Glacier Fluctuations in Garibaldi Provincial Park, Coast Mountains, British Columbia, Canada Johannes Koch,1* Gerald D

The Holocene 17,8 (2007) pp. 1069–1078

Pre-‘Little Ice Age’ glacier fluctuations in Garibaldi Provincial Park, Coast Mountains, British Columbia, Canada Johannes Koch,1* Gerald D. Osborn2 and John J. Clague1

( 1Department of Earth Sciences, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada; 2Department of Geology and Geophysics, University of Calgary, Calgary, Alberta T2N 1N4, Canada)

Received 21 July 2006; revised manuscript accepted 10 June 2007

Abstract: Holocene glacier fluctuations prior to the ‘Little Ice Age’ in Garibaldi Provincial Park in the British Columbia Coast Mountains were reconstructed from geomorphic mapping and radiocarbon ages on 37 samples of growth-position and detrital wood from glacier forefields. Glaciers in Garibaldi Park were smaller than at present in the early Holocene, although some evidence exists for minor, short-lived advances at this time. The first well-documented advance dates to 7700–7300 14C yr BP. Subsequent advances date to 6400–5100, 4300, 4100–2900 and 1600–1100 14C yr BP. Some glaciers approached their maximum Holocene limits several times during the past 10 000 years. Periods of advance in Garibaldi Park are broadly synchronous with advances elsewhere in the Canadian Cordillera, suggesting a common climatic cause. The Garibaldi Park glacier record is also broadly synchronous with the record of Holocene sunspot numbers, supporting previous research that suggests solar activity may be an important climate forcing mechanism.

Key words: Glacier advances, dendroglaciology, Holocene, solar forcing, Garibaldi Park, Coast Mountains, British Columbia.

Introduction The most direct evidence of pre-‘Little Ice Age’ glacier activity is found in glacier forefields and includes in situ tree stumps Recent studies point to significant and rapid fluctuations of climate (Ryder and Thomson, 1986; Luckman et al., 1993; Wiles et al., throughout the Holocene (Bond et al., 2001; Mayewski et al., 1999; Wood and Smith, 2004), detrital logs and branches (Ryder 2004). Alpine glaciers have long been used to document these fluc- and Thomson, 1986; Luckman et al., 1993; Wiles et al., 1999), tuations (Denton and Karlén, 1973), because they respond rapidly and organic soils and detrital wood exposed in composite lateral to changes in their mass balance and thus to changes in tempera- moraines (Röthlisberger, 1986; Osborn et al., 2001; Reyes and ture and precipitation. Unfortunately, most studies of past glacier Clague, 2004). Here, we present a detailed study of Holocene fluctuations allow reconstruction of climate variability only on glacier fluctuations prior to the ‘Little Ice Age’ in Garibaldi centennial and decadal timescales. Furthermore, many studies of Provincial Park in the southern Coast Mountains of British Holocene glacier fluctuations suffer from the fact that glacier Columbia (Figure 1) based on such evidence. Our objectives are advances in the Northern Hemisphere during the past millennium to: (1) summarize new data from Garibaldi Park; (2) compare the (‘Little Ice Age’) were the most extensive of the Holocene and record from the park with other records of Holocene glacier obliterated or obscured most of the evidence of previous advances. activity in western Canada; and (3) discuss the likely climate Pre-‘Little Ice Age’ moraines are rare in western Canada and their forcing mechanisms. Evidence for ‘Little Ice Age’ and twenti- ages are generally not well constrained (Osborn, 1985; Ryder and eth-century glacier fluctuations in the park is presented else- Thomson, 1986; Osborn and Karlstrom, 1988; Osborn and Gerloff, where and is not discussed further here (Koch et al., 2007). 1996; Larocque and Smith, 2003). Sediments in lakes downvalley of glaciers can provide a more complete record of Holocene glacial Study area activity (Leonard, 1986a, b; Desloges and Gilbert, 1995; Leonard and Reasoner, 1999; Menounos et al., 2004), but the record com- Garibaldi Provincial Park is located in the southern Coast monly is complicated by non-climatic factors. Mountains about 70 km north of Vancouver, British Columbia *Author for correspondence (e-mail: [email protected]) (Figure 1). The park contains more than 150 glaciers, which are

© 2007 SAGE Publications Downloaded from http://hol.sagepub.com at COLLEGE OF WOOSTER on January 18, 2008 10.1177/0959683607082546 © 2007 SAGE Publications. All rights reserved. Not for commercial use or unauthorized distribution. 1070 The Holocene 17,8 (2007)

Canada

British Columbia Alberta Pemberton

Study area Lillooet Lake Paciic Ocean U.S.A. 500 km 1

Whistler 2 3 Lillooet

Squamish R. 4 R. 50°N

R. 5

6 7 8 Cheakamus

alpine 10 N Squamish glaciers lakes/streams Howe Sound 4 km

123°W

Figure 1 Location of Garibaldi Provincial Park and glaciers investigated in this study. 1, Wedgemount Glacier; 2, Spearhead Glacier; 3, Decker Glacier; 4, Overlord Glacier; 5, Helm Glacier; 6, Sphinx Glacier; 7, Sentinel Glacier; 8, Warren Glacier; 9, Lava Glacier; 10, West Stave Glacier; 11, Stave Glacier

among the southernmost glaciers in the Coast Mountains. The The study area is located in the Mountain Hemlock biogeocli- total area of ice cover in the park is about 390 km². matic zone, which is characterized by long, cool, wet winters and The landscape of Garibaldi Park has been shaped by Quaternary short, cool summers (Brooke et al., 1970). The growing season is continental and alpine glaciation and locally by Quaternary volcan- short because of heavy snowfall in winter. Arboreal vegetation in ism (Mathews, 1958). The park is underlain mainly by granitic forefields investigated in this study is dominated by mountain rocks of the Coast Plutonic Complex and Cretaceous metasedimen- hemlock (Tsuga mertensiana) and subalpine fir (Abies lasiocarpa), tary and volcanic rocks of the Gambier Group (Monger and but locally includes Engelmann spruce (Picea engelmannii), white- Journeay, 1994). The southwestern part of the park is dominated by bark pine (Pinus albicaulis) and yellow cedar (Chamaecyparis rocks of the Plio-Pleistocene Mount Garibaldi volcanic complex nootkatensis). (Mathews, 1958). The northwest-trending Coast Mountains form an orographic barrier to moisture-laden air flowing from the Pacific Ocean, thus Methods there is a strong west–east environmental gradient across Garibaldi Park. Climate is maritime in the southwestern part of the Glacier forefields were visited in 2002, 2003 and 2004 and sys- park but becomes increasingly continental to the north and east. tematically searched for detrital and in situ fossil wood. Discs were Average annual precipitation at Squamish, at the head of Howe cut from fossil wood found in lateral and end moraines and at the Sound, is 2370 mm, but it is only 1230 mm at Whistler, 60 km to surface. They were air dried and prepared for analysis by sanding the north. Overall, climate is humid and cool, with very wet win- with progressively finer grades of sandpaper to enhance the defini- ters and dry summers. tion and contrast of annual tree-ring boundaries. Tree rings were

Table 1 Pre ‘Little Ice Age’ radiocarbon ages in Garibaldi Park

Glacier Site Laboratory no. 14 C age Cal. yr Comment (yr BP) BP

Wedgemount Beta-170671 8650 ± 60 9540–9630 branch; 90 m from snout Spearhead Beta-157268a 3900 ± 80 4230–4430 branch; near snout Beta-168423a 3900 ± 60 4280–4420 branch; near snout Decker Beta-157265a 3200 ± 70 3350–3480 in situ stump on cliff Beta-157262a 2960 ± 50 3060–3220 log near stumps Beta-157263a 2960 ± 40 3070–3210 in situ snag on cliff Beta-157264a 2920 ± 50 2990–3160 in situ stump on cliff Overlord ovgl-b Beta-170665a 6170 ± 70 6980–7160 log; on surface 50 m from snout ovgl-a Beta-170660a 5980 ± 70 6730–6910 log; in till 140 m from snout ovgl-a Beta-170667a 5890 ± 70 6630–6800 log; on surface 100 m from snout Helm hegl-a Beta-168430 8900 ± 60 9920–10 090 partially buried log 140 m from 1997 snout hegl-b Beta-186523 4080 ± 40 4520–4620 stump; melted out of ice in 2003 Sphinx spgl-e GSC-6770b 7720 ± 80 8420–8560 branch; 100 m from snout GSC-1993c 7640 ± 80 8380–8480 log; on surface; location uncertain spgl-a Beta-186509 5830 ± 60 6560–6700 snag; in till 300 m from snout spgl-b Beta-208685 4280 ± 70 4810–4960 log; in till 500 m from snout spgl-c Beta-186510 3560 ± 70 3820–3930 snag; in till 800 m from snout spgl-d Beta-186511 1570 ± 40 1450–1520 snag; on surface below bedrock knoll 600 m from snout Sentinel segl-c Beta-148787b 7720 ± 70 8430–8550 branch; on surface near snout segl-c Beta-157267b 7470 ± 80 8280–8360 branch; on surface near snout segl-c Beta-148786b 7380 ± 80 8160–8320 branch; on surface near snout GSC-1477d 6170 ± 150 6890–7250 branch; in till 2 km inside ‘Little Ice Age’ limit segl-b Beta-186508 6040 ± 60 6790–6950 snag in till 300 m from present snout GSC-2027c 5300 ± 70 5990–6130 in situ stump 1 km inside ‘Little Ice Age’ limit Warren wagl-a Beta-168425 8050 ± 60 8950–9030 stick 250 m from 2000 snout wagl-d Beta-148789 6370 ± 70 7250–7330 in situ stump 95 m from 2000 snout wagl-d Beta-148790 6360 ± 80 7250–7340 in situ stump 100 m from 2000 snout wagl-c Beta-148788 5780 ± 70 6500–6660 in situ stump 600 m from 2000 snout wagl-b Beta-168424 5700 ± 50 6410–6540 partially buried large log Lava lagl-a Beta-168426 6170 ± 60 7000–7160 in situ stump, Garibaldi Neve lagl-a Beta-168427 6050 ± 50 6840–6970 in situ stump, Garibaldi Neve lagl-Y Y-140 bise 5850 ± 180 6450–6860 in situ stump, Garibaldi Neve lagl-Y Y-140 bisf 5260 ± 200 5890–6280 in situ stump, re-date of Y-140 bis lagl-b Beta-186521 5760 ± 60 6490–6640 in situ stump 400 m from snout lagl-f Beta-186520 5130 ± 40 5890–5930 stump on surface lagl-e Beta-186517 3190 ± 40 3380–3450 log in woody layer in lateral moraine West Stave wsgl-a Beta-170668 1080 ± 60 930–1010 small log in lateral moraine Stave stgl-a Beta-171096 6250 ± 70 7150–7260 detrital stump in till

Note: Dated samples are outer-perimeter wood comprising less than 25 rings. a Osborn et al. (2007). b Menounos et al. (2004). c Lowdon and Blake (1975). d Lowdon and Blake (1973). e Preston et al. (1955). f Stuiver et al. (1960).

measured on a Velmex stage with a precision of ± 0.001 mm using be crossdated with living trees were radiocarbon dated. Standard the software MeasureJ2X. Two to four radii were measured to radiocarbon ages on outer rings were calibrated using the program replicate data and reduce the possibility of missing rings or false CALIB 5.0 (Stuiver et al., 2005). Calibrated ages, shown in brack- rings (Stokes and Smiley, 1968). Floating chronologies were ets in this paper, are 1σ ranges. developed for sites where more than one tree was sampled. They Interpretation of radiocarbon ages from glacier forefields requires show that many trees at a site were killed at about the same time consideration of the provenance and location of the dated material and support the argument that tree death was caused by an advanc- (Osborn, 1986; Röthlisberger, 1986; Ryder and Thomson, 1986; ing glacier. The total number of rings is a minimum for the length Luckman, 1998). Stumps in growth position in Garibaldi Park show of time the site was not covered by ice and thus a minimum for the evidence of having been sheared off by glaciers. Bark is commonly interval between successive glacier advances. The floating preserved as a result of burial of the stumps in sediment. Detrital chronologies were visually compared to correlate marker rings and wood in glacier forefields shows evidence of glacial transport, checked and verified using the International Tree-Ring Data Bank including missing bark, abrasion, embedded sediment and flatten- (ITRDB) software program COFECHA. They were then cross- ing. This wood is interpreted to have been eroded from in situ trees dated (50-yr dated segments lagged by 25 years, with a critical by glaciers and transported at basal and englacial positions within level of correlation (99%) set at 0.32) to create master ring-width the glaciers. Preservation of bark or relatively small branches or chronologies (Holmes, 1983). Floating chronologies that could not roots is interpreted to indicate short transport. Only samples in

Figure 2 Forefield of Warren Glacier in 2002, showing study sites (photograph by J. Koch). View is to the southeast

growth position provide unequivocal evidence for glacier advance caused by a massive discharge of freshwater into the North Atlantic and extent at a given time. Detrital wood in a stratigraphic context, around 8470 cal. yr BP (Alley and Ágústsdóttir, 2005). Two small, such as a lateral moraine or till in a glacier forefield, provides a shattered and partially buried fragments of coniferous wood were maximum age for the advance. It also defines the minimum extent found about 100 m from the 2002 snout of Sphinx Glacier (site e of the glacier, because the glacier must have reached at least as far in Figure 3). One of the fragments yielded a radiocarbon age of as the wood and probably farther. The possibility must be consid- 7720 ± 80 14C yr BP (8420–8560 cal. BP; Menounos et al., 2004). ered that detrital wood within till could have avalanched into the Another, similar age was obtained on a 2 m long stem recovered forefield or died of old age, but in such cases the wood nevertheless from among large boulders in a meltwater channel near the snout still provides a maximum age for the advance. If tree-ring or radio- of Sphinx Glacier in the 1970s (7640 ± 80 14C yr BP (8380–8480 carbon ages on detrital wood in one glacier forefield are similar to cal. yr BP); Lowdon and Blake, 1975). The locations of both sam- those in other forefields, it is unlikely that the samples were intro- ples indicate that, prior to the event, Sphinx Glacier was less exten- duced by avalanches or died of old age. sive than at present. Three small pieces of detrital wood 50–400 m from the snout of Sentinel Glacier gave ages of 7720 ± 70 14C yr BP (8430–8550 cal. yr BP), 7470 ± 80 14C yr BP (8280–8360 cal. yr Results BP) and 7380 ± 80 14C yr BP (8160–8330 cal. yr BP; Menounos et al., 2004). Sentinel Glacier was less extensive at the time of this Early-Holocene activity inferred advance than today. Neither Sphinx nor Sentinel glaciers Detrital wood in three glacier forefields in Garibaldi Park suggests advanced far beyond their present limit during the 8.2 ka event. that glaciers were generally less extensive in the early Holocene than in 2002–2004, but that they may have advanced on several Advances between 6400 and 5100 14C yr BP occasions to near present-day glacier margins. A large, abraded (7300–5800 cal. yr BP) and partially buried log about 140 m from the 1997 snout of Helm Evidence for one or more glacier advances during this period was Glacier yielded a radiocarbon age of 8900 ± 60 14C years BP found in six glacier forefields in Garibaldi Park, showing the (9920–10 090 cal. yr BP; Table 1). A split and frayed fragment of regional significance of the event. A degraded, detrital stump detrital wood, likely the remains of a small conifer trunk, recov- recovered from till about 800 m from the 2002 snout of Stave ered from the top of a bedrock knob about 90 m from the 2002 Glacier gave a radiocarbon age of 6250 ± 70 14C yr BP (7150–7260 margin of Wedgemount Glacier gave an age of 8650 ± 60 14C years cal. yr BP), indicating that the glacier was more extensive at that BP (9540–9630 cal. yr BP). A shredded stick found on a bar of a time than today. meltwater stream about 250 m from the 2000 snout of Warren Surface detrital wood 40–200 m from the 2002 snout of Glacier (site a in Figure 2) yielded an age of 8050 ± 60 14C years Overlord Glacier gave ages of 6170 ± 70 14C yr BP (6980–7160 BP (8950–9030 cal. yr BP). cal. yr BP) and 5890 ± 70 14C yr BP (6630–6800 cal. yr BP). A third sample, embedded in till 40 m farther downstream, yielded Advance between 7700 and 7300 14C yr BP an age of 5980 ± 70 14C yr BP (6730–6910 cal. yr BP). The loca- (8500–8100 cal. yr BP) tions of the three samples indicate that Overlord Glacier was prob- Evidence was found in two glacier forefields for a small advance at ably less extensive than today prior to this event and advanced into the time of the ‘8.2 ka event’, an abrupt cooling event most likely mature forest around 6000 14C yr BP. One of the dated samples

Figure 3 Forefield of Sphinx Glacier in 2002 and study sites (photograph by J. Koch). View is to the southeast. Dashed line delineates the glacier’s ‘Litte Ice Age’ limit crossdated with two other pieces of detrital wood, providing a collected in 1973 and dated at 5300 ± 70 14C yr BP (5990–6130 cal. floating chronology (Table 2). yr BP; Lowdon and Blake, 1975). Although we were unable to Branches and snags were found in a woody layer between two locate this stump, it is within 1 km of the maximum ‘Little Ice Age’ tills and in an adjacent stream about 300 m from the snout of the margin of Sentinel Glacier (Lowdon and Blake, 1975). south tributary glacier of Sphinx Glacier (site a in Figure 3). One The radiocarbon ages from Sentinel Glacier afford a more of the snags gave an age of 5830 ± 60 14C yr BP (6560–6700 cal. detailed reconstruction of this event than the ages from Stave, yr BP). A floating ring chronology was built from two of the sam- Overlord and Sphinx glaciers. When Sentinel Glacier advanced ples in till and one in the creek (Table 2). The evidence from this into forest 6100 14C yr BP, it was about as extensive as today. The site indicates that Sphinx Glacier was about its present size prior dated wood shows little evidence of transport and thus likely had to an advance that overrode forest around 5800 14C yr BP. been growing near the sample site prior to the advance. By 5300 Wood collected from till near the snout of Sentinel Glacier 14C yr BP, Sentinel Glacier was at least 1 km more extensive than (Figure 1) in 1970 yielded a radiocarbon age of 6170 ± 150 14C yr at present and at least half its ‘Little Ice Age’ maximum size. The BP (6890–7250 cal. yr BP; Lowdon and Blake, 1973). The exact glacier thus expanded between 6100 and 5300 14C yr BP, although location of this site is unknown, but it is likely to be the same site it is not known if glacier growth was slow and continuous or the that we sampled in 2002 (Figure 4a). Our samples range from small result of two separate advances. trunks to large snags; one of the snags gave an age of 6040 ± 60 14C The Warren Glacier forefield has a similar record (sites b, c, and yr BP (6790–6950 cal. yr BP). The two ages overlap at their 1σ d in Figure 2). Two in situ stumps (Figure 4c) were found at site limits, supporting the inference that they are from the same site. d about 100 m from the 2000 glacier margin. They yielded ages of Two samples from the till and two samples in a meltwater stream 6370 ± 70 14C yr BP (7250–7330 cal. yr BP) and 6360 ± 80 14C yr adjacent to the till exposure were used to construct a floating BP (7250–7340 cal. yr BP). An exposed and fragmented in situ chronology (Table 2). An in situ stump partially buried in till was stump (Figure 4b) at site c about 600 m from the 2000 glacier

Table 2 Floating tree-ring chronologies for subalpine fir samples from glacier forefields in Garibaldi Park

Glacier Chronology 14C age Length Correlation No. radii/trees (yr BP) (yr)

Overlord site ovgl-a 5890 ± 70 138 0.562 13/4 Helm sites hegl-b and -c 4080 ± 40 135 0.612 22/13 Sphinx site spgl-a 5830 ± 60 184 0.494 6/3 site spgl-b 4280 ± 70 115 0.698 4/2 site spgl-c 3560 ± 70 197 0.427 5/3 Sentinel sites segl-a and -b 6040 ± 60 149 0.574 8/4 Lava sites lagl-b, -c, and -d 5760 ± 60 482 0.437 15/8 site lagl-f 5130 ± 40 263 0.477 7/3

Figure 4 (a) Wood in lateral moraine of Sentinel Glacier (site segl-b; 6040 ± 60 14C yr BP; photograph by J. Koch). (b) In situ stump at Warren Glacier (site wagl-d; 6360 ± 80 14C yr BP; photograph by G. Osborn). (c) In situ stump at Warren Glacier (site wagl-c; 5780 ± 70 14C yr BP; photograph by G. Osborn)

margin gave an age of 5780 ± 70 14C yr BP (6500–6660 cal. yr in bedrock and till. The surface detrital wood is derived from a BP). A large weathered log partially buried in till at site b yielded wood layer separating two tills within the gorge (arrow near site f an age of 5700 ± 50 14C yr BP (6410–6540 cal. yr). in Figure 5). Unfortunately, the site could not be safely accessed. We interpret these ages as follows. Warren Glacier was about Three detrital stumps at site f were crossdated (Table 2), and a the same size as today when it advanced into forest at site d about radiocarbon age of 5130 ± 40 14C yr BP (5890–5930 cal. yr BP) 6350 14C yr BP. By 5800 14C yr BP, the glacier had advanced was obtained on one of them. about 600 m downvalley and was overriding a forest at site c. The The ages from Garibaldi Neve indicate a thickening of ice dated log at site b, farther downvalley, shows that the glacier con- between 6100 and 5900/5200 14C yr BP, either slowly or during tinued to advance until at least 5700 14C yr BP. As at Sentinel two separate events. Lava Glacier advanced into mature forests Glacier, it is not known if Warren Glacier advanced slowly over a with trees more than 450 years and 250 years old 5800 and 5100 period of 650 years or two or more times during this interval. 14C yr BP, respectively. It likely had the same extent 5800 14C yr Garibaldi Neve, an icefield east of Mt Garibaldi, feeds six gla- BP as today. By 5100 14C yr BP, when it deposited a till at site f, ciers, including Lava Glacier (Figure 5). Two in situ stumps on a Lava Glacier was more than half its ‘Little Ice Age’ size. ridge at the northeast corner of the neve (site a in Figure 5) yielded radiocarbon ages of 6170 ± 60 14C years BP (7000–7160 cal. yr Advance about 4300 14C yr BP (4900 cal. yr BP) and 6050 ± 50 14C yr BP (6840–6970 cal. yr BP). An in situ BP) stump on a nunatak in the neve was sampled in the 1950s (site Y Evidence for this advance was found only at Sphinx Glacier (site in Figure 5). It gave ages of 5850 ± 180 14C yr BP (6450–6860 cal. b in Figure 3). Detrital branches and large logs were found in a yr BP; Preston et al., 1955) and 5260 ± 200 14C yr BP (5890–6280 meltwater stream in the glacier forefield and within a woody layer cal. yr BP; Stuiver et al., 1960); the latter is assumed to be the separating two tills about 500 m from the snout of the southern more reliable age (Stuiver et al., 1960). The exact location of this tributary glacier. The outer 15 rings of one of the logs yielded a sample is unknown, but Figure 5 shows the two possible nunataks radiocarbon age of 4280 ± 70 14C yr BP (4810–4960 cal. BP). A in the icefield. Two in situ and three detrital stumps were recov- floating chronology, spanning 115 years, was constructed for two ered along the stream draining Lava Glacier about 400 m from the samples collected from the till (Table 2). It is unknown if the 2003 snout (site b, Figure 5). One of the in situ stumps yielded an lower till at site b correlates to the lower till at site a (Figure 3, see age of 5760 ± 60 14C yr BP (6490–6640 cal. yr BP). Two more ‘Advances between 6400 and 5100 14C yr BP’), thus indicating a sites with detrital wood were found in the same area, site c c. 50 m single advance, or if the upper till at site a is the lower till at site southeast of site b and site d c. 110 m northeast of site b. Samples b, indicating two separate advances. However, evidence at other from sites b, c and d were successfully crossdated, providing a forefields indicates that glaciers reached much farther downvalley floating chronology of almost 500 years (Table 2). Numerous at the end of the previous advance period. It thus is more likely branches, large logs, snags and stumps were found on an alluvial that the tills record two advances and that Sphinx Glacier receded surface (site f, Figure 5), 20–100 m downstream of a gorge eroded after the 6400–5100 BP advance period to an unknown position

Figure 5 Forefield and study sites at Lava Glacier and Garibaldi Neve in 2003 (photograph by J. Koch). View is to the north. The exact location of site Y is unknown. Wood sampled on the floodplain (site f) was eroded from a wood layer in a gully (white arrow)

upvalley of site b for at least 115 years. This issue aside, an advance occurred about 4300 14C yr BP, reaching at least site b.

Advances between 4100 and 2900 14C yr BP (4600–3000 cal. yr BP) Evidence for one or more advances during this period was found in five glacier forefields in Garibaldi Park. The evidence shows that glaciers became more extensive over time during this period. Thirteen branches and stumps were found in till near the termi- nus of Helm Glacier (Figure 6a) in 2003. They appear to be asso- ciated with a weathering horizon in the till. A radiocarbon age of 4080 ± 40 14C yr BP (4520–4620 cal. yr BP) was obtained on the outermost 12 rings of the sample shown in Figure 6a, and a floating chronology was constructed from all of the samples (Table 2). The evidence suggests that Helm Glacier was less extensive than today for at least 135 years around 4100 14C yr BP. Shortly after- wards, it advanced to a more extensive position than at present. Small wood fragments about 20 m above the present surface of Spearhead Glacier date to 3900 ± 80 14C yr BP (4230–4430 cal. yr BP) and 3900 ± 60 14C yr BP (4280–4420 cal. yr BP; Osborn et al., 2007). They suggest that Spearhead Glacier was thicker and thus more extensive 3900 14C yr BP than today. Additional evidence for this event was found along the creek draining the southern tributary of Sphinx Glacier (Figure 1) about 800 m from the 2002 snout (site c in Figure 3). A layer of branches and snags occurs within till, and one of the snags gave an age of 3560 ± 70 14C yr BP (3820–3930 cal. yr BP). A floating chronology was built from three samples (Table 2). The evidence indicates that the glacier was at least 800 m more extensive 3600 14C yr BP than at present. A large log in the west lateral moraine of Lava Glacier (Figure Figure 6 Fossil wood deposited during glacier advances between 4600 14 6b) yielded a radiocarbon age of 3190 ± 40 C yr BP (3380–3450 and 3000 cal. yr BP. (a) Wood melting out of Helm Glacier (site hegl-b; cal. yr BP). The log is part of a wood layer that can be traced over 4080 ± 40 14C yr BP). (b) Wood layer in the lateral moraine of Lava a distance of 110 m across several gullies. The till overlying the Glacier. (site lagl-e; 3190 ± 40 14C yr BP) (photographs by J. Koch)

14C years BP 10,000 9000 8000 7000 6000 5000 4000 3000 2000 1000 0 min (a) ???

max (b) Overlord Helm Sphinx Sentinel Warren Garibaldi Lava Stave West Stave 120 Decker (c) Wedgemount Spearhead 100

0 11,00010,000 9000 8000 7000 6000 5000 4000 3000 2000 1000 0 Cal years BP

Figure 7 Relation between Holocene glacier activity in Garibaldi Park and sunspot numbers. (a) Generalized reconstruction of relative glacier extent in Garibaldi Park. (b) Life spans of trees killed by glacier advance. (c) Reconstructed decadal (thin line) and smoothed (bold line) sunspot numbers (Solanki et al., 2004). Vertical dark grey bars indicate periods of glacier advance in Garibaldi Park

wood layer was deposited by Lava Glacier shortly after 3200 14C embedded in the outermost lateral moraine close to its crest yr BP, when it was about as extensive as at the ‘Little Ice Age’ yielded an age of 1080 ± 60 14C yr BP (930–1010 cal. yr BP). maximum. Decker Glacier also was near its ‘Little Ice Age’ limit at this time. In situ snags and stumps on a bedrock cliff 40–75 m above Discussion the present glacier surface yielded radiocarbon ages of 3200 ± 70 14C yr BP (3350–3480 cal. yr BP), 2960 ± 40 14C yr BP Chronology (3070–3210 cal. yr BP) and 2920 ± 50 14C yr BP (2990–3160 cal. Glaciers in Garibaldi Park were less extensive than at present yr BP; Osborn et al., 2007). A detrital log below the bedrock cliff throughout the early Holocene. Radiocarbon ages from Wedge- gave an age of 2960 ± 50 14C yr BP (3060–3220 cal. yr BP). mount, Helm and Warren glaciers may record minor advances Decker Glacier thickened between 3200 and 2900 14C yr BP to between 8900 and 8000 14C yr BP (Figure 7). However, prior to near its ‘Little Ice Age’ maximum extent. the 8.2 ka event (Menounos et al., 2004), glaciers must have been less extensive than today, because detrital wood recovered near Advances between 1600 and 1100 14C yr BP the margins of Sphinx and Sentinel glaciers dates to 7700–7300 (1500–1000 cal. yr BP) 14C yr BP. Evidence for one or more glacier advances in the first millennium Warren, Stave, Sentinel, Sphinx, Overlord and Lava glaciers 14 AD was found in the forefields of two glaciers in Garibaldi Park. A advanced between 6400 and 5100 C yr BP. The glaciers advanced detrital snag with relatively fine roots, located below a bedrock over forests up to 800 m downvalley from present snouts between knob at Sphinx Glacier (site d in Figure 3), yielded an age of 6400 and 5800 14C yr BP. Sentinel and Lava glaciers were no more 1570 ± 40 14C yr BP (1450–1520 cal. yr BP). The roots indicate than 1–1.5 km from their maximum Holocene limits between 5300 short transport, and it is likely that the stump was rooted on the and 5100 14C yr BP. It is possible that this event was a single con- bedrock knob. The site is only 600 m from the 2002 ice margin, tinuous advance that happened over 1300 years, but more likely it but the glacier would have to thicken considerably to cover it; thus was a period like the ‘Little Ice Age’ with several advances. Sphinx Glacier was much more extensive 1600 14C yr BP than at Evidence for an advance around 4300 14C yr BP was found only present. Supporting evidence for the same advance or a younger at Sphinx Glacier. There, ice advanced at least 500 m farther one comes from the forefield of West Stave Glacier. A small log downvalley than at present (Figure 7). Taken alone, the evidence

Downloaded from http://hol.sagepub.com at COLLEGE OF WOOSTER on January 18, 2008 © 2007 SAGE Publications. All rights reserved. Not for commercial use or unauthorized distribution. Johannes Koch et al.: Pre-‘Little Ice Age’ glacier flucuations in British Columbia 1077 at Sphinx Glacier could be interpreted to indicate slow growth of timescale over the past millennium (Lawrence, 1950; Wiles et al., glaciers between 6000 and 4300 14C yr BP. Combined with evi- 2004; Luckman and Wilson, 2005; Koch et al., 2007). Solanki et al. dence from other forefields, however, it is more likely that glaciers (2004) inferred sunspot numbers over the past 11 000 years from receded between 5300 and 4300 14C yr BP to positions similar to differences in the production of atmospheric 14C recorded in trees. the present before readvancing (Figure 7). Comparison of this record with the record of Holocene glacier fluc- Some glaciers achieved present-day extents prior to 4100 14C yr tuations in Garibaldi Park suggests that the major periods of glacier BP, the time that Helm Glacier advanced into forest and deposited advance correspond with times of low sunspot numbers (Figure 7). till at the site of its present snout. Spearhead Glacier thickened, This correspondence suggests that changes in solar activity may and Sphinx Glacier advanced up to 800 m, between 3900 and have affected glacier behaviour in Garibaldi Park and likely else- 3600 14C yr BP. Lava and Decker glaciers thickened and advanced where during the Holocene. The period between 3000 and 4500 cal. into mature forests between 3200 and 2900 14C yr BP, reaching to yr BP, however, shows little correspondence between glacier activ- within 500 m of their Holocene maximum positions at this time. It ity and solar activity and requires other explanations. is not known whether this was a single advance with slow growth over 1200 years or was more complex with several advances. Sphinx Glacier retreated to near its present margins after this Conclusions advance period, before readvancing into mature forest around 1600 14C yr BP. Stave Glacier was near its Holocene maximum by about 1100 Holocene glacier fluctuations in Garibaldi Provincial Park were 14C yr BP. This advance period was also followed by recession, before determined through geomorphic mapping and radiocarbon dating the start of the ‘Little Ice Age’ about AD 1000 (Koch et al., 2007). of detrital and in situ fossil wood in glacier forefields. Glaciers in the park were smaller than at present in the early Holocene. Five Regional comparisons major periods of pre-‘Little Ice Age’ glacier advance date to Evidence of glacier activity in the early Holocene in western 7700–7300, 6400–5100, 4300, 4100–2900 and 1600–1100 14C yr Canada is sparse, but available data indicate that glaciers were BP. These periods are broadly synchronous with advances docu- smaller than today at that time (Ryder and Thomson, 1986; mented elsewhere in western Canada. The evidence from Garibaldi Luckman, 1988). Advances during the early Holocene were likely Park suggests that Holocene climate was much more varied than minor and short-lived. Menounos et al. (2004) summarized evi- previously thought. Glaciers approached their Holocene maximum dence for an advance in Garibaldi Park at the time of the 8.2 ka positions on three occasions prior to the ‘Little Ice Age’. Glaciers cooling event, and a glacier forefield in the Rocky Mountains in Garibaldi Park, notably Sphinx Glacier, afford the most com- (Luckman, 1988) also has evidence for this event. Dated samples plete record of Holocene glacier activity in western Canada. The in Garibaldi Park are near present-day glacier margins, indicating glacial record is in good agreement with the record of reconstructed that ice extent was less than today prior to the advance and that the sunspot numbers during the Holocene, suggesting that glacier fluc- advance was minor. tuations in Garibaldi Park may have been forced in part by changes Glacier advances between 6000 and 5000 14C yr BP in western in solar activity. Canada have been termed the ‘Garibaldi phase’ (Ryder and Thomson, 1986). Evidence for this event has previously been lim- ited to a few sites in the Coast Mountains (Ryder and Thomson, Acknowledgements 1986; Laxton et al., 2003; Smith, 2003). Detrital wood in the Canadian Rocky Mountains dating to this period has been inter- We thank Chris Platz and the other rangers of Garibaldi Park for preted to record treelines higher than today (Luckman et al., their support, and Sami Solanki for providing data on sunspot num- 1993), but it may also indicate glacier advance at this time. The bers. Will Keats-Osborn, Janet Guglich, Chanone Ryane, Vanessa Garibaldi phase evidently was a lengthy period during which gla- Vallis, Clay Carlson, Scott Carlson and Matt Macleod provided ciers achieved fairly extensive positions. It is likely a much more assistance in the field. The Natural Sciences and Engineering complex event than evidence currently suggests. Research Council of Canada and Geological Society of America Glacier advances between 3300 and 1900 14C yr BP are termed the provided funding for the research. Early drafts of the manu- ‘Tiedemann Advance’ in the Coast Mountains (Ryder and Thomson, script benefited from reviews by B.H. Luckman, K. Nicolussi, 1986). The same event in the Rocky Mountains, although there dated C. Schlüchter and D.J. Smith. to between 3300 and 2500 14C yr BP, is termed the ‘Peyto Advance’ (Luckman et al., 1993). Evidence for advances at this time is wide- spread in western Canada (Denton and Stuiver, 1966; Rampton, 1970; References Denton and Karlén, 1977; Osborn, 1986; Osborn and Karlstrom, 1989; Alley, R.B. and Ágústsdóttir, A.M. 2005: The 8 ka event: cause and Luckman et al., 1993; Luckman, 1995, 2006; Jackson and Smith, consequences of a major Holocene abrupt climate change. Quaternary 2005; Lewis and Smith, 2005; Smith et al., 2005). In most areas, gla- Science Reviews 24, 1123–49. ciers achieved extents only slightly smaller than during the ‘Little Ice Bond, G., Kromer, B., Beer, J., Muscheler, R., Evans, M.N., Age’. The Tiedemann/Peyto phase was probably as complex as the Showers, W., Hoffmann, S., Lotti-Bond, R., Hajdas, I. and Bonani, ‘Little Ice Age’ and included multiple advances (Luckman, 1995; G. 2001: Persistent solar influence on North Atlantic climate during Reyes and Clague, 2004; Haspel et al., 2005). the Holocene. Science 294, 2130–36. Evidence for an advance in the first millennium AD is wide- Brooke, R.C., Peterson, E.B. and Krajina, V.J. 1970: The subalpine spread in western North America (Reyes et al., 2006). Glaciers mountain hemlock zone. Ecology of Western North America 2, probably achieved extents at this time that were comparable with 148–349. those of the preceding and following advance periods. Denton, G.H. and Karlén, W. 1973: Holocene climatic variations – their pattern and possible cause. Quaternary Research 3, 155–205. ––— 1977: Holocene glacial and tree-line variations in the White Climate forcing River Valley and Skolai Pass, Alaska and Yukon Territory. Some researchers have noted a relation between Holocene glacier Quaternary Research 7, 63–111. fluctuations and changes in solar activity (Denton and Karlén, 1973; Denton, G.H. and Stuiver, M. 1966: Neoglacial chronology, north- Karlén and Kuylenstierna, 1996). Sunspot numbers and glacier eastern St. Elias Mountains, Canada. American Journal of Science fluctuations in Alaska and western Canada correspond on a decadal 264, 577–99.

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