The glacial geomorphology and Pleistocene history of South America between 38°S and 56°S

The glacial geomorphology and Pleistocene history of South America between 38°S and 56°S

ARTICLE IN PRESS Quaternary Science Reviews 27 (2008) 365–390 The glacial geomorphology and Pleistocene history of South America between 381S and 56...

12MB Sizes 0 Downloads 21 Views

ARTICLE IN PRESS

Quaternary Science Reviews 27 (2008) 365–390

The glacial geomorphology and Pleistocene history of South America between 381S and 561S Neil F. Glassera,, Krister N. Janssonb, Stephan Harrisonc, Johan Klemanb a

Centre for Glaciology, Institute of Geography and Earth Sciences, University of Wales, Aberystwyth SY23 3DB, Wales, UK b Department of Physical Geography and Quaternary Geology, Stockholm University, SE-10691 Stockholm, Sweden c Department of Geography, University of Exeter, Cornwall Campus, Penryn, Cornwall TR10 9EZ, UK Received 30 May 2007; received in revised form 14 November 2007; accepted 15 November 2007

Abstract This paper presents new mapping of the glacial geomorphology of southern South America between latitudes 381S and 561S, approximately the area covered by the former Patagonian Ice Sheets. Glacial geomorphological features, including glacial lineations, moraines, meltwater channels, trimlines, sandur and cirques, were mapped from remotely sensed images (Landsat 7 ETM+, pansharpened Landsat 7 and ASTER). The landform record indicates that the Patagonian Ice Sheets consisted of 66 main outlet glaciers, together with numerous local cirque glaciers and independent ice domes in the surrounding mountains. In the northern part of the mapped area, in the Chilean Lake District (38–421S), large piedmont glaciers developed on the western side of the Andes and the maximum positions of these outlet glaciers are, in general, marked by arcuate terminal moraines. To the east of the Andes between 381S and 421S, outlet glaciers were more restricted in extent and formed ‘‘alpine-style’’ valley glaciers. Along the eastern flank of the Andes south of 451S a series of large fast-flowing outlet glaciers drained the ice sheet. The location of these outlet glaciers was topographically controlled and there was limited scope for interactions between individual lobes. West of the Andes at this latitude, there is geomorphological evidence for an independent ice cap close to sea level on the Taitao Peninsula. The age of this ice cap is unclear but it may represent evidence of glacier growth during the Antarctic Cold Reversal and/or Younger Dryas Chronozone. Maximum glacier positions are difficult to determine along much of the western side of the Andes south of 421S because of the limited land there, and it is assumed that most of these glaciers had marine termini. In the south-east of the mapped area, in the Fuegan Andes (Cordillera Darwin), the landform record provides evidence of ice-sheet initiation. By adding published dates for glacier advances from the literature we present maps of pre-Last Glacial Maximum (LGM) glacier extent, LGM extent and the positions of other large mapped moraines younger than LGM in age. A number of large moraines occur within the known LGM limits. The age of these moraines is unknown but, since many of them lie well outside the established maximum Neoglacial positions, the possibility that they reflect a return to glacial climates during the Younger Dryas Chronozone or Antarctic Cold Reversal cannot be discounted. r 2008 Elsevier Ltd. All rights reserved.

1. Introduction 1.1. Study rationale and aim Palaeoglaciological reconstructions already exist for the two largest Northern Hemisphere former mid-latitude ice sheets, the Laurentide Ice Sheet (Boulton and Clark, 1990) and the Fennoscandian Ice Sheet (Kleman et al., 1997; Boulton et al., 2001). However, the bed of the former Corresponding author.

E-mail address: [email protected] (N.F. Glasser). 0277-3791/$ - see front matter r 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.quascirev.2007.11.011

Patagonian Ice Sheet, the next largest of these former midlatitude ice masses, and the largest in the Southern Hemisphere, remains largely unmapped and hence the role of this ice sheet in climate–cryosphere interactions is poorly understood. Of particular importance is an understanding of whether the rapid climatic shifts in the Quaternary in the North Atlantic region were communicated on a global scale (Blunier and Brook, 2001). Data concerning the nature of glacial events from the Southern Hemisphere is required for inter-hemispheric comparisons of the timing of glaciations and to test hypotheses concerning the role of the Southern Westerlies during the glacial–interglacial

ARTICLE IN PRESS 366

N.F. Glasser et al. / Quaternary Science Reviews 27 (2008) 365–390

transitions (Denton et al., 1999a; Sugden et al., 2005; Schaefer et al., 2006). The Patagonian icefields are one of only three areas in the Southern Hemisphere (the others are New Zealand and Tasmania) containing a geomorphological record suitable for testing this inter-hemispheric synchroneity. The aim of this paper is therefore to present new mapping from remotely sensed images of the glacial geomorphology of southern South America between latitudes 381S and 561S, approximately the area covered by the former Patagonian Ice Sheets. This study marks a first attempt at geomorphological mapping of subglacial and ice-marginal landforms in this area on an ice-sheet wide scale using remotely sensed images. By integrating our geomorphological mapping with known chronologies, we use these data to make reconstructions of the geometry of the former Patagonian Ice Sheets and its outlet glaciers at various time slices, including the extent of pre-Last Glacial Maximum (LGM) ice sheets, the extent of the LGM itself and the possible location of post-LGM ice margins. Our ice-sheet scale mapping allows us to begin to assess and understand the major drivers and influences on glacial landform development at the landscape scale. While this approach necessarily reduces the opportunity to identify small-scale landforms and reconstruct the processes which produced them, largescale analysis is seen increasingly as a fundamental requirement of geomorphological study (cf. Harrison, 1999; Summerfield, 2005). 1.2. Current knowledge of the former Patagonian Ice Sheets In this paper, we consider in detail the glacial geomorphology of South America between latitudes 381S and 561S. Two major ice masses (the North and South Patagonian Icefields) and numerous snow- and ice-capped volcanoes and mountain icefields currently exist in the region. The North Patagonian Icefield (471000 S, 731390 W) is some 120 km long and 40–60 km wide, capping the Andean Cordillera between altitudes of 700 and 2500 m a.s.l. (Fig. 1). The icefield covers some 3953 km2 (Rivera et al., 2007). Annual precipitation 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. before decreasing sharply on the eastern side (Escobar et al., 1992). The South Patagonian Icefield covers an area of ca 13,000 km2 (Aniya, 1999) and runs north–south for 360 km between 481500 S and 511300 S, with a mean width of 40 km (Fig. 1). The South Patagonian Icefield also has steep climatic gradients between the maritime west side and continental east side. Smaller mountain icefields, glaciercapped volcanoes and isolated cirque glaciers also exist in many places along the north–south spine of the Andes, as well as in the very southern part of the study area in the Cordillera Darwin. Records of atmospheric circulation across southern South America show strong inter-annual, inter-decadal

Fig. 1. Shuttle Radar Topographic Mission (SRTM) digital elevation model of Southern South America at 90 m horizontal resolution. The locations of the two largest contemporary ice masses, the North and South Patagonian Icefields are indicated, as are other significant localities (see later figures for detailed place name localities). The dashed line indicates approximate limit of heavily ice-scoured terrain (to the west of the line) where glacial depositional landforms are scarce.

and inter-centennial variability (Glasser et al., 2004). Climatic changes in South America are associated directly or indirectly through long-term (Ma) mountain-range uplift (Hartley, 2003); atmospheric teleconnections, with large-scale atmospheric/oceanic forcing such as the El Nin˜o-Southern Oscillation (ENSO) (Aceituno, 1988, Allan et al., 1995; Diaz and Markgraf, 2000); the temperature gradient between tropical and extra-tropical region; the sea surface temperatures of the South Atlantic and South Pacific oceans, and the circum-Antarctic ocean circulation (Villalba et al., 1997; Lamy et al., 2004). During the Quaternary the icefields expanded and contracted in response to this climatic forcing a number of times

ARTICLE IN PRESS N.F. Glasser et al. / Quaternary Science Reviews 27 (2008) 365–390

(Heusser, 2003; Harrison, 2004; Sugden et al., 2005). At times they coalesced to form the much larger Patagonian Ice Sheet. Modelling studies (Hulton et al., 1994, 2002) and evidence from marine sediment cores (Lamy et al., 2004; Kaiser et al., 2007) are in close agreement that the regional ice maximum coincided with a 6 1C sea surface temperature lowering in the south-east Pacific off southern Chile. Current understanding of the terrestrial extent of the former Patagonian Ice Sheets owes much to the pioneering study of Caldenius (1932), who first mapped moraine systems around the contemporary icefields. Caldenius (1932) distinguished four separate moraine belts to the east of the icefields. He concluded from their state of preservation that the three inner moraine systems were relatively young. In accordance with the stages of the last Weichselian Glaciation in northern Europe, Caldenius named the three moraine limits (from inner to outer) the ‘‘Finiglacial’’, the ‘‘Gotiglacial’’, and the ‘‘Daniglacial’’. Later, the Finiglacial moraines were correlated to the LGM and the Daniglacial and the Gotiglacial moraine systems to the mid-Pleistocene (Mo¨rner and Sylwan, 1989). The fourth (outermost) moraine system, termed the ‘‘Initioglacial’’ by Caldenius (1932), is still poorly constrained in age, but is thought to be between 1.1 and 2.3 Ma in age (Mercer, 1969; Mo¨rner and Sylwan, 1989; Meglioli, 1992; Singer et al., 2004). Coronato et al. (2004) and Rabassa et al. (2000, 2005) have produced seminal reviews of glaciations in South America. These authors have argued from a synthesis of records that the oldest known Patagonian glaciations took place between approximately 7 and 5 Ma but moraine systems from these glaciations are not preserved and their occurrence is inferred mainly on stratigraphic and sedimentological grounds. Rabassa et al. (2005) suggest a minimum of eight glaciations occurred in the Middle–Late Pliocene (Oxygen Isotopic Stages (OIS) 54–82). The ‘‘Great Patagonian Glaciation’’ developed between 1.168 and 1.016 Ma (OIS 30–34; Early Pleistocene). After the Great Patagonian Glaciation, 14–16 cold (glacial/stadial) events alternated with corresponding warm (interglacial/interstadial) equivalents (Rabassa et al., 2005). They argue that the LGM occurred between 25,000 and 16,000 cal. yr ago (OIS 2; Late Pleistocene), and that two readvances (or still stands) took place during the Lateglacial (15,000–10,000 14C yr BP). Numerous local and regional studies exist within the area covered by the former ice sheets. Studied areas include the Chilean Lake District (e.g. Porter, 1981; Andersen et al., 1999; Denton et al., 1999b), the area around the North Patagonian ice field (Glasser and Jansson, 2005; Glasser et al., 2005, 2006; Turner et al., 2005), the eastern Andes (Wenzens, 1999, 2000, 2002, 2003, 2004, 2005, 2006a, b; Kaplan et al., 2004, 2005; Douglass et al., 2005, 2006), the Magellan Strait/Fuegan area (Rabassa et al., 1990, 2000; Porter et al., 1992; Clapperton et al., 1995; Coronato, 1995; Benn and Clapperton, 2000; Coronato et al., 2004; Bentley et al., 2005) and the Torres del Paine area (Marden, 1993, 1997; Marden and Clapperton, 1995).

367

There are also a number of palaeocological studies that indicate the environmental conditions prevailing during Pleistocene times (e.g. Heusser and Rabassa, 1987; Heusser, 1989a–c, 1990, 1998, 2003; Markgraf, 1993; Moreno, 1997; Bennett et al., 2000; McCulloch et al., 2000; Massaferro and Brooks, 2002; Massaferro et al., 2005). From a synthesis of key proxy records, McCulloch et al. (2000) concluded that there was a sudden rise in temperature that initiated deglaciation of the Patagonian Ice Sheet sychronously over 161 of latitude at 14,600–14,300 14C yr BP (17,500–17,150 cal. yr). There was a second step of warming in the Chilean Lake District at 13,000–12,700 14C yr BP (15,650–15,350 cal. yr), which saw temperatures rise to close to modern values. A third warming step, particularly clear in southern Chile, occurred ca 10,000 14C yr BP (11,400 cal. yr). Following the initial warming, there was a lagged response in precipitation as the westerlies, after a delay of ca 1600 yr, migrated from their northern glacial location to their present latitude, which was attained by 12,300 14C yr BP (14,300 cal. yr) (McCulloch et al., 2000).

1.3. Glacier response during the Younger Dryas Chronozone (YDC) and Antarctic Cold Reversal (ARC) A number of dating techniques have been applied to the Patagonian moraine systems and their associated glacigenic deposits, including radiocarbon (14C) dating of moraines, peat bogs and lacustrine deposits (e.g. Mercer, 1965, 1968, 1976; Aniya, 1995; Denton et al., 1999b; Hajdas et al., 2003; McCulloch et al., 2005), cosmogenic isotope dating (Kaplan et al., 2004, 2005, 2007; Fogwill and Kubik, 2005; McCulloch et al., 2005; Douglass et al., 2006), optically stimulated luminescence (OSL) dating (Winchester et al., 2005; Glasser et al., 2006), and 40Ar/39Ar and K–Ar dating of lava flows interbedded with glacigenic and glaciofluvial deposits (Wenzens, 2000, 2006b; Singer et al., 2004). Numerical ice-sheet modelling experiments have also significantly increased our understanding of the extent and dimensions of the former ice sheets and their interaction with climate (e.g. Hulton et al., 1994, 2002; Sugden et al., 2002; Hubbard et al., 2005). The evidence for climate change during the Late Pleistocene–Holocene transition in the zone of the Southern Westerlies between 401S and 501S comes from sites with dated glacier advances and palaeoecological data. For instance, in the Chilean Lake District at around 411S a glacial advance at Lago Mascadi has been dated using radiocarbon dating to between 11,400 and 10,150790 14C yr BP (Hajdas et al., 2003), preceding the Younger Dryas by around 550 yr. In the Exploradores valley of the North Patagonian Icefield, Glasser et al. (2005) used cosmogenic isotope dating and OSL methods to date a significant advance of glaciers between 12,500 and 9600 yr. At Glacier Grey on the southern side of the South Patagonian Icefield, a glacial advance dated

ARTICLE IN PRESS 368

N.F. Glasser et al. / Quaternary Science Reviews 27 (2008) 365–390

by tephrochronology occurred between 12,010 and 91807120 14C yr BP (McCulloch et al., 2000). However, despite this glacial evidence, the palaeoecological signal of climate deterioration around this time is equivocal. Near Alerce in the Chilean Lake District at 411S Heusser and Streeter (1980) employed palynology to show reduced temperature and increased precipitation at around 10,400 14C yr BP. Further south at 431S on the Taitao Peninsula west of the North Patagonian Icefield, Massaferro and Brooks (2002) used chironomid data to show cooling during the YDC. This contrasts with Hoganson and Ashworth (1992) who used beetle remains to suggest that no cooling occurred during this time in the region. However, in southern Patagonia White et al. (1994) presented evidence for considerable warming at 10,000 and 12,800 14C yr BP. As a result, the evidence to show cooling from palaeoecological studies in the vicinity of the Chilean Lake District and the North Patagonian Icefield is equivocal. Some studies indicate a climate shift during the Pleistocene–Holocene transition (e.g. Heusser, 1993), although others do not (Ashworth et al., 1991; Markgraf, 1991, 1993; Lumley and Switsur, 1993; Bennett et al., 2000). One potential solution to this debate is to consider the ice-sheetwide geomorphological record, a topic we address in this paper.

2. Methods 2.1. Image interpretation Glacial geomorphological features, including glacial lineations, moraines, meltwater channels, trimlines, sandur and cirques, together with other topographic features such as lakes, shorelines, deltas, plateaux, rivers and volcanoes were mapped from Landsat 7 ETM+ scenes (30 m spatial resolution), pan-sharpened Landsat 7 scenes and ASTER (15 m spatial resolution) satellite images in ArcMap GIS software. We interpreted the entire area covered by former Patagonian Ice Sheets using 33 Landsat 7 ETM+ and pansharpened Landsat 7 scenes and 167 individual ASTER images. The criteria used in landform identification and mapping are shown in Table 1 and an example of satellite image interpretation given in Fig. 2. Satellite image interpretation was performed using multiple band combinations and standard image enhancement procedures (contrast stretching and histogram equalisation) to improve the landform signal strength (Jansson and Glasser, 2005). Images were overlaid on a Digital Elevation Model (DEM) based on 90 m Shuttle Radar Topographic Mission (SRTM) data to provide topographic context and to aid landform identification in areas of complex terrain (Fig. 1). Mapping was carried out at 1:50,000 scale. Multiple images were used for the mapping in areas where cloud cover was present.

2.2. Chronological information After the mapping was completed, the ages of securely dated moraine systems were added from the published literature. There is huge volume of literature on former South American glacier variations; so, as a primary filter, information on dated Patagonian Ice Sheet moraines was only added from papers where the precise geographical location of samples is provided and where the stratigraphic context of sample collection and their significance is clearly stated (e.g. Denton et al., 1999b; McCulloch et al., 2005). We have excluded dates relating to advances of local mountain ice caps and cirque glaciers (e.g. Douglass et al., 2005) because although these advances may be securely dated, mountain glaciers are not necessarily in phase with fluctuations of the main ice sheet. Information on dated moraines includes those dated directly or indirectly by 40 Ar/39Ar and K–Ar dating, 14C radiocarbon techniques, cosmogenic isotope dating of boulders on moraine and drift surfaces, and OSL dating. For the purposes of this exercise, dates are reported in the format in which they were originally published. Dates originally reported as 14 C yr BP (i.e. as uncalibrated ages) are clearly labelled as such. We have not attempted to convert ages originally reported in 14C years to calendar years. The majority of published dates relate to the LGM because (a) this time period has historically received the most attention and (b) the LGM moraines and associated glacigenic deposits lie within the limits of conventional radiocarbon (i.e.14C) dating. Pre-LGM moraines and associated glacigenic deposits are more difficult to date because they often lie outside the limits of 14C dating. Newer dating techniques (e.g. cosmogenic isotope dating) have helped to provide age estimates for some of these preLGM moraines, but the application of this technique to Patagonian glacial deposits is not without its problems (see Kaplan et al. (2005, 2007) and Douglass et al. (2006) for full discussion). 40Ar/39Ar and K–Ar dating of basaltic lava flows interbedded with glacial deposits (e.g. Singer et al., 2004) and with fluvial and glaciofluvial terraces (e.g. Wenzens, 2000, 2006b), and palaeomagnetic studies (Mo¨rner and Sylwan, 1989) provide the basis for age estimates of middle Pleistocene and older glacial advances. We have not added information on the most recent (e.g. ‘‘Little Ice Age’’ and earlier Holocene) moraines because these moraines are generally too closely spaced to be differentiated at the scale at which the mapping is presented. 3. Results The area between latitudes 381S and 561S is geographically and climatologically diverse. We therefore present the results of our mapping of the glacial landforms in three sectors, hereafter referred to as the Northern, Central and Southern sectors of the former ice sheet. The results of the mapping are displayed using a nested approach, in which

ARTICLE IN PRESS N.F. Glasser et al. / Quaternary Science Reviews 27 (2008) 365–390

369

Table 1 Landforms identified on satellite imagery and criteria used in identification Landform/feature

Identification criteria

Possible identification errors

Significance

Minor over-estimate in glacier extent possible where confused with snow cover.

Foci for ice discharge from the contemporary icefields.

Possible underestimate where bedrock obscured by vegetation cover.

Evidence for extensive areas of former glacier ice at its pressure-melting point.

Possible, but unlikely, confusion with other subhorizontal or horizontal features such as glacial lake shorelines.

Former vertical dimensions of glaciers. Possible englacial thermal boundary.

In bedrock, change in surface structure compared to surrounding terrain.

Possible under–estimate in areas of thin debris cover.

Show ice-flow direction and may indicate high former ice velocities, when highly attenuated.

In debris, different colour compared to surrounding terrain due to change in vegetation cover. Shadowing due to change in height or relative relief. Change in colour because of different soil and vegetation cover compared to surrounding terrain.

Bedrock landforms may be confused with bedrock structures in certain lithologies. Possible, but unlikely, confusion with trimlines where moraines have low relative height. Possible confusion with shorelines around lake margins and in coastal areas. Possible confusion with landslip material beneath volcanic plateaux.

Flat, mainly light red areas with medium grey where there is thin vegetation cover. Erosional scars and sharp boundaries with surrounding terrain. Terrace edges have sharp boundaries. Obvious break of slope with surrounding terrain.

Possible, but unlikely, confusion with deltas or icecontact deposits.

Marks major drainage routes from contemporary glaciers and other glacierfed streams.

Possible, but unlikely, confusion with shorelines near lakes.

Individual terraces indicate down-cutting and aggradational events.

Homogeneous surface texture with flat upper surfaces, erosional scars and sharp boundaries with surrounding terrain.

Possible, but unlikely, confusion with sandur or alluvial fans.

Fan-shaped accumulation with sharp boundary with terrain due to change in surrounding vegetation

Possible to misinterpret as fossil delta or ice-contact deposit.

Sediments deposited by meltwater streams draining tributary valleys onto/ against glacier ice in main valleys. Indicates thickness and extent of ice in the main valley. Shows former glacial lake levels. Reworking of unconsolidated material by contemporary meltwater channels and streams.

Morphology

Colour/structure/texture

Contemporary glaciers and glacier debris

Bare ice, snow and debris. Surface structures (e.g. crevasses, foliation) are common.

Ice-scoured bedrock

Widespread exposures of bare or lightly vegetated bedrock. Numerous small lake basins and open joints visible.

Trimlines

Sub-horizontal lines on valley sides separating areas of non-vegetated and vegetated land or areas covered by different types of vegetation. Parallel features indicating ice-flow direction. Formed in bedrock by glacial erosion or by sediment accumulation.

Snow and ice appear white to light blue. Surface smooth to rough. Debris appears as grey to black in colour. Grey to light pink when vegetation cover is present. Bedrock structures and faults often present. Upper surface often has a rough and irregular texture. Sharp altitudinal change in surface colour and texture due to change in vegetation cover.

Glacial lineations

Moraines and moraine complexes

Sandur/fluvial sediment

Terrace edge in sandur

Delta or ice-contact deposits

Alluvial fans

Prominent cross-valley single or multiple ridges with positive relief. Linear, curved, sinuous or sawtoothed in plan. May occur as single moraines or in more complicated moraine systems. Often associated with other ice-marginal features such as meltwater channels, ice-contact landforms and sandar. Valley floor accumulations of sediment, commonly dissected by a braided stream pattern.

Break of slope in sandur deposits. High-level terraces may be graded to the same elevation as moraines. Flat-topped sediment accumulations above the present day valley floor, commonly with a steep delta front.

Sub-horizontal fans on valley sides. Typically fed by a meltwater channel or stream.

Moraines mark the former terminal position of glaciers.

ARTICLE IN PRESS 370

N.F. Glasser et al. / Quaternary Science Reviews 27 (2008) 365–390

Table 1 (continued ) Landform/feature

Identification criteria Morphology

Volcanoes/cinder cones

Isolated conical peaks associated with former or contemporary volcanism.

Shorelines

Breaks of slope running parallel or sub-parallel to coastline in coastal areas (marine shorelines) or around lakes (lake shorelines).

Glacial lake outburst flood (GLOF) tracks

Prominent accumulations of sand and gravel, often on steep slopes and located below contemporary glaciers or breached moraines.

Cirques

Large amphitheatre-shaped hollows on mountain flanks or incised into plateau edges.

Meltwater channels

Linear features with abrupt inception and termination. Often contain no contemporary drainage. Channels may follow or cut across local slope direction.

Lakes

Large freshwater bodies within enclosed basins.

Plateau edges

Break of slope around plateau edges; particularly common around basalt plateaux. Sub-horizontal or gently sloping lines on valley sides separating different types of drift, or separating driftcovered slopes from bedrock.

Drift limit

Possible identification errors

Significance

Possible, but unlikely, confusion with nonvolcanic mountains.

Indicates former or contemporary volcanism.

Possible confusion with moraines, especially around major lakes where both shorelines and moraines may be present.

Indicates former lake or sea levels. Some lake shorelines indicate the presence of former ice-dammed lakes.

Possible, but unlikely, confusion with sandur or alluvial fans.

Catastrophic failure of moraine-dammed or glacier-dammed lakes.

Possible, but unlikely, confusion with massmovement or landslip scars especially beneath volcanic plateaux. Possible, but unlikely, confusion with contemporary drainage routes.

Indicates presence of localised or restricted mountain glaciations.

Colour/structure/texture cover. Pattern of braided streams on upper surface. Volcanoes rise sharply above surrounding terrain, are snow- or ice-capped and contain open surface craters. Flanks may show evidence of lava flows with sharp boundaries with surrounding terrain. Shadowing due to change in height or relative relief. Change in colour if former shorelines are vegetated. Many shorelines mirror the shape of existing coastline or lake margins. Sediment accumulation with sharp boundary with terrain due to change in surrounding vegetation cover. Often located below a breached moraine or drained lake. Sharp boundaries with surrounding terrain, including cliffs.

Well-defined channel edges and sharp boundaries with surrounding terrain. Shadowing due to change in height or relative relief. Channel floors may be different in colour to surrounding land. Lakes appear as blue, black or other dark colours due to high reflectance. Sharp boundaries with surrounding terrain. Variety of shapes possible. Plateau edges have sharp boundaries. Obvious break of slope with surrounding terrain. Sharp vertical or horizontal change in surface colour and texture due to change in vegetation cover, or change from drift-covered slopes to bedrock.

we first present a regional-scale geomorphological map for each sector before presenting more detailed geomorphological maps of key areas within each of these sectors. A total of 66 main outlet glaciers, together with numerous local cirque glaciers and independent ice domes in the surround-

Indicates large volumes of meltwater production. Channels may indicate position of former ice margin, especially when viewed in association with moraines and sandur.

Areas in shadow within regions of high relative relief or cloud shadows may be mistaken for lakes.

Lakes indicate impeded drainage. High frequency of lakes may indicate presence of rock basins formed by glacial over-deepening.



Indicates scarp retreat?

Possible, but unlikely, confusion with other subhorizontal or horizontal features such as glacial lake shorelines.

Former vertical and horizontal dimensions of glaciers.

ing mountains, were identified in this study. The geomorphology of the former outlet glaciers in the three sectors is described in Sections 3.1–3.3 and their regional significance and relationship to other events in southern South America during the Quaternary are discussed in Sections 4.1–4.3.

ARTICLE IN PRESS N.F. Glasser et al. / Quaternary Science Reviews 27 (2008) 365–390

371

Fig. 2. Landsat sub-scene (left panel) and interpretation (right panel) showing the glacial geomorphology of the area around former outlet glacier 56 in Seno Otway (see Fig. 9 for location). Glacial lineations representing two separate ice-flow systems are clearly visible on the former ice-sheet bed in this area.

3.1. The northern sector of the former Patagonian Ice Sheet This sector includes the area to both the east and west of the Andes between roughly 381S and 441S, from the Chilean Lake District in the north to Isla Chiloe´ in the south (Fig. 3). This area contains both the main spine of the Andes (highest summits typically 2400 m a.s.l.) as well as a number of higher outlying peaks to the east (e.g. Cerro Tronador, 3554 m a.s.l.) and isolated volcanoes (e.g. Volcan Osorno, 2652 m a.s.l.). South of Puerto Montt, a deep north–south orientated channel separates Isla Chiloe´ from the mainland. The geomorphological evidence indicates that at least 13 separate glaciers drained the western flank of the ice sheet in this area. The arcuate moraine systems associated with these western glaciers, labelled 1–13 in Fig. 3, indicate that the outlet glaciers formed large piedmont lobes. The glaciers eroded deep basins as they emerged from the Andean mountain front, and their terminal moraines now impound the lakes that give their name to the Chilean Lake District. The terminal moraines are generally complex

features with multiple ridges and crests (e.g. at Lago Llanquihue, Lago Rupanco and Lago Ranco). Meltwater channels and other breaches in the moraines lead to westward-directed sandar. South of Golfo de Ancud (Glacier 1), SE–NW aligned glacial lineations, meltwater channels and sandur on Isla Chiloe´ indicate that a large piedmont lobe advanced westward from the Andes onto the southernmost part of Isla Chiloe´. There is, however, no terminal moraine to mark the maximum position of this lobe. On the eastern side of the Andes, the outlet glaciers were more restricted in extent (Fig. 3). The maximum extent of these glaciers is marked by cross-valley moraines composed generally of single ridges. These eastern terminal moraines (e.g. those marking the former extent of glaciers 14–33) are smaller and less distinct that their western counterparts. In some cases, breaches in the moraines lead to eastwarddirected sandar (e.g. glaciers 15 and 16 at Rio Biobl and Icalma) but large sandur are not always present. Glacial lineations are absent from the beds of these former glaciers. The moraine morphology and sandur indicate that these

ARTICLE IN PRESS 372

N.F. Glasser et al. / Quaternary Science Reviews 27 (2008) 365–390

Fig. 3. The glacial geomorphology of the Northern sector of the former Patagonian Ice Sheet. Numbers indicate former outlet glaciers identified in this study. Landforms indicate the presence of large piedmont outlet glaciers to the west of the Andes, but more restricted glaciation to the east of the mountains.

ARTICLE IN PRESS N.F. Glasser et al. / Quaternary Science Reviews 27 (2008) 365–390

373

Fig. 4. The glacial geomorphology of the Central sector of the former Patagonian Ice Sheet. Numbers indicate former outlet glaciers identified in this study. Inset boxes indicate locations of detailed maps. Landforms indicate that a number of large outlet glaciers developed in the valleys to the east of the Andes.

ARTICLE IN PRESS 374

N.F. Glasser et al. / Quaternary Science Reviews 27 (2008) 365–390

glaciers were ‘‘alpine-style’’, with topographically constrained outlet glaciers following narrow valleys. 3.2. The central sector of the former Patagonian Ice Sheet This sector includes the area west of the Andes between roughly 441S and 511S, from Isla Chiloe´ in the north to the southern end of the South Patagonian Icefield in the south

(Fig. 4). This area contains the main spine of the southern Andes (highest summits typically 2500–3000 m a.s.l.) as well as the pampas to the east. There are strong structural and tectonic geological influences on the landscape in this region (e.g. the north–south orientated Ofqui Fault in the vicinity of the North Patagonian Icefield). With the exception of Isla Wellington and the Taitao Peninsula, there is little land to the west of the North and South Patagonian Icefields so that

Fig. 5. The glacial geomorphology of part of the Taitao Peninsula to the west of the contemporary North Patagonian Icefield (see Fig. 4 for location). Moraine complexes and associated sandur around the southern and eastern margins of Lago Presidente Rios on the Taitao Peninsula provide evidence for an independent ice mass centred on the peninsula. The timing of this event and its relationship to the expansion of outlet glaciers of the Northern Patagonian Icefield are unclear (see text for full discussion).

ARTICLE IN PRESS N.F. Glasser et al. / Quaternary Science Reviews 27 (2008) 365–390

landform information is limited in this area. East of the North and South Patagonian Icefields, however, there is geomorphological evidence for the existence of a number of large outlet glacier lobes and glacier extent can be reconstructed here with more confidence. The Taitao Peninsula lies to the north-west of the contemporary North Patagonian Icefield, and is joined to the mainland partly by a large sandur (Fig 5.). Two outlet glaciers from the icefield, the San Quintin glacier and the San Rafael glacier, currently terminate on the eastern margin of this sandur. Their former extent is marked by large arcuate moraines, marking maxima in the late 20th century (San Quintin glacier) and the early Holocene (San Rafael glacier) (Winchester and Harrison, 1996). However, further west on the Taitao Peninsula itself moraine complexes occur at the eastern and southern ends of the arms of Lago Presidente Rios (Fig. 5). Glacial lineations indicate an ice dispersal centre somewhere to the northwest of Lago Presidente Rios. Outside these arcuate moraine systems are extensive sandar, which grade into the sandur plain that separates the Taitao Peninsula from the mainland. Collectively, this evidence indicates the existence, at some stage in the past, of an independent ice mass on the Peninsula. East of the Andes, the landscape is dominated by large moraine-dammed lakes, including Lago Buenos Aires/ Lago General Carrera (former outlet glacier 45), Lago Cochrane/ Pueyrredo´n (former outlet glacier 46), Lago O’Higgins/Lago San Martin (former outlet glacier 49), Lago Viedma (former outlet glacier 50) and Lago Argentino (former outlet glacier 51). These moraine complexes comprise extensive arcuate moraine belts and associated sandur. Lateral meltwater channels are common along their flanks. In some cases, valleys contain only one moraine complex (e.g. glacier 44 around Balmaceda; Fig. 6; glaciers 39–45). Here glacial lineations can be traced along the valley floor directly to the moraine complex. In some valleys (e.g. glacier 42; Fig. 6) more than one separate moraine complex exists. In these situations, glacial lineations can be traced to two separate ice-marginal positions. In other valleys, the situation is even more complex with as many as four identifiable moraine belts in close proximity within a single valley (e.g. former outlet glacier 45 at Lago General Carerra/Lago Buenos Aires and former outlet glacier 46 at Lago Cochrane/Pueyrrendon; Figs. 6 and 7; former outlet glaciers 52 and 53; Fig. 8). In other valleys (e.g. former outlet glacier 48; Fig. 7), large moraine complexes are separated by 50 km. Above the valleys are large mesetas or plateaus composed of lava flows. The outlet glacier lobes advanced between, but did not cover these mesetas. 3.3. The southern sector of the former Patagonian Ice Sheet This sector includes the area both west and east of the Andes between roughly 511S and 561S, from the South Patagonian Icefield in the north to Isla Grande de Tierra del

375

Fuego in the south (Fig. 9). To the west of the Andes, this area is a mountainous fjord landscape, with highest summits typically 2000 m a.s.l., dominated by scoured bedrock. East of the Andes, the land is lower-lying with a number of marine inlets through which flowed former outlet glaciers (e.g. former outlet glacier 55 in Seno Skyring, former outlet glacier 56 in Seno Otway, former outlet glacier 57 in Estrecho Magallenes and former outlet glacier 58 in Bahı´ a Inu´til; Fig. 10). In the far south of this area, and separated from the mainland by Seno Almirantazgo, is the glacierised Cordillera Darwin (highest peaks around 2400 m a.s.l.). The largest and best-developed moraine complexes are those developed in the areas occupied by former outlet glacier in Seno Skyring, Seno Otway, Estrecho Magallenes and Bahı´ a Inu´til. In some locations (e.g. the former outlet glacier in Seno Otway; Fig. 11) large moraine complexes lie outside inferred LGM limits (Rabassa et al., 2000; Bentley et al., 2005; Sugden et al., 2005). Well-developed glacial lineations occur in association with these moraine complexes (Fig. 2) and marginal meltwater channels are common features along the lateral margins of the former outlet glaciers (e.g. the former outlet glacier in Seno Otway; Fig. 11; D.E. Sugden, pers. comm.). The location and behaviour of these glaciers appears to be strongly topographically controlled, with former outlet glaciers repeatedly occupying the low-lying topographic depressions and receding up-valley from their maximum positions. To the south-east, in the Seno Almirantazgo area, glacial lineations are aligned NW–SE through Seno Almirantazgo towards Lago Fagnano (Fig. 12). On the northern flank of Seno Almirantazgo, however, the positions of three former outlet glaciers (glaciers 59–61; Fig. 12) flowing at 901 to this direction are marked by large arcuate end moraines and associated northward-flowing meltwater channels and sandur. 4. Interpretation and discussion 4.1. The northern sector of the former Patagonian Ice Sheet The Northern Sector indicates strong East–West contrasts in the style of glaciation and amount of landscape modification by glaciation and climate. On the eastern side of the Andes, the pre-glacial fluvial landscape remains largely intact, with well-developed fluvial valleys and dendritic drainage patterns (e.g. the valleys occupied by former outlet glaciers 14–25; Fig. 13). On the western side of the Andes, however, the pre-glacial fluvial landscape has been removed by glacial erosion and the landscape is dominated by short, wide, deep valleys (e.g. the valleys occupied by former outlet glaciers 9–13; Fig. 13). Another major difference between the east and the west of the Andes in this area is the distribution of cirques. Cirques are rare or absent in the catchments of the westward-flowing former outlet glaciers 9–13 (Fig. 13) but they are abundant on the flanks of the mountains above the valleys occupied by the eastward-flowing former outlet glaciers 14–25 (Fig. 13). The interpretation is that glaciation on the

ARTICLE IN PRESS 376

N.F. Glasser et al. / Quaternary Science Reviews 27 (2008) 365–390

ARTICLE IN PRESS N.F. Glasser et al. / Quaternary Science Reviews 27 (2008) 365–390

western side of the Andes was dominated by major piedmont outlet glaciers draining an ice cap/ice sheet, whereas on the eastern side of the Andes, cirque glaciation dominated and the outlet glaciers were ‘‘alpine’’ in style. In the dry area on the east side of the Andes there are large mesetas or plateaus compromised of lava flows that were probably not ice-covered at the LGM. Here, the mesetas have been uplifted with old material preserved on the uplands, and younger geomorphology in the lowlands between the mesetas where outlet glacier lobes were present. The absence of glacial lineations on the beds of these eastern glaciers, together with limited proglacial sandur development, indicates a much colder, drier climate to the east of the Andes at the LGM and the possibility that these eastern glaciers were cold-based or experienced relatively slow velocities compared to the glaciers on the maritime side of the Andes. It is also possible that these contrasts reflect differences in sediment availability between the west and east sides of the former ice sheet, with abundant deformable material to the west of the Andes in the lake basins (cf. Bentley, 1996) and limited deformable material to the east of the Andes. The overall inference is that the impact of glacial erosion has been far greater on the western side of the Andes than on the eastern side, and we speculate that this directly reflects a contrast between the more maritime, temperate climate on the west and the colder, drier climate on the eastern flank of the Andes. These contrasts in the style and extent of glaciation between the east and west of the Andes in agreement with modelling studies that indicate a marked contrast between the maritime and continental flanks of the modelled ice sheet, with positive mass balance exceeding 2 m in the west and declining tenfold to the east (Hulton et al., 2002). Dates for the expansion of the piedmont lobes into the lowland of the Chilean Lake District come from 14C dating of peat and organic deposits associated with moraines, kame terraces and meltwater channels (Mercer, 1976; Porter, 1981; Lowell et al., 1995; Bentley, 1997; Denton et al., 1999b). Mercer (1976) provided the first radiocarbon dates for the terminal moraines around the largest lake basin, at Lago Llanquihue, demonstrating that the innermost moraines belonged to the last glaciation and that there had been at least three, and probably four, prior advances. The earliest two advances occurred prior to 50,000 yr BP and prior to 39,000 yr BP based on 14C ages. The glacial maximum occurred at ca 19,450 yr BP and a final advance reached the western shore of Lago Llanquihue at 13,000 yr BP. Porter (1981) confirmed and refined the chronology with many more radiocarbon dates and demonstrated that the advances occurred before

377

30,000 yr BP, between 20,000 and 19,000 yr BP, and shortly after 13,000 yr BP. Recent work on the timing of Llanquihue glacial advances has yielded a more comprehensive picture of Lake District glaciation (Bentley, 1997; Denton et al., 1999b). Denton et al. (1999b) dated LGM positions to the interval 29,400–14,550 14C yr BP with a maximum extent ca 21,000 14C yr BP. The high-resolution radiocarbon chronology of Lowell et al. (1995) identified at least six glacier advances during the later part of the last glaciation. Radiocarbon dates on three glacier lobes (Llanquihue, Seno Reloncavi and Castro) have established that advances occurred at least once before 35,000, at 29,200, 26,900, 23,100 and 21,000, and between 14,500 and 14,700 yr BP. Unfortunately, no data exist for the ages of the glacier advances east of the Andes in this sector. The 14C dates in the northern Chilean Lake District indicate that the piedmont lobes reached their maximum extent during the LGM sometime between 29,400 and 14,550 14C yr BP (Bentley, 1997; Denton et al., 1999b). The southern lobes also advanced to maximum positions some time before 49,892 14C yr BP (Denton et al., 1999a, b). There is therefore reasonable certainty that the large arcuate moraines formed in front of glaciers 1–13 represent a number of separate advances, most recently during the LGM. The expansion of glaciers into the Chilean lake basins occurred during an interval of known global cooling, but it has also been suggested that the advance was driven largely by a northwards migration of the polar front, which resulted in a substantial increase in precipitation in the Lake District (Heusser, 1989c, 1990; Hulton et al., 1994; Lamy et al., 2004). 4.2. The central sector of the former Patagonian Ice Sheet West of the Andes, there is geomorphological evidence in the form of terminal moraines along the eastern and southern arms of Lago Presidente Rios for an independent ice mass on the Taitao Peninsula. Heusser (2002) also mapped these moraines and suggested that they formed sometime after 14,355 14C yr BP (based on a minimum date from nearby Laguna Stibnite provided by Lumley and Switsur, 1993). The arrangement of the moraines clearly indicates that a locally nourished ice cap developed on the peninsula, which was entirely independent of the nearby North Patagonian Icefield. The existence and preservation of these moraines at this latitude and thus close to sea level is difficult to explain for two reasons: (a) If the Taitao ice cap is LGM or pre-LGM in age then this implies severely restricted expansion of glaciers (o10 km of expansion) from the North Patagonian

Fig. 6. The glacial geomorphology of the area between former outlet glaciers 39 and 45. Dates for expansion of ice into the Lago General Carrera/Lago Buenos Aires lake basin indicate an LGM maximum at 23–16 ka, based on cosmogenic exposure age dates for the Fenix moraines (Kaplan et al., 2004; Douglass et al., 2006). A pre-LGM ice advance created the Moreno moraine complex at 4109 ka (Kaplan et al., 2005, 2006). Note that Wenzens (2006a, b) has argued on geomorphological grounds that both the Fenix and Moreno moraines are LGM in age. The innermost moraine (the Menucos moraine) has been dated to 14.47900 ka by Douglass et al. (2006) on the basis of cosmogenic exposure age dates.

ARTICLE IN PRESS 378

N.F. Glasser et al. / Quaternary Science Reviews 27 (2008) 365–390

ARTICLE IN PRESS N.F. Glasser et al. / Quaternary Science Reviews 27 (2008) 365–390

Icefield at the LGM. This is difficult to reconcile with dated geomorphological evidence elsewhere (e.g. the Chilean Lake District immediately to the north) where large west-flowing outlet glaciers developed at the LGM. It is also difficult to imagine a climatological setting where temperature and precipitation allowed the growth of a substantial ice cap on the low-lying Taitao Peninsula but little or no expansion of existing glaciers in the high-accumulation area of the Andes currently occupied by the North Patagonian Icefield. If the Taitao ice cap is LGM in age, one possible explanation is that outlet glaciers from the LGM Patagonian Ice Sheet were prevented from overrunning the Taitao Peninsula because of vigorous ice flow and associated iceberg calving in the deep NE-SW Elefantes Channel, which separates the peninsula from the mainland. This would allow a separate LGM ice mass to develop on the peninsula. (b) If the Taitao ice cap is not LGM or pre-LGM in age then it must have formed some time after the LGM. In this case, it most likely dates from a period of lower temperatures recorded in Antarctic ice cores, termed the ARC, at 14,800–12,700 cal. yr BP (Blunier et al., 1997; Raynaud et al., 2000) or from glacier expansion during the YDC (13,300–12,000 cal. yr BP; 11,400– 10,200 14C yr BP; Hajdas et al., 2003). Glacier expansion in this area during the YDC is, however, incompatible with palaecological evidence derived from lake cores on the peninsula that suggests no significant cooling occurred in the YDC (Bennett et al., 2000), although YDC cooling has been reported from palaeocological records further south on Tierra del Fuego (Heusser and Rabassa, 1987). Indeed, a radiocarbon-dated pollen sequence from nearby Laguna Stibnite on the Taitao Peninsula provides evidence for an early deglaciation (before 14,000 yr BP) and no evidence for a YDC climatic reversal in this region of Chile (Lumley and Switsur, 1993). Evidence from the chironomid (midge) assemblage record is equivocal, with changes in assemblages during the Lateglacial and Holocene indicating that the climate may have become cooler and drier during the YDC at nearby Laguna Stibnite (Massaferro and Brooks, 2002), but not 300 km to the north at Laguna Facil (Massaferro et al., 2005). Further dates are clearly required from the Lago Presidente Rios moraines in order to determine their age and palaeoclimatological significance. Based on the geomorphological record, we prefer the former scenario, in which the LGM Patagonian Ice Sheet was prevented from over-running the Taitao Peninsula because of the deep NE-

379

SW Elefantes Channel. This would allow a separate LGM ice mass to develop on the peninsula at this time without the need to invoke glacier advances during the ACR or YDC. East of the North Patagonian Icefield, glacial lineations indicate that ice discharge was concentrated into large, fast-flowing, topographically determined outlet glaciers (Glasser and Jansson, 2005). Dates for advances of these eastern outlet glaciers have been obtained from cosmogenic exposure age dating (Kaplan et al., 2004, 2005, 2006; Turner et al., 2005; Douglass et al., 2006), using 40Ar/39Ar and K–Ar dating (Singer et al., 2004), 14C dating (Wenzens, 2006b), and using a combination of cosmogenic exposure age and OSL dating (Glasser et al., 2006). The area at the eastern end of Lago General Carrera/Lago Buenos Aires in Argentina is one of the most comprehensively dated in this area of South America. Working eastward from the lake shore, the youngest moraines here (the Menucos moraines) have been dated to 14.4 ka (Douglass et al., 2006). The next moraine system to the east, the Fenix moraines, has been dated to the LGM at between 15 and 23 ka (Kaplan et al., 2004). Outside the Fenix moraines, the Moreno moraines have been dated to 140–150 ka (Kaplan et al., 2004). Outside these moraines are another set of moraines dated to o1016 ka but 4760 ka (Singer et al., 2004). The maximum extent of glaciation is dated to ca 1100 ka (Singer et al., 2004). Note, however, that Wenzens (2006a) has challenged these ages and argued on geomorphological grounds (mainly the relationship between the moraines and dated outwash terraces) that both the Fenix and Moreno moraines are in fact LGM in age. 4.3. The southern sector of the former Patagonian Ice Sheet The terminal moraines at the heads of Lago Viedma and Lago Argentino (Fig. 8) have been dated to the LGM by Wenzens (1999, 2005). Further west, at Puerto Bandera, the prominent moraines that protrude into Lago Argentino have been dated to between 10,390 and 13,000 14C yr BP (Strelin and Malagnino, 2000). Recession from the Puerto Bandera moraines is indicated by dates of 67407130 and 10,0007140 14C yr BP from within this limit (Mercer, 1968). To the south, around the margins of the contemporary South Patagonian Icefield in the Torres del Paine area, Marden and Clapperton (1995) defined the LGM extent at a point only ca 70 km from the contemporary icefield (Fig. 8). Younger moraines, located closer to the contemporary South Patagonian Icefield, are dated to 13.270.8 ka (Fogwill and Kubik, 2005) and between 9100 and 12,700 14C yr BP (Marden and Clapperton, 1995).

Fig. 7. The glacial geomorphology of the area between former outlet glaciers 46 and 49. The geomorphology indicates that large outlet glaciers advanced down the Lago Cochrane/Pueyrrendon, Belgrano, Nansen, Lago O’Higgins/San Martin and Lago Viedma Valleys both before and during the LGM. Interfluves south of Lago Argentino were probably covered by the outlet glaciers, but the presence of cirques and associated moraines on the interfluves north of Lago Argentino indicate these areas supported independent ice-covered at times. Location of figure is marked in Fig. 9.

ARTICLE IN PRESS 380

N.F. Glasser et al. / Quaternary Science Reviews 27 (2008) 365–390

ARTICLE IN PRESS N.F. Glasser et al. / Quaternary Science Reviews 27 (2008) 365–390

Large moraine complexes, consisting of multiple moraine sets and associated glacial lineations, are developed in the areas occupied by former outlet glacier in Seno Skyring, Seno Otway, Estrecho Magallenes and Bahı´ a Inu´til (Figs. 9–11). The LGM in this area is reasonably well established at 23–25 ka for a terminal moraine in the Magellan Strait (McCulloch et al., 2005) and 18–20 ka in Bahia Inu´til (McCulloch et al., 2005; Kaplan et al., 2007) (Fig. 10). A deglacial recessional stage of the LGM (between 10,315 and 12,700 14C yr BP) on Isla Dawson has also been reported by Rabassa et al. (1986). Wherever large moraine complexes lie outside the LGM glaciers (e.g. the former outlet glacier in Seno Otway; Fig. 11) there is clear evidence for pre-LGM advances, although these remain undated. Well-developed glacial lineations occur in association with all moraine complexes and in places these can be traced to pre-LGM ice margins, providing evidence that the former outlet glaciers were largely wet-based. Marginal meltwater channels are common features along the lateral margins of the former outlet glaciers (e.g. the former outlet glacier in Seno Otway; Fig. 11; cf. Benn and Clapperton, 2000). Glacial lineations aligned NW–SE indicate sustained and vigorous ice flow towards the SE through Seno Almirantazgo towards Lago Fagnano (Fig. 12). Cirques on the northern flank of Seno Almirantazgo also appear to have been over-ridden in the same direction, suggesting this was a widespread and prolonged event. However, arcuate end moraines and associated northward-directed sandar from former outlet glaciers 59–61 indicate ice flow at 90 degrees to this direction from the S–N. Landforms created during the NW–SE ice flow event clearly truncate those formed during the S–N event, suggesting that the NW–SE event is the more recent of the two. The inference is that the moraines on the north side of Seno Almirantazgo formed during an initial advance of glaciers out of Cordillera Darwin across the fjord. During the later event, with an ice dispersal centre to the NW (presumably under a thicker ice sheet during the LGM), ice advanced directly down Seno Almirantazgo, removing traces of this earlier event from within the fjord but allowing preservation of the moraines from former outlet glaciers 59–61 at higher elevations. If the NW–SE ice flow is LGM in age, then the S to N event must pre-date the LGM. We speculate that this represents an early phase in ice-sheet build-up, possibly during icesheet inception, when maximum accumulation was centred over Cordillera Darwin. Finally, we note that there is evidence of glaciation (glacial lineations and meltwater channels) extending nearly all the way to the southern tip of South America on Isla Grande de Tierra del Fuego (Fig. 9), supporting the

381

sedimentological studies of Bujalesky et al. (1997) and Malagnino and Olivero (1999), who concluded that the whole of Isla Grande de Tierra del Fuego was covered by a former Patagonian Ice Sheet. However, we acknowledge that further work, especially field study, is required in this area to establish the absolute number and extent of glacier advances that took place in this area (Rabassa et al., 2000; Coronato et al., 2004; Kaplan et al., 2007). 4.4. Regional landform distribution 4.4.1. Cirques Glacial cirques are found in the mountainous regions throughout the study area. Cirques are particularly welldeveloped in the Andes in the Northern and Central sectors in the area between the North Patagonian Icefield and the Chilean Lake District (Figs. 3 and 4). Here cirques are developed on both the eastern and western flanks of the Andes. Cirques face generally east or south-east on the eastern flank of the Andes and west or south-west on the western flank of the Andes, although there is considerable local variation because of the influence of topography. Further south, there are concentrations of cirques in the area to the west of the South Patagonian Icefield (Fig. 9). In the extreme southern part of South America southfacing cirques are developed on the mountains that flank Seno Almirantazgo and Lago Fagnano (Fig. 10). 4.4.2. Trimlines Trimlines (sub-horizontal lines on valley sides separating areas of non-vegetated and vegetated land or areas covered by different types of vegetation) are developed close to the snouts of many contemporary glaciers throughout the study area. In many places, they merge down-glacier with lateral and terminal moraines, marking recent (post ‘‘Little Ice Age’’) glacier recession. These trimlines are most apparent around the snouts of the small glaciers that occur in the area between the North Patagonian Icefield and the Chilean Lake District (Figs. 3 and 4). Trimlines are also developed around the snouts of the eastern outlet glaciers of both the North and South Patagonian Icefields (Fig. 4). 4.4.3. Meltwater channels Meltwater channels occur throughout the study area at a variety of spatial scales. Close to the contemporary glaciers are small meltwater channels that mark recent recession of these glaciers. Further from the contemporary glaciers, meltwater channels are associated with large terminal moraine complexes, for example, those that formed around the margins of the former outlet glaciers on the eastern side

Fig. 8. The glacial geomorphology of the area between former outlet glaciers 49 and 53. Dates for expansion of outlet glaciers from the Southern Patagonian Icefield in the Torres del Paine area are based on 14C dates obtained by Marden and Clapperton (1995) and Marden (1993, 1997) and on the basis of cosmogenic exposure age dates obtained by Fogwill and Kubik (2005). Further north, a recessional stage of the Lago Argentino palaeoglacier at Puerto Bandera has been dated to between 13,000 and 10,390 14C yr BP by Strelin and Malagnino (2000). Location marked in Fig. 9.

ARTICLE IN PRESS 382

N.F. Glasser et al. / Quaternary Science Reviews 27 (2008) 365–390

Fig. 9. The glacial geomorphology of the Southern sector of the former Patagonian Ice Sheet. Numbers indicate former outlet glaciers identified in this study. Inset boxes indicate locations of detailed maps.

of the North and South Patagonian Icefields (Figs. 6 and 7). Lateral and marginal meltwater channels are also common features along the lateral margins of the former outlet glaciers (e.g. the former outlet glaciers in the Magellan Strait and Seno Otway; Fig. 11). Here the channels are sub-parallel to the former glacier margins, often merging down-glacier into moraine complexes.

4.5. Reconstruction of palaeoglaciological events Major moraine systems, marking the limits of former glacier expansion, occur over the entire length of Patagonia between latitudes 381S and 561S (Fig. 14A). These moraine systems are particularly well-developed to the east of the Andes, where multiple moraine sets occur within many of

ARTICLE IN PRESS N.F. Glasser et al. / Quaternary Science Reviews 27 (2008) 365–390

383

Fig. 10. The glacial geomorphology of the area between former outlet glaciers 57 and 63. LGM moraines are labelled on the basis of cosmogenic exposure age dates obtained by McCulloch et al. (2005) and Kaplan et al. (2007). Location marked in Fig. 9.

ARTICLE IN PRESS 384

N.F. Glasser et al. / Quaternary Science Reviews 27 (2008) 365–390

Fig. 11. Landsat sub-scene (left panel) and interpretation (right panel) showing the glacial geomorphology of the area around the former outlet glacier in Seno Otway. Location marked in Fig. 9. Multiple moraine systems indicate a number of outlet glacier advances through Seno Otway and the Magellan Strait.

the East–West trending valleys. Here, major eastwardflowing outlet glaciers from the ice-sheet occupied these valleys. Upland areas surrounding the termini of the outlet glaciers (e.g. around Lago Buenos Aires) were not icecovered. However, closer to the ice-sheet centre the uplands contain cirques and associated moraines on the interfluves between these fast-flowing outlet glaciers, indicating that these upland areas supported independent glaciers during the LGM (Fig. 7). However, the lack of evidence for widespread subglacial modification on the interfluves (e.g. the absence of glacial lineations) indicates that these areas were probably covered in thin, cold-based ice with low velocities. Interestingly, the largest moraines systems are those developed in the southern sector of the study area around the Fuegan Andes, an area of limited contemporary glacierisation, and not those close to the North and South Patagonian Icefields, which are the foci of contemporary

glacierisation. Moraine systems in the region of the Fuegan Andes also occur at larger distances (up to 300 km) from the Andes than moraine systems in the region of the contemporary North and South Patagonian Icefields. Clapperton et al. (1995) have speculated that these greater glacier lengths reflect the influence of subglacial deforming bed conditions in the south, allowing glaciers to expand long distances from their accumulation areas as lowgradient outlet lobes. However, it is also possible that the greater glacier lengths in the south are a function simply of the colder climate here and enhanced accumulation rates under full-glacial climates. Using the distribution of the distal moraine systems, the patterns of glacial lineations identified in satellite images, and the topographic context, it is possible to infer the patterns of ice flow and ice limits at the maximum extent of glaciation in Patagonia (Fig. 14B). The age of this event is unknown but it most likely dates from the ‘‘Great

ARTICLE IN PRESS N.F. Glasser et al. / Quaternary Science Reviews 27 (2008) 365–390

385

Fig. 12. Landsat sub-scene (left panel) and interpretation (right panel) showing the glacial geomorphology of the area between the Cordillera Darwin (glacierised area in the bottom of the image) and north of Seno Almirantazgo. Location marked in Fig. 9. Although there is a strong structural bedrock control on the direction of glacial lineations, the glacial lineations aligned NW–SE indicate sustained and vigorous ice flow towards the SE through Seno Almirantazgo. Arcuate end moraines and associated northward-directed sandar from former outlet glaciers 59–61 indicate ice flow at 901 to this direction from the S–N. Our interpretation is that the moraines on the north side of Seno Almirantazgo formed during an initial advance of glaciers out of Cordillera Darwin across the fjord. During a later event (LGM?), glaciers with an ice dispersal centre to the NW advanced directly down Seno Almirantazgo forming the glacial lineations.

Patagonian Glaciation’’ (Mercer, 1976), dated to sometime between 1.1 and 2.3 Ma (Singer et al., 2004; Rabassa et al., 2005). It is unlikely that all outlet glaciers reached their maximum extent at the same time so this reconstruction remains speculative, but it does provide some insight into the form of the maximum glaciation of Patagonia. Using the distribution of published dates, we have also been able to reconstruct the maximum LGM ice extent in Patagonia (Fig. 14C). In this reconstruction, the LGM ice margin has been drawn at securely dated positions obtained from published studies (see Sections 4.1–4.3). In valleys where the LGM limit has not yet been securely dated, the ice margin has been drawn at the innermost large

moraine complex. Again, we recognise that not all lobes reached their maximum extent at exactly the same time because of changes in accumulation and ablation related to the migration of the precipitation-bearing south westerlies during ice-sheet growth and decay (McCulloch et al., 2000). However, this reconstruction is important because within the known LGM limits are numerous other large moraine systems that are clearly younger than LGM in age. The age of these moraines is unknown but, since many of them lie well outside the established maximum Neoglacial positions, the possibility that they reflect a return to glacial climates during the YDC and/or ARC cannot be discounted.

ARTICLE IN PRESS 386

N.F. Glasser et al. / Quaternary Science Reviews 27 (2008) 365–390

Fig. 13. SRTM DEM (left panel) and geomorphological interpretation of the same area from satellite imagery (right panel) showing the transition between a predominantly fluvial landscape with dendritic drainage patterns and cirques on higher land (in the east of the image) and a glacial landscape with shorter, deeper and wider valleys and over-deepened basins (in the west of the image). Location marked in Fig. 3.

5. Concluding statements In this paper, we have presented new mapping of the glacial geomorphology of the whole of southern South America between latitudes 381S and 561S, approximately the area covered by the former Patagonian Ice Sheets. Features mapped include glacial lineations, moraines, meltwater channels, trimlines, sandur and cirques. We draw the following conclusions. 1. Glacial lineations are developed in many areas of the bed of the former ice sheet. These glacial lineations indicate that in these areas the ice sheet was largely warm-based. The distribution of glacial lineations also indicates that ice discharge from the former ice sheet was concentrated into large, fast-flowing, topographically determined outlet glaciers. This is especially the case to the east of the Andes. 2. Moraines and associated sandar often mark the former extent of outlet glaciers of the Patagonian Ice Sheet. The largest moraines systems are those developed in

the central and southern sectors of the study area to the east of the Andes around Lago Buenos Aires, Lago Argentino and Lago Viedma, but there are also large moraines present in the Fuegan Andes around Bahia Inutil and the Magellan Strait. 3. Meltwater channels occur throughout the study area at a variety of sizes. They are often associated with large terminal moraine complexes, for example, those that formed around the margins of the former outlet glaciers on the eastern side of the North and South Patagonian Icefields. Lateral and marginal meltwater channels are also common features along the margins of the former outlet glaciers (e.g. the former outlet glaciers in the Magellan Strait and Seno Otway) where meltwater channels are sub-parallel to the former glacier margins. 4. Cirques are found in the mountainous regions throughout the study area on both the eastern and western flanks of the Andes. Cirques face generally east or south-east on the eastern flank of the Andes and west or south-west on the western flank of the Andes,

ARTICLE IN PRESS N.F. Glasser et al. / Quaternary Science Reviews 27 (2008) 365–390

387

Fig. 14. Reconstructions of glacier extent in Patagonia based on the geomorphological mapping presented in this paper. (A) The major moraine systems of Patagonia. (B) Inferred patterns of ice flow and ice limits in Patagonia. Ice flow directions are based on patterns of glacial lineations identified in satellite images and topographic context in SRTM DEM. Note that it is possible that not all lobes reached their maximum extent at the same time. (C) Reconstruction of LGM ice extent in Patagonia. Wherever possible, the LGM ice margin has been drawn at securely dated positions. In valleys where the LGM limit has not been securely dated, the ice margin has been drawn at the innermost large moraine. Note that it is possible that not all lobes reached their maximum extent at the same time. Also indicated are the positions of other large mapped moraines younger than LGM in age.

although there is considerable local variation because of the influence of topography. 5. Trimlines are developed close to the snouts of many contemporary glaciers throughout the study area. In many places, they merge down-glacier with lateral and terminal moraines, marking recent (post ‘‘Little Ice Age’’) glacier recession. These trimlines are most apparent around the snouts of the small glaciers that occur in the area between the North Patagonian Icefield and the Chilean Lake District. but trimlines are also developed around the snouts of the eastern outlet glaciers of both the North and South Patagonian Icefields. 6. There are strong contrasts in the style and extent of glaciation over short distances. For example, glaciation in the Chilean Lake District was severely restricted on the eastern side of the Andes in comparison with the western side, where large piedmont lobes formed at the LGM. Equally, some glaciers draining the western side of the contemporary South Patagonian Icefield only advanced ca 70 km to their LGM maximum extent, whilst others advanced over 300 km from their source

areas. Further work is required to determine whether this reflects external (i.e. climatological) controls or internal (i.e. glaciodynamic) controls on former glacier expansion. 7. The palaeoglaciology of the former Patagonian Ice Sheets was strongly dominated by topography. Along the eastern flank of the Andes, outlet glaciers repeatedly followed the same discharge routes during successive glaciations. The landform evidence indicates that these outlet glaciers were fast-flowing and that they drained significant proportions of the former ice sheet. Upland areas surrounding the termini of some of the outlet glaciers (e.g. around Lago Buenos Aires) were not ice-covered at the LGM. However, closer to the ice-sheet centre the uplands contain cirques and associated moraines on the interfluves between these fast-flowing outlet glaciers, indicating that these upland areas supported independent glaciers during the LGM. 8. There are numerous, as yet undated, moraine systems in this area of South America. Some of these moraine systems lie inside the LGM limit, so the occurrence of a Lateglacial event or glacier expansion during the ACR

ARTICLE IN PRESS 388

N.F. Glasser et al. / Quaternary Science Reviews 27 (2008) 365–390

or YDC cannot be discounted. Dating the moraine systems within the LGM limit is clearly a priority in order to resolve the issue of whether or not the ACR affected this area and whether or not the YDC was an inter-hemispheric event. 9. There is geomorphological evidence that an independent ice mass developed close to sea level on the Taitao Peninsula to the west of the North Patagonian Icefield. The age of this event is unclear, but it probably reflects a period of glacier expansion at some point after the LGM. 10. The geomorphological data set compiled in this paper provides a test for numerical ice-sheet models of glaciations in southern South America between latitudes 381S and 561S.

Acknowledgements This work was supported by a Leverhulme Trust Research Fellowship to NFG. We thank journal referees Mike Kaplan and David Sugden for their reviews.

References Aceituno, P., 1988. On the functioning of the Southern oscillation in the South American sector, Part I: surface climate. Monthly Weather Review 116, 505–524. Allan, R., Lindesay, J., Parker, D., 1995. El Nin˜o Southern Oscillation and Climatic Variability. CSIRO, Collingwood, Australia. Andersen, B.G., Denton, G.H., Lowell, T.V., 1999. Glacial geomorphologic maps of Llanquihue drift in the area of the southern lake district, Chile. Geografiska Annaler 81A, 155–166. Aniya, M., 1995. Holocene glacial chronology in Patagonia: Tyndall and Upsala Glaciers. Arctic, Antarctic and Alpine Research 27, 311–322. Aniya, M., 1999. Recent glacier variations of the Hielos Patagonicos, South America, and their contribution to sea-level change. Arctic, Antarctic and Alpine Research 31, 165–173. Ashworth, A.C., Markgraf, V., Villagran, C., 1991. Late Quaternary climatic history of the Chilean Channels based on fossil pollen and beetle analyses, with an analysis of the modern vegetation and pollen rain. Journal of Quaternary Science 6, 279–291. Benn, D.I., Clapperton, C.M., 2000. Pleistocene glacitectonic landforms and sediments around central Magellan Strait, southernmost Chile: evidence for fast outlet glaciers with cold-based margins. Quaternary Science Reviews 19, 591–612. Bennett, K.D., Haberle, S.G., Lumley, S.H., 2000. The Last Glacial–Holocene transition in Southern Chile. Science 290, 325–328. Bentley, M., 1996. The role of lakes in moraine formation, Chilean Lake District. Earth Surface Processes and Landforms 21, 493–507. Bentley, M., 1997. Relative and radiocarbon chronology of two former glaciers in the Chilean Lake District. Journal of Quaternary Science 12, 25–33. Bentley, M., Sugden, D., Hulton, N., McCulloch, R., 2005. The landforms and pattern of deglaciation in the Strait of Magellan and Bahı´ a Inu´til, southernmost South America. Geografiska Annaler 87A, 313–334. Blunier, T., Brook, E., 2001. Timing of millenial-scale climate change in Antarctica and Greenland during the Last Glacial Period. Science 291, 109–112. Blunier, T., Schwander, J., Stauffer, B., Stocker, T.F., Da¨llenbach, A., Indermu¨hle, A., Tschumi, J., Chappellaz, J., Raynaud, D., Barnola, J.-M., 1997. Timing of the Antarctic Cold Reversal and the

atmospheric CO2 increase with respect to Younger Dryas Event. Geophysical Research Letters 24, 2683–2686. Boulton, G.S., Clark, C.D., 1990. A highly mobile Laurentide ice sheet revealed by satellite images of glacial lineations. Nature 346, 813–817. Boulton, G.S., Dongelmans, P., Punkari, M., Broadgate, M., 2001. Palaeoglaciology of an ice sheet through a glacial cycle: the European ice sheet through the Weichselian. Quaternary Science Reviews 20 (4), 591–625. Bujalesky, G.G., Heusser, C.J., Coronato, A.M., Roig, C.E., Rabassa, J.O., 1997. Pleistocene glaciolacustrine sedimentation at Lago Fagnano, Andes of Tierra del Fuego, Southernmost South America. Quaternary Science Reviews 16, 767–778. Caldenius, C.C., 1932. Las glaciaciones cuaternarios en la Patagonia y Tierra del Fuego. Geografiska Annaler 14, 1–164 (English summary, pp. 144–157). Clapperton, C.M., Sudgen, D.E., Kaufman, D.S., McCulloch, R.D., 1995. The last glaciation in Central Magellan Strait, Southernmost Chile. Quaternary Research 44, 133–148. Coronato, A.M., 1995. The last Pleistocene Glaciation in tributary valleys of the Beagle Channel, Southernmost South America. Quaternary of South America and Antarctic Peninsula 9, 153–171. Coronato, A., Martinez, O., Rabassa, J., 2004. Glaciations in Argentine Patagonia, Southern South America. In: Ehlers, J., Gibbard, P.L. (Eds.), Pleistocene Glaciations: Extent and Chronology. INQUA Working Group 5, Elsevier, Amsterdam, pp. 49–67. Diaz, H.F., Markgraf, V., 2000. El Nin˜o and the Southern Oscillation. Cambridge University Press, Cambridge, MA. Denton, G.H., Heusser, C.J., Lowell, T.V., Moreno, P.I., Andersen, B.G., Heusser, L.E., Schlu¨chter, C., Marchant, D.R., 1999a. Interhemispheric linkage of paleoclimate during the last glaciation. Geografiska Annaler 81A, 107–153. Denton, G., Lowell, T., Heusser, C., Schlu¨chter, C., Andersen, B., Heusser, L., Moreno, P., Marchant, R., 1999b. Geomorphology, stratigraphy and radiocarbon chronology of Llanquihue drift in the area of the Southern Lake District, Seno Reloncavı´ and Isla de Chiloe´, Chile. Geografiska Annaler 81A, 167–229. Douglass, D.C., Singer, B.S., Kaplan, M.R., Ackert, R.P., Mickelson, D.M., Caffee, M.W., 2005. Evidence of early Holocene glacial advances in Southern South America from cosmogenic surfaceexposure dating. Geology 33, 237–240. Douglass, D.C., Singer, B.S., Kaplan, M.R., Mickleson, D.M., Caffee, M.W., 2006. Cosmogenic nuclide surface exposure dating of boulders on last-glacial and late-glacial moraines, Lago Buenos Aires, Argentina: interpretative strategies and paleoclimate implications. Quaternary Geochronology 1, 43–58. Escobar, F., Vidal, F., Garı´ n, C., Naruse, R., 1992. Water balance in the Patagonian Icefield. In: Naruse, R., Aniya, M. (Eds.), Glaciological Researches in Patagonia, 1990. Japanese Society of Snow and Ice, pp. 109–119. Fogwill, C.J., Kubik, P.W., 2005. A glacial stage spanning the Antarctic cold reversal in Torres del Paine (511S), Chile, based on preliminary cosmogenic exposure ages. Geografiska Annaler 87A, 403–408. Glasser, N.F., Jansson, K.N., 2005. Fast-flowing outlet glaciers of the Last Glacial maximum Patagonian Icefield. Quaternary Research 63, 206–211. Glasser, N.F., Harrison, S., Winchester, V., Aniya, M., 2004. Late Pleistocene and Holocene palaeoclimate and glacier fluctuations in Patagonia. Global and Planetary Change 43, 79–101. Glasser, N.F., Jansson, K.N., Harrison, S., Rivera, A., 2005. Geomorphological evidence for variations of the North Patagonian Icefield during the Holocene. Geomorphology 71, 263–277. Glasser, N.F., Harrison, S., Ivy-Ochs, S., Duller, G.A.T., Kubik, P., 2006. Evidence from the Rio Bayo valley on the extent of the North Patagonian Icefield during the Late Pleistocene–Holocene transition. Quaternary Research 65, 70–77. Hajdas, I., Bonani, G., Moreno, P.I., Ariztegui, D., 2003. Precise radiocarbon dating of Late-Glacial cooling in mid-latitude South America. Quaternary Research 59, 70–78.

ARTICLE IN PRESS N.F. Glasser et al. / Quaternary Science Reviews 27 (2008) 365–390 Harrison, S., 1999. The problem with landscape: some philosophical and practical questions. Geography 84 (4), 355–363. Harrison, S., 2004. The Pleistocene glaciations of Chile. In: Ehlers, J., Gibbard, P.L. (Eds.), Pleistocene Glaciations: Extent and Chronology. INQUA Working Group 5, Elsevier, Amsterdam, pp. 89–103. Hartley, A.J., 2003. Andean uplift and climate change. Journal of Geological Society of London 160, 7–10. Heusser, C., 1989a. Climate and chronology of Antarctica and adjacent South America over the past 30,000 yr. Palaeogeography, Palaeoclimatology, Palaeoecology 76, 31–37. Heusser, C., 1989b. Late Quaternary vegetation and climate of southern Tierra del Fuego. Quaternary Research 31, 396–406. Heusser, C.J., 1989c. Southern westerlies during the last glacial maximum. Quaternary Research 31, 423–425. Heusser, C., 1998. Deglacial palaeoclimate of the American sector of the Southern Ocean: Late Glacial–Holocene records from the latitude of Canal Beagle (551S), Argentine Tierra del Fuego. Palaeogeography, Palaeoclimatology, Palaeoecology 141, 277–301. Heusser, C.J., 1990. Ice age vegetation and climate of subtropical Chile. Palaeogeography, Palaeoclimatology, Palaeoecology 80, 107–127. Heusser, C.J., 1993. Late-glacial of southern South America. Quaternary Science Reviews 12, 345–350. Heusser, C.J., 2002. On glaciation of the southern Andes with special reference to the Penı´ nsula de Taitao and adjacent Andean Cordillera (461300 S). Journal of South American Earth Sciences 15, 577–589. Heusser, C., 2003. Ice Age Southern Andes. A chronicle of palaeocological events. In: Jim, Rose (Ed.), Developments in Quaternary Science, vol. 3. Elsevier, Amsterdam, p. 240. Heusser, C.J., Rabassa, J., 1987. Cold climatic episode of Younger Dryas age in Tierra del Fuego. Nature 328, 609–611. Heusser, C.J., Streeter, S.S., 1980. A temperature and precipitation record of the past 16,000 years in southern Chile. Science 210, 1345–1347. Hoganson, J.W., Ashworth, A.C., 1992. Fossil beetle evidence for climatic change 18,000–10,000 years BP in south-central Chile. Quaternary Research 37, 101–116. Hubbard, A., Hein, A.S., Kaplan, M.R., Hulton, N.R.J., Glasser, N.F., 2005. A modelling reconstruction of the late glacial maximum ice sheet and its deglaciation in the vicinity of the Northern Patagonian Icefield, South America. Geografiska Annaler 87A, 375–391. Hulton, N.R.J., Sugden, D.E., Payne, A.J., Clapperton, C.M., 1994. Glacier modelling and the climate of Patagonia during the last glacial maximum. Quaternary Research 42, 1–19. Hulton, N.R.J., Purves, R.S., McCulloch, R.D., Sugden, D.E., Bentley, M.J., 2002. The Last Glacial maximum and deglaciation in Southern South America. Quaternary Science Research 21, 233–241. Jansson, K.N., Glasser, N.F., 2005. Using Landsat 7 ETM+ imagery and digital terrain models for mapping glacial lineaments on former ice sheet beds. International Journal of Remote Sensing 26, 3931–3941. Kaiser, J., Lamy, F., Arz, H.W., Hebbeln, D., 2007. Dynamics of the millennial-scale sea surface temperature and Patagonian Ice Sheet fluctuations in southern Chile during the last 70 kyr (ODP Site 1233). Quaternary International 161, 77–89. Kaplan, M.R., Ackert, R.P., Singer, B.S., Douglass, D.C., Kurz, M.D., 2004. Cosmogenic nuclide chronology of millenial-scale glacial advances during O-isotope Stage 2 in Patagonia. Bulletin of the Geological Society of America 116, 308–321. Kaplan, M.R., Douglass, D.C., Singer, B.S., Ackert, R.P., Caffee, M.W., 2005. Cosmogenic nuclide chronology of pre-last glacial maximum moraines at Lago Buenos Aire, 461S, Argentina. Quaternary Research 63, 301–315. Kaplan, M.R., Singer, B.S., Douglass, D.C., Ackert, R.P., Caffee, M.W., 2006. Reply to Wenzens, G. 2006. Comment on: cosmogenic nuclide chronology of pre-last glacial maximum moraines at Lago Buenos Aire, 461S, Argentina [Letter to the Editor]. Quaternary Research 66, 367–369. Kaplan, M.R., Coronato, A., Hulton, N.R.J., Rabassa, J.O., Kubik, P.W., Freeman, S.P.H.T., 2007. Cosmogenic nuclide measurements in

389

southernmost South America and implications for landscape change. Geomorphology 87, 284–301. Kleman, J., Hattestrand, C., Borgstrom, I., Stroeven, A.P., 1997. Fennoscandian paleoglaciology reconstructed using a glacial geological inversion model. Journal of Glaciology 43, 283–299. Lamy, F., Kaiser, J., Ninnemann, U., Hebbeln, D., Arz, H.W., Stoner, J., 2004. Antarctic timing of surface water changes off Chile and Patagonian ice sheet response. Science 304, 1959–1962. Lumley, S.H., Switsur, R., 1993. Late Quaternary chronology of the Taitao Peninsula, Southern Chile. Journal of Quaternary Science 8, 161–165. Lowell, T.V., Heusser, C.J., Andersen, B.G., Moreno, P.I., Hauser, A., Heusser, L.E., Schlu¨chter, C., Marchant, D.R., Denton, G.H., 1995. Interhemispheric correlation of Late Pleistocene glacial events. Science 269, 1541–1549. Malagnino, E.C., Olivero, E.B., 1999. New evidence of the total glaciation of the Isla Grande de Tierra del Fuego. Journal of South American Earth Sciences 12, 343–348. Marden, C.J., 1993. Lateglacial and Holocene variations of the Grey Glacier, an outlet of the South Patagonian Icefield. Scottish Geographical Magazine 109, 27–31. Marden, C.J., 1997. Late-glacial fluctuations of South Patagonian icefield, Torres del Paine National Park, southern Chile. Quaternary International 38/39, 61–68. Marden, C.J., Clapperton, C.M., 1995. Fluctuations of the Southern Patagonian Icefield during the last glaciation and the Holocene. Journal of Quaternary Science 10, 197–209. Markgraf, V., 1991. Younger Dryas in Southern South America? Boreas 20, 63–69. Markgraf, V., 1993. Paleoenvironments and paleoclimates in Tierra del Fuego and southernmost Patagonia, South America. Palaeogeography, Palaeoclimatology, Palaeoecology 102, 53–68. Massaferro, J., Brooks, S.J., 2002. Response of chironomids to Late Quaternary environmental change in the Taitao Peninsula, southern Chile. Journal of Quaternary Science 17, 101–111. Massaferro, J., Brooks, S.J., Haberle, S.G., 2005. The dynamics of chironomid assemblages and vegetation during the Late Quaternary at Laguna Facil, Chonos Archipelago, Southern Chile. Quaternary Science Reviews 24, 22522–25101. McCulloch, R.D., Bentley, M.J., Purves, R.S., Sugden, D.E., Hulton, N.R.J., Clapperton, C., 2000. Climatic inferences from glacial and palaeoecological evidence at the last glacial termination, Southern South America. Journal of Quaternary Science 15, 409–417. McCulloch, R., Fogwill, C., Sudgen, D., Bentley, M., Kubik, P., 2005. Chronology of the Last Glaciation in Central Strait of Magellan and Bahı´ a Inu´til, Southernmost South America. Geografiska Annaler 87A (2), 289–312. Meglioli, A., 1992. Glacial Geology of Southernmost Patagonia, the Strait of Magellan and northern Tierra del Fuego. PhD Thesis, Lehigh University, Bethlehem, USA. 216pp. Mercer, J.H., 1965. Glacier variations in Southern Patagonia. Geographical Review 55, 390–413. Mercer, J.H., 1968. Variations of some Patagonian glaciers since the LateGlacial. American Journal of Science 266, 91–109. Mercer, J.H., 1969. Glaciation in Southern Argentina more than two million years ago. Science 164, 823–825. Mercer, J.H., 1976. Glacial history of southernmost South America. Quaternary Research 6, 125–166. Moreno, P.I., 1997. Vegetation and climate near lago Llanquihue in the Chilean lake District between 20,200 and 9500 14C yr BP. Journal of Quaternary Science 12, 485–500. Mo¨rner, N.A., Sylwan, C., 1989. Magnetostratigraphy of the Patagonian moraine sequence at Lago Buenos Aires. Journal of South American Earth Sciences 2, 385–389. Porter, S.C., 1981. Pleistocene glaciation in the Southern Lake District of Chile. Quaternary Research 16, 263–292. Porter, S.C., Clapperton, C.M., Sudgen, D.E., 1992. Chronology and dynamics of deglaciation along and near the Strait of Magellan,

ARTICLE IN PRESS 390

N.F. Glasser et al. / Quaternary Science Reviews 27 (2008) 365–390

southernmost South America. Sveriges Geologiska Underso¨kning, Series Ca 81, 233–239 (Stockholm). Rabassa, J., Heusser, C., Stuckenrath, R., 1986. New data on Holocene Sea transgression in the Beagle Channel: Tierra del Fuego, Argentina. Quaternary of South America and Antarctic Peninsula 4, 291–309. Rabassa, J., Heusser, C., Rutter, N., 1990. Late-Glacial and Holocene of Argentine Tierra del Fuego. Quaternary of South America and Antarctic Peninsula 7, 327–351. Rabassa, J., Coronato, A.M., Bujalesky, G., Roig, C., Salemme, M., Meglioli, A., Heusser, C., Gordillo, S., Roig Jun˜ent, F., Borromei, A., Quatrocchio, M., 2000. Quaternary of Tierra del Fuego, Southernmost South America: an updated review. Quaternary International 68–71, 217–240. Rabassa, J., Coronato, A.M., Salemme, M., 2005. Chronology of the Late Cenozoic Patagonian glaciations and their correlation with biostratigraphic units of the Pampean region (Argentina). Journal of South American Earth Sciences 20, 81–103. Raynaud, D., Barnola, J.-M., Chappellaz, J., Blunier, T., Indermu¨hle, A., Stauffer, B., 2000. The ice record of greenhouse gases: a view in the context of future changes. Quaternary Science Reviews 19, 9–17. Rivera, A., Benham, T., Casassa, G., Bamber, J., Dowdeswell, J.A., 2007. Ice elevation and areal changes of glaciers from the Northern Patagonia Icefield, Chile. Global and Planetary Change 59, 126–137. Schaefer, J.M., Denton, G.H., Barrell, D.J.A., Ivy-Ochs, S., Kubik, P.W., Andersen, B.G., Phillips, F.M., Lowell, T.V., Schlu¨chter, C., 2006. Near-synchronous interhemispheric termination of the Lastglacial maximum in mid-latitudes. Science 312, 1510–1513. Singer, B.S., Ackert, R.P., Guillou, H., 2004. 40Ar/39Ar and K–Ar chronology of Pleistocene glaciations in Patagonia. GSA Bulletin 116, 434–450. Strelin, J.A., Malagnino, E.C., 2000. Late-glacial history of Lago Argentino, Argentina, and age of the Puerto Bandera Moraines. Quaternary Research 54, 339–347. Sugden, D.E., Hulton, N.R.J., Purves, R.S., 2002. Modelling the inception of the Patagonian ice sheet. Quaternary International 95–96, 55–64. Sugden, D.E., Bentley, M.J., Fogwill, C.J., Hulton, N.R.J., McCulloch, R.D., Purves, R.S., 2005. Late-glacial glacier events in southernmost South America: a blend of ‘Northern’ and ‘Southern’ hemispheric climate signals? Geografiska Annaler 87A, 273–288. Summerfield, M.A., 2005. A tale of two scales, or the two geomorphologies. Transactions of the Institute of British Geographers 30 (4), 402–415.

Turner, K.J., Fogwill, C.J., McCulloch, R.D., Sugden, D.E., 2005. Deglaciation of the eastern flank of the North Patagonian Icefield and associated continental-scale lake diversions. Geografiska Annaler 87A, 363–374. Villalba, R., Cook, E.R., D’Arrigo, R.D., Jacoby, G.C., Jones, P.D., Salinger, M.J., Palmer, J., 1997. Sea-level pressure variability around Antarctica since AD 1750 inferred from subantarctic tree-ring records. Climate Dynamics 13, 375–390. Wenzens, G., 1999. Fluctuations of outlet and valley glaciers in the Southern Andes (Argentina) during the past 13,000 years. Quaternary Research 51, 238–247. Wenzens, G., 2000. Pliocene piedmont glaciation in the Rio Shehuen Valley, Southeast Patagonia, Argentina. Arctic, Antarctic and Alpine Research 32, 46–54. Wenzens, G., 2002. The influence of tectonically derived relief and climate on the extent of the last Glaciation east of the Patagonian ice fields (Argentina, Chile). Tectonophysics 345, 329–344. Wenzens, G., 2003. Comment on: ‘‘The Last Glacial Maximum and deglaciation in Southern South America’’. Quaternary Science Reviews 22, 751–754. Wenzens, G., 2004. Comment on: ‘‘Modelling the inception of the Patagonian Ice Sheet’’. Quaternary International 112, 105–109. Wenzens, G., 2005. Glacier advances east of the Southern Andes between the Last Glacial Maximum and 5000 BP compared with lake terraces of the endorrheic Lago Cariel (491S, Patagonia, Argentina. Zeitschrift fur Geomorphologie 49, 433–454. Wenzens, G., 2006a. Comment on: Cosmogenic nuclide chronology of pre-last glacial maximum moraines at Lago Buenos Aires, 461S, Argentina [Letter to the Editor]. Quaternary Research 66, 364–366. Wenzens, G., 2006b. Terminal moraines, outwash plains, and lake terraces in the vicinity of Lago Cardiel (491S; Patagonia, Argentina)—evidence for Miocene Andean foreland glaciations. Arctic, Antarctic and Alpine Research 38, 276–291. Winchester, V., Harrison, S., 1996. Recent Oscillations of the San Quintin and San Rafael Glaciers, Patagonian Chile. Geografiska Annaler 78A, 35–49. Winchester, V., Harrison, S., Bailey, R., 2005. A 2.5 kyr luminescence date for a terminal moraine in the Leones valley, Southern Chile. Journal of Glaciology 51, 186–188. White, J.W.C., Cias, P., Figge, I.A., Kenny, R., Markgraf, V., 1994. A high-resolution record of atmospheric CO2 content from carbon isotopes in peat. Nature 367, 53–156.