Late Pleistocene and Holocene Palaeoclimate and Glacier Fluctuations in Patagonia

Home , Tronador, Tyndall Glacier (Chile)

Global and Planetary Change 43 (2004) 79–101 www.elsevier.com/locate/gloplacha

Late Pleistocene and Holocene palaeoclimate and glacier fluctuations in Patagonia

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

a Centre for Glaciology, Institute of Geography and Earth Sciences, University of Wales, Aberystwyth, Ceredigion SY23 3DB, Wales UK b School 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 Patago´nico Norte (47j00VS, 73j39VW) and the Hielo Patago´nico 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 (10,000–5000 14C 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

* Corresponding author. Tel.: +44-1970-622785; fax: +44-1970-622659. E-mail address: [email protected] (N.F. Glasser).

1. Introduction contrast, Blunier et al. (1998) suggested that Antarc- tic climate change is out of phase with the northern 1.1. Climatological background Hemisphere, perhaps as a result of an oceanic mechanism such as the bipolar seesaw (Broecker, 1998). Records of atmospheric circulation across southern Other authors (e.g., McCulloch et al., 2000) have South America show strong interannual, interdecadal argued from a synthesis of key proxy records that and intercentennial variability. Climatic changes in these comparisons are complicated by the fact that South America are associated directly or indirectly climate changes were regionally variable. For exam- through long-term (Ma) mountain-range uplift (Hart- ple, in South America there was a sudden rise in ley, 2003); atmospheric teleconnections, with large- temperature that initiated deglaciation synchronously scale atmospheric/oceanic forcing such as the El Nin˜o- over 16j of latitude at 14,600–14,300 14C years BP Southern Oscillation (ENSO) (Aceituno, 1988; Allan (17,500–17,150 cal. years BP). There was a second et al., 1995; Diaz and Markgraf, 2000); the tempera- step of warming in the Chilean Lake District at ture gradient between tropical and extratropical region; 13,000–12,700 14C years BP (15,650–15,350 cal. the sea-surface temperatures of the South Atlantic and years BP), which saw temperatures rise close to South Pacific oceans, and the circum-Antarctic ocean modern values. A third warming step, particularly circulation (Villalba et al., 1997). clear in the south, occurred at c. 10,000 14C years BP Understanding the pace and timing of climatic (11,400 cal. years BP), thus achieving Holocene changes in the Late Pleistocene and Holocene is a levels of warmth. Following the initial warming, key issue in southern South America for three main there was a lagged response in precipitation as the reasons. First, these changes reflect changes in cli- Westerlies, after a delay of c. 1600 years, migrated matic gradients across the region, e.g., the latitudinal from their northern glacial location to their present migration of the precipitation-bearing Southern West- latitude, which was attained by 12,300 14C years BP erlies (Heusser, 1995; Veit, 1996; Lamy et al., 2000, (14,300 cal. years BP). The latitudinal contrasts in the 2001). Second, this climatic background provides timing of maximum precipitation are reflected in constraints on studies of relative sea level, glacioisos- regional contrasts in vegetation change and in glacier tasy and glacier fluctuations (Ivins and James, 1999; behaviour. Since the delay in the migration of the Rostami et al., 2000; Rignot et al., 2003). Third, the Westerlies coincides with the Heinrich 1 iceberg timing of glacier expansion and contraction in differ- event in the North Atlantic, McCulloch et al. (2000) ent parts of the region provides information on the argued that the suppressed global thermohaline cir- forcing mechanisms of climate change (Aniya and culation at the time may have affected sea-surface Enomoto, 1986; van Geel et al., 2000; Markgraf and temperatures in the South Pacific, and the return of Seltzer, 2001). Previous studies have concentrated on the Westerlies to their present southerly latitude only the uncertainty concerning interhemispheric timing of followed ocean reorganisation to its present intergla- climatic changes during the last glacial–interglacial cial mode. transition (e.g., Lowell et al., 1995; Steig et al., 1998; In Patagonia there is considerable evidence that Denton et al., 1999) and Holocene (Wasson and glaciers and icefields have expanded and contracted Claussen, 2002). Different hypotheses, relying on in the past in response to variations in climate different lines of evidence, point variously to the systems (Fig. 1). The outlet glaciers extend to lower Northern Hemisphere leading the Southern Hemi- latitudes than those of any other substantial ice sphere and vice versa, or to synchrony between the masses in the world and the icefields are nourished hemispheres. by midlatitude weather systems characterised by For many years changes in Antarctic climate and abundant precipitation, causing high ablation rates, glaciers were assumed to lag the northern hemi- steep mass-balance gradients and high ice velocities sphere. Recently, however, ice-core evidence led (Rottetal.,1998;MatsuokaandNaruse,1999). Steig et al. (1998) to suggest that climate change These circumstances, together with sharp local topo- was synchronous in both hemispheres, implying an graphic and climatological contrasts, create a dynam- atmospheric mechanism of rapid climate change. In ic glacier system (Hulton and Sugden, 1997). N.F. Glasser et al. / Global and Planetary Change 43 (2004) 79–101 81

Fig. 1. Southern South America showing the location of the major icefields (Hielo Patago´nico Norte and Hielo Patago´nico 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.

1.2. Field setting dillera between altitudes of 700–2500 m a.s.l. (Fig. 2). The icefield covers some c. 4200 km2. Annual pre- In this paper we consider in detail the area of cipitation on the western side of the icefield increases Patagonia south of 46jS and Tierra del Fuego. Two from 3700 mm at sea level to an estimated maximum major ice masses exist in the region: of 6700 mm at 700 m a.s.l. (Escobar et al., 1992). (1) The Hielo Patago´nico Norte or North Patago- Precipitation decreases sharply on the eastern side of nian Icefield (47j00VS, 73j39VW) is some 120 km the icefield although few reliable precipitation data are long and 40–60 km wide, capping the Andean Cor- available (Kobayashi and Saito, 1985; Fukami et al., 82 N.F. Glasser et al. / Global and Planetary Change 43 (2004) 79–101

Fig. 2. The major outlet glaciers of the Hielo Patago´nico Norte.

1987). Of the 30 or so outlet glaciers of the Hielo width of c. 40 km (Fig. 3). The Hielo Patagońico Patagońico Norte only a few have been studied in any Sur covers an area of c. 13,000 km2. Warren and detail. Sugden (1993) reviewed recent fluctuations of 28 (2) The Hielo Patagońico Sur or South Patagonian outlet glaciers of the Hielo Patagońico Sur, but little Icefield is much larger, running north–south for 360 is known about the behaviour or characteristics of the km between 48j50VSand51j30VSwithamean remaining outlet glaciers. N.F. Glasser et al. / Global and Planetary Change 43 (2004) 79–101 83

1.3. Aims Warren and Sugden, 1993; Aniya et al., 1997; Luck- man and Villalba, 2001; Heusser, 2002)andthe Whilst there have been reviews of contemporary palaeoecology of the region (e.g., Markgraf, 1989), and historical Patagonian glacier behaviour (e.g., the glacier data have never been considered in the context of Late Pleistocene and Holocene palaeoclimate. 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 fluctuations 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 Fig. 3. The major outlet glaciers of the Hielo Patago´nico Sur. The (1967) proposed the term ‘‘Neoglaciation’’ for this location of satellite glaciers at San Lorenze Este, Narvaez, Dos interval. In Patagonia, where glaciers appear to have Lagos and in the Rio Guanaco are also indicated. advanced on more than one occasion during the 84 N.F. Glasser et al. / Global and Planetary Change 43 (2004) 79–101

Neoglacial, this interval is conveniently subdivided exclusively on 14C dating of organic material (e.g., into four parts (Neoglacial Advances I–IV). wood, peat and limnic sediments) in and around moraine ridges. Other 14C dates in Patagonia have 2.2. Methods been obtained from organic remains in and around vegetation trimlines (e.g., Aniya, 1996), from tree Glacier fluctuations in Patagonia during Neoglacial remains embedded in moraines and from trees killed Advance IV (the ‘‘Little Ice Age’’) have been recon- by glacier advances (e.g., Glasser et al., 2002). Some structed using a variety of methods. Historical sources workers (e.g., Mercer, 1968, 1970) collected samples include scientific reports from expeditions to the for 14C dating from the base of sections excavated in glaciers and icefields (e.g., Steffen, 1947; Lawrence peat deposits within these moraine ridges. Mercer and Lawrence, 1959) and accounts of early travellers (1970, p. 6) fully acknowledged that basal peat ‘‘gives to the region (e.g., Darwin, 1839; Simpson, 1875). In a minimal age for a feature but not necessarily a close the absence of large-scale and accurate maps, aerial minimal age, because the interval between the expo- photographs of the glaciers have proved invaluable in sure of a surface from beneath ice or water and the marking their former limits. For instance, the first start of peat growth must depend on several factors, vertical aerial photographs of the Hielo Patagońico the most important of which are climate, microrelief, Norte were taken in 1974 and these provided the base and composition of the surface material’’. for the subsequent 1:50,000 scale maps, which are the Evidence for Holocene palaeoclimates in Patagonia largest scale available. Much of the ground coverage comes chiefly from palynological analysis of 14C dated is obscured by cloud (a perennial problem in this records of sediments and associated organic remains region). Complete aerial photograph coverage of the obtained from surface exposures and cored deposits. Hielo Patagońico Sur was taken for the first time These palaeoecological archives include peat bogs, between 1979 and 1984 by the Chilean Instituto freshwater lakes, playa lakes and dune fields (Bianchi Geographico Militar. Lower oblique photographs et al., 1999; Haberle et al., 2000; Gilli et al., 2001). were then taken by the Japanese in 1986, 1990 and 1993 (Aniya, 1992; Wada and Aniya, 1995; Aniya et al., 1996). The latest Instituto Geogra´phico Militar 3. The Late Pleistocene aerial photographic coverage dates from 1997 to 1998. The ‘‘air force division’’ of the US army took 3.1. The Last Glacial Maximum and Younger Dryas Trimetrogen oblique photographs (using three cam- eras to give a 180j field of vision) of the region in Caldenius (1932) laid the foundations of Patago- 1944/1945. These have allowed Aniya (1988) to nian glacial chronologies, establishing the existence of compare the glacier frontal positions of the icefield four main moraines systems east of the Andes, which between 1944 and 1986 and Winchester and Harrison are situated at or before the entrances of the Cor- (2000) to construct regional lichenometric and den- dilleras, several tens of kilometres or more from the drochronological dating schemes. modern ice fronts. These appear to represent the Last Lichenometry (using Placopsis patagonica and P. Glacial Maximum extent in Patagonia (e.g., Porter, perrugosa, the most common rock-inhabiting species 1989; Hulton et al., 1994). However, Caldenius (1932, in the area) and dendrochronology (using Nothofagus p. 148) also observed that behind the four principal nitida, N. betuloides, N. pumilio, and N. antarctica) moraine systems are ‘‘still some others, situated far in have been employed at a number of proglacial loca- the valleys of the Cordilleras and one rather near to tions to date constructional landforms, boulders, and the present glaciation’’. The moraine systems within bedrock surfaces exposed by the receding glaciers these valleys represent the Holocene fluctuations of since the peak of the Little Ice Age. However, the the modern glaciers. The moraine systems closest to early and mid-Holocene glacier advances in Patagonia the modern glacier margins date from the Little Ice lie outside the limits of dendrochronological and Age advances (Harrison, 2004). lichenometric dating methods and earlier Holocene Palaeoclimatic studies of southern South America advances in Patagonia are therefore based almost 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; cardi, occurred during the Younger Dryas Chrono- Markgraf, 1989; Rabassa and Clapperton, 1990; Stine zone (Ariztegui et al., 1997; Hajdas et al., 2003). and Stine, 1990; Heusser et al., 1996; Ariztegui et al., Data from an ice core retrieved from Huascarań 1997; Mancini, 1998; Coronato et al., 1999; Paez et (Peru´)byThompson et al. (2000) show a sharp al., 1999; Thompson et al., 2000; McCulloch et al., decrease of d18O concentrations at f 10,000 14C 2000; Hodell et al., 2001; Heusser, 2002). According years BP, indicating a change in the warm conditions to McCulloch et al. (2000), glaciers still covered in South America before this period. From a site on large areas of southern Chile and a considerable the Taitao Peninsula, Massaferro and Brooks (2002) portion of the eastern section of the southern Andes suggest a cooling around Younger Dryas times. In at approximately 14,600 14C years BP. By 10,000 14C contrast, Bennett et al. (2000) contend that conditions years BP, after several warming episodes, the Pata- on the Taitao Peninsula, to the west of the Hielo gonian Ice Field of the Last Glacial Maximum had Patagońico Norte, were as warm as present during the separated into the Hielo Patagońico Norte and Hielo Younger Dryas. Overall, the palaeoenvironmental Patagońico Sur. East of the Andes, the middle and record in Patagonia seems to indicate that the period high latitudes of South America warmed uniformly 13,000–5000 14C years BP was marked by relatively and rapidly from 13,000 14CyearsBP,withno warm temperatures (Heusser and Streeter, 1980; indication of subsequent climate fluctuations equiva- Rabassa and Clapperton, 1990). This period may or lent to those of the Northern Hemisphere Younger may not have been punctuated between 11,000 and Dryas cooling event (the Younger Dryas Chronozone, 10,000 14C years BP by a Younger Dryas-like cold datedto11,000–10,00014C years BP (12,700– epoch. Rabassa and Clapperton (1990) even sug- 11,500 cal. years BP). This chronology agrees broad- gested that the icefields might have been substantially ly with that of Mercer (1968, 1969, 1970, 1976, smaller during the period 13,000–5000 14C years 1982) who postulated that glaciers in Patagonia had BP than at present, although this has yet to be become smaller than now by 11,000 14C years BP substantiated. and remained diminished until the advances of the Markgraf (1993) presented a continuous palaeo- last few millennia. climatic history for the past 14,000 14C years BP in Clapperton (1993) pointed out that Mercer’s hy- South America based on palynological records from pothesis that glaciers in southernmost South America south of latitude 50jS. Prior to 12,500 14C years BP, receded rapidly after 13,000 14C years BP and did not dry Empetrum heathlands dominated throughout the readvance until the Neoglacial was based on obser- high southern latitudes, indicating high winds, annual vations from compressed peat with a radiocarbon precipitation of less than 300 mm, and freezing year- date of c. 11,070 14C years BP in the basal layer of round temperatures. After 12,500 14CyearsBP, two moraine systems: at Punta Bandera on the east steppe replaced the heathlands, suggesting a decrease side of ice field, some 22 km east of the Moreno in wind intensity, an increase in effective moisture, glacier, and at Te´mpano Glacier, a sea-terminating and increased temperatures. Low moisture levels outlet from the northwest part of the Hielo Patago´- prior to 12,500 14C years BP between latitudes 45j co Sur. Mercer (1976, p.156) concluded from this and 55jS suggest that the westerly storm tracks that the Te´mpano Glacier had remained at least as responsible for precipitation patterns in southern small as it is today from 11,000 14C years BP until South America may have been located closer to the the beginning of the Neoglacial interval. However, equator than today. The precipitation increase at Clapperton (1993) pointed out that because Te´mpano 12,500 14C years BP, extending only as far south as Glacier terminates in the sea it may not reliably 50jS, indicates that the stormtracks had shifted reflect small-scale changes in climate and that the poleward, but did not reach Tierra del Fuego. By dates obtained from the moraines at Punta Bandera 9000 14C years BP, the stormtracks had shifted to the were interpreted incorrectly on geomorphological high southern latitudes. grounds (see also Strelin and Malagnino, 2000). McCulloch and Davies (2001) described late-gla- Furthermore, a significant advance of the Tronador cial and early Holocene palaeoclimate from two sites, ice-cap, Argentina, which feeds proglacial Lake Mas- Puerto del Hambre and Estancia Esmeralda II, in the 86 N.F. Glasser et al. / Global and Planetary Change 43 (2004) 79–101 central section of the Strait of Magellan, southern 4.2. Holocene palaeoclimates Chile. Climatic warming commenced at 14,470 14C years BP, although mean annual temperatures contin- The earliest phase of the Holocene is generally ued to be cooler than present until c. 10,300 14C years considered an interval of ameliorating climatic con- BP. These authors considered that there was a sharp ditions with temperatures in the Chilean Lake District, decrease in effective moisture at c. 12,550 14C years 600 km north of the present icefields, peaking at about BP, after which moisture levels fluctuated but 2 jC above modern values either between 8500 and remained relatively low until c.10,300 14C years BP. 6500 14C years BP (Heusser, 1974) or between 9410 After 10,300 14C years BP, a shift to warmer con- and 8600 14C years BP (Clapperton, 1990). Other ditions occurred. palaeoclimatic studies of southern South America (Rabassa and Clapperton, 1990; Mancini, 1998; 3.2. Late Pleistocene (the Last Glacial Maximum and Thompson et al., 2000; Hodell et al., 2001) have Younger Dryas) palaeoclimates: summary identified the existence of a strong cooling episode at 5000 14C years BP resulting in glacier advances. Palaeoclimatic studies of southern South America For example, Mancini (1998) argued that, based on have yielded a variety of results concerning the rates palynological records, prior to 8000 14C years BP, a and timing of Late Pleistocene environmental change. grass steppe extended east of the Andes, indicating It seems likely that glaciers still covered large areas of relatively high precipitation under cold conditions. southern Chile and a considerable portion of the Between 8000 and 6000 14C years BP, an increase eastern section of the southern Andes at approximate- in shrub–steppe taxa dominated by Asteraceae tubuli- ly 14,600 14C years BP. After 13,000 14C years BP, florae represents an increase in temperature, whilst the palaeoenvironmental record in Patagonia seems to precipitation remained in the previous range of about indicate relatively warm temperatures (Heusser and 200 mm. The mid-Holocene (around 5000 14C years Streeter, 1980; Rabassa and Clapperton, 1990). This BP) is reflected by the brief return of steppe taxa, period may or may not have been punctuated between primarily grasses, indicating either cold conditions 11,000 and 10,000 14C years BP by a Younger Dryas- similar to those of the early Holocene or an increase like cold epoch. in precipitation. Certainly by 4500 14C years BP, the vegetation is represented by grass–shrub steppe dominated by Asteraceae tubuliflorae, with these condi- 4. Palaeoenvironmental evidence of Holocene tions continuing after 3500 14C years BP and the climate change in Patagonia development of more extensive late Holocene forest suggesting greater effective moisture, probably related 4.1. Sources of information to cooler temperatures. Schabitz (1994) cored 17 playa lakes in Patagonia Tables 1, 2 and 3 present details of the palae- between 39j and 47jS with the aim of reconstructing oclimatic significance of the palaeoenvironmental their vegetational, climatic and geomorphological his- evidence obtained by studies from sites in Patagonia tory, presenting palynological results from two lakes, to the east of the Andes, to the west of the Andes Salina Anzoategui (39j00V23US, 63j46V30UW) and and in southernmost South America (including Tierra Salina Piedra (40j34V59US, 62j40V26UW). Both the del Fuego). We quote in these tables only sites in sedimentological and the palynological results suggest southern South America below 46jS avoiding those prevailing arid climatic conditions with mainly aeo- from further afield, such as the Chilean Lake District lian morphodynamic processes active during the mid- (Heusser, 1984; Heusser and Streeter, 1980) and the Holocene. In late Holocene times, the climate changed semiarid regions of Norte Chico, central and north- to more semiarid conditions, with a higher rainfall ern Chile (Veit, 1996; Lamy et al., 2000, 2001; frequency and more frequent fluvial input into the Jenny et al., 2002; Maldonado and Villagrań, lake, possibly reflecting greater influence from the 2002), where climatic influences may have been Atlantic high pressure cell leading to more distinct different. seasonality. N.F. Glasser et al. / Global and Planetary Change 43 (2004) 79–101 87

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 Before 6500 Arid; colder than present Pollen analysis Mancini et al., Moreno, Santa Cruz, 2002 Argentina Parque Nacional Perito 6500–2700 Increase in summer Pollen analysis Mancini et al., Moreno, Santa Cruz, temperatures; higher 2002 Argentina moisture availability Parque Nacional Perito 2700–2000 Decrease in temperature; Pollen analysis Mancini et al., Moreno, Santa Cruz, increase in precipitation 2002 Argentina Parque Nacional Perito 1200–250 Increase in temperature; Pollen analysis Mancini et al., Moreno, Santa Cruz, precipitation similar to 2002 Argentina present Cerro Verlika, Santa Cruz, 4500–3600 Colder and moister Pollen analysis Mancini, 2001 Argentina than present Cerro Verlika, Santa Cruz, 3600–3000 Increase in temperature; Pollen analysis Mancini, 2001 Argentina decrease in moisture Cave Las Buitreras, Before 8000 Increase in summer Pollen analysis Prieto et al., Santa Cruz, Argentina temperatures; decrease 1998 in precipitation Cave Las Buitreras, 7600–4500 Higher moisture Pollen analysis Prieto et al., Santa Cruz, Argentina availability 1998 Santa Cruz, Argentina Before 8000 Cold; relatively high Pollen analysis Mancini, 1998 precipitation Santa Cruz, Argentina 8000–6000 Increase in temperature; Pollen analysis Mancini, 1998 precipitation relatively high Santa Cruz, Argentina C 5000–4000 Cold; relatively high Pollen analysis Mancini, 1998 precipitation Santa Cruz, Argentina After 3500 Cold; relatively high Pollen analysis Mancini, 1998 precipitation 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; Pollen analysis Schabitz, 1994 increased precipitation Rio Negro, Argentina Entire Holocene Significantly drier Ostracoda Whatley and conditions than late Cusminsky, 1999 Pleistocene Co´rdoba Province, 3500–1000 Drier conditions 14C dating of Iriondo (1989) Argentina than present dune fields Lago Argentino, 5730 Decrease in summer 14C dating of Strelin and Argentina temperatures; onset of peat bog Malagnino, 2000 increased precipitation formation All dates are quoted in 14C years BP.

Markgraf’s (1993) synthesis of pollen records for openness of the early Holocene forests, including the past 14,000 14C years in South America from those of the rainward part of the region, indicates south of latitude 50jS indicates that along the rain- precipitation levels between 500 and 800 mm, com- ward side of the Andes at 9000 14C years BP there parable to those of today’s forest/steppe transition. was forest expansion, with this occurring on the After a pronounced mid-Holocene dry event, the late rainshadow side, at 8000 14C years BP. The greater Holocene forests appeared more closed than those of 88 N.F. Glasser et al. / Global and Planetary Change 43 (2004) 79–101

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.

the early Holocene, suggesting greater effective mois- 4.3. Holocene palaeoclimates: summary ture, probably related to cooler temperatures. The large seasonal latitudinal shift comparable to the There appears to be strong evidence that both modern situation, equatorwards in winter and pole- temperature and precipitation have fluctuated consid- wards in summer, did not develop until after 4500 14C erably during the Holocene to the east of the Andes years BP. McCulloch and Davies (2001) demonstrated (Table 1). The period between 10,000 and 8000 14C an extreme arid phase between c. 10,300 and 8550 years BP is a time of climatic amelioration, with 14C years BP before an increase in available moisture increasing summer temperatures and decreasing pre- allowed the eastward spread of Nothofagus forest at c. cipitation. Temperatures continued to increase, this 8550 14C years BP. time accompanied by increased precipitation, between Finally, Iriondo (1989) described the results of 8000 and 6000 14C years BP. The period between 14C dating of aeolian silts and sands forming exten- 6000 and 3600 14C years BP appears to have been sive dune fields to the east of the Andes in the colder and wetter than present, followed by an arid Argentine pampas. These dates indicate that this area phase from 3600 to 3000 14C years BP. From 3000 was drier than today between 3500 and 1000 14C 14C years BP to the present day, there is evidence of a years BP. Wind action caused erosion of the existing cold phase, with relatively high precipitation. West of surficial sediment and deposition of the eroded the Andes, the available evidence points to periods of material in extensive silt and sand dune fields. drier than present conditions between 9400–6300 and Analysis of palaeodune orientation led Iriondo 2400–1600 14C years BP (Table 2). In southernmost (1989) to conclude that a seasonal anticyclonic South America, climatic amelioration is evident be- system was centred over the northeastern Co´rdoba tween 10,300 and 8550 14C years BP (Table 3). After province at this time. this time, there was an increase in available moisture,

Table 3 Palaeoclimatic information for the Holocene from selected sites in southernmost South America Location Dates Inferred climatic Type of evidence Reference regime Magellan Strait 10,300–8550 14C years BP Extremely arid Pollen analysis McCulloch and Davies, 2001 Magellan Strait c. 8550 14C years BP Increase in moisture Pollen analysis McCulloch and Davies, 2001 Tierra del Fuego 9000–8000 14C years BP Precipitation similar Pollen analysis Markgraf, 1993 to present Tierra del Fuego ‘‘Mid-Holocene’’ Increased aridity Pollen analysis Markgraf, 1993 Tierra del Fuego ‘‘Late Holocene’’ Cooler temperatures; Pollen analysis Markgraf, 1993 greater effective moisture Tierra del Fuego 6000–5000 cal years BP Warming temperatures; Pollen analysis Pendall et al., 2001 reduced precipitation Tierra del Fuego After 5000 cal years BP Warming temperatures; Pollen analysis Pendall et al., 2001 Increased precipitation All dates are quoted in 14C years BP. N.F. Glasser et al. / Global and Planetary Change 43 (2004) 79–101 89 followed by a period of increased aridity in the mid- Norte, Ofhidro Sur, Bernardo, Tempano and Ham- Holocene (around 5000 14C years BP). After 5000 mick), from an end moraine near Puerto Eden (Isla 14C years BP, there is evidence for an increasing Wellington), from the eastern side of the Hielo Pata- cooler and wetter climate. These climatic inferences gońico Sur around Moreno Glacier and Punta Ban- compare favourably with those of Heusser and Stree- dera, and from satellite glaciers east of the Hielo ter (1980) who found evidence for warmer than Patagońico Sur at San Lorenze and Narvaez in average periods in the Chilean Lake District between Argentina (Mercer, 1968, 1970). On the basis of these 9410 and 8600 14C years BP, and cold periods with dates, he proposed three Neoglacial advances of the successive minima between 4950 and 3160 14C years Icefield outlet glaciers since 5000 14CyearsBP, BP and between 3160 and 800 14C years BP. During namely those at 4700–4200 14C years BP, at 2700– the cold period between 4950 and 3160 14C years BP, 2000 14C years BP and during the Little Ice Age of the Heusser and Streeter (1980) inferred that mean annual last three centuries (Fig. 4). Aniya (1995, 1996) later temperature may have dropped by as much as 2jC obtained radiocarbon dates from moraines on the whilst mean annual precipitation rose by as much as eastern side of the Hielo Patagońico Sur (the Tyndall, 3000 mm. The cooling trend of the last 5000 14C Upsala and Ameghino glaciers) and suggested a years was interrupted twice, at around 3000 and 350 revision of this chronology to include four Holocene 14C years BP, when temperatures were higher than advances with maxima at 3600, 2300, 1600–1400 14C present. The maxima in the precipitation record years BP and again during the last three centuries roughly correspond with the temperature minima, (Fig. 4). Both scenarios are equally valid, simply with the most pronounced precipitation peak between because these chronologies are based on data from 4950 and 3160 14C years BP, followed by another different outlet glaciers that may indeed have different peak sometime between 3160 and 800 14C years BP fluctuation histories. These chronologies also reflect and a final peak between 350 14C years BP and the the availability of suitable organic material for dating present day. purposes at these sites.

5.1. Holocene glacial fluctuations of the San Rafael 5. The timing of Holocene glacier advances in and adjacent glaciers Patagonia Three of the outlet glaciers on the northwest side of The only report of an early Holocene glacier the Hielo Patago´nico Norte (Glaciers Gualas, San advance in Patagonia is a date of between 8600 and Rafael and San Quintin) have large and conspicuous 8200 14C years BP for volcanic ash overlying mor- arcuate moraines, at distances of 15, 10 and 2 km aines (Geyh and Ro¨thlisberger, 1986). Rabassa and from their modern ice fronts, respectively, marking the Clapperton (1990) consider the evidence upon which extent of former immense piedmont lobes (Bru¨ggen, these dates were founded to be questionable as there 1950; Lawrence and Lawrence, 1959; Heusser, 1960; was no control on the time elapsed between deposi- Casassa and Marangunic, 1987) (Table 5). Muller tion of the moraines and deposition of the overlying (1960), working at San Rafael, termed these moraines ash. The moraines are therefore probably older than Tempanos I, II and III. The Tempanos I moraine the apparent date, possible even of Last Glacial (furthest from the glacier) was regarded as the oldest, Maximum or Younger Dryas age. the Tempanos II moraine (which forms a large part of The established chronology for Neoglacial glacier the rim of the modern Laguna San Rafael) the next fluctuations in the Patagonian Andes after 5000 14C oldest, and Tempanos III (closest to the glacier) the years BP is based on radiocarbon dates obtained for youngest. All three moraines were considered by groups of moraines in front of the outlet glaciers of the Muller to have formed during a single phase of two icefields (Mercer, 1968, 1970, 1976, 1982) (Table glaciation (the ‘‘Tempanos glaciation’’), with individ- 4 and Figs. 2 and 3). Mercer obtained a series of ual moraine ridges presumably representing oscilla- moraine dates, from the northwestern margins of the tions of the ice front during this time. Despite several Hielo Patago´nico Sur (including Glaciers Ofhidro attempts to date these moraines, their precise age 90 N.F. Glasser et al. / Global and Planetary Change 43 (2004) 79–101

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 San Rafael Glacier, Hielo Patagońico Norte Before 3610 14C years BP, possibly as early as ‘‘Tempanos’’ glaciation 5000 14C years BP (Heusser, 1960; Muller, 1960) O’ Higgins Glacier, Hielo Patagońico Sur 4700–3300 14C years BP (Geyh and Ro¨thlisberger, 1986) San Lorenze Este Glacier (satellite glacier to 4590 BP 14C years BP (Mercer, 1968) east of Hielo Patagońico Sur) Various Precordilleran glaciers (to east of 4500–4200 14C years BP (Wenzens, 1999) Hielo Patagońico Sur) Narvaez Glacier (satellite glacier to east of 4300 14C years BP (Mercer, 1968) Hielo Patagońico Sur) Ofhidro Sur Glacier, Hielo Patagońico Sur 4060 14C years BP (Mercer, 1970, 1978) Tempano Glacier, Hielo Patagońico Sur 4120 14C years BP (Mercer, 1970, 1978) Frias Glacier, Hielo Patagońico Sur 3465 14C years BP (Mercer, 1976) Tyndall Glacier, Hielo Patagońico 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 Patagońico Sur 2800 14C years BP (Mercer, 1970) ‘‘Pearson I’’ of Mercer (1965) Upsala Glacier, Hielo Patagońico Sur 2310 14C years BP (Mercer, 1965) ‘‘Hermanita’’ of Aniya (1995) Upsala Glacier, Hielo Patagońico Sur 2400–2200 14C years BP (Aniya, 1995) Huemul Glacier, Volcan Hudson 2500 14C years BP (Geyh and Ro¨thlisberger, 1986) Tyndall Glacier, Hielo Patagońico Sur 2300 14C years BP (Aniya, 1995) Neoglacial Advance III Dos Lagos Glacier 1600 14C years BP (Mercer, 1965) Upsala Glacier, Hielo Patagońico Sur 1600–900 14C years BP (Aniya, 1995) Subantarctic islands 1300–1000 14C years BP (Clapperton and Sugden, 1988) Soler Glacier, Hielo Patagońico Norte 1300 14C years BP (Aniya and Naruse, 1999) Tyndall Glacier, Hielo Patagońico Sur 1400 14C years BP (Aniya, 1995) Neoglacial Advance IV Soler Glacier, Hielo Patagońico Norte AD 1220–1340 (Glasser et al., 2002) ‘‘Pearson II’’ of Mercer (1965) Huemul Glacer, Volcan Hudson AD 1180–1295 (Ro¨thlisberger, 1987) ‘‘Little Ice Age’’ Perro Glacier AD 1250 (Ro¨thlisberger, 1987) Ofhidro Glacier, Hielo Patagońico Sur AD 1290 (Mercer, 1970) France´s Glacier, Torres del Paine AD 1305 (Ro¨thlisberger, 1987) Ameghino Glacier, Hielo Patagońico Sur AD 1600–1700 (Aniya, 1996) Hielo Patagońico Sur AD 1600–1890 (Marden and Clapperton, 1995) Hielo Patagońico Sur AD 1650 (Heusser and Streeter, 1980) Tyndall Glacier, Hielo Patagońico Sur AD 1700 (Aniya, 1995) Soler Glacier, Hielo Patagońico Norte AD 1730 (Aniya and Naruse, 1999) Tempano Glacier, Hielo Patagońico 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. remains unknown. Basal peat in a kettle hole between pressed Nothofagus at a depth of 45 cm in a 65-cm- the Tempanos I and II moraines near Ofqui and basal thick peat layer beneath unweathered till, c. 60 m from peat in a 182.5 cm organic zone over laminated silt the 1959 edge of the glacier, yielded a date of near the north end of Rio Tempanos were dated to 6850 F 200 14C years BP (Heusser, 1960). Clapperton 3600 14C years BP (Muller, 1960). Heusser (1960) and Sugden (1988) cited this as evidence that the therefore estimated the moraine to be c. 4000 14C glacier has not advanced beyond its 20th Century years old, but the data clearly give only a minimal age limits for more than 7000 14C years but this cannot be and the moraine could be very much older. A lower the case given that Simpson (1875) observed the limiting age for the moraine is provided by a date terminus in AD 1871 to be about 9 km beyond the from an ‘‘interfluctuational section’’ where com- mountain front, which is about 3 km inside the N.F. Glasser et al. / Global and Planetary Change 43 (2004) 79–101 91

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).

outermost Tempanos moraine that encloses Laguna Heusser and Streeter (1980) used the fluctuations of San Rafael. This position may therefore mark the San Rafael Glacier as a test of their palynologically maximum Little Ice Age extent of Glaciar San Rafael derived temperature and precipitation record in south- (Winchester and Harrison, 1996; Warren, 1993). Cer- ern Chile over the last 16,000 years. This test rests on tainly, the oldest trees growing on the uppermost 19th the assumption that around 6850 14C years BP the century trimline above the glacier surface imply glacier was smaller than today and later advanced three exposure by 1876 (Winchester and Harrison, 1996). times: between 5000 and 4000 14C years BP, some time

Table 5 Patterns of contemporary ice-front behaviour and dates of historical glacier recession obtained by the authors for outlet glaciers of the Hielo Patagońico Norte Glacier Surface AAR % Calving type Date of Contemporary Reference area Calving glacier ice-front behaviour (km) recession (date of observation) San Quintin 765 0.9:1 100 Freshwater 1879 Receding Harrison et al., 2001 San Rafael 760 3.3:1 100 Tidal 1895 Receding (2004) Warren, 1993; Winchester and Harrison, 1996 Gualas 167 2.3:1 50 Freshwater 1876 Advance (1994) Harrison and Winchester, 1998 Reicher 92 2.9:1 100 Freshwater 1876 Unknown Leones 62 2.1:1 50 Freshwater 1867–1877 Advance (2000) Authors field observations Calafate N/a N/a 0 Not calving 1874–1885 Unknown Nef 164 1.5:1 100 Freshwater 1863–1878 Stable (1998) Winchester et al., 2001 Soler 51 2.5:1 0 Not calving 1730 Receding (2000) Glasser et al., 2002 Colonia 437 2.7:1 50 Freshwater pre-1878 Advance (1996) Harrison and Winchester, 2000 Arenales N/a N/a 0 Not calving 1883 Advance (1996) Harrison and Winchester, 2000 Arco 41 6.8:1 0 Not calving 1881 Unknown 92 N.F. Glasser et al. / Global and Planetary Change 43 (2004) 79–101 between 3740 and 500 14C years BP and during the advances is confirmed by a further series of dates 19th Century. The advance alleged to have occurred from the Ameghino Glacier, another eastern outlet of between 5000 and 4000 14C years BP was the most the Hielo Patagońico Sur (Aniya, 1996). extensive, forming the Tempanos moraines some 10 km beyond the glacier’s present position. Heusser and 5.3. Holocene glacial fluctuations of Soler Glacier Streeter (1980) hypothesised that these advances are correlated with the three cool, moist intervals in their Glasser et al. (2002) presented radiocarbon dates climate record. Furthermore, these authors correlated from samples of tree remains in reworked glaciola- the greatest advance (between 5000 and 4000 14C years custrine sediments in the proglacial area of Soler BP) with the period of heaviest precipitation. This Glacier, an eastern outlet of the Hielo Patagońico glacier fluctuation–climate relationship cannot be rec- Norte, demonstrating that the glacier overrode a lake onciled with the view of Clapperton and Sugden (1988) bed sometime between 1015 F 55 and 597 F 40 14C that the glacier has not advanced outside its 20th years BP (from AD 1330 to AD 900). Contorted trees Century limits during the last 7000 14C years. plastered onto a large boulder in front of the glacier constrain this advance to the period between AD 1220 5.2. Holocene glacial fluctuations of the Tyndall, and AD 1340. All the samples taken for 14C dating Upsala and Ameghino Glaciers were obtained directly from within the glacial deposits (i.e., not from basal peat which only yields Aniya (1995) obtained radiocarbon dates indicat- minimal dates) so that this advance of Soler Glacier ing four Neoglacial advances of the Tyndall and is tightly constrained in age (Glasser and Hambrey, Upsala Glaciers, two eastern outlets of the Hielo 2002). Glasser et al. (2002) noted that this advance Patagońico Sur. At Tyndall Glacier the Neoglacial precedes by several hundred years the maximum Advance I, marked by obscure terminal moraines and Little Ice Age extent of other Hielo Patagońico Norte distinctive lateral moraines, occurred c. 3600 14C outlet glaciers in c. AD 1700 (Aniya, 1995, 1996), years BP, whilst Neoglacial Advance II, dated to c. with this therefore suggesting either an early date for 2300 14C years BP, is indicated by conspicuous trim- the onset of Little Ice Age conditions or a previously lines on the side-valley wall and on the flank of the unrecognised period of glacier advance. Since Soler lateral moraines of Neoglacial Advance I. Neoglacial Glacier overrode and displaced a lake bed during its Advance III, distinguished by different coloured sur- advance from c. AD 1220 to AD 1340, these authors face deposits, occurred c. 1400 14C years BP, whilst argued that, prior to c. AD 1222, the glacier was more Neoglacial Advance IV occurred c. AD 1700. At recessed than at present. The AD 1220–1340 dates Upsala Glacier, Aniya (1995) presented a new scheme for the advance of Soler Glacier are comparable to modifying that of Mercer. The new scheme identified recorded advances of four other southern Patagonian two Neoglacial Advances from radiocarbon dates of c. glaciers, Ofhidro (Mercer, 1970), Huemul, Perro and 3600 14C years BP, and c. 2300 14C years BP (Pearson France´s (Ro¨thlisberger, 1987).Thiswasaperiod I), and the Little Ice Age glaciation (Pearson II) when there was a poleward shift in precipitation between AD 1600 and 1760 from dendrochronolog- (Lamy et al., 2001) and winter precipitation was ical analyses. In this study, ‘‘Herminita’’ moraines above the long-term mean (Villalba, 1994a).The were dated to c. 2400–2200 years BP corresponding coincidence of higher than average winter precipita- to the Neoglacial Advance II. Pearson I moraines, tion with a glacier advance suggests that the advance believed to date from c. 2300 14C years BP, were may have been related to changes in precipitation dated to c. 1600, 1400, and 900 14C years BP with rather than changes in atmospheric temperature. Such these dates being close to those of Neoglacial Ad- a relationship has been demonstrated for modern vance III. The existence of Neoglacial Advance I at c. outlet glaciers from the Hielo Patagońico Norte in- 3600 14C years BP was not directly supported by new cluding the San Quintin and San Rafael glaciers data. However, the data from Tyndall and other (Warren, 1993; Winchester and Harrison, 1996), the glaciers suggest that it probably did also occur at Gualas and Reicher glaciers (Harrison and Winches- Upsala Glacier. A framework of four Neoglacial 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 Mercer (1978) however argued that climatic trends between increased precipitation and increased glacier in southern South America differed markedly from volume has also been found in modelling experiments those in much of the Northern Hemisphere, but were in the more arid areas of the Chilean Andes (Kull, similar to those over the sub-Antarctic ocean, demon- 1999; Kull and Grosjean, 2000). 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- 6. Correlation with events elsewhere Antarctic islands in the Scotia Sea (e.g., Falkland Islands, South Georgia, South Sandwich islands, 6.1. Patagonian satellite glaciers South Orkney Islands and South Shetland Islands) led Clapperton et al. (1978, p. 103) to question this Wenzens (1999) investigated the Holocene chro- assertion. These latter authors concluded ‘‘there is no nology of satellite glaciers in the Rio Guanaco in the clear and obvious correlation between the Neoglacial Precordillera immediately to the east of the Hielo history of southern South America and that of the Patagońico Sur (Fig. 3). He identified 10 valley– adjacent sub-Antarctic’’. Clapperton et al. (1978) glacier advances in this area. Like the nearby Viedma showed that recession of the Last Glacial Maximum Glacier, an outlet glacier of the Hielo Patagońico Sur, ice cap in South Georgia was marked by a stillstand or the valley glaciers advanced three times during late- re-advance of valley glaciers at the mouths of troughs glacial times (14,000–9500 14C years BP). The youn- that occurred earlier than 9000 14C years BP. Follow- gest advance correlates with the Younger Dryas, based ing recession there have been two re-advances, one a on two minimum AMS 14C dates of 9588 F 45 and modest event 100–200 years ago and the other a very 9482 F 49 14C years BP. During the first half of the minor readvance in the early 20th Century. No evi- Holocene (c. 10,000–5000 14C years BP) advances dence for the onset of the Neoglaciation at 4500 14C culminated around 8500, 8000–7500, and 5800– years BP is present in South Georgia. In the South 5500 14C years BP. During the second half of the Shetland Islands, Sugden and John (1973) demon- Holocene, advances occurred among 4500–4200, strated a similar history to that of South Georgia, with 3600–3300, 2300–2000, 1000–1300 14C years BP a stillstand or re-advance of valley glaciers around and AD 1600–1850. 9000 14C years BP ago followed by a re-advance, marked by moraines 1–3 km from outlet glacier 6.2. The sub-Antarctic islands and Antarctica snouts dated to 500–750 14C years BP. Finally, Wilson et al. (2002) have identified periods of in- Hays (1978) reviewed faunal and isotopic evidence creased aridity on the Falkland Islands at 2925–1925 in sub-Antarctic and Antarctic ocean cores and con- 14C years BP and during the 400-year cold event at cluded that over long time scales (i.e., the last 200,000 7800–7400 cal. years BP recognised by Rosqvist et years) climatic changes in the area were in phase or al. (1999) on South Georgia. nearly in phase with Northern Hemisphere glacial Independent evidence concerning the nature of advance and recession. However, changes in sub- Holocene climate variability comes from comparisons Antarctic sea-surface temperatures in much of the of the climate records contained in Antarctic ice cores record precede (by around 3000 years) changes in (Masson et al., 2000). These ice-core records confirm Northern Hemisphere glaciers. In the Holocene, for the existence of an Antarctic early Holocene optimum example, sub-Antarctic surface waters reached a tem- between 11,500 and 9000 cal. years BP. Records from perature maximum around 9000 14C years BP and the Ross Sea sector show a secondary optimum have been cooling since, whilst today they are half 7000–5000 cal. years BP. This optimum is recorded way between interglacial maximum and glacial min- later, between 6000 and 3000 cal. years BP, in records imum temperatures. This provides strong evidence from East Antarctica although there are few data that Southern Hemisphere climates are not being available on glacier fluctuations from the Antarctic driven by changes in the volume of Northern Hemi- Peninsula, the area in closest proximity to southern sphere ice sheets. South America with which to make high-resolution 94 N.F. Glasser et al. / Global and Planetary Change 43 (2004) 79–101 comparisons. The Antarctic ice-core evidence also 6.3.3. The 8.2 ka cold event confirms the existence of the previously documented There is no published evidence in Patagonia for the widespread cold event at 8200 cal. years BP in widepread cold event at 8.2 ka (Alley et al., 1997; Antarctica (e.g., von Grafenstein et al., 1998) marking Stager and Mayewski, 1997), which has been the transition from the Early to mid-Holocene climates recorded in Antarctic ice cores (Masson et al., 2000) (Stager and Mayewski, 1997). Overall, there appears and in Europe and Greenland (von Grafenstein et al., to be little similarity in patterns of glacier behaviour 1998). Since this abrupt climate change has been between Patagonia and the adjacent sub-Antarctic, explained by a weakening of the North Atlantic although the lack of dated evidence for Holocene thermohaline circulation due to a change in freshwater glacier fluctuations on the Antarctic Peninsula is input, possibly related to catastrophic drainage of the clearly an obstacle to these comparisons. Laurentide lakes (Barber et al., 1999), it appears that such a weakening of the thermohaline circulation has 6.3. Global climatic context little impact on the climate of Patagonia.

In this section, we place the Late Pleistocene and 6.3.4. Glacial advances at 4700–4200 14C years BP Holocene glacial advances recognised in Patagonia Mercer (1978, pp. 89–90) argued that the c. 4500 into other key global climatic changes during this 14C years BP glacier advance in southern South Amer- time. ica was the greatest of the three Holocene advances, whereas in the Northern Hemisphere glacier advances 6.3.1. The Last Glacial Maximum were relatively minor. This led Mercer (1978, p. 74) to There is still little agreement regarding the extent suggest that the inferred cooling around 4500 14C years to which the timing of the Last Glacial Maximum BP was caused by an event specific to the high varies throughout the different regions of the world southern latitudes, perhaps greatly increased calving (Mix et al., 2001). However, the timing of the Last from West Antarctica, although no causal mechanism Glacial Maximum in Patagonia appears to be broadly was proposed. The glacier advances noted by Mercer at in phase with these global changes (Harrison, 2004). this time coincide with major dry spells recorded in African lake levels (Gasse, 2000), although the rela- 6.3.2. The Younger Dryas tionship between these events is unclear. Evidence for an equivalent of the Northern Hemi- sphere Younger Dryas Chronozone in Patagonia is 6.3.5. Glacier advances at 2700–2000 14C years BP equivocal (Markgraf, 1991), with some records point- The identified glacier advances at 2700–2000 14C ing to the existence of such a cold episode (e.g., years BP in Patagonia form part of a body of evidence Ariztegui et al., 1997; Hajdas et al., 2003) and other for global climatic change around this time (e.g., records suggesting it did not occur (e.g., Bennett et al., Grosjean et al., 1998; Wasson and Claussen, 2002), 2000). Nowhere in Patagonia has a glacier advance which coincides with an abrupt decrease in solar been directly dated to the Younger Dryas Chronozone. activity. This led van Geel et al. (2000) to suggest Globally, however, it appears that a body of evidence that variations in solar irradiance are more important is emerging in support of a Southern Hemisphere as a driving force in variations in climate than Younger Dryas. Elsewhere in the Southern Hemi- previously believed, although this hypothesis remains sphere, moraine exposure dates (Ivy-Ochs et al., to be fully tested. 1999) and radiocarbon dates (Denton and Hendy, 1994) suggest that Younger Dryas glacier advances 6.3.6. Glacier advances during the Little Ice Age in the Southern Alps of New Zealand were synchro- Most analysis of Little Ice Age fluctuations of nous with those in the European Alps. Marine records glaciers comes from work carried out on the Hielo also demonstrate cooling events elsewhere in the Patagońico Norte (e.g., Winchester and Harrison, Southern Hemisphere (Great Australian Bight), which 1996; Harrison and Winchester, 2000; Glasser et al., are synchronous with the Northern Hemisphere Youn- 2002). It is clear that the outlet glaciers of the Hielo ger Dryas (Andres et al., 2003). Patagońico Norte receded from their late historic 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 terminal marine or lacustrine basins). The dynamics of similar pattern can be observed in other parts of calving glaciers have produced some striking excep- southern Chile (e.g., Kuylenstierna et al., 1996; Koch tions to the regional trend for glacier recession through and Kilian, 2001). Whether such glacier recession is the 20th Century. Glaciers with very high accumula- synchronous globally is more difficult to assess. In tion/area ratios have produced sustained advances areas peripheral to the North Atlantic and in central (e.g., Glacier Pio XI, Glaciar Perito Moreno), acceler- Asia the available evidence shows that glaciers un- ated recession (e.g., Glaciar O’Higgins, Glaciar derwent significant recession at this time (cf. Grove, Marinelli), and long-maintained stillstands (e.g., Gla- 1988; Savoskul, 1997). In North America, many ciar Calvo) (Warren and Aniya, 1999). glaciers receded from their late-historic limits slightly Another explanation for the observed trends in earlier than those of the Hielo Patagońico Norte. On glacier fluctuations is the idea that the location of Mount Rainier, the Nisqually glacier receded from its the main icefield divide fluctuates over time. Rabassa Little Ice Age limit by about 1825 (Porter, 1981b).In and Clapperton (1990), and Clapperton (1993) exam- the Canadian Rockies, the oldest moraines of historic ined in detail all the radiocarbon dates on Neoglacial age show a wide range of ages from the 17th to the fluctuations obtained by Mercer and observed that the 19th centuries (Luckman, 2000). 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 7. Possible explanations for the patterns of BP). Conversely, the eastern glaciers were less exten- observed glacier fluctuations sive during the first of these advances than during the subsequent advance. They hypothesised that this may 7.1. Changes related to the internal characteristics of be due to an eastward migration of the ice divide over the icefields time.

Even under contemporary climatic conditions, the 7.2. Changes in the extent of Antarctic sea-ice cover frontal positions of the outlet glaciers of the Hielo Patagońico Norte and Hielo Patagońico Sur have Observations that changes in the climate of Pata- shown contrasting behaviour. Thus, although there is gonia are in phase with those of the Antarctic have led a general trend for glacier recession through the 20th some authors to suggest that there could be a causal Century (e.g., Aniya, 1988, 1999; Aniya and Enomoto, mechanism. For example, Pendall et al. (2001) com- 1986; Aniya et al., 1997) some glaciers have oscillated pared the Antarctic Taylor Dome ice-core record rapidly whilst maintaining quasi-stable frontal positions obtained by Steig et al. (1998) with a palynological (Warren, 1993) and others have advanced to their record of palaeotemperature and palaeoprecipitation Neoglacial maximum (Warren and Rivera, 1994; Riv- obtained from Harberton Bog, Tierra del Fuego and era et al., 1997). Superimposed on climatic trends are they concluded that the temperature changes in south- glacier fluctuations driven by changes that are internal ern South America are related to circum-Antarctic to the glacier system (Hubbard, 1997; Warren and temperature changes, specifically changes in the ex- Aniya, 1999). For example, the possibility of cyclic tent of sea-ice cover. Sea-ice changes have been advances of surge-type glaciers in response to reorga- shown to relate to changes in the intensity of the nization of subglacial drainage systems, changes in thermohaline circulation, which in turn provides an substrate rheology, and the effects of changes in the interhemispheric link with temperature events in the thickness and extent of surface-debris cover. In addi- North Atlantic (Blunier et al., 1998). Because such an tion, and particularly pertinent to the Patagonian Ice- interhemispheric link would produce temperature fields, is the possibility that glacier termini fluctuate in trends that are out of phase between the North and response to gross changes in their terminal environ- South Atlantic, Pendall et al. (2001) considered that ment (e.g., the transition from calving to noncalving the temperature increase recorded in the Harberton and vice versa, and changes internal to that environ- Bog data at 16,000 cal. years BP reflects the Southern ment (e.g., changes in the bathymetry and geometry of Hemisphere’s lead in terms of global temperature 96 N.F. Glasser et al. / Global and Planetary Change 43 (2004) 79–101 changes at the end of the Last Glacial Maximum. than average precipitation in Patagonia between 9500 Again, although an initially appealing hypothesis, and 5700 cal. years BP. The palynological record there are insufficient data to extend this conclusion obtained by Maldonado and Villagrań (2002) from into the Holocene. f 32jS in Chile shows two wet phases in the late Holocene (at 4200–3200 cal. years BP, and after 1300 7.3. Atmospheric/oceanic coupling-induced climate cal. years BP) and two distinctive arid phases, at variability (ENSO) 6100–4200 and 1800–1300 cal. years BP. Lamy et al. (2001), drawing on evidence from geochemical The lack of high-resolution climate records makes and clay mineralogy of marine sediment cores on the the potential effects of ENSO on glacier fluctuations Chilean continental slope at 41jS, demonstrated in- in the early Holocene in Patagonia difficult to assess. creased rainfall and an equatorward shift of the Markgraf and Diaz (2000), after reviewing the avail- Southern Westerlies during the Little Ice Age. able range of palaeoclimate indicators for studying the El Ninõ/Southern Oscillation (ENSO) phenomenon, 7.5. Short-term variations in atmospheric tempera- found little evidence for ENSO-related atmospheric ture and precipitation circulation patterns before 6000 14C years BP. Only after about 6000 14C years BP do the climate associ- There is a well-established link between short-term ations related to changes in sea-surface temperature variations in atmospheric temperature and precipita- and ENSO-related atmospheric circulation patterns tion and glacier fluctuations (e.g., Aniya and Eno- begin to be systematically recorded in the palaeocli- moto, 1986; Aniya et al., 1997; Hulton et al., 1994; mate record. Kerr and Sugden, 1994). For example, reconstruction of winter rainfall variations in central Chile from tree- 7.4. Systematic changes in synoptic conditions ring records show that rainfall was above the long- term mean between AD 1220 and 1280, and again Patterns of accumulation across the icefields are between AD 1450 and 1550 (Villalba, 1994a). Tem- likely to be affected by changes in broad-scale syn- perature deviations in northern Patagonia derived optic weather patterns. The latitudinal migration of the from tree-ring records show that summer temperatures Southern Westerlies could be the chief mechanism were below the long-term mean between AD 900 and driving change, since the position of these moisture- 1070, and again between AD 1270 and 1380 (Vil- bearing winds are known to determine patterns of lalba, 1994b). These periods bracketed the Medieval precipitation at a variety of temporal scales (Heusser, Warm Period, lasting from AD 1080 to 1250 (Villalba, 1995; Veit, 1996; McCulloch et al., 2000; Lamy et al., 1994a). From AD 1270 to 1660a there was a long 2000, 2001). Much of the evidence to support this cold–moist interval, with Little Ice Age temperature contention comes not from Patagonia, but from the minima around AD 1340 and 1640 (Cardich, 1980; arid and semiarid areas to the north at latitudes 30– Villalba, 1994a). Thus, most land-terminating glaciers 35jS, where several authors (e.g., Jenny et al., 2002; in Patagonia reached their maximum Little Ice Age Maldonado and Villagrań, 2002) have tendered palae- extent between AD 1600 and 1700 (Luckman and oenvironmental evidence for latitudinal displacement Villalba, 2001), with this pattern applying regionally of the Southern Westerlies. Jenny et al. (2002) noted at least as far away as the Central Region of Argentina evidence for an arid early to mid-Holocene (9500– (Cioccale, 1999). Thus, there appears to be a tentative 5700 cal. years BP) event at 33jS, with a precipitation link between short-term variations in atmospheric increase beginning after 5700 cal. years BP. Modern temperature and precipitation and glacier advances humid conditions were established at these latitudes in Patagonia, although not all glaciers display syn- by around 3200 cal. years BP. These authors hypoth- chronicity with these climatic parameters (Fig. 4). esised that during the early and mid-Holocene, the The link between short-term variations in atmos- Southern Westerlies were blocked by the subtropical pheric temperature and precipitation and glacier fluc- high-pressure cell and hence deflected southwards tuations is illustrated by evidence that the San Rafael over Patagonia. We would therefore expect higher 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, Both Mercer- and Aniya-type chronologies are following an assessment of the steepness of the based largely on radiocarbon-dated records, many of precipitation gradient over the icefields, that glaciers which are minimal dates, and from calving glaciers on the western flanks of the icefields respond to that may react to climate in a nonlinear fashion. changes in precipitation and are ‘‘accumulation-driv- Indeed, contrasting histories have been obtained for en’’, whilst the fluctuations of those on the eastern the behaviour of land-terminating glaciers within flanks are driven by changes in temperature and hence relatively short distances of each other. The validity are ‘‘ablation-driven’’. However, the synchronicity of and uncritical use of such chronologies in interhemi- terminus fluctuations on either side of the Hielo spheric comparative studies is therefore questionable. Patagońico Norte over the last 150 years or so, Proxy climate data indicate that many of these questions the validity of this argument. Harrison and broad regional trends can be explained by changes Winchester (2000) therefore proposed that the mech- in precipitation and atmospheric temperature rather anism driving variability in glacier frontal positions is than systematic changes related to the internal char- simply variability in precipitation in their accumula- acteristics of the icefields. However, the individual tion zones. response of specific glaciers depends to certain extent on changes in their terminal environment brought about by advance and recession (e.g., the transition 8. Conclusions from calving to noncalving and vice versa), and changes internal to that environment (e.g., changes Palaeoenvironmental evidence and dated glacier in the bathymetry and geometry of terminal marine or fluctuations suggest that during the early Holocene lacustrine basins). (10,000–5000 14C years BP) glaciers in Patagonia This review confirms the overall conclusion of were smaller than at present, with atmospheric tem- Strelin and Malagnino (2000) that extreme caution peratures east of the Andes about 2 jC above modern is required in setting boundaries for the end of a values in the period 8500–6500 14C years BP. The glacial readvance by using minimum dates from the period between 6000 and 3600 14C years BP appears basal levels of ancient peat bogs in front of moraine to have been colder and wetter than present, followed ridges. The dates obtained for these surfaces do not by an arid phase from 3600 to 3000 14C years BP. take account of the potentially considerable time From 3000 14C years BP to the present, there is elapsed between moraine ridge formation and the evidence of a cold phase, with relatively high precip- onset of peat formation. 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. Acknowledgements Neoglacial glacier advances in Patagonia did not begin until some time after 6000 14C years BP, Fieldwork in Patagonia has been funded from a coincident with a strong cooling episode at this time. number of sources including the Royal Geographical Holocene glacier advances can be assigned to one of Society, the UK Natural Environment Research three time periods following a ‘Mercer-type’ chronol- Council (grant NER/B/S/2002/00282) and The Uni- ogy, or one of four time periods following an ‘Aniya- versity of Wales, Aberystwyth Academic Research type’ chronology. The ‘Mercer-type’ chronology has Fund. We thank all colleagues who have spent time glacier advances among 4700–4200, 2700–2000 14C with us in the field, especially Mike Hambrey and years BP and during the Little Ice Age. The ‘Aniya- Charles Warren. We also thank Raleigh International type’ chronology has glacier advances at 3600 and for field logistical support over a number of years. 2300 14C years BP, between 1600–1400 14C years BP Sarah Davies and Stephen Porter provided comments and during the Little Ice Age. These chronologies are on an earlier version of the manuscript. Comments by best regarded as broad regional trends, since there are the three journal referees (C.J. Heusser, Bas van Geel dated examples of glacier advances outside these time and an anonymous referee) are also acknowledged. periods. Figures were drawn by Antony Smith of the Institute 98 N.F. Glasser et al. / Global and Planetary Change 43 (2004) 79–101 of Geography and Earth Science at the University of Blunier, T.et al., 1998. Asynchrony of Antarctic and Greenland Wales, Aberystwyth. climate during the last glacial period. Nature 394, 739–743. Broecker, W.S., 1998. Paleocean circulation during the last deglaciation: a bi-polar see-saw? 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