JOURNAL OF QUATERNARY SCIENCE (2000) 15 (4) 409–417
Copyright  2000 John Wiley & Sons, Ltd.
Climatic inferences from glacial and
palaeoecological evidence at the last glacial
termination, southern South America
R. D. McCULLOCH1*, M. J. BENTLEY1, R. S. PURVES1, N. R. J. HULTON1, D. E. SUGDEN1 and C. M. CLAPPERTON2
Department of Geography, University of Edinburgh, Edinburgh, EH8 9XP, Scotland
2
Department of Geography, University of Aberdeen, Aberdeen, AB9 2UF, Scotland
1
McCulloch, R. D., Bentley, M. J., Purves, R. S., Hulton, N. R. J., Sugden, D. E. and Clapperton, C. M. 2000. Climatic inferences from glacial and
palaeoecological evidence at the last glacial termination, southern South America. J. Quaternary Sci., Vol. 15, pp. 409–417. ISSN 0267-8179.
Received 15 October 1999; Revised 20 January 2000; Accepted 29 January 2000
ABSTRACT: There is uncertainty about the interhemispheric timing of climatic changes during
the last glacial–interglacial transition. Different hypotheses, relying on different lines of evidence,
point variously to the Northern Hemisphere leading the Southern Hemisphere and vice versa,
or to synchrony between the hemispheres. Southern South America is well placed to test the
various alternatives using both glacial and palaeoecological evidence. We argue here from a
synthesis of key proxy records that there was a sudden rise in temperature that initiated
deglaciation sychronously over 16° 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 the south, occurred at ca. 10 000 14C yr BP (11 400 cal. yr),
the latter achieving Holocene levels of warmth. 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). The latitudinal contrasts in the timing of maximum precipitation are reflected
in regional contrasts in vegetation change and in glacier behaviour. The large scale of a 80-km
glacier advance in the Strait of Magellan at 12 700–10 300 14C yr BP (15 350–12 250 cal. yr),
which spans the Antarctic Cold Reversal and the Younger Dryas, was influenced by the return
of the westerlies to southern latitudes. The delay in the migration of the westerlies coincides
with the Heinrich 1 iceberg event in the North Atlantic. The suppressed global thermohaline
circulation at the time may have affected sea-surface temperatures in the South Pacific, and the
return of the westerlies to their present southerly latitude only followed ocean reorganisation to
its present interglacial mode. Copyright  2000 John Wiley & Sons, Ltd.
KEYWORDS:
South America; Patagonia; last glacial termination; palaeoecology; ice sheets.
Introduction
The aim of this paper is to discuss the evidence in southern South America that can help to constrain different
hypotheses of interhemispheric climate change at the end
of the last glacial termination. At present the hypotheses
fall into three broad groups, depending on the mechanisms
thought to be driving global climate change. Some point
* Correspondence to: R. D. McCulloch, Department of Geography, The University of Edinburgh, Drummond Street, Edinburgh EH8 9XP, Scotland.
Email: rdm얀geo.ed.ac.uk
Contract grant sponsor: Natural Environemnt Research Council (UK)
to change driven either from the northern or southern
hemisphere and transmitted world-wide by the oceans;
others favour atmospheric processes that affect the whole
atmosphere synchronously. A key way forwards is to
identify leads and lags in different components of the
system in different locations.
The advantage of southern South America is its location
(Fig. 1). It lies athwart the southern westerlies and spans
several climatic zones from subpolar in the south (55°S) to
warm temperate in the north (36°S). The mountainous crest
of the southern Andes supports glaciers that are sensitive to
climate and hold a record of change during the last glacial–
interglacial transition. An ice sheet 1800 km long built up
along the axis of the Andes during the Last Glacial Maximum
(Hollin and Schilling, 1981). An additional advantage of the
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Figure 1 Southern South America showing distribution of present glaciers and the main climatic features, from Romero (1985). The
seasonal migration of the westerlies is also shown (inset), from Lawford (1993).
Copyright  2000 John Wiley & Sons, Ltd.
J. Quaternary Sci., Vol. 15(4) 409–417 (2000)
CLIMATIC INFERENCES FROM SOUTHERN SOUTH AMERICA
southern Andes is the rich vegetation record preserved in
abundant lakes and bogs, which offers an independent
record of environmental change.
Hypotheses of interhemispheric climate
change
A long-standing group of hypotheses about interhemispheric
climatic change focuses on the role of changes in the thermohaline circulation of the North Atlantic in driving global
ocean processes (Broecker and Denton, 1990). Variations in
the density of the North Atlantic surface water, associated
with changing temperature and meltwater fluxes, affect the
turnover of the conveyor, thus linking ocean circulation in
the northern and southern hemispheres and modifying patterns of global heat transport to high latitudes. Meltwater
derived from Northern Hemisphere ice sheets slowed or
suppressed the conveyor, thus introducing changes associated with Milankovitch insolation cycles (Imbrie et al., 1992)
or with ice rafting events (Bond et al., 1993; Macayeal,
1993; Bond and Lotti, 1995). Such a view of the leading
role of the North Atlantic is partially supported by an analysis
of oxygen isotopes from ice-sheet cores, which suggested
that changes in Greenland may have preceded those in the
Antarctic (Bender et al., 1994). The implication of these
ideas is that the ocean–ice-sheet–atmosphere system in the
Northern Hemisphere has been leading changes in the
Southern Hemisphere.
A second group of hypotheses points to changes in the
Southern Hemisphere leading those in the Northern Hemisphere. At one level this has been apparent in the ice-core
records, which show that the overall trend of warming in
the Vostok core in Antarctica began before the culmination
of the Last Glacial Maximum in the Northern Hemisphere,
but it has been confirmed by more recent correlations of
Antarctic and Greenland cores (Sowers and Bender, 1995).
Using atmospheric methane trapped in air bubbles as a
means of correlation, it appears that certain Dansgaard–
Oeschger warming events picked up in Greenland lag their
counterparts in Antarctica by 2000–3000 yr (Blunier et al.,
1998). In addition, the Antarctic cores reveal a late-glacial
Antarctic Cold Reversal (ACR) event that precedes the apparent equivalent Northern Hemisphere Younger Dryas (YD)
cooling by at least 1800 yr (Blunier et al., 1998). These
conclusions have built on evidence from marine cores. Hays
et al. (1976) argued for early warming of the Southern Ocean
on the basis of radiolarian abundances in cores. Further
analyses of stable isotope ratios of benthic and planktonic
foraminifers in Southern Ocean cores suggest that changes
in the Northern Hemisphere lagged those in the Southern
Hemisphere by up to several thousand years (Pichon et al.,
1992; Charles et al., 1996; Labeyrie et al., 1996).
It is difficult to relate these records to mechanisms. One
reason may simply be that the apparent leads and lags are
out-of-phase oscillations at a particular time-scale, and hence
Broecker’s suggestion of a polar see-saw in which the source
of polar deep water alternates between the North Atlantic
and the Southern Ocean (Broecker, 1998). Alternatively,
changes in the Southern Ocean may influence ocean circulation in the North Atlantic (Toggweiler and Samuels, 1995).
Perhaps the nature and character of the response varies
according to the stage of glacial cycle. At sensitive times a
warming of a particular magnitude in the south might be
Copyright  2000 John Wiley & Sons, Ltd.
411
sufficient to trigger a termination. At other times it may have
little effect (Blunier et al., 1998).
The third group of hypotheses leans towards synchrony
between the hemispheres and is based on studies of glacier
fluctuations and associated palaeoecological change. Working in the Chilean Lake District and New Zealand, Denton
and co-workers have a closely dated record of glacier fluctuations which correlates with Dansgaard–Oeschger events
in the North Atlantic region (Lowell et al., 1995; Denton
et al., 1999). The good fit between the two sets of records
implies interhemispheric symmetry of the structure and timing of the last glacial–interglacial transition. This conclusion
is borne out by evidence of Younger Dryas-equivalent glacier
advances in the Southern Hemisphere, for example, in Ecuador (Clapperton et al., 1997) and New Zealand (Denton
and Hendy, 1994; Ivy-Ochs et al., 1999) Such synchrony
points towards atmospheric mechanisms of change, perhaps
initiated by changes in water vapour in the tropics (Denton
et al., 1999). These views, based on glacial geomorphological evidence, have received support from the recent analysis
of the Taylor ice dome on the ice sheet margins flanking
the Ross Sea (Steig et al., 1998). The latter results seem to
imply synchrony between the abrupt climatic changes in a
coastal region of Antarctica and those in the Northern Hemisphere.
Role of southern South America
The past climate record from southern South America has
the potential to throw light on these wider global problems.
The area is linked to global climate via the southern
westerlies, which respond to changes in the location and
intensity of pressure gradients between the subtropical high
and subpolar realms. During glacial episodes the core of
the westerlies migrated northwards to latitudes 45–50°S,
bringing the moisture and cooler conditions necessary to
glaciate the Andes in the Chilean Lake District at around
latitude 41°S (Hubbard, 1997; Denton et al., 1999), while
at the same time reducing snowfall in the south (50–55°S)
where glacier expansion was proportionately less (Hulton
et al., 1994). Following the last termination, the westerlies
returned to their present latitude and the nature and timing
of their migration would help constrain the alternative global
scenarios outlined above. A reconstruction of the migration
of the westerlies is possible because the proxy records
obtained from glacier fluctuations and palaeoecological records reflect changes in both temperature and precipitation
over a latitudinal spread of sites.
It is helpful to refine the global scenarios into a series of
more specific questions about the last glacial–interglacial
transition in southern South America.
1. Does deglaciation in southernmost South America start
earlier than in the Northern Hemisphere? This would be
expected if the southern tip was influenced by Antarctic
conditions as indicated by some Southern Ocean cores
and ice cores from the interior of Antarctica.
2. Is the start of deglaciation synchronous over a range
of latitudes in South America and with the Northern
Hemisphere? This question arises from the work of
Denton and co-workers in the mid-latitudes of South
America and New Zealand and by the good match of
the Taylor ice-core with Northern Hemisphere records. If
so, as Denton points out, it could suggest an atmospheric
J. Quaternary Sci., Vol. 15(4) 409–417 (2000)
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trigger to the last termination, perhaps related to water
vapour in the tropics.
3. If deglaciation starts synchronously in South America,
how long does it take for the westerlies to return to their
current latitude? If there is a lag, then it gives some
indication of the time needed for the ocean–atmosphere
to achieve reorganisation following the last termination.
If there is no lag, then it points to sudden changes
instigated in the Southern Ocean.
4. Are short global fluctuations such as the Younger Dryas
reversal visible in records from southern South America?
Following Denton et al. (1999) and assuming that the
effects of Younger Dryas cooling derived from a thermohaline switch in the North Atlantic were transmitted via
atmospheric mechanisms, then the answer should be yes.
If transmission was via ocean mechanisms, then the 1000yr duration of the event may have been too short to
leave an unambiguous mark.
The evidence from southern South America
We review here the glacial and palaeoecological evidence
of environmental change in southern South America with
examples from three key areas: the Chilean Lake District
(40–43°S), the vicinity of the present-day ice fields (45–50°S)
and the Strait of Magellan (53–55°S). The overriding feature
is the evidence of warming in three distinctive steps. The
first, which followed a glacier advance, occurred at 14 600–
14 300 14C yrs BP and affected all latitudes. The second at
13 000–12 700 14C yr BP is clearest in the Chilean Lake
District, whereas the third step at around 10 000 14C yr BP
is dominant in the south. Another marked feature is the
lagged precipitation signal that saw the southerly migration
of a zone of high precipitation over the ca. 1600 yr following
the first warming step; this produced changes in glacier
behaviour and vegetation composition that sometimes were
out of phase in different latitudes. The key evidence is
shown in Figs 2 and 3. Figure 2 shows a reconstruction of
glacier extent (a) immediately prior to the first warming step,
(b) following deglaciation triggered by the first warming and
(c) immediately preceding the third warming step. Figure 3
shows representative pollen profiles in each latitudinal zone;
these also show the chronological relationships of glacier
advances and inferred changes in temperature and
precipitation.
Chilean Lake District (40–43°S)
A detailed programme of glacial geomorphological mapping
and stratigraphical studies by George Denton and coworkers, thoroughly supported by many 14C dates, has identified a glacial advance at 14 805–14 550 14C yr BP as the
last of a series of four in the last 30 000 yr (Denton et al.,
1999). During this advance lobes extended westwards from
the high Andes across lake basins, such as Llanquihue,
Rupanco and Puyehue and crossed the Golfo Corcovado to
bisect Isla Grande de Chiloe (Fig. 2a). In places the last
advance was as extensive as any in the last glaciation, but
more commonly it is slightly more limited than the largest.
At 14 600 14C yr BP the glaciers retreated rapidly and had
withdrawn to within 10 km of their sources in the high
Andes by 12 310 14C yr BP (Lowell et al., 1995). There is
Copyright  2000 John Wiley & Sons, Ltd.
no direct evidence of any advance later than that at 14 805–
14 550 14C yr BP. However, grain-size, chironomid and
pollen variations in Lake Mascardi fed from the Mount
Tronador ice-cap in the high Andes in the same latitude as
Lago Llanquihue have been interpreted as showing a
Younger Dryas-age advance of a small mountain glacier
(Ariztegui et al., 1997).
Pollen records in the Chilean Lake District also have been
studied in association with the above glacial record (Heusser
et al., 1996; Moreno, 1997; Moreno et al., 1999). A representative profile is shown in Fig. 3a. Two steps in warming
have been identified, separated by a transitional phase. The
pollen data from numerous cores show that at the time of
initial glacier retreat, there was a change from a cold-tolerant
Nothofagus forest (Nothofagus dombeyi type) and grassland
to a warmth-loving vegetation, characterised by Myrtaceae,
at 14 600–13 000 14C yr BP (Denton et al., 1999; Moreno
et al., 1999). Comparison of past vegetation types with their
present-day counterparts suggests that temperatures during
the last glacial advance were 6–7°C colder than present,
but with twice the present annual precipitation. The pollen
records point to a transitional stage when warmth-loving
trees coexisted with plants typical of cold Magellanic moorland. Persistence of the latter implies that precipitation
remained high for ca. 1600 yr after the initial warming,
perhaps because the westerlies remained in their northern
latitude (Denton et al., 1999). A second step in warming
occurred at 13 000–12 700 14C yr BP. This coincides with
the disappearance of Magellanic moorland plants and the
spread of warmth-loving forest trees over the lowlands of
the Chilean Lake District. The beetle records from the Chilean Lake District agree with pollen evidence in that they
show that moorland and/or open woodland taxa were
replaced by closed forest beetle assemblages at ca. 14 000
14
C yr BP (Ashworth and Hoganson, 1984, 1993; Hoganson
and Ashworth, 1992). The transition from glacial to postglacial coleopteran assemblages took place over ca. 1500 yr
(Ashworth and Hoganson, 1993). Thus, glacial geological,
pollen and beetle evidence are in agreement that there was
a marked warming beginning at 14 600–14 000 14C yr BP
in the Chilean Lake District followed by either a gradual
transition or a stepped increase in temperature that culminated at ca 13 000–12 700 14C yr BP.
There is less certainty about the nature of a possible
Younger Dryas climatic reversal in the Chilean Lake District.
Heusser et al. (1999) interpret an opening of the forest canopy and an expansion of cold-tolerant species as indicating
a climatic reversal after ca. 12 200 until 10 000 14C yr BP.
This spans the Younger Dryas and Heusser et al. (1999)
estimated that the temperature decline was equal to or less
than 2–3°C. There is a counter argument, suggesting that
the climatic impact may have been less. Heusser et al.’s
(1999) interpretation depends on the assumption that certain
pollen types, which include plant taxa from a wide range of
environments, indicate colder climatic conditions. Markgraf
(1989) suggested that such palynological changes could be
related to non-climatic factors such as soil and groundwater
levels. Also, the presence of charcoal in many profiles complicates interpretation (Heusser et al., 1996, 1999). Moreno
et al. (1999) attributed the charcoal to fires caused by palaeoindian burning and also possibly to the volcanism that is
endemic in the area. Whatever their origin, it is likely that
the fires could reflect a drier climate and this in turn could
explain part of the vegetation change. Finally, it is puzzling
that the beetle records do not show evidence of a Younger
Dryas cooling (Hoganson and Ashworth, 1992; Ashworth
and Hoganson, 1993). Thus, although the pollen evidence
J. Quaternary Sci., Vol. 15(4) 409–417 (2000)
(a)
Key to ice extent maps
Present ice fields
Approx. extent of
ice during periods
shown
12.5 ka
Major meltwater
routes and 14C date
of opening
Figure 2a. Glacier reconstruction inferred from the study areas marked. The glacier limits outside
those areas remain speculative at this stage. Glacier extent immediately prior to deglaciation at ca.
14 600–14 000 14C yr BP. Also shown is the outermost Quaternary glacier limit.
Copyright © 2000 John Wiley & Sons, Ltd.
J. Quaternary Sci., Vol. 15 (2000)
(b)
Figure 2b. Glacier reconstruction inferred from the study areas marked. The glacier limits outside those areas
remain speculative at this stage. Glacier extent following deglaciation triggered by the initial warming event
at ca. 14 600–14 000 14C yr BP.
Copyright © 2000 John Wiley & Sons, Ltd.
J. Quaternary Sci., Vol. 15 (2000)
(c)
Figure 2c. Glacier reconstruction inferred from the study areas marked. The glacier limits outside
those areas remain speculative at this stage. Glacier extent immediately prior to the third warming step
at ca. 10 000 14C yr BP
Copyright © 2000 John Wiley & Sons, Ltd.
J. Quaternary Sci., Vol. 15 (2000)
(a)
Climate inferences from pollen diagrams
Temperature
Warmer
Precipitation
Colder
Wetter
Drier
Figure 3a. Summaries of key pollen profiles. Canal Puntilla in the Chilean Lake District
(40°57’S; 72°54’W), after Moreno et al. (1999).
Copyright © 2000 John Wiley & Sons, Ltd.
J. Quaternary Sci., Vol. 15 (2000)
(b)
Figure 3b. Summaries of key pollen profiles. Taitao Peninsula (46°25’S; 74°24’W), after Lumley and
Switsur (1993).
Copyright © 2000 John Wiley & Sons, Ltd.
J. Quaternary Sci., Vol. 15 (2000)
Copyright © 2000 John Wiley & Sons, Ltd.
J. Quaternary Sci., Vol. 15 (2000)
(c)
Figure 3c. Summaries of key pollen profiles. Puerto del Hambre (53°36’S, 70°55’W), after McCulloch and Davies (submitted).
CLIMATIC INFERENCES FROM SOUTHERN SOUTH AMERICA
may reflect a Younger Dryas cold reversal, it could represent
only a relatively minor depression in temperature.
413
and 11 000 14C yr BP. Also, it is important to stress that
no pollen or stratigraphical evidence has been found of
a cooling during the Younger Dryas chronozone on the
Taitao peninsula (Lumley and Switsur, 1993) or near
Puerto Eden (Ashworth et al., 1991).
Central latitudes (45–50°S)
Relatively little evidence exists about glacier fluctuations
centred on the North Patagonian Icefield during the Lateglacial. The Taitao Peninsula at a point 50 km from the
present ice margin (46°25′S) was deglaciated prior to
14 335 14C yr BP (Lumley and Switsur, 1993). Ice had
retreated from the Chilean Channels around Puerto Eden
(49°08′S) by 12 960 ± 150 14C yr BP (Ashworth et al.,
1991). The twentieth century retreat of Glacier Tempano
(48°45′S) exposed peat sections that were dated to
11 070 ± 160 and 11 100 ± 170 14C yr BP. This implies
that following the last glacial maximum, glaciers were
within their present margins by about 11 000 14C yr BP
and also that there was no Younger Dryas advance beyond
the limits of the glaciers’ early twentieth century extent
(Mercer, 1976). There is tentative evidence that deglaciation had proceeded sufficiently to separate the northern
and southern Patagonian icefields by 11 245 ± 245 14C yr
BP. The basis of the argument is that prior to separation
the ice cap formed a continuous divide that dammed the
Rio Baker on its route across the mountain crest to the
Pacific. As a result an ice-dammed lake built up and
drained to the Atlantic via a spillway in Argentinian Patagonia (Fig. 2b and c). A radiocarbon date shows that
this spillway was abandoned by 11 245 ± 245 14C yr BP
presumably as a result of the drainage of the lake through
the ice cap axis into the Pacific (Mercer, 1976). Finally,
Wenzens (1999) studied the record of outlet and valley
glacier fluctuations around Lago Viedma (49°S) and suggested that these glaciers advanced three times in the
period from 14 000 to 10 000 14C yr BP. On the basis of
a number of minimum radiocarbon dates, the youngest
was attributed to the Younger Dryas. A problem arises,
however, in that this latter moraine seems morphologically
equivalent to the Sarmiento limit at the eastern end of
the Parque Nacional Torres del Paine, which is older than
the Younger Dryas (Marden, 1997). To summarise the
limited evidence in the vicinity of the North Patagonian
Ice Field, deglaciation was well under way by 14 335 14C
yr BP and there is no direct evidence of any Younger
Dryas advance.
The best dated and most continuous pollen core from
the central latitude channels is from Laguna Stibnite
(46°25′; 74°24′) and is summarised in Fig. 3b (from Lumley and Switsur, 1993). Following deglaciation, Nothofagus beech forest was present by 14 000 14C yr BP.
Between 12 300 and 11 000 14C yr BP Pilgerodenron
uviferum increased rapidly, probably in response to wetter
conditions and then gave way to a rise in Podocarpaceae.
After ca. 10 000–9500 14C yr BP there was a rise in
Tepualia stipularis in response to warming and thereafter
the forest remained constant until the late Holocene. We
interpret this pollen sequence as indicating a two-step
warming, the first leading to the retreat of the North
Patagonian Icefield some time before 14 335 14C yr BP
and allowing the expansion of Nothofagus forest. The
second step in warming occurred around ca. 9500 14C yr
BP and introduced the stable climatic conditions of the
early and mid-Holocene. Interestingly, the pollen data
and particularly the sharp rise in Pilgerodenron, suggest
higher levels of precipitation than present between 12 300
Copyright  2000 John Wiley & Sons, Ltd.
Strait of Magellan (53–55°S)
In the Magellan region glacier ice was more persistent.
Gently sloping ice tongues, aided by sliding on soft sediments (Benn and Clapperton, in press), spread down the
strait from an ice cap centred over the crest of the Andes
to the west and southwest. Numerous minimum dates within
a moraine limit, together with the presence of older dates
immediately outside the limit suggest that the glacier had
already retreated over 60 km from its position close to Punta
Arenas by 14 260 14C yr BP (Clapperton et al., 1995; McCulloch and Bentley, 1998). Retreat of the glacier into the fjords
of Cordillera Darwin is suggested by drainage of an icedammed lake in the Strait of Magellan by 13 300 14C yr BP
(Fig. 2b). Subsequently, between 12 700 and 10 300 14C yr
BP, the ice readvanced up the Strait of Magellan and culminated as much as 80 km beyond its present margins (Fig. 2c).
This advance dammed a large proglacial lake responsible
for the major raised shorelines in the area, which did not
drain finally until 10 300 14C yr BP. The association of lake
deposits with a Volcan Reclús tephra layer dated at 12 010
14
C yr BP means that we are able to constrain the culmination of the advance to between 12 010 and 10 300 14C
yr BP. This advance spans the Antarctic Cold Reversal. The
implication of this evidence is that deglaciation was well
underway by 14 260 14C yr BP, but that extensive ice persisted in the west and southwest and readvanced substantially again between 12 700 and 10 300 14C yr BP. The
main feature is that ice lingered for 4000 yr longer than
it did in comparable lowlands in the Lake District and
central latitudes.
A smaller advance of similar late glacial age has been
identified on the Grey outlet glacier draining the southern
reaches of the Southern Patagonian Icefield. The advance is
dated to between a maximum age of 12 010 14C yr BP,
provided by pumice from the eruption of Volcan Reclús
incorporated in the till fabric of terminal moraines, and a
minimum age of 9180 ± 120 14C yr BP (S. Porter, personal
communication, cited in Stern, 1990).
New palaeoecological information has been obtained from
both sides of the Strait of Magellan and yields a consistent
environmental story. Details of the pollen, stratigraphy and
diatoms are covered elsewhere (McCulloch and Davies, in
press), and Fig. 3c shows a summary of some key elements
of a core from Puerto del Hambre (53°36′S 70°55′W). This
is the oldest continuous core yet discovered in the Strait of
Magellan area and the age of the bottom sediments is
constrained by three AMS 14C dates from the deepest part
of the basin (McCulloch and Davies, in press). There was a
climatic cooling between 15 600 and 14 300 14C yr BP,
suggested by an increase in heathland plants and a loss of
Myriophyllum. At the same time the Magellan glacier was
close to the environs of Punta Arenas. There followed a
cool, relatively dry period of ca. 2000 yr, as indicated by
stratigraphical and pollen evidence, notably the dominance
of grasses, Acaena and Compositae. Such an assemblage
has been recorded more widely in the central and southern
Magellan region (Heusser, 1989, 1995, 1998; Rabassa et al.,
1990; Markgraf, l993). From 14 300 to 12 300 14C yr BP the
J. Quaternary Sci., Vol. 15(4) 409–417 (2000)
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pollen changes, and in particular the return of Myriophyllum
suggests a warming of ca. 3°C, but it was still colder than
present. Between 12 300 and 10 300 14C yr BP there are
frequent changes between grassland and heathland but they
are of short duration (ca. 100–200 yr) and do not provide
an unambiguous signal of any climatic cooling. Then at
10 300 14C yr BP, following the retreat of late glacial glaciers,
the first trees, Nothofagus, arrived and indicate a substantial
warming to near present-day temperatures. At the same time
steppe and heathland pollen declined. So the main evidence
is of a two-step change with an initial warming at 14 300
14
C yr BP and a second stepped warming at 10 300 14C
yr BP.
Superimposed on this broad temperature pattern is a fluctuating moisture signal. Between 12 300 and 10 300 14C yr
BP the pollen evidence of increased heathland vegetation
reflects an increase in effective moisture when compared
with the previous 2000 yr. This wetter phase is coincident
with the last advance of ice along the Strait of Magellan.
The second step of warming was associated with a shift to
arid conditions at 10 000–8500 14C yr BP. The dry conditions
favoured the higher frequency of fires indicated by high
concentrations of charcoal throughout the Magellan region.
The arid signal is also indicated by the state of deterioration
of pollen at Puerto del Hambre caused by drying out of the
bog (McCulloch, 1994). After 8500 14C yr BP precipitation
levels began to rise towards their present-day values,
allowing Nothofagus forest to migrate eastwards across the
previously dry areas of Tierra del Fuego. Nothofagus reached
the northern peninsula of Isla Dawson, southwest of Punta
Arenas, by 8500 14C yr BP (McCulloch, 1994; McCulloch
and Davies, in press) and further eastwards to Onamonte
by 5000 14C yr BP (Heusser, 1993).
Synthesis of evidence from southern South
America
Having looked at the evidence in three different latitudinal
zones, it is now useful to view them as a whole (Fig. 2).
First, the glacial evidence shows that wholesale deglaciation
occurred at around 14 550–14 260 14C yr BP. Taking the
youngest end of the range in the Chilean Lake District, the
earliest radiocarbon dates for deglaciation at each site all
lie within 200 yr. The dates are 14 550 14C yr BP in the
Chilean Lake District, 14 335 14C yr BP in the Taitao Peninsula and 14 260 14C yr BP in the Strait of Magellan. In the
Lake District and in the Strait of Magellan deglaciation is
known to have followed an advance culminating over 1000
yr or so. Only in the Strait of Magellan area is there evidence
of a later, significant glacial advance in the interval from
12 700 to 10 300 14C yr BP, beginning in the Antarctic Cold
Reversal interval. However, a small Younger Dryas advance
of a mountain glacier is inferred from sediments in Lago
Mascardi in the vicinity of the Lake District. The Strait of
Magellan glacier had retreated by 10 300 14C yr BP, as
demonstrated by the drainage of its ice-dammed lake.
The palaeoecological evidence points to three main steps
in warming, but with their relative importance varying from
latitude to latitude. The first evidence of warming in the
Lake District was an expansion in warmth-loving species at
14 600–14 300 14C yr BP. Warming allowed Nothofagus to
replace ice at 14 335 14C yr BP on the Taitao Peninsula. In
the Strait of Magellan area pollen data show a change at
Copyright  2000 John Wiley & Sons, Ltd.
14 300 14C yr BP equivalent to a rise in temperature of ca.
3°C. Together these records provide powerful evidence for
an abrupt warming at ca. 14 600–14 300 14C yr BP. The
second warming step is evident in the Chilean Lake District
at 13 000–12 700 14C yr BP; following a transitional period
of ca. 1600 yr, temperatures rose to values close to those of
today. There is no evidence of this warming in the pollen
records around the Strait of Magellan. The third warming
step occurs at ca. 10 000 14C yr BP in all three latitudes,
although it is more marked in the south than the north. In
the Taitao Peninsula it saw the establishment of the Holocene forest with warmth-loving species. In the Magellan area
it saw the arrival of the Nothofagus forest, which displaced
an open steppe.
The pollen evidence also points to a period of increased
precipitation that is out of phase in different latitudes. In the
Lake District high precipitation persisted for ca. 1600 yr
between 14 600–13 000 14C yr BP. In the Taitao area a
period of high precipitation occurred between 12 300–
11 000 14C yr BP. In the Magellan area there was an increase
in precipitation that began around 12 300 14C yr BP and
persisted until ca. 10 100 14C yr BP. This was followed by
an arid phase in the Magellan area between 10 100 and
8500 14C yr BP.
At first sight the apparent synchrony of the main steps in
the temperature record are difficult to relate to the contrasts
in the precipitation record. However, we believe it can be
explained relatively simply by the lagged response of the
westerlies to the main pulse of warming at ca. 14 600–
14 300 14C yr BP. As suggested earlier, the core of the
westerlies and their associated storms were located some
degrees of latitude further north during glacial episodes. This
is necessary, not only to nourish glaciers extending into the
lowlands of the Lake District, but also to explain the
enhanced precipitation recorded by the vegetation. Also, it
is necessary to explain the reduction in precipitation during
glacial episodes experienced by the areas of greatest precipitation today in latitudes 48–53°S. As suggested by Denton
et al. (1999), the high precipitation that followed the initial
warming in the Chilean Lake District is best explained if
the westerlies retained their northerly position for a further
ca. 1600 yr. We argue that, following this delay, it was the
southerly shift of the westerlies that subsequently increased
precipitation in the latitude of the Taitao Peninsula at
12 300–11 000 14C yr BP and in the latitude of the Strait of
Magellan from 12 300 to 10 300 14C yr BP.
If this hypothesis is correct then it points to synchronous
temperature change in all latitudes at 14 600–14 300 14C yr
BP followed by a lagged response of the westerlies. There
was little migration of the westerlies for ca. 1600 yr and then
it took a further 1000 years for the westerlies to reach their
approximate latitudinal position of today.
Global context of the southern South
American evidence
The evidence is of rapid deglaciation and associated warming beginning synchronously over 16° of latitude at 14 600–
14 300 14C yr BP (17 500–17 150 cal. yr). As been argued
convincingly elsewhere (Lowell et al., 1995; Denton et al.,
1999; Denton, 2000, this issue) this stepped warming is
global in extent and identified in glacier records, pollen
records and ocean cores around the world. Following
J. Quaternary Sci., Vol. 15(4) 409–417 (2000)
CLIMATIC INFERENCES FROM SOUTHERN SOUTH AMERICA
Denton (2000, this issue), it seems likely that such global
synchrony points to atmospheric drivers of change, such as
might result from changes in water vapour content. It represents the initial step in the transition from a glacial to
interglacial world. With reference to the questions about
interhemispheric leads and lags outlined earlier, it is interesting to record that deglaciation did not start earlier in
southernmost South America than in the Northern Hemisphere. This is in spite of a longer-term warming trend, as
indicated in the Vostok ice-core and in sediments from the
Southern Ocean. Also, there is apparently no lag in southern
South America as would be expected if Northern Hemisphere glaciers were driving change in response to orbital
insolation cycles and transmitting the change to the Southern
Hemisphere via the ocean.
Following this initial phase of deglaciation, the southern
South American evidence suggests that it took ca. 2500 yr
for the westerlies to recover from their northerly glacial
latitudes and to return to their latitude of today centred on
50°S. This conclusion is based on the assumption that in
this part of the world high precipitation is related to storms
associated with the westerlies and is related intimately to
offshore ocean surface temperatures. Such a connection is
well illustrated by modelling studies in Northern Hemisphere
mid-latitudes (Purves and Hulton, 2000). If correct, then the
implication is that the migration of the westerlies took place
only after reorganisation of the global ocean following the
last termination. This took 2500 yr to complete and began
only after a delay of ca. 1600 yr. As noted by Denton (2000),
the delay coincides with the Heinrich 1 iceberg discharge
event in the North Atlantic (16 900–15 400 cal. yr BP),
which suppressed the global thermohaline circulation. It is
tempting to suggest that the Heinrich event delayed the
reorganisation of the global ocean and that it was only the
start of a vigorous thermohaline circulation after Heinrich 1
that changed sea-surface temperatures off southern South
America and allowed the westerlies to migrate south. This
scenario explains the ca. 1600 yr wet transitional period
following the initial warming in the Chilean Lake District
and the precipitation peaks in the Taitao and Magellan areas
some 2500 yr after the initial warming.
Our dating constraints show that an advance of Magellan
ice between 12 700 and 10 300 14C yr BP spans both the
Antarctic Cold Reversal and the Younger Dryas intervals.
As the advance occurred immediately after a substantial
reorganisation of precipitation patterns, we are unable to
determine whether the advance was solely the result of
increased precipitation following the southward shift in the
westerlies, or whether there was a further temperature signal
(ACR or YD) superimposed on this reorganisation. The Magellan ice cap was receiving high precipitation during this
period and thus would have been sensitive to any atmospheric cooling. It could well have responded by advancing
and damming the Strait of Magellan. After glacier retreat at
10 300 14C yr BP, the surface of the ice dome over the
mountain crest would have fallen as the warming of the
start of the Holocene took hold. The prominent rise in
available moisture in Magellan pollen profiles at about 8500
14
C yr BP may reflect the final lowering of the ice dome,
which allowed storms to cross east of the Andes more easily.
There is no Younger Dryas temperature signal in the
Magellan palaeoecology. If the interpretation of the Lake
District profiles is correct and there was a Younger Dryas
cooling of 2–3°C, we would expect to see something similar
further south. One possibility is that the vegetation assemblages at the Magellan core sites were not sensitive to
small temperature changes. Another possibility is that the
Copyright  2000 John Wiley & Sons, Ltd.
415
temperature signal, which originated in the Northern Hemisphere, probably in the North Atlantic, and however transmitted, was attenuated away from its source. The cooling
in the Chilean Lake District of 2–3°C is much less that the
6°C around the North Atlantic and by the time the signal
extended a further 2000 km south it may have been too
small to register. Rather than a temperature signal in the
Magellan area, there is palaeoenvironmental evidence of an
increase in moisture during an interval that spans both the
Younger Dryas and the Antarctic Cold Reversal. Thus this
advance also could be linked to the reorganisation of the
oceans following the start up of the thermohaline circulation
after its suppression during Heinrich 1 events.
Conclusions
1. There is glacial geomorphological and palaeoecological
evidence of sychronous temperature change in southern
South America following the last glacial at 14 600–14 300
14
C yr BP (17 500–17 150 cal. yr) and at around 10 000
14
C yr BP (11 450 cal. yr).
2. Precipitation changes were asynchronous in different latitudes and reflect the lagged return of the westerlies to
their present latitude following the warming at 14 600–
14 300 14C yr BP. After a delay of ca. 1600 yr, the
westerlies took a further 1000 yr to achieve their present
latitude by 12 300 14C yr BP (14 300 cal. yr BP).
3. A significant glacier advance in the Strait of Magellan
between 12 700 and 10 300 14C yr BP (15 350–12 250
cal. yr BP) coincides with either of or both the Antarctic
Cold Reversal and Younger Dryas intervals. It is possible
that this is due to increased precipitation as a result of
the return of the westerlies.
4. The lagged response of the westerlies and the timing of
the Strait of Magellan glacier advance, which coincided
with the Antarctic Cold Reversal, can be seen both as a
response to the vigorous oceanic thermohaline circulation
that started up around 15 650–15 350 cal. yr ago, following its earlier suppression during Heinrich 1 events.
Acknowledgements. We are grateful for support from the UK Natural Environment Research Council and to Dr D. Harkness, Dr B.
Miller and Dr C. Bryant at the NERC Radiocarbon Laboratory, East
Kilbride for radiocarbon dating support. The Carnegie Trust for the
Universities of Scotland kindly contributed to the cost of colour
reproduction. Professor G. Denton and an anonymous referee provided constructive reviews. Bob McCulloch, Mike Bentley, Ross
Purves, Nick Hulton and David Sugden are very grateful to Chalmers
Clapperton who instigated this research in 1990.
References
Ariztegui D, Bianchi MM, Masaferro J, LaFargue E, Niessan F. 1997.
Interhemispheric synchrony of late-glacial climatic instability as
recorded in proglacial Lake Mascardi, Argentina. Journal of Quaternary Science 12: 133–138.
Ashworth AC, Hoganson JW. 1984. Testing the Late Quaternary
climatic record of southern Chile with evidence from fossil
Coleoptera. In: Late Cainozoic Palaeoclimates of the Southern
Hemisphere, Vogel JC (ed). Balkema: Rotterdam; 85–102.
Ashworth AC, Hoganson JW. 1993. The magnitude and rapidity of
the climate change marking the end of the Pleistocene in the midlatitudes of South America. Palaeogeography, Palaeoclimatology,
Palaeoecology 101: 263–270.
J. Quaternary Sci., Vol. 15(4) 409–417 (2000)
416
JOURNAL OF QUATERNARY SCIENCE
Ashworth AC, 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.
Bender M, Sowers T, Dickson ML, Orchardo J, Grootes J, Mayewski
PA, Meese DA. 1994. Climate correlations between Greenland and
Antarctica during the past 100,000 years. Nature 372: 663–666.
Benn D, Clapperton CM. in press. Pleistocene glaciotectonic landforms and sediments around central Magellan Strait, southernmost
Chile: evidence for fast outlet glaciers with cold-based margins.
Quaternary Science Reviews.
Blunier T, Chappellaz J, Schwander J, Dällenbach A, Stauffer B,
Stocker TF, Raynaud D, Jouzel J, Clausen HB, Hammer CV,
Johnsen SJ. 1998. Asynchrony of Antarctic and Greenland climate
during the last glacial period. Nature 394: 739–743.
Bond G, Lotti R. 1995. Iceberg discharges into the North Atlantic
on millennial time scales during the last glaciation. Science 267:
1005–1010.
Bond G, Broecker W, Johnsen S, McManus J, Layberie L, Jouzel J,
Bonani G. 1993. Correlations between climate records from North
Atlantic sediments and Greenland ice. Nature 365: 143–147.
Broecker WS. 1998. Paleocean circulation during the last deglaciation: a bi-polar seesaw? Paleoceanography 13: 119–121.
Broecker WS, Denton GH. 1990. The role of ocean-atmosphere
reorganizations in glacial cycles. Quaternary Science Reviews 9:
305–343.
Charles CD, Lynch-Stieglitz J, Ninneman US, Fairbanks RG. 1996.
Climate connections between the hemispheres revealed by deep
sea sediment core/ice core correlations. Earth and Planetary
Science Letters 142: 19–27.
Clapperton CM, Sugden DE, Kauffman D, McCulloch RD. 1995.
The last glaciation in central Magellan Strait, southermost Chile.
Quaternary Research 44: 133–148.
Clapperton CM, Hall M, Mothers P, Hole MJ, Still JW, Helmens
KF, Kuhry P, Gemmell AMD. 1997. A Younger Dryas ice cap in
the equatorial Andes. Quaternary Research 47: 13–28.
Denton GH. 2000. Does an asymmetric thermohaline–oscillator
drive 100 000-yr glacial cycles? Journal of Quaternary Science
15: 301–318.
Denton GH, Hendy CH. 1994. Younger Dryas age advance of Franz
Josef glacier in the southern Alps of New Zealand. Science 264:
1434–1437.
Denton GH, Heusser CJ, Lowell TV, Moreno PI, Andersen BG,
Heusser LE, Schlüchter C, Marchant DR. 1999. Interhemispheric
linkage of paleoclimate during the last glaciation. Geografiska.
Annaler 81A(2): 107–153.
Hays JD, Lozano JA, Shackleton N, Irving G. 1976. Reconstruction
of the Atlantic and western Indian Ocean sectors of the 18,000
B.P. Antarctic Ocean. Memoir of the Geological Society of America 145: 337–372.
Heusser CJ. 1983. Quaternary pollen record from Laguna de Tagua
Tagua, Chile. Science 219: 1429–1432.
Heusser CJ. 1989. Late Quaternary vegetation and climate of southern Tierra del Fuego. Quaternary Research 31: 396–406.
Heusser CJ. 1993. Late Quaternary forest – steppe contact zone,
Isla Grande de Tierra del Fuego, subantarctic South America.
Quaternary Science Reviews 12: 169–178.
Heusser CJ. 1995. Three late Quaternary pollen diagrams from
southern Patagonia and their palaeoecological implications.
Palaeogeography, Palaeoclimatology and Palaeoecology 118: 1–
24.
Heusser CJ. 1998. Deglacial palaeoclimate of the American sector
of the Southern Ocean: Late-glacial–Holocene records from the
latitude of Canal Beagle (55°S), Argentine Tierra del Fuego.
Palaeogeography, Palaeoclimatology and Palaeoecology 141:
277–301.
Heusser CJ, Heusser LE, Hauser A. 1992. A 12,000 yr BP tephra
layer at Bahia Inutil (Tierra del Fuego, Chile). Anales del Instituto
de la Patagonia 19: 39–49.
Heusser CJ, Lowell TV, Heusser LE, Hauser A, Andersen BG, Denton
GH. 1996. Full-glacial–late-glacial palaeoclimate of the southern
Andes: evidence from pollen, beetle and glacial records. Journal
of Quaternary Science 11: 173–184.
Copyright  2000 John Wiley & Sons, Ltd.
Heusser CJ, Heusser LE, Lowell TV. 1999. Palaeoecology of the
southern Chilean Lake District–Isla Grande de Chiloé during
middle–late Llanquihue glaciation and deglaciation. Geografiska
Annaler 81A(2): 231–284.
Hoganson JW, Ashworth AC. 1992. Fossil beetle evidence for climatic change 18,000–10,000 years B.P. in south-central Chile.
Quaternary Research 37: 101–116.
Hollin JT, Schilling DH. 1981. Late Wisconsin – Weichselian mountian glaciers and small ice caps. In: The Last Great Ice Sheets,
Denon GH, Hughes TJ (eds). Wiley: New York; 179–220.
Hubbard AL. 1997. Modelling climate, topography and palaeoglacier fluctuations in the Chilean Andes. Earth Surface Processes
and Landforms 22: 79–92.
Hulton NRJ, Sugden DE, Payne A, Clapperton CM. 1994. Glacier
modeling and the climate of Patagonia during the Last Glacial
Maximum. Quaternary Research 42: 1–19.
Imbrie J, Boyle EA, Clemens SC, Duffy A, Howard WR, Kukla G,
Kutzbach J, Martinson DG, McIntyre A, Mix AC, Molfino B,
Morley JJ, Peterson LC, Pisias NG, Prell WL, Raymo ME, Shackleton NJ, Toggweiler JR. 1992. On the structure and origin of major
glaciation cycles: 1. Linear responses to Milankovitch forcing.
Paleooceanography 7: 701–738.
Ivy-Ochs S, Schlüchter C, Kubik PW, Denton GH. 1999. Moraine
exposure dates imply synchronous Younger Dryas advances in
the European Alps and in the Southern Alps of New Zealand.
Geografiska Annaler 81A(2): 313–323.
Labeyrie L, Labracherie M, Gorfti N, Pichon JJ, Vautravers M, Arnold
M, Duplessy J-C, Paterne M, Michel E, Duprat J, Caralp M, Turon,
J-L. 1996. Hydrographic changes of the Southern Ocean (southeast
Indian sector) over the last 230 kyr. Paleoceanography 11: 57–76.
Lawford RG. 1993. Regional hydrologic response to global change
in western North America. In Earth System Responses to Global
Change: Contrasts between North and South America, Mooney
HA, Fuentes ER, Kronberg BI (eds). Academic Press: 73–99.
Lowell TV, Heusser CJ, Andersen BG, Moreno PI, Hauser A, Heusser
LE, Schlüchter C, Marchant DR, Denton GH. 1995. Interhemispheric correlation of Late Pleistocene glacial events. Science 269,
1541–1549.
Lumley SH, Switsur R. 1993. Late Quaternary chronology of the
Taitao Peninsula, southern Chile. Journal of Quaternary Science
8: 161–165.
Macayeal DR. 1993. Binge/purge oscillations of the Laurentide ice
sheet as a cause of the North Atlantic’s Heinrich events. Paleooceanography 8: 775–784.
Marden DJ. 1997. Late-glacial fluctuations of South Patagonian
icefield, Torres del Paine National Park, southern Chile. Quaternary International 38/39: 61–68.
Markgraf V. 1989. Reply to C. J. Heusser’s ‘Southern Westerlies during
the Last Glacial Maximum’. Quaternary Research 31: 426–432.
Markgraf V. 1993. Younger Dryas in southernmost South America—
an update. Quaternary Science Reviews 12: 351–355.
McCulloch RD. 1994. Palaeoenvironmental evidence for the Late
Wisconsin/Holocene transition in the Strait of Magellan, southern
Patagonia. Unpublished PhD thesis, University of Aberdeen.
McCulloch RD, Bentley MJ. 1998. Late glacial ice advances in the
Strait of Magellan, southern Chile. Quaternary Science Reviews
17: 775–787.
McCulloch RD, Davies SJ. In press. Palaeoenvironmental evidence
for the Late-glacial/Holocene transition in the Magellan Region,
southernmost Chile. Palaeogeography, Palaeoclimatology, Palaeoecology.
Mercer JH. 1976. Glacial history of southernmost South America.
Quaternary Research 6: 125–166.
Moreno PI. 1997. Vegetation and climate near Lago Llanquihue in
the Chilean Lake District between 20 200 and 9500 14Cyr BP.
Journal of Quaternary Science 12(6): 485–500.
Moreno PI, Lowell TV, Jacobson GL Jr, Denton GH. 1999. Abrupt
vegetation and climate changes during the last glacial maximum
and the last termination in the Chilean Lake District: a case study
from Canal de la Puntilla (41°S). Geografiska Annaler 81A(2):
285–311.
Pichon JJ, Labeyrie LD, Bareille G, Labracherie M, Duprat J, Jouzel
J. 1992. Surface water temperature changes in the high latitudes
J. Quaternary Sci., Vol. 15(4) 409–417 (2000)
CLIMATIC INFERENCES FROM SOUTHERN SOUTH AMERICA
of the Southern Hemisphere over the last glacial–interglacial cycle.
Paleooceanography 7: 289–318.
Purves RS, Hulton NRJ. In press. A climatic-scale precipitation
model compared with the UKCIP baseline climate. International
Journal of Climatology.
Rabassa J, Heusser CJ, Rutter N. 1990. Late-glacial and Holocene
of Tierra del Fuego. Quaternary of South America and Antarctic
Peninsula 7, 327–351.
Romero H. 1985. Geografia de Chile: geografia de los climas.
Instituto Geografico Militar: Santiago.
Sowers T, Bender M. 1995. Climate records covering the last
deglaciation. Science 269: 210–214.
Copyright  2000 John Wiley & Sons, Ltd.
417
Steig EJ, Brook EJ, White JWC, Sucher CM, Bender ML, Lehman
SJ, Morse DL, Waddington ED, Clow GD. 1998. Synchronous
climate changes in Antarctica and the North Atlantic. Science
282: 92–95.
Stern CR. 1990. Tephrochronology of southernmost Patagonia.
National Geographic Research 6: 110–126.
Toggweiler JR, Samuels B. 1995. Effect of Drake Passage on the
global thermohaline circulation. Deep sea research Pt 1. Oceanographic Research Papers 42(4): 477–500.
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.
J. Quaternary Sci., Vol. 15(4) 409–417 (2000)