moister

than present

Pollen analysis Mancini, 2001

Cerro Verlika, Santa Cruz,

Argentina

3600–3000 Increase in temperature;

decrease in moisture

Pollen analysis Mancini, 2001

Cave Las Buitreras,

Santa Cruz, Argentina

Before 8000 Increase in summer

temperatures; decrease

in precipitation

Pollen analysis Prieto et al.,

1998

Cave Las Buitreras,

Santa Cruz, Argentina

7600–4500 Higher moisture

availability

Pollen analysis Prieto et al.,

1998

Santa Cruz, Argentina Before 8000 Cold; relatively high

precipitation

Pollen analysis Mancini, 1998

Santa Cruz, Argentina 8000–6000 Increase in temperature;

precipitation relatively high

Pollen analysis Mancini, 1998

Santa Cruz, Argentina C 5000–4000 Cold; relatively high

precipitation

Pollen analysis Mancini, 1998

Santa Cruz, Argentina After 3500 Cold; relatively high

precipitation

Pollen analysis Mancini, 1998

Rio Limay, Argentina 1800–1300 Drier summers Pollen analysis Markgraf et al.,

1997

Playa lakes, Argentina ‘‘Mid-Holocene’’ Arid climatic conditions Pollen analysis Schabitz, 1994

Playa lakes, Argentina ‘‘Late Holocene’’ Semiarid conditions;

increased precipitation

Pollen analysis Schabitz, 1994

Rio Negro, Argentina Entire Holocene Significantly drier

conditions than late

Pleistocene

Ostracoda Whatley and

Cusminsky, 1999

Cordoba Province,

Argentina

3500–1000 Drier conditions

than present

14C dating of

dune fields

Iriondo (1989)

Lago Argentino,

Argentina

5730 Decrease in summer

temperatures;

increased precipitation

14C dating of

onset of peat bog

formation

Strelin and

Malagnino, 2000

All dates are quoted in 14C years BP.

N.F. Glasser et al. / Global and Planetary Change 43 (2004) 79–101 87

Markgraf’s (1993) synthesis of pollen records for

the past 14,000 14C years in South America from

south of latitude 50jS indicates that along the rain-

ward side of the Andes at 9000 14C years BP there

was forest expansion, with this occurring on the

rainshadow side, at 8000 14C years BP. The greater

openness of the early Holocene forests, including

those of the rainward part of the region, indicates

precipitation levels between 500 and 800 mm, com-

parable to those of today’s forest/steppe transition.

After a pronounced mid-Holocene dry event, the late

Holocene forests appeared more closed than those of

Table 2

Palaeoclimatic information for the Holocene from selected sites west of the Andes

Location Dates Inferred climatic regime Type of evidence Reference

Taito Peninsula, Chile 9400–6300 Drier than present Chironomid midges Massaferro and Brooks, 2002

Taito Peninsula, Chile 2400–1600 Drier than present Chironomid midges Massaferro and Brooks, 2002

All dates are quoted in 14C years BP.

N.F. Glasser et al. / Global and Planetary Change 43 (2004) 79–10188

the early Holocene, suggesting greater effective mois-

ture, probably related to cooler temperatures. The

large seasonal latitudinal shift comparable to the

modern situation, equatorwards in winter and pole-

wards in summer, did not develop until after 4500 14C

years BP. McCulloch and Davies (2001) demonstrated

an extreme arid phase between c. 10,300 and 855014C years BP before an increase in available moisture

allowed the eastward spread of Nothofagus forest at c.

8550 14C years BP.

Finally, Iriondo (1989) described the results of14C dating of aeolian silts and sands forming exten-

sive dune fields to the east of the Andes in the

Argentine pampas. These dates indicate that this area

was drier than today between 3500 and 1000 14C

years BP. Wind action caused erosion of the existing

surficial sediment and deposition of the eroded

material in extensive silt and sand dune fields.

Analysis of palaeodune orientation led Iriondo

(1989) to conclude that a seasonal anticyclonic

system was centred over the northeastern Cordoba

province at this time.

Table 3

Palaeoclimatic information for the Holocene from selected sites in southe

Location Dates Inferred clim

regime

Magellan Strait 10,300–8550 14C years BP Extremely a

Magellan Strait c. 8550 14C years BP Increase in

Tierra del Fuego 9000–8000 14C years BP Precipitation

to present

Tierra del Fuego ‘‘Mid-Holocene’’ Increased ar

Tierra del Fuego ‘‘Late Holocene’’ Cooler temp

greater effec

Tierra del Fuego 6000–5000 cal years BP Warming te

reduced pre

Tierra del Fuego After 5000 cal years BP Warming te

Increased pr

All dates are quoted in 14C years BP.

4.3. Holocene palaeoclimates: summary

There appears to be strong evidence that both

temperature and precipitation have fluctuated consid-

erably during the Holocene to the east of the Andes

(Table 1). The period between 10,000 and 8000 14C

years BP is a time of climatic amelioration, with

increasing summer temperatures and decreasing pre-

cipitation. Temperatures continued to increase, this

time accompanied by increased precipitation, between

8000 and 6000 14C years BP. The period between

6000 and 3600 14C years BP appears to have been

colder and wetter than present, followed by an arid

phase from 3600 to 3000 14C years BP. From 300014C years BP to the present day, there is evidence of a

cold phase, with relatively high precipitation. West of

the Andes, the available evidence points to periods of

drier than present conditions between 9400–6300 and

2400–1600 14C years BP (Table 2). In southernmost

South America, climatic amelioration is evident be-

tween 10,300 and 8550 14C years BP (Table 3). After

this time, there was an increase in available moisture,

rnmost South America

atic Type of evidence Reference

rid Pollen analysis McCulloch and

Davies, 2001

moisture Pollen analysis McCulloch and

Davies, 2001

similar Pollen analysis Markgraf, 1993

idity Pollen analysis Markgraf, 1993

eratures;

tive moisture

Pollen analysis Markgraf, 1993

mperatures;

cipitation

Pollen analysis Pendall et al., 2001

mperatures;

ecipitation

Pollen analysis Pendall et al., 2001

N.F. Glasser et al. / Global and Planetary Change 43 (2004) 79–101 89

followed by a period of increased aridity in the mid-

Holocene (around 5000 14C years BP). After 500014C years BP, there is evidence for an increasing

cooler and wetter climate. These climatic inferences

compare favourably with those of Heusser and Stree-

ter (1980) who found evidence for warmer than

average periods in the Chilean Lake District between

9410 and 8600 14C years BP, and cold periods with

successive minima between 4950 and 3160 14C years

BP and between 3160 and 800 14C years BP. During

the cold period between 4950 and 3160 14C years BP,

Heusser and Streeter (1980) inferred that mean annual

temperature may have dropped by as much as 2jCwhilst mean annual precipitation rose by as much as

3000 mm. The cooling trend of the last 5000 14C

years was interrupted twice, at around 3000 and 35014C years BP, when temperatures were higher than

present. The maxima in the precipitation record

roughly correspond with the temperature minima,

with the most pronounced precipitation peak between

4950 and 3160 14C years BP, followed by another

peak sometime between 3160 and 800 14C years BP

and a final peak between 350 14C years BP and the

present day.

5. The timing of Holocene glacier advances in

Patagonia

The only report of an early Holocene glacier

advance in Patagonia is a date of between 8600 and

8200 14C years BP for volcanic ash overlying mor-

aines (Geyh and Rothlisberger, 1986). Rabassa and

Clapperton (1990) consider the evidence upon which

these dates were founded to be questionable as there

was no control on the time elapsed between deposi-

tion of the moraines and deposition of the overlying

ash. The moraines are therefore probably older than

the apparent date, possible even of Last Glacial

Maximum or Younger Dryas age.

The established chronology for Neoglacial glacier

fluctuations in the Patagonian Andes after 5000 14C

years BP is based on radiocarbon dates obtained for

groups of moraines in front of the outlet glaciers of the

two icefields (Mercer, 1968, 1970, 1976, 1982) (Table

4 and Figs. 2 and 3). Mercer obtained a series of

moraine dates, from the northwestern margins of the

Hielo Patagonico Sur (including Glaciers Ofhidro

Norte, Ofhidro Sur, Bernardo, Tempano and Ham-

mick), from an end moraine near Puerto Eden (Isla

Wellington), from the eastern side of the Hielo Pata-

gonico Sur around Moreno Glacier and Punta Ban-

dera, and from satellite glaciers east of the Hielo

Patagonico Sur at San Lorenze and Narvaez in

Argentina (Mercer, 1968, 1970). On the basis of these

dates, he proposed three Neoglacial advances of the

Icefield outlet glaciers since 5000 14C years BP,

namely those at 4700–4200 14C years BP, at 2700–

2000 14C years BP and during the Little Ice Age of the

last three centuries (Fig. 4). Aniya (1995, 1996) later

obtained radiocarbon dates from moraines on the

eastern side of the Hielo Patagonico Sur (the Tyndall,

Upsala and Ameghino glaciers) and suggested a

revision of this chronology to include four Holocene

advances with maxima at 3600, 2300, 1600–1400 14C

years BP and again during the last three centuries

(Fig. 4). Both scenarios are equally valid, simply

because these chronologies are based on data from

different outlet glaciers that may indeed have different

fluctuation histories. These chronologies also reflect

the availability of suitable organic material for dating

purposes at these sites.

5.1. Holocene glacial fluctuations of the San Rafael

and adjacent glaciers

Three of the outlet glaciers on the northwest side of

the Hielo Patagonico Norte (Glaciers Gualas, San

Rafael and San Quintin) have large and conspicuous

arcuate moraines, at distances of 15, 10 and 2 km

from their modern ice fronts, respectively, marking the

extent of former immense piedmont lobes (Bruggen,

1950; Lawrence and Lawrence, 1959; Heusser, 1960;

Casassa and Marangunic, 1987) (Table 5). Muller

(1960), working at San Rafael, termed these moraines

Tempanos I, II and III. The Tempanos I moraine

(furthest from the glacier) was regarded as the oldest,

the Tempanos II moraine (which forms a large part of

the rim of the modern Laguna San Rafael) the next

oldest, and Tempanos III (closest to the glacier) the

youngest. All three moraines were considered by

Muller to have formed during a single phase of

glaciation (the ‘‘Tempanos glaciation’’), with individ-

ual moraine ridges presumably representing oscilla-

tions of the ice front during this time. Despite several

attempts to date these moraines, their precise age

Table 4

Summary of Neoglacial glacier advances (since c. 5000 14C years BP) identified in southern South America

Chronology Glacier Age (author)

Neoglacial Advance I

‘‘Tempanos’’ glaciation

San Rafael Glacier, Hielo Patagonico Norte Before 3610 14C years BP, possibly as early as

5000 14C years BP (Heusser, 1960; Muller, 1960)

O’ Higgins Glacier, Hielo Patagonico Sur 4700–3300 14C years BP

(Geyh and Rothlisberger, 1986)

San Lorenze Este Glacier (satellite glacier to

east of Hielo Patagonico Sur)

4590 BP 14C years BP (Mercer, 1968)

Various Precordilleran glaciers (to east of

Hielo Patagonico Sur)

4500–4200 14C years BP (Wenzens, 1999)

Narvaez Glacier (satellite glacier to east of

Hielo Patagonico Sur)

4300 14C years BP (Mercer, 1968)

Ofhidro Sur Glacier, Hielo Patagonico Sur 4060 14C years BP (Mercer, 1970, 1978)

Tempano Glacier, Hielo Patagonico Sur 4120 14C years BP (Mercer, 1970, 1978)

Frias Glacier, Hielo Patagonico Sur 3465 14C years BP (Mercer, 1976)

Tyndall Glacier, Hielo Patagonico Sur 3600 14C years BP (Aniya, 1995)

Cordillera Darwin, Tierra del Fuego 3060 14C years BP (Kuylenstierna et al., 1996)

Precordilleran glaciers 3600–3300 14C years BP (Wenzens, 1999)

Neoglacial Advance II Hammick Glacier, Hielo Patagonico Sur 2800 14C years BP (Mercer, 1970)

‘‘Pearson I’’ of Mercer (1965) Upsala Glacier, Hielo Patagonico Sur 2310 14C years BP (Mercer, 1965)

‘‘Hermanita’’ of Aniya (1995) Upsala Glacier, Hielo Patagonico Sur 2400–2200 14C years BP (Aniya, 1995)

Huemul Glacier, Volcan Hudson 2500 14C years BP (Geyh and Rothlisberger, 1986)

Tyndall Glacier, Hielo Patagonico Sur 2300 14C years BP (Aniya, 1995)

Neoglacial Advance III Dos Lagos Glacier 1600 14C years BP (Mercer, 1965)

Upsala Glacier, Hielo Patagonico Sur 1600–900 14C years BP (Aniya, 1995)

Subantarctic islands 1300–1000 14C years BP

(Clapperton and Sugden, 1988)

Soler Glacier, Hielo Patagonico Norte 1300 14C years BP (Aniya and Naruse, 1999)

Tyndall Glacier, Hielo Patagonico Sur 1400 14C years BP (Aniya, 1995)

Neoglacial Advance IV Soler Glacier, Hielo Patagonico Norte AD 1220–1340 (Glasser et al., 2002)

‘‘Pearson II’’ of Mercer (1965) Huemul Glacer, Volcan Hudson AD 1180–1295 (Rothlisberger, 1987)

‘‘Little Ice Age’’ Perro Glacier AD 1250 (Rothlisberger, 1987)

Ofhidro Glacier, Hielo Patagonico Sur AD 1290 (Mercer, 1970)

Frances Glacier, Torres del Paine AD 1305 (Rothlisberger, 1987)

Ameghino Glacier, Hielo Patagonico Sur AD 1600–1700 (Aniya, 1996)

Hielo Patagonico Sur AD 1600–1890 (Marden and Clapperton, 1995)

Hielo Patagonico Sur AD 1650 (Heusser and Streeter, 1980)

Tyndall Glacier, Hielo Patagonico Sur AD 1700 (Aniya, 1995)

Soler Glacier, Hielo Patagonico Norte AD 1730 (Aniya and Naruse, 1999)

Tempano Glacier, Hielo Patagonico Sur AD 1750–1800 (Mercer, 1970)

To avoid ambiguity, dates and ages are quoted directly from the literature with no attempt to convert these into calibrated ages. Note that most of

these dates are 14C dates of glacier advances and that most only provide a minimum age for the advance.

N.F. Glasser et al. / Global and Planetary Change 43 (2004) 79–10190

remains unknown. Basal peat in a kettle hole between

the Tempanos I and II moraines near Ofqui and basal

peat in a 182.5 cm organic zone over laminated silt

near the north end of Rio Tempanos were dated to

3600 14C years BP (Muller, 1960). Heusser (1960)

therefore estimated the moraine to be c. 4000 14C

years old, but the data clearly give only a minimal age

and the moraine could be very much older. A lower

limiting age for the moraine is provided by a date

from an ‘‘interfluctuational section’’ where com-

pressed Nothofagus at a depth of 45 cm in a 65-cm-

thick peat layer beneath unweathered till, c. 60 m from

the 1959 edge of the glacier, yielded a date of

6850F 200 14C years BP (Heusser, 1960). Clapperton

and Sugden (1988) cited this as evidence that the

glacier has not advanced beyond its 20th Century

limits for more than 7000 14C years but this cannot be

the case given that Simpson (1875) observed the

terminus in AD 1871 to be about 9 km beyond the

mountain front, which is about 3 km inside the

Fig. 4. Neoglacial chronologies proposed for the fluctuation of Patagonian glaciers in the Holocene by Mercer (1970, 1976, 1982) and by

Aniya (1995, 1996). Shaded areas represent periods of glacier expansion. The ‘Mercer-type’ chronology has glacier advances at

approximately 4700–4200 14C years BP, 2700–2000 14C years BP and during the Little Ice Age. The ‘Aniya-type’ chronology has glacier

advances at approximately 3600 14C years BP, 2300 14C years BP, 1600–1400 14C years BP and during the Little Ice Age. Note that the

overall ice volume is schematic and is not intended to represent specific volumes at any one moment in time. Diagram modified from ideas

presented by Ivins and James (1999).

N.F. Glasser et al. / Global and Planetary Change 43 (2004) 79–101 91

outermost Tempanos moraine that encloses Laguna

San Rafael. This position may therefore mark the

maximum Little Ice Age extent of Glaciar San Rafael

(Winchester and Harrison, 1996; Warren, 1993). Cer-

tainly, the oldest trees growing on the uppermost 19th

century trimline above the glacier surface imply

exposure by 1876 (Winchester and Harrison, 1996).

Table 5

Patterns of contemporary ice-front behaviour and dates of historical glaci

Patagonico Norte

Glacier Surface

area

(km)

AAR %

Calving

Calving type Date

glacie

recess

San Quintin 765 0.9:1 100 Freshwater 1879

San Rafael 760 3.3:1 100 Tidal 1895

Gualas 167 2.3:1 50 Freshwater 1876

Reicher 92 2.9:1 100 Freshwater 1876

Leones 62 2.1:1 50 Freshwater 1867

Calafate N/a N/a 0 Not calving 1874

Nef 164 1.5:1 100 Freshwater 1863

Soler 51 2.5:1 0 Not calving 1730

Colonia 437 2.7:1 50 Freshwater pre-1

Arenales N/a N/a 0 Not calving 1883

Arco 41 6.8:1 0 Not calving 1881

Heusser and Streeter (1980) used the fluctuations of

San Rafael Glacier as a test of their palynologically

derived temperature and precipitation record in south-

ern Chile over the last 16,000 years. This test rests on

the assumption that around 6850 14C years BP the

glacier was smaller than today and later advanced three

times: between 5000 and 4000 14C years BP, some time

er recession obtained by the authors for outlet glaciers of the Hielo

of

r

ion

Contemporary

ice-front behaviour

(date of observation)

Reference

Receding Harrison et al., 2001

Receding (2004) Warren, 1993; Winchester and

Harrison, 1996

Advance (1994) Harrison and Winchester, 1998

Unknown

–1877 Advance (2000) Authors field observations

–1885 Unknown

–1878 Stable (1998) Winchester et al., 2001

Receding (2000) Glasser et al., 2002

878 Advance (1996) Harrison and

Winchester, 2000

Advance (1996) Harrison and Winchester, 2000

Unknown

N.F. Glasser et al. / Global and Planetary Change 43 (2004) 79–10192

between 3740 and 500 14C years BP and during the

19th Century. The advance alleged to have occurred

between 5000 and 4000 14C years BP was the most

extensive, forming the Tempanos moraines some 10

km beyond the glacier’s present position. Heusser and

Streeter (1980) hypothesised that these advances are

correlated with the three cool, moist intervals in their

climate record. Furthermore, these authors correlated

the greatest advance (between 5000 and 4000 14C years

BP) with the period of heaviest precipitation. This

glacier fluctuation–climate relationship cannot be rec-

onciled with the view of Clapperton and Sugden (1988)

that the glacier has not advanced outside its 20th

Century limits during the last 7000 14C years.

5.2. Holocene glacial fluctuations of the Tyndall,

Upsala and Ameghino Glaciers

Aniya (1995) obtained radiocarbon dates indicat-

ing four Neoglacial advances of the Tyndall and

Upsala Glaciers, two eastern outlets of the Hielo

Patagonico Sur. At Tyndall Glacier the Neoglacial

Advance I, marked by obscure terminal moraines and

distinctive lateral moraines, occurred c. 3600 14C

years BP, whilst Neoglacial Advance II, dated to c.

2300 14C years BP, is indicated by conspicuous trim-

lines on the side-valley wall and on the flank of the

lateral moraines of Neoglacial Advance I. Neoglacial

Advance III, distinguished by different coloured sur-

face deposits, occurred c. 1400 14C years BP, whilst

Neoglacial Advance IV occurred c. AD 1700. At

Upsala Glacier, Aniya (1995) presented a new scheme

modifying that of Mercer. The new scheme identified

two Neoglacial Advances from radiocarbon dates of c.

3600 14C years BP, and c. 2300 14C years BP (Pearson

I), and the Little Ice Age glaciation (Pearson II)

between AD 1600 and 1760 from dendrochronolog-

ical analyses. In this study, ‘‘Herminita’’ moraines

were dated to c. 2400–2200 years BP corresponding

to the Neoglacial Advance II. Pearson I moraines,

believed to date from c. 2300 14C years BP, were

dated to c. 1600, 1400, and 900 14C years BP with

these dates being close to those of Neoglacial Ad-

vance III. The existence of Neoglacial Advance I at c.

3600 14C years BP was not directly supported by new

data. However, the data from Tyndall and other

glaciers suggest that it probably did also occur at

Upsala Glacier. A framework of four Neoglacial

advances is confirmed by a further series of dates

from the Ameghino Glacier, another eastern outlet of

the Hielo Patagonico Sur (Aniya, 1996).

5.3. Holocene glacial fluctuations of Soler Glacier

Glasser et al. (2002) presented radiocarbon dates

from samples of tree remains in reworked glaciola-

custrine sediments in the proglacial area of Soler

Glacier, an eastern outlet of the Hielo Patagonico

Norte, demonstrating that the glacier overrode a lake

bed sometime between 1015F 55 and 597F 40 14C

years BP (from AD 1330 to AD 900). Contorted trees

plastered onto a large boulder in front of the glacier

constrain this advance to the period between AD 1220

and AD 1340. All the samples taken for 14C dating

were obtained directly from within the glacial depos-

its (i.e., not from basal peat which only yields

minimal dates) so that this advance of Soler Glacier

is tightly constrained in age (Glasser and Hambrey,

2002). Glasser et al. (2002) noted that this advance

precedes by several hundred years the maximum

Little Ice Age extent of other Hielo Patagonico Norte

outlet glaciers in c. AD 1700 (Aniya, 1995, 1996),

with this therefore suggesting either an early date for

the onset of Little Ice Age conditions or a previously

unrecognised period of glacier advance. Since Soler

Glacier overrode and displaced a lake bed during its

advance from c. AD 1220 to AD 1340, these authors

argued that, prior to c. AD 1222, the glacier was more

recessed than at present. The AD 1220–1340 dates

for the advance of Soler Glacier are comparable to

recorded advances of four other southern Patagonian

glaciers, Ofhidro (Mercer, 1970), Huemul, Perro and

Frances (Rothlisberger, 1987). This was a period

when there was a poleward shift in precipitation

(Lamy et al., 2001) and winter precipitation was

above the long-term mean (Villalba, 1994a). The

coincidence of higher than average winter precipita-

tion with a glacier advance suggests that the advance

may have been related to changes in precipitation

rather than changes in atmospheric temperature. Such

a relationship has been demonstrated for modern

outlet glaciers from the Hielo Patagonico Norte in-

cluding the San Quintin and San Rafael glaciers

(Warren, 1993; Winchester and Harrison, 1996), the

Gualas and Reicher glaciers (Harrison and Winches-

ter, 1998), and the Arco and Colonia glaciers (Harri-

N.F. Glasser et al. / Global and Planetary Change 43 (2004) 79–101 93

son and Winchester, 2000). A similar relationship

between increased precipitation and increased glacier

volume has also been found in modelling experiments

in the more arid areas of the Chilean Andes (Kull,

1999; Kull and Grosjean, 2000).

6. Correlation with events elsewhere

6.1. Patagonian satellite glaciers

Wenzens (1999) investigated the Holocene chro-

nology of satellite glaciers in the Rio Guanaco in the

Precordillera immediately to the east of the Hielo

Patagonico Sur (Fig. 3). He identified 10 valley–

glacier advances in this area. Like the nearby Viedma

Glacier, an outlet glacier of the Hielo Patagonico Sur,

the valley glaciers advanced three times during late-

glacial times (14,000–9500 14C years BP). The youn-

gest advance correlates with the Younger Dryas, based

on two minimum AMS 14C dates of 9588F 45 and

9482F 49 14C years BP. During the first half of the

Holocene (c. 10,000–5000 14C years BP) advances

culminated around 8500, 8000–7500, and 5800–

5500 14C years BP. During the second half of the

Holocene, advances occurred among 4500–4200,

3600–3300, 2300–2000, 1000–1300 14C years BP

and AD 1600–1850.

6.2. The sub-Antarctic islands and Antarctica

Hays (1978) reviewed faunal and isotopic evidence

in sub-Antarctic and Antarctic ocean cores and con-

cluded that over long time scales (i.e., the last 200,000

years) climatic changes in the area were in phase or

nearly in phase with Northern Hemisphere glacial

advance and recession. However, changes in sub-

Antarctic sea-surface temperatures in much of the

record precede (by around 3000 years) changes in

Northern Hemisphere glaciers. In the Holocene, for

example, sub-Antarctic surface waters reached a tem-

perature maximum around 9000 14C years BP and

have been cooling since, whilst today they are half

way between interglacial maximum and glacial min-

imum temperatures. This provides strong evidence

that Southern Hemisphere climates are not being

driven by changes in the volume of Northern Hemi-

sphere ice sheets.

Mercer (1978) however argued that climatic trends

in southern South America differed markedly from

those in much of the Northern Hemisphere, but were

similar to those over the sub-Antarctic ocean, demon-

strating the dominant influence of the Antarctic area

on the climate of southern South America during the

termination of glacial conditions. Research in the Sub-

Antarctic islands in the Scotia Sea (e.g., Falkland

Islands, South Georgia, South Sandwich islands,

South Orkney Islands and South Shetland Islands)

led Clapperton et al. (1978, p. 103) to question this

assertion. These latter authors concluded ‘‘there is no

clear and obvious correlation between the Neoglacial

history of southern South America and that of the

adjacent sub-Antarctic’’. Clapperton et al. (1978)

showed that recession of the Last Glacial Maximum

ice cap in South Georgia was marked by a stillstand or

re-advance of valley glaciers at the mouths of troughs

that occurred earlier than 9000 14C years BP. Follow-

ing recession there have been two re-advances, one a

modest event 100–200 years ago and the other a very

minor readvance in the early 20th Century. No evi-

dence for the onset of the Neoglaciation at 4500 14C

years BP is present in South Georgia. In the South

Shetland Islands, Sugden and John (1973) demon-

strated a similar history to that of South Georgia, with

a stillstand or re-advance of valley glaciers around

9000 14C years BP ago followed by a re-advance,

marked by moraines 1–3 km from outlet glacier

snouts dated to 500–750 14C years BP. Finally,

Wilson et al. (2002) have identified periods of in-

creased aridity on the Falkland Islands at 2925–192514C years BP and during the 400-year cold event at

7800–7400 cal. years BP recognised by Rosqvist et

al. (1999) on South Georgia.

Independent evidence concerning the nature of

Holocene climate variability comes from comparisons

of the climate records contained in Antarctic ice cores

(Masson et al., 2000). These ice-core records confirm

the existence of an Antarctic early Holocene optimum

between 11,500 and 9000 cal. years BP. Records from

the Ross Sea sector show a secondary optimum

7000–5000 cal. years BP. This optimum is recorded

later, between 6000 and 3000 cal. years BP, in records

from East Antarctica although there are few data

available on glacier fluctuations from the Antarctic

Peninsula, the area in closest proximity to southern

South America with which to make high-resolution

N.F. Glasser et al. / Global and Plane94

comparisons. The Antarctic ice-core evidence also

confirms the existence of the previously documented

widespread cold event at 8200 cal. years BP in

Antarctica (e.g., von Grafenstein et al., 1998) marking

the transition from the Early to mid-Holocene climates

(Stager and Mayewski, 1997). Overall, there appears

to be little similarity in patterns of glacier behaviour

between Patagonia and the adjacent sub-Antarctic,

although the lack of dated evidence for Holocene

glacier fluctuations on the Antarctic Peninsula is

clearly an obstacle to these comparisons.

6.3. Global climatic context

In this section, we place the Late Pleistocene and

Holocene glacial advances recognised in Patagonia

into other key global climatic changes during this

time.

6.3.1. The Last Glacial Maximum

There is still little agreement regarding the extent

to which the timing of the Last Glacial Maximum

varies throughout the different regions of the world

(Mix et al., 2001). However, the timing of the Last

Glacial Maximum in Patagonia appears to be broadly

in phase with these global changes (Harrison, 2004).

6.3.2. The Younger Dryas

Evidence for an equivalent of the Northern Hemi-

sphere Younger Dryas Chronozone in Patagonia is

equivocal (Markgraf, 1991), with some records point-

ing to the existence of such a cold episode (e.g.,

Ariztegui et al., 1997; Hajdas et al., 2003) and other

records suggesting it did not occur (e.g., Bennett et al.,

2000). Nowhere in Patagonia has a glacier advance

been directly dated to the Younger Dryas Chronozone.

Globally, however, it appears that a body of evidence

is emerging in support of a Southern Hemisphere

Younger Dryas. Elsewhere in the Southern Hemi-

sphere, moraine exposure dates (Ivy-Ochs et al.,

1999) and radiocarbon dates (Denton and Hendy,

1994) suggest that Younger Dryas glacier advances

in the Southern Alps of New Zealand were synchro-

nous with those in the European Alps. Marine records

also demonstrate cooling events elsewhere in the

Southern Hemisphere (Great Australian Bight), which

are synchronous with the Northern Hemisphere Youn-

ger Dryas (Andres et al., 2003).

6.3.3. The 8.2 ka cold event

There is no published evidence in Patagonia for the

widepread cold event at 8.2 ka (Alley et al., 1997;

Stager and Mayewski, 1997), which has been

recorded in Antarctic ice cores (Masson et al., 2000)

and in Europe and Greenland (von Grafenstein et al.,

1998). Since this abrupt climate change has been

explained by a weakening of the North Atlantic

thermohaline circulation due to a change in freshwater

input, possibly related to catastrophic drainage of the

Laurentide lakes (Barber et al., 1999), it appears that

such a weakening of the thermohaline circulation has

little impact on the climate of Patagonia.

6.3.4. Glacial advances at 4700–4200 14C years BP

Mercer (1978, pp. 89–90) argued that the c. 450014C years BP glacier advance in southern South Amer-

ica was the greatest of the three Holocene advances,

whereas in the Northern Hemisphere glacier advances

were relatively minor. This led Mercer (1978, p. 74) to

suggest that the inferred cooling around 4500 14C years

BP was caused by an event specific to the high

southern latitudes, perhaps greatly increased calving

from West Antarctica, although no causal mechanism

was proposed. The glacier advances noted byMercer at

this time coincide with major dry spells recorded in

African lake levels (Gasse, 2000), although the rela-

tionship between these events is unclear.

6.3.5. Glacier advances at 2700–2000 14C years BP

The identified glacier advances at 2700–2000 14C

years BP in Patagonia form part of a body of evidence

for global climatic change around this time (e.g.,

Grosjean et al., 1998; Wasson and Claussen, 2002),

which coincides with an abrupt decrease in solar

activity. This led van Geel et al. (2000) to suggest

that variations in solar irradiance are more important

as a driving force in variations in climate than

previously believed, although this hypothesis remains

to be fully tested.

6.3.6. Glacier advances during the Little Ice Age

Most analysis of Little Ice Age fluctuations of

glaciers comes from work carried out on the Hielo

Patagonico Norte (e.g., Winchester and Harrison,

1996; Harrison and Winchester, 2000; Glasser et al.,

2002). It is clear that the outlet glaciers of the Hielo

Patagonico Norte receded from their late historic

tary Change 43 (2004) 79–101

N.F. Glasser et al. / Global and Planetary Change 43 (2004) 79–101 95

moraine limits at the end of the 19th century, and a

similar pattern can be observed in other parts of

southern Chile (e.g., Kuylenstierna et al., 1996; Koch

and Kilian, 2001). Whether such glacier recession is

synchronous globally is more difficult to assess. In

areas peripheral to the North Atlantic and in central

Asia the available evidence shows that glaciers un-

derwent significant recession at this time (cf. Grove,

1988; Savoskul, 1997). In North America, many

glaciers receded from their late-historic limits slightly

earlier than those of the Hielo Patagonico Norte. On

Mount Rainier, the Nisqually glacier receded from its

Little Ice Age limit by about 1825 (Porter, 1981b). In

the Canadian Rockies, the oldest moraines of historic

age show a wide range of ages from the 17th to the

19th centuries (Luckman, 2000).

7. Possible explanations for the patterns of

observed glacier fluctuations

7.1. Changes related to the internal characteristics of

the icefields

Even under contemporary climatic conditions, the

frontal positions of the outlet glaciers of the Hielo

Patagonico Norte and Hielo Patagonico Sur have

shown contrasting behaviour. Thus, although there is

a general trend for glacier recession through the 20th

Century (e.g., Aniya, 1988, 1999; Aniya and Enomoto,

1986; Aniya et al., 1997) some glaciers have oscillated

rapidlywhilstmaintaining quasi-stable frontal positions

(Warren, 1993) and others have advanced to their

Neoglacial maximum (Warren and Rivera, 1994; Riv-

era et al., 1997). Superimposed on climatic trends are

glacier fluctuations driven by changes that are internal

to the glacier system (Hubbard, 1997; Warren and

Aniya, 1999). For example, the possibility of cyclic

advances of surge-type glaciers in response to reorga-

nization of subglacial drainage systems, changes in

substrate rheology, and the effects of changes in the

thickness and extent of surface-debris cover. In addi-

tion, and particularly pertinent to the Patagonian Ice-

fields, is the possibility that glacier termini fluctuate in

response to gross changes in their terminal environ-

ment (e.g., the transition from calving to noncalving

and vice versa, and changes internal to that environ-

ment (e.g., changes in the bathymetry and geometry of

terminal marine or lacustrine basins). The dynamics of

calving glaciers have produced some striking excep-

tions to the regional trend for glacier recession through

the 20th Century. Glaciers with very high accumula-

tion/area ratios have produced sustained advances

(e.g., Glacier Pio XI, Glaciar Perito Moreno), acceler-

ated recession (e.g., Glaciar O’Higgins, Glaciar

Marinelli), and long-maintained stillstands (e.g., Gla-

ciar Calvo) (Warren and Aniya, 1999).

Another explanation for the observed trends in

glacier fluctuations is the idea that the location of

the main icefield divide fluctuates over time. Rabassa

and Clapperton (1990), and Clapperton (1993) exam-

ined in detail all the radiocarbon dates on Neoglacial

fluctuations obtained by Mercer and observed that the

western glaciers were more extensive during the first

of these advances (4700–4200 14C years BP) than

during the subsequent advance (2700–2000 14C years

BP). Conversely, the eastern glaciers were less exten-

sive during the first of these advances than during the

subsequent advance. They hypothesised that this may

be due to an eastward migration of the ice divide over

time.

7.2. Changes in the extent of Antarctic sea-ice cover

Observations that changes in the climate of Pata-

gonia are in phase with those of the Antarctic have led

some authors to suggest that there could be a causal

mechanism. For example, Pendall et al. (2001) com-

pared the Antarctic Taylor Dome ice-core record

obtained by Steig et al. (1998) with a palynological

record of palaeotemperature and palaeoprecipitation

obtained from Harberton Bog, Tierra del Fuego and

they concluded that the temperature changes in south-

ern South America are related to circum-Antarctic

temperature changes, specifically changes in the ex-

tent of sea-ice cover. Sea-ice changes have been

shown to relate to changes in the intensity of the

thermohaline circulation, which in turn provides an

interhemispheric link with temperature events in the

North Atlantic (Blunier et al., 1998). Because such an

interhemispheric link would produce temperature

trends that are out of phase between the North and

South Atlantic, Pendall et al. (2001) considered that

the temperature increase recorded in the Harberton

Bog data at 16,000 cal. years BP reflects the Southern

Hemisphere’s lead in terms of global temperature

N.F. Glasser et al. / Global and Planetary Change 43 (2004) 79–10196

changes at the end of the Last Glacial Maximum.

Again, although an initially appealing hypothesis,

there are insufficient data to extend this conclusion

into the Holocene.

7.3. Atmospheric/oceanic coupling-induced climate

variability (ENSO)

The lack of high-resolution climate records makes

the potential effects of ENSO on glacier fluctuations

in the early Holocene in Patagonia difficult to assess.

Markgraf and Diaz (2000), after reviewing the avail-

able range of palaeoclimate indicators for studying the

El Nino/Southern Oscillation (ENSO) phenomenon,

found little evidence for ENSO-related atmospheric

circulation patterns before 6000 14C years BP. Only

after about 6000 14C years BP do the climate associ-

ations related to changes in sea-surface temperature

and ENSO-related atmospheric circulation patterns

begin to be systematically recorded in the palaeocli-

mate record.

7.4. Systematic changes in synoptic conditions

Patterns of accumulation across the icefields are

likely to be affected by changes in broad-scale syn-

optic weather patterns. The latitudinal migration of the

Southern Westerlies could be the chief mechanism

driving change, since the position of these moisture-

bearing winds are known to determine patterns of

precipitation at a variety of temporal scales (Heusser,

1995; Veit, 1996; McCulloch et al., 2000; Lamy et al.,

2000, 2001). Much of the evidence to support this

contention comes not from Patagonia, but from the

arid and semiarid areas to the north at latitudes 30–

35jS, where several authors (e.g., Jenny et al., 2002;

Maldonado and Villagran, 2002) have tendered palae-

oenvironmental evidence for latitudinal displacement

of the Southern Westerlies. Jenny et al. (2002) noted

evidence for an arid early to mid-Holocene (9500–

5700 cal. years BP) event at 33jS, with a precipitation

increase beginning after 5700 cal. years BP. Modern

humid conditions were established at these latitudes

by around 3200 cal. years BP. These authors hypoth-

esised that during the early and mid-Holocene, the

Southern Westerlies were blocked by the subtropical

high-pressure cell and hence deflected southwards

over Patagonia. We would therefore expect higher

than average precipitation in Patagonia between 9500

and 5700 cal. years BP. The palynological record

obtained by Maldonado and Villagran (2002) from

f 32jS in Chile shows two wet phases in the late

Holocene (at 4200–3200 cal. years BP, and after 1300

cal. years BP) and two distinctive arid phases, at

6100–4200 and 1800–1300 cal. years BP. Lamy et

al. (2001), drawing on evidence from geochemical

and clay mineralogy of marine sediment cores on the

Chilean continental slope at 41jS, demonstrated in-

creased rainfall and an equatorward shift of the

Southern Westerlies during the Little Ice Age.

7.5. Short-term variations in atmospheric tempera-

ture and precipitation

There is a well-established link between short-term

variations in atmospheric temperature and precipita-

tion and glacier fluctuations (e.g., Aniya and Eno-

moto, 1986; Aniya et al., 1997; Hulton et al., 1994;

Kerr and Sugden, 1994). For example, reconstruction

of winter rainfall variations in central Chile from tree-

ring records show that rainfall was above the long-

term mean between AD 1220 and 1280, and again

between AD 1450 and 1550 (Villalba, 1994a). Tem-

perature deviations in northern Patagonia derived

from tree-ring records show that summer temperatures

were below the long-term mean between AD 900 and

1070, and again between AD 1270 and 1380 (Vil-

lalba, 1994b). These periods bracketed the Medieval

Warm Period, lasting from AD 1080 to 1250 (Villalba,

1994a). From AD 1270 to 1660a there was a long

cold–moist interval, with Little Ice Age temperature

minima around AD 1340 and 1640 (Cardich, 1980;

Villalba, 1994a). Thus, most land-terminating glaciers

in Patagonia reached their maximum Little Ice Age

extent between AD 1600 and 1700 (Luckman and

Villalba, 2001), with this pattern applying regionally

at least as far away as the Central Region of Argentina

(Cioccale, 1999). Thus, there appears to be a tentative

link between short-term variations in atmospheric

temperature and precipitation and glacier advances

in Patagonia, although not all glaciers display syn-

chronicity with these climatic parameters (Fig. 4).

The link between short-term variations in atmos-

pheric temperature and precipitation and glacier fluc-

tuations is illustrated by evidence that the San Rafael

Glacier responds rapidly to changes in precipitation

N.F. Glasser et al. / Global and Planetary Change 43 (2004) 79–101 97

(Warren, 1993). Warren and Sugden (1993) argued,

following an assessment of the steepness of the

precipitation gradient over the icefields, that glaciers

on the western flanks of the icefields respond to

changes in precipitation and are ‘‘accumulation-driv-

en’’, whilst the fluctuations of those on the eastern

flanks are driven by changes in temperature and hence

are ‘‘ablation-driven’’. However, the synchronicity of

terminus fluctuations on either side of the Hielo

Patagonico Norte over the last 150 years or so,

questions the validity of this argument. Harrison and

Winchester (2000) therefore proposed that the mech-

anism driving variability in glacier frontal positions is

simply variability in precipitation in their accumula-

tion zones.

8. Conclusions

Palaeoenvironmental evidence and dated glacier

fluctuations suggest that during the early Holocene

(10,000–5000 14C years BP) glaciers in Patagonia

were smaller than at present, with atmospheric tem-

peratures east of the Andes about 2 jC above modern

values in the period 8500–6500 14C years BP. The

period between 6000 and 3600 14C years BP appears

to have been colder and wetter than present, followed

by an arid phase from 3600 to 3000 14C years BP.

From 3000 14C years BP to the present, there is

evidence of a cold phase, with relatively high precip-

itation. West of the Andes, the available evidence

points to periods of drier than present conditions

between 9400–6300 and 2400–1600 14C years BP.

Neoglacial glacier advances in Patagonia did not

begin until some time after 6000 14C years BP,

coincident with a strong cooling episode at this time.

Holocene glacier advances can be assigned to one of

three time periods following a ‘Mercer-type’ chronol-

ogy, or one of four time periods following an ‘Aniya-

type’ chronology. The ‘Mercer-type’ chronology has

glacier advances among 4700–4200, 2700–2000 14C

years BP and during the Little Ice Age. The ‘Aniya-

type’ chronology has glacier advances at 3600 and

2300 14C years BP, between 1600–1400 14C years BP

and during the Little Ice Age. These chronologies are

best regarded as broad regional trends, since there are

dated examples of glacier advances outside these time

periods.

Both Mercer- and Aniya-type chronologies are

based largely on radiocarbon-dated records, many of

which are minimal dates, and from calving glaciers

that may react to climate in a nonlinear fashion.

Indeed, contrasting histories have been obtained for

the behaviour of land-terminating glaciers within

relatively short distances of each other. The validity

and uncritical use of such chronologies in interhemi-

spheric comparative studies is therefore questionable.

Proxy climate data indicate that many of these

broad regional trends can be explained by changes

in precipitation and atmospheric temperature rather

than systematic changes related to the internal char-

acteristics of the icefields. However, the individual

response of specific glaciers depends to certain extent

on changes in their terminal environment brought

about by advance and recession (e.g., the transition

from calving to noncalving and vice versa), and

changes internal to that environment (e.g., changes

in the bathymetry and geometry of terminal marine or

lacustrine basins).

This review confirms the overall conclusion of

Strelin and Malagnino (2000) that extreme caution

is required in setting boundaries for the end of a

glacial readvance by using minimum dates from the

basal levels of ancient peat bogs in front of moraine

ridges. The dates obtained for these surfaces do not

take account of the potentially considerable time

elapsed between moraine ridge formation and the

onset of peat formation.

Acknowledgements

Fieldwork in Patagonia has been funded from a

number of sources including the Royal Geographical

Society, the UK Natural Environment Research

Council (grant NER/B/S/2002/00282) and The Uni-

versity of Wales, Aberystwyth Academic Research

Fund. We thank all colleagues who have spent time

with us in the field, especially Mike Hambrey and

Charles Warren. We also thank Raleigh International

for field logistical support over a number of years.

Sarah Davies and Stephen Porter provided comments

on an earlier version of the manuscript. Comments by

the three journal referees (C.J. Heusser, Bas van Geel

and an anonymous referee) are also acknowledged.

Figures were drawn by Antony Smith of the Institute

N.F. Glasser et al. / Global and Planetary Change 43 (2004) 79–10198

of Geography and Earth Science at the University of

Wales, Aberystwyth.

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