This Article Was Published in an Elsevier Journal. the Attached Copy Is Furnished to the Author for Non-Commercial Research

This article was published in an Elsevier journal. The attached copy is furnished to the author for non-commercial research and education use, including for instruction at the author’s institution, sharing with colleagues and providing to institution administration. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier’s archiving and manuscript policies are encouraged to visit:

http://www.elsevier.com/copyright Author's personal copy

Available online at www.sciencedirect.com

Palaeogeography, Palaeoclimatology, Palaeoecology 257 (2008) 244–259 www.elsevier.com/locate/palaeo

Midge-inferred Holocene summer temperatures in Southeastern British Columbia, Canada ⁎ Marianne Chase a, Christina Bleskie b, Ian R. Walker b, , Daniel G. Gavin c, Feng Sheng Hu d

a Department of Biological Sciences, 2500 University Drive N.W., University of Calgary, Calgary, Alberta, Canada T2N 1N4 b Biology, and Earth & Environmental Sciences, University of British Columbia Okanagan, 3333 University Way, Kelowna, British Columbia, Canada V1V 1V7 c Department of Geography, University of Oregon, Eugene, OR 97403-1251, USA d Department of Plant Biology, University of Illinois, Urbana, IL 61801, USA Received 6 December 2006; received in revised form 3 October 2007; accepted 5 October 2007

Abstract

Using fossil midge stratigraphies, we inferred Holocene summer temperatures at three subalpine lakes in eastern British Columbia. The late-glacial sediment indicated cool conditions, with an abundance of Microspectra atrofasciata/radialis type fossils at Thunder Lake and Redmountain Lake, and Sergentia at Windy Lake. Sergentia and Tanytarsus lugens/Corynocera oliveri type were dominant in the early Holocene, together with Chironomus at Redmountain Lake. At Thunder and Windy lakes, the early Holocene was dominated by warm-adapted taxa such as Microtendipes. Quantitative midge-temperature inference models reconstruct a 4 to 8 °C rise in mean July air temperature for Windy and Thunder lakes at the Pleistocene/Holocene transition. Early- Holocene temperatures averaged 3 to 4 °C warmer than those extant today. In contrast, no long-term temperature trend was evident at Redmountain Lake. This site may not reflect actual trends in air temperature due to runoff from a persistent snow pack in the watershed. Comparison of midge and pollen data suggests an inverse relationship between summer temperature and precipitation through the middle to late Holocene. © 2007 Elsevier B.V. All rights reserved.

Keywords: Chironomidae; Transfer function; Palaeotemperature reconstruction; Holocene; British Columbia; Climate change

1. Introduction 2006; Briner et al., 2006). Although the number of fossil midge records is still small relative to the number Identifiable remains of Chironomidae and other of fossil-pollen studies, the network of sites is growing midges are abundant in lake sediments and used widely rapidly. Midge-based palaeoclimate studies have been for quantitative palaeoclimate reconstruction (e.g., conducted throughout much of the world, including Walker, 1995; Porinchu et al., 2003; Antonsson et al., locations in Europe (e.g., Brooks, 2006), New Zealand (e.g., Woodward and Shulmeister, 2007), Africa, South America (e.g., Verschuren and Eggermont, 2006), and ⁎ Corresponding author. Fax: +1 250 807 8004. North America (e.g., Walker and Cwynar, 2006). As the E-mail address: [email protected] (I.R. Walker). density of study sites and geographic coverage

M. Chase et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 257 (2008) 244–259 245 increases, midge-based palaeoclimatology will soon 1988, 1989). Subsequent midge research established allow spatial patterns in postglacial climatic change to quantitative reconstructions of both temperature and be examined. salinity, farther to the east, in the southern interior region In 1987, the first postglacial record of fossil midges (Heinrichs et al., 1997; Smith et al., 1998; Heinrichs in British Columbia (BC) was published by Walker and et al., 1999; Heinrichs et al., 2001; Palmer et al., 2002; Mathewes (1987). Three additional records were soon Rosenberg et al., 2004). Palaeosalinity records from added in southern coastal BC (Walker and Mathewes, low-elevation interior sites were regarded as indicators

Fig. 1. a. Location of our study region (rectangle) in southern British Columbia, Canada. b. Locations of Redmountain Lake, Thunder Lake, and Windy Lake in our study region. Locations of other midge palaeotemperature sites in this region are also indicated: 1. Hippa Lake (Walker and Mathewes, 1988), 2. Misty Lake (Walker and Mathewes, 1989), 3. Marion and Mike Lakes (Walker and Mathewes, 1987, 1989), 4. Frozen Lake (Rosenberg et al., 2004), 5. Cabin Lake and 3M Pond (Smith et al., 1998; Palmer et al., 2002), 6. Crater Lake and Lake of the Woods (Palmer et al., 2002), 7. Eagle Lake (Rosenberg et al., 2004). c–e. Shaded relief maps of the study lakes showing major streams and ice fields. Author's personal copy

246 M. Chase et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 257 (2008) 244–259 of hydrological balance (precipitation–evaporation) important to obtain several midge reconstructions within a (Heinrichs and Walker, 2006). Sites at alpine tree-line, region to improve the strength of the temperature signal where a cool and wet climate results in little evaporative (e.g., Velle et al., 2005). As the midge reconstructions are enrichment of lake water, served as sensitive palaeo- compared to other proxies, the strength of the signal is thermometers (Walker and Cwynar, 2006). further enhanced. Midge reproduction depends upon summer air temper- In this paper we outline midge records and derive ature, and as such, past temperature may be well reflected in palaeoclimatic inferences for three new sites from the their relative species abundances preserved within the fossil Columbia Mountains in eastern British Columbia, Canada. record (Larocque and Hall, 2003). However, the midge life These sites expand the British Columbia network farther to cycle is also influenced by other aspects of their the north and east. We also compare the temperature re- environment such as pH (e.g., Velle et al., 2005), salinity constructions with a moisture reconstruction inferred from (Walker et al., 1991) and trophic status (e.g., Broderson and a major late-Holocene vegetation change. Anderson, 2002). For example, Rosenberg et al. (2004) found that one site produced markedly different midge 2. Study sites assemblages relative to surrounding sites, possibly due to changing water depths through the Holocene. Other site- Windy Lake, Thunder Lake and Redmountain Lake specific factors that might decouple the midge assemblage (informal names; Fig. 1) are small subalpine lakes from air temperature are persistent snow-banks or springs located within the Engelmann Spruce Subalpine Fir that maintain a low water temperature through the summer (ESSF) biogeoclimatic zone in the ‘interior wet belt’ of (Brooks and Birks, 2000a), or high lakewater salinities eastern British Columbia. The ESSF is characterized by derived from high evaporative enrichment. Therefore, it is cool, moist, snowy conditions, and a mean annual

Table 1 AMS radiocarbon dates and volcanic tephras from sediment cores from Redmountain Lake, Thunder Lake, and Windy Lake, British Columbia Depth Laboratory number or tephra a14C age Material dated 2σ calibrated age range b Windy Lake 42–42.5 St. Helens Wn –– 471 c 115 114,132 2245±70 Cone bract 2153–2342 173 101,681 4020±100 Wood (unidentified) 4318–4804 223 114,133 4800±60 Abies wood 5472–5597 287–373 Mazama ash –– 7627 d 420 101,682 8350±80 Bark 9275–9472 475 101,683 9950±120 Pinus needle 11,234–11,697

Thunder Lake 63 114,128 1325±70 Abies needle 1178–1302 96 114,856 2610±90 Abies and Pinus needles 2506–2844 103 114,129 4115±70 Pinus albicaulis needle and fascicles, Picea needle 4524–4820 125 101,693 4595±80 e 1 Abies needle; 2 pieces of wood 5059–5464 130 114,857 5330±80 Abies lasiocarpa needle 5994–6267 170–202 Mazama ash –– 7627 d 285 114,130 8630±70 Needle fragments and woody stems 9534–9671 318 114,131 9710±70 3 woody twigs 10,892–11,222

Redmountain Lake 128 114,126 1215±70 Abies needle 1059–1261 236 101,694 2315±80 Abies needle 2159–2458 409 101,695 4420±80 Cone scale 4867–5276 520 114,127 8885±100 Abies needle 9779–10,186 a Laboratory numbers assigned by the Center for Accelerator Mass Spectrometry (CAMS), Lawrence Livermore National Laboratory. Tephra names in italics. b Minimum and maximum of 2σ age ranges only. Calibration follows Reimer et al. (2004). c From Yamaguchi (1983). d From Zdanowicz et al. (1999). e Date rejected. Author's personal copy

M. Chase et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 257 (2008) 244–259 247 temperature ranging from −2to+2°C(Coupé et al., Redmountain Lake; 2003) during the summer. All lakes 1991). Average monthly temperatures may remain were cored using a 5-cm diameter Livingstone piston below 0 °C for more than five months, while corer (Wright, 1967) from a platform on inflatable rafts. temperatures greater than 10 °C may only occur for up Two cores with overlapping 1-m drives were obtained to two months out of the year, if at all. Precipitation is from each lake and transported to a 4 °C cold room. highly variable in this zone, and may vary from as little Cores were split longitudinally and described visually. as 400 mm per year to 2200 mm per year depending on Loss-on-ignition at 550 °C (LOI) was determined on the area. Due to cool conditions, more than half of 1 ml samples taken every 5 to 10 cm (Heiri et al., 2001). the annual precipitation is received as snowfall (Coupé A total of 16 AMS radiocarbon dates (Table 1) were et al., 1991). At our study sites, annual precipitation obtained from terrestrial plant macrofossils from the ranges from 1200–1500 mm (Daly et al., 1994). The three sediment cores (Redmountain: 4; Thunder: 7; low-elevation forest below each study site is dominated Windy: 5). In addition, three tephra layers could be by western hemlock (Tsuga heterophylla) and western positively identified at one or more of the study sites red cedar (Thuja plicata). based on their stratigraphic position and known tephra Windy Lake (49°48′48″N, 117°52′38″W; 1813 m a.s. trajectories in the region (Foit et al., 2004). The dates l.), in the Selkirk Mountains between Arrow Lake and the were converted to calibrated ages using the INTCAL04 Slocan River (Fig. 1c), is a 3.2 ha cirque basin with a calibration curve (Reimer et al., 2004) and CALIB 5.0.1 maximum depth of 3.9 m. The bedrock of the area is (http://depts.washington.edu/qil/calib/calib.html) with composed of granite, monzonite, and granodiorite (Massey the atmospheric decadal calibration data set. et al., 2005). Windy Lake is surrounded by continuous At Windy Lake and Redmountain Lake, the lack of forest of Engelmann spruce (Picea engelmannii)and stratigraphic discontinuities and the strong visual corre- subalpine fir (Abies lasiocarpa). On the east shore, forests lation between parallel core drives (not shown) suggest are interrupted by a fen and avalanche tracks. little local perturbation of the sediment. We therefore used Thunder Lake (52°13′42″N, 119°20′54″W; 1539 m samples from well-correlated overlapping core drives to a.s.l.), in the Cariboo Mountains 13 km north of Blue derive a continuous, composite record of the lakes' River, British Columbia (Fig. 1d), is a 19.7 ha basin with sediment. Ages were assigned to sample depths by inter- a maximum depth of 2.9 m. The bedrock is composed of polating between dates using a cubic spline curve fit. At gneiss and biotite–quartz schist (Massey et al., 2005). Thunder Lake, above the Mazama tephra, parallel core Trees in the subalpine parkland near the lake consist drives correlated poorly with each other. Therefore, we mainly (N90%) of subalpine fir, with Engelmann spruce obtained samples from a single core. Subsequent and whitebark pine (Pinus albicaulis) also present. radiocarbon dating revealed a major age discontinuity Surrounding meadows consist mainly of sedges (Carex), between two core drives at 100 cm, resulting in a gap in mountain heather (Cassiope, Phyllodoce) and pussytoes the record between 2700 and 4600 cal yr BP. We (Antennaria). conservatively assigned sample ages at Thunder Lake Redmountain Lake (53°55′17″N; 121°17′39″W; using linear interpolation. 1590 m a.s.l.), 96 km east of Prince George near the Fraser River (Fig. 1e), is a 5.9 ha cirque basin with a 3.2. Midge analyses maximum depth of 2.8 m. The bedrock in the area is composed of calcareous shale and dolomite (Massey Sediments were processed following the standard et al., 2005). Redmountain Lake is located at local procedures outlined in Walker (2001).Sediment treeline with sparse patches of subalpine fir and lush volumes were measured by displacement in de-ionized meadows of marsh-marigold (Caltha), false hellebore water. Pretreatment procedures involved carbonate (Veratrum), glacier lily (Erythronium), mountain-heath- removal in 10% HCl and deflocculation in warm 5% er, buttercups (Ranunculus), anemones (Anenome), and KOH. The resulting slurry was washed on a 95 μm valerian (Valeriana). Nitex sieve. Sediment retained on the sieve was back- washed with de-ionized water into a beaker. This residue 3. Methods was later hand-sorted in a Bogorov counting tray using a dissecting microscope at 25–50× magnification, and 3.1. Sampling methods and chronology fine-tipped forceps. In addition to chironomid (non- biting midge), ceratopogonid (biting midge) and The three lakes were accessed by either logging road simuliid (black fly) head capsules, the remains of (Windy Lake; 2002) or by helicopter (Thunder Lake and Acari (mites), and mandibles of Chaoborus (phantom Author's personal copy

248 M. Chase et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 257 (2008) 244–259 midges) and Ephemeroptera (mayflies) were separated (Grimm, 1987), following square-root transformation of from the sediment. The fossil remains were transferred the data. onto coverslips, allowed to air dry, and ultimately Mean July air temperature was estimated for each mounted onto glass slides using Entellan® mounting fossil midge assemblage using a database of 53 modern medium. midge assemblages from lake sites in southern British Sampling was focused at Windy Lake because this site Columbia that occur over a geographic gradient of had the best sediment chronology and chironomid summer temperature (Rosenberg et al., 2004). Several preservation. At Windy Lake 0.5 to 2.5 ml of sediment rare taxa in the fossil midge assemblages were merged was processed from 75 intervals spanning 45 to 575 cm. into higher taxonomic groups to harmonize the fossil At Thunder Lake 0.5 to 1.5 ml of sediment was processed midge taxonomy with that used by Rosenbergetal. from 20 intervals spanning 15 to 350 cm. At Redmountain (2004). We used seven inference models for the tem- Lake 0.4 to 5.4 ml of sediment was processed from 31 perature reconstructions because of strengths and intervals spanning 1 to 575 cm. We sought to obtain a weaknesses associated with each model (Lotter et al., minimum of 50 midge remains from each level (Heiri and 1999). The modeling methods included 1) Weighted Lotter, 2001; Larocque, 2001; Quinlan and Smol, 2001). averaging (with both classical (WAclass) and inverse Because sufficient sediment was not available for the deshrinking (WAinv), with and without tolerance analyses, this quota was not met at a few levels, most downweighting (WA(tol)class and WA(tol)inv); weight- notably in the earliest postglacial sediments. ed-averaging partial least squares (WAPLS-2), and Identifications were made using BH-2 and BX51 partial least squares regression (PLS-1) in CALI- Olympus compound microscopes at magnifications of BRATE vers. 0.82 (ter Braak and Juggins, 1993; ter 100–400×. Chironomids were identified primarily Braak et al., 1993; Juggins, 1997). Descriptions of the according to illustrations, keys and descriptions con- models may be found in Palmer et al. (2002).Forlack tained within Oliver and Roussel (1983), Wiederholm of a ‘best’ model, we present all model results, and a (1983), Schmid (1993), and the WWW Field Guide to robust mean that down-weights outliers (Tukey Subfossil Midges (Walker, 2000) as well as a photo- biweight mean; Mosteller and Tukey, 1977), for each graphic reference collection maintained at the Univer- sample. sity of British Columbia Okanagan. 4. Results 3.3. Data analysis 4.1. Windy Lake Data were collated using TILIAversion 2.0.b.4 (Grimm, 1993). TGVIEW 2.0.2 was used to prepare percentage 4.1.1. Sediment lithology and chronology stratigraphic diagrams (Grimm, 2004). The stratigraphies The Windy Lake sediment core (590 cm) consisted were subdivided into a series of zones via CONISS of sand, silt, and clay (b3% LOI) from the base to

Fig. 2. Age–depth relationships (dashed line) and loss-on-ignition (LOI; solid line) from sediment cores from Windy Lake, Thunder Lake, and Redmountain Lake, British Columbia. Circles indicate the median calibrated radiocarbon age and bars above and below the circles indicate the 2σ age range of the calibrated ages. The thick Mazama tephra layers and the thin St. Helens Wn tephra are shown. Note the gap in the Thunder Lake chronology at 100 cm and the different LOI-axis scale at Redmountain Lake. Author's personal copy .Caee l aaoegah,Pleciaooy aaoclg 5 20)244 (2008) 257 Palaeoecology Palaeoclimatology, Palaeogeography, / al. et Chase M. – 259

Fig. 3. Percent midge stratigraphy diagram for Windy Lake. Chironomid species are ordered by increasing temperature optima from left to right. Taxa without known optima for our area are placed to the right of the diagram. A few rare taxa have been excluded. 249 Author's personal copy

250 M. Chase et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 257 (2008) 244–259

Fig. 4. Chironomid-inferred reconstructions of mean July air temperature at a) Windy, b) Thunder, and c) Redmountain lakes, British Columbia: WAINV (Weighted Averaging, deshrinking by inverse regression), WAINV(tol) (Weighted Averaging with tolerance down-weighting, deshrinking by inverse regression), WACLS (Weighted Averaging, deshrinking by classical regression), WACLS(tol) (Weighted Averaging with tolerance downweighting, deshrinking by classical regression), WAPLS-2 (Weighted averaging partial least squares with 2 components), PLS-1 (Partial least squares with 1 component), PLS-2 (Partial least squares with 2 components). The fitted line is based on a robust mean of the seven temperature estimates from each sample. The approximate modern mean July temperature at each site is estimated to be ca. 10 °C, and is indicated for each site for reference. The horizontal bars indicate major climatic events, including glacial advances as identified elsewhere in the Columbia and Rocky Mountains (Peyto Advance, Luckman et al., 1993; Little Ice Age, Luckman, 2000). Author's personal copy

M. Chase et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 257 (2008) 244–259 251

476 cm. At 476 cm (11,400 cal yr BP), the sediment zone WIN-3, suggesting a decrease in summer tempera- transitioned abruptly to gyttja (Fig. 2). With the tures during the middle Holocene. exception of a thick Mazama tephra at 373–287 cm, the sediment consisted of uniform dark brown gyttja 4.1.2.4. Zone WIN-4 (267.5–45 cm; 6900–500 cal (30–45% LOI) from 476 cm to the surface. The BP). Subtribe Tanytarsina, Procladius, Cricotopus/ radiocarbon dates indicate a relatively constant sedi- Orthocladius and Psectrocladius dominate this zone. ment accumulation rate through the Holocene. Warm-water midges (e.g., Microtendipes, Polypedilum) constitute only a trace of the fauna. In contrast, several 4.1.2. Midge stratigraphy cold-adapted and eurythermic midges (e.g.,Psectrocla- The subtribe Tanytarsina and Procladius dominate dius, Micropsectra, Cricotopus/Orthocladius, Protany- throughout most of the core (Fig. 3). In addition to large pus, Diamesa, Oliveridia/Hydrobaenus, Pagastia, numbers of lacustrine species, small numbers of Pseudodiamesa,andTanytarsus lugens/Corynocera rheophilous midges (e.g., Rheocricotopus) are present oliveri type) are more abundant. This suggests a further throughout, and are likely derived from small, possibly decrease in summer temperatures during the late intermittent streams or seeps entering the lake. CONISS Holocene. and visual inspection suggested four zones (Fig. 3). 4.1.3. Temperature reconstruction 4.1.2.1. Zone WIN-1 (525–455 cm; 13,000–10,700 cal During the late-glacial period, summer tempera- BP). This zone is characterized by the high abundance tures at Windy Lake ranged between 6.5 and 12 °C of subtribe Tanytarsina, and by the occurrence of two (Fig. 4a). The coldest temperatures are inferred ca. cold-stenothermic taxa, Stictochironomus and Tanytar- 12,500 cal yr BP in the midst of the Younger Dryas sus lugens/Corynocera oliveri type. Warm water taxa chronozone. The transition from the late glacial to early such as Polypedilum and Tribe Pentaneurini occur Holocene was marked by a rapid increase in inferred sporadically within the zone, but only at trace summer temperatures, rising to 13.5 to 14.5 °C ca. abundance. The warm-adapted Dicrotendipes is an 11,500 to 10,500 cal yr BP. Early-Holocene summer exception, and accounts for nearly 20% of the midges temperatures remained 3 to 4 °C warmer than today at the beginning of this zone. The abundance of cold from 10,500 to 9000 cal yr BP. Early-Holocene tem- stenotherms and dearth of warm-water taxa is typical for peratures reached a low of 10.4° ca. 8250 cal yr BP. late-glacial assemblages, reflecting the cold climate that Midge-inferred temperatures then rose by a couple of prevailed during deglaciation (Walker and Mathewes, degrees, until ca. 6000 cal yr BP, when air temperatures 1987, 1989; Thompson et al., 1993; Smith et al., 1998; cooled to nearly 9 °C, and remained around an average Palmer et al., 2002; Rosenberg et al., 2004). of 9.5 °C throughout the remainder of the mid to late Holocene (Fig. 4a). 4.1.2.2. Zone WIN-2 (455–403.5 cm; 10,700–8800 cal BP). Overall this zone is characterized by an abun- 4.2. Thunder Lake dance of warm-adapted taxa, and a decrease in cold- stenotherms. Stictochironomus and Tanytarsus lugens/ 4.2.1. Sediment lithology and chronology Corynocera oliveri type are rare. Warm-adapted midges The Thunder Lake sediment core consisted of sand, such as Microtendipes, Endochironomus, Glyptoten- silt, and clay (ca. 5% LOI) from the core base (345 cm) dipes, Stempellinella/Zavrelia,andChaoborus are more to 318 cm (Fig. 2). With the exception of a 32-cm abundant in zone WIN-2 than elsewhere in the core. Mazama tephra layer, the sediment above 295 cm con- This zone is also marked by a lower abundance of sisted of uniform dark brown gyttja (30–40% LOI). subtribe Tanytarsina than observed for the other three The start of the transition to organic sediments at zones. The prevalence of warm-adapted taxa is 318 cm dated to ca. 11,000 cal yr BP. indicative of significantly higher temperatures during the early Holocene than today. 4.2.2. Midge stratigraphy The Thunder Lake midge stratigraphy was divided into 4.1.2.3. Zone WIN-3 (403.5–267.5 cm; 8800–6900 cal three major zones based on cluster analysis and visual BP). Dominant taxa include Tanytarsina, Procladius inspection (Fig. 5). The subtribe Tanytarsina dominated and Chironomus. Warm water midges, such as Micro- the chironomid community throughout the core; however, tendipes, Endochironomus, Glyptotendipes, Stempelli- this is a broad taxonomic group and as such does not nella/Zavrelia,andChaoborus decrease or disappear in provide much information regarding temperature (Smith, Author's personal copy 252 .Caee l aaoegah,Pleciaooy aaoclg 5 20)244 (2008) 257 Palaeoecology Palaeoclimatology, Palaeogeography, / al. et Chase M. – 259

Fig. 5. Percent midge stratigraphy diagram for Thunder Lake. Chironomid species are ordered by increasing temperature optima from left to right. Taxa without known optima for our area are placed to the right of the diagram. A few rare taxa have been excluded. Author's personal copy .Caee l aaoegah,Pleciaooy aaoclg 5 20)244 (2008) 257 Palaeoecology Palaeoclimatology, Palaeogeography, / al. et Chase M. – 259

Fig. 6. Percent midge stratigraphy diagram for Redmountain Lake. Chironomid species are ordered by increasing temperature optima from left to right. Taxa without known optima for our area are placed to the right of the diagram. A few rare taxa have been excluded. 253 Author's personal copy

254 M. Chase et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 257 (2008) 244–259

1997). Psectrocladius, a eurythermic genus was also uous light gray silts and clays with indistinct banding are abundant throughout much of the core (Fig. 5). evident between 550 and 300 cm, but these are also inorganic (b10% LOI; Fig. 2).Above300cmthesediment 4.2.2.1. Zone THU-1 (350–300 cm; 12,700–10,300 cal core consisted of distinctly banded brown–gray silts and BP). This zone is characterized by the very high clays (ca. 4% LOI). Radiocarbon dates indicate very slow abundance of subtribe Tanytarsina head capsules. The sediment accumulation rates before ca. 5000 cal yr BP zone begins with Microspectra atrofasciata/radialis (400 cm) and a fairly constant sediment accumulation rate type, a cold stenothermous taxon, accounting for nearly thereafter (Fig. 2). No volcanic tephras were evident in this 15% of the midges found. Subsequently, M. atrofas- core. ciata/radialis type decreases in abundance. Near the end of the zone there is a small peak in the warm indicator 4.3.2. Midge stratigraphy Pagastiella. A large proportion of the midge remains were uni- dentifiable owing to poor preservation in the Red- 4.2.2.2. Zone THU-2 (300–97.5 cm; 10,300–3000 cal mountain Lake core, and had to be excluded from the BP). This zone has a much more diverse midge statistical analysis and interpretation. The subtribe assemblage. It is distinguished especially by the greatly Tanytarsina were the dominant midges throughout the decreased abundance of Tanytarsina, and by high Redmountain Lake core. Chironomus and Sergentia relative abundances of Cladotanytarsus mancus and were the next most prominent, followed by Tanytarsus Chironomus. Although two Chironomus species are lugens/Corynocera oliveri type, and Procladius. Rheo- reported from the high arctic (Danks, 1981), most cricotopus, Parametriocnemus type, Limnophyes and Chironomus are associated with warm water habitats. Doithrix/Pseudorthocladius type are rheophilous taxa Psectrocladius are eurythermic and much more abun- derived from small streams entering Redmountain Lake. dant in zone THU-2 than previously. A broad peak in CONISS identified two zones in the Redmountain Lake Microtendipes abundance, and the peak abundance of stratigraphy (Fig. 6). Chaoborus suggest that summer temperatures may have been highest early in this zone. Several other 4.3.2.1. Zone REDMTN-1 (580–540 cm; 10,700– midge taxa commonly associated with warm, low- 10,500 cal BP). This zone is distinguished especially elevation lakes (e.g., Polypedilum, Tribe Pentaneurini, by the great abundance of Microspsectra atrofasciata/ Cladopelma and Glyptotendipes) also occur as trace radialis type. components of this zone's fauna. 4.3.2.2. Zone REDMTN-2 (540–0 cm; 10,500 cal BP– 4.2.2.3. Zone THU-3 (97.5–15 cm; 3000–250 cal BP). present). The subtribe Tanytarsina remains dominant This zone is distinguished by a return to Tanytarsina through this zone, but Micropsectra now constitutes only a dominance, and a reduction of warm-water taxa including trace component of the fauna. The subzones are indistinct, Chironomus. Although Psectrocladius remains abundant but reflect an increased abundance of Chironomus remains in zone THU-3, the assemblage is otherwise very similar to in the upper half of the Redmountain Lake core. that in THU-1, suggesting a return to climatic conditions similar to those extant during the late glacial or earliest 4.3.3. Temperature reconstruction Holocene. In contrast to Windy Lake and Thunder Lake, Redmountain Lake temperature reconstructions indi- 4.2.3. Temperature reconstruction cate very little millennial-scale trend (Fig. 4c). In Midge-inferred temperatures of the early Holocene particular, the four early-Holocene samples from Red- fluctuate about an average of 11.7° at Thunder Lake mountain Lake do not show higher summer tempera- (Fig. 4b). The temperature trend is similar to that of Windy turesthanthesamplesfromthemidtolateHolocene. Lake, with the late Holocene being cooler than the early Throughout the Holocene temperatures range from 8.0° Holocene (by about 1.5°). to 11.2°, with an average of 9.6°.

4.3. Redmountain Lake 5. Discussion

4.3.1. Sediment lithology and chronology Redmountain Lake exhibits very little trend in Below 550 cm sediments were highly inorganic temperature. However, the Holocene temperature recon- (LOIb2%) and chironomid remains were absent. Contin- struction for Thunder Lake parallels that of Windy, with a Author's personal copy

M. Chase et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 257 (2008) 244–259 255 warm early Holocene and cool late Holocene. The validity Rosenberg et al., 2004). On an international scale, the of the reconstructions is supported by a general trend, timing of the transition from Younger Dryas to early most striking in the early Holocene, of decreasing Holocene corresponds to that recorded in the GISP2 core temperatures with increasing latitude, from Windy Lake of Greenland, and cores from France and Norway, to Redmountain Lake (Fig. 4). although the magnitude of warming in Greenland and Our discussion of palaeoclimate records focuses on our France is two or three times that observed in the Windy southernmost site, Windy Lake, since this site provides Lake core (Grootes et al., 1993; Brooks and Birks, 2000c; the longest, best-dated, and highest-resolution record. The Ponel et al., 2007). Windy Lake record comprises three distinct phases: 1) a Early-Holocene summer temperatures remained 3 to cold late-glacial interval prior to 11,000 cal yr BP, 2) an 4 °C warmer than today from 10,500 to 9000 cal yr BP. early-Holocene thermal maximum (ca. 10,500 to 6500 cal This inference is also supported by palaeobotanical and yr BP), and 3) a comparatively cool late-Holocene interval midge evidence at other sites (Mathewes, 1985; Hebda, (ca. 6000 cal yr BP to today). 1995; Palmer et al., 2002; Walker and Pellatt, 2003; Rosenberg et al., 2004). Tree-line in BC, for example, 5.1. Late-glacial climate was higher than present during the early to mid- Holocene, as especially indicated by radiocarbon dates Midge-inferred summer temperatures at Windy Lake on stumps preserved above the present-day limit of trees varied from about 6.5 to 12 °C through the late glacial, (Clague and Mathewes, 1989). averagingabout1to2°Ccoolerthantoday.Thesample The lowest early-Holocene temperature inference resolution is inadequate to confidently resolve the late- dates to ca. 8250 cal yr BP (ca. 2 °C cooler than the glacial pattern of climatic change; higher resolution adjacent periods), and coincides with a brief cold epi- sampling would be necessary to fully resolve a Younger sode recorded in the GISP2 ice core and possibly in Dryas signal, or the signature of any similar late-glacial palaeoclimate records from other regions of the northern climatic oscillations. The Younger Dryas' occurrence has hemisphere (Alley et al., 1997). Pisaric et al. (2003) been well-documented in eastern Canada (e.g., Levesque have suggested that depression of treeline at a small lake et al., 1997; Whitney et al., 2005), and throughout much of in northeastern British Columbia might have been trig- Europe (e.g., Brooks and Birks, 2000b; Ponel et al., 2007). gered by a cooling ca. 8200 cal yr BP. In contrast, Kurek It has also been reported by Mathewes (1993) and et al. (2004) found that chironomid records from eastern Mathewes et al. (1993) in coastal British Columbia, and North America were unable to detect the 8200 cal yr BP by Reasoner et al. (1994) from the Canadian Rocky event, possibly because this event was relatively short- Mountains. Walker and Pellatt (2003) argue, however, that lived (i.e., centennial-scale; Alley et al., 1997). While a temperature oscillation is not clearly evident in the records interesting, our record does not have sufficient temporal from western Canada, and the observed changes possibly resolution to properly evaluate the correspondence of pertain to shifts in prevailing wind directions and the Windy Lake early-Holocene minimum with the precipitation, accompanying the Cordilleran Ice retreat. GISP2 8200 cal yr BP cooling event. They argue that the late-glacial changes in southwestern For the interval 8000 to 6500 cal yr BP, inferred British Columbia may be part of a time-transgressive summer temperatures remained 1.5 to 2.5 °C warmer sequence south of the Cordilleran ice sheet with a cause than today. Similar temperatures to those of today were separate from that of the Younger Dryas event. established by about 6000 cal yr BP, and temperatures continued to decrease until ca. 4000 cal yr BP (Fig. 4). 5.2. Early-Holocene climate This general trend of decreasing summer temperature has been widely documented in western North America At Windy Lake inferred summer temperature warmed (e.g., Hebda, 1995; Walker and Pellatt, 2003) and is rapidly at the late-glacial/Holocene transition to 13.5 to consistent with decreasing summer insolation through 14.5 °C. The range in temperature from the late glacial to this period (Thompson et al., 1993). the early Holocene exceeds the standard error of estimates Redmountain Lake temperature reconstructions fail from individual models, which are typically about 2 °C to display a significant trend. Because the Redmountain (Palmer et al., 2002). This early-Holocene warming is Lake sediments were very low in organic content and similar in magnitude and timing to those inferred at five midge concentrations, the record is relatively sparsely sites to the west of our study region on the Thompson sampled. However, additional samples would not likely Plateau and in the Cascade Mountains of southwestern affect the lack of a millennial-scale trend at this site. This British Columbia (Smith et al., 1998; Palmer et al., 2002; lake occupies a high-elevation cirque where snowfields Author's personal copy

256 M. Chase et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 257 (2008) 244–259 are likely to persist throughout the summer. Meltwater transition to cooler temperatures at Windy Lake occurs at from these snowfields may rapidly replenish the lake as approximately 6000 cal yr BP, while that at Thunder may be indicated by the presence of rheophilous taxa appears to occur sometime between 4500 and 3000 cal yr such as Rheocricotopus, Parametriocnemus type, Lim- BP, with Redmountain Lake maintaining cool tempera- nophyes and Doithrix/Pseudorthocladius type (Gan- tures throughout the Holocene. Other evidence of cooler douin and Franquet, 2002). This, and the shade offered periods within the late Holocene includes an oxygen by steep mountains ridges to the south and west likely isotope record from the Yukon Territory (Anderson et al., maintain cooler conditions at Redmountain Lake than 2005) and widespread evidence of nearby glacial ad- would otherwise be expected at this elevation (Living- vances in the Columbia and Rocky Mountains (Osborn stone et al., 1999; Brooks and Birks, 2000a). and Karlstrom, 1988; Luckman et al., 1993; Luckman, The above explanation for the insensitivity of the 2000). In the Yukon Territory, an initial drop in tem- Redmountain Lake record would be consistent with this perature is observed at approximately 4500 yr BP, before site being situated far from an aquatic ecotone. For warming at 3500 cal yr BP and cooling once more at example, Heegaard et al. (2006) note that distinct 1200 cal yr BP (Anderson et al., 2005). In the Columbia aquatic ecotones exist in the Swiss Alps; such ecotones and Rocky Mountains, periodic glacial advances are likely also exist in the Cordillera. Sites close to ecotonal recorded from approximately 3300 cal yr BP (Osborn boundaries are likely highly sensitive to climatic and Karlstrom, 1988; Luckman et al., 1993) and 800 cal changes while sites distant from these boundaries may yr BP onward (Luckman, 2000). be insensitive (e.g., Weckström and Korhola, 2001; The late-Holocene temperature reconstructions pre- Nyman et al., 2005; Walker, 2006). Unlike their sented here agree well with five of the six midge- terrestrial counterparts, aquatic ecotones are inconspic- palaeotemperature records previously published for uous and their positions can only be recognised after British Columbia (Palmer et al., 2002; Rosenberg extensive regional surveys of lake biota. et al., 2004). These sites generally indicate a mid- Although the existence of an early-Holocene warm Holocene cooling trend, with cool temperatures pre- interval is well established in southern British Columbia, vailing through the late Holocene. Rosenberg et al.'s few palaeoclimatic studies have been conducted in the (2004) Eagle Lake site is anomalous, indicating a late- northern or central regions of the province; thus, the Holocene warming. pattern of Holocene climatic change will require The late-Holocene temperature reconstructions pre- further study in these areas. Recent midge analyses at sented here also agree well with the climatic interpretation sites farther north, in the Yukon and Alaska (Barley, 2004; of vegetation changes. A major feature of the late-Holocene Stepanovic', 2006), suggest that the early-Holocene vegetation in our study area is the establishment of the low- thermal maximum, if it existed in eastern Beringia, was elevation dominant forest species, western hemlock and much weaker than is evident in southern BC. western red cedar, ca. 3000–4000 yr BP (Rosenberg et al., 2003). The modern distributions of these species are 5.3. Late-Holocene climate characterized by a main coastal range and a disjunct interior range in the Columbia Mountains near our study sites, the All three sites show generally cool temperatures and latter of which is commonly referred to as the ‘interior wet little millennial-scale trend during the late Holocene. The belt’. This region contrasts with surrounding areas due to

Fig. 7. Comparison of Cooley Lake western hemlock pollen record (7600 yr BP to present) with the Windy Lake temperature reconstruction. Author's personal copy

M. Chase et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 257 (2008) 244–259 257 increased evapotranspiration from more moist summers structed summer moisture inferred from western hemlock and a lack of a moisture deficit (Gavin and Hu, 2006). Thus, pollen suggests an inverse relationship between summer the pollen record of western hemlock expansion in the late temperature and precipitation through the mid to late Holocene may reflect increasing effective summer mois- Holocene. ture. This interpretation of western hemlock pollen contrasts with that from records a short distance east of Acknowledgements the coastal hemlock zone. In these coastal areas, hemlock pollen has been interpreted as a proxy of the strength of Thank you to Erin Barley, Martin Soste, and Karlyn onshore winds that transport pollen inland (Cwynar, 1993; Westover for assistance with field work, Shelley McIsaac Spooner et al., 2003). This mechanism is not applicable at for the help in processing the sediments, and Lydia our sites, which are quite removed (200–400 km) from the Stepanovic' for the help with identifications. This coastal hemlock populations. research was supported by a grant from the National We overlaid the western hemlock pollen record from Science Foundation to Hu and Gavin. Cooley Lake (39 km to the SE of Windy Lake; Gavin et al., 2006), with the temperature reconstruction from Windy References Lake (Fig. 7). This comparison shows that hemlock increased in the region within 1000 yr of temperatures Alley, R.B., Mayewski, P.A., Sowers, T., Stuiver, M., Taylor, K.C., reaching values typical of the neoglacial cooling at ca. Clark, P.U., 1997. Holocene climatic instability: a prominent, – 4600 cal yr BP. Such a time lag is possible considering the widespread event 8200 yr ago. Geology 25, 483 486. Anderson, L., Abbott, M.B., Finney, B.P., Burns, S.J., 2005. Regional long life span of western hemlock, the competitive post-fire atmospheric circulation change in the North Pacific during the conditions which are frequent in the region, and its possible Holocene inferred from lacustrine carbonate oxygen isotopes, Yukon dispersal route. We suggest two ways in which effective Territory, Canada. Quat. Res. 64, 21–35. moisture increased at ca. 4600 cal yr BP. First, lower Antonsson, K., Brooks, S.J., Seppä, H., Telford, R.J., Birks, H.J.B., 2006. summer temperatures would have placed less evaporative Quantitative palaeotemperature records inferred from fossil pollen and chironomid assemblages from Lake Gilltjärnen, northern central demand on trees, reducing drought injury on species Sweden. J. Quat. Sci. 21, 831–841. susceptible to moisture deficits, such as western hemlock. Barley E.M., 2004. Palaeoclimate Analysis of southwestern Yukon Second, lower summer temperatures may be associated Territory using subfossil chironomid remains from Antifreeze with increased onshore flow, delivering Pacific moisture to Pond. M.Sc. Thesis, Simon Fraser University, Burnaby, Canada. the interior. Such periods would be characterized by a Briner, J.P., Michelutti, N., Francis, D.R., Miller, G.H., Axford, Y., Wooller, M.J., Wolfe, A.P., 2006. A multi-proxy lacustrine record relatively weak Pacific Subtropical High, and would be of Holocene climate change on northeastern Baffin Island, Arctic consistent with decreasing summer insolation through the Canada. Quat. Res. 65, 431–442. late Holocene at this latitude (Thompson et al., 1993). Broderson, K.P., Anderson, N.J., 2002. Distribution of chironomids Therefore, a late-Holocene weakening of the Pacific (Diptera) in low arctic West Greenland lakes: trophic conditions, Subtropical High could result in both cooler summer temperature and environmental reconstruction. Freshw. Biol. 47, 1137–1157. temperature and increased precipitation. Brooks, S.J., 2006. Fossil midges (Diptera: Chironomidae) as palaeoclimatic indicators for the Eurasian region. Quat. Sci. Rev. 6. Conclusion 25, 1894–1910. Brooks, S.J., Birks, H.J.B., 2000a. Chironomid-inferred air tempera- Midge-inferred palaeoclimatic reconstructions suggest tures from Lateglacial and Holocene sites in north-west Europe: progress and problems. Quat. Sci. Rev. 20, 1723–1741. an initial warm period during the early Holocene followed Brooks, S.J., Birks, H.J.B., 2000b. Chironomid-inferred late-glacial air by cooler conditions beginning in the mid or late temperatures at Whitrig Bog, southeast Scotland. J. Quat. Sci. 15, Holocene at both Thunder and Windy lakes. The 759–764. palaeoclimatic reconstruction at Windy and Thunder Brooks, S.J., Birks, H.J.B., 2000c. Chironomid-inferred late-glacial lakes follows the trend observed for five of the six and early-Holocene mean July air temperatures for Kråkenes Lake, western Norway. J. Paleolimnol. 23, 77–89. documented lakes within southern British Columbia, but Clague, J.J., Mathewes, R.W., 1989. Early Holocene thermal maximum with a summer-temperature minimum at 8250 cal yr BP at in western North America: new evidence from Castle Peak, British Windy Lake. The palaeoclimatic reconstruction for Columbia. Geology, 17, 277–280. Redmountain Lake lacks evidence of a warmer early Coupé, R., Stewart, A.C., Wikeem, B.M., 1991. Ch. 15: Engelmann Holocene. This site may be affected by local climate spruce-subalpine fir zone (http://www.for.gov.bc.ca/hfd/pubs/ Docs/Srs/SRs06/chap15.pdf, last accessed 13 June 2007) In: conditions such that runoff from local snowpack Meidinger, D., Pojar, J. (Eds.), Ecosystems of British Columbia, influences summer water temperatures. Comparison of Special Report Series No. 6. British Columbia Ministry of Forests, these summer temperature reconstructions with recon- Victoria, pp. 223–236. Author's personal copy

258 M. Chase et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 257 (2008) 244–259

Cwynar, L.C., 1993. The abundance of exotic western hemlock pollen analysis for Holocene temperature reconstructions. Quat. Sci. Rev. at Waterdevil Lake, White Pass, northern British Columbia: 23, 627–639. a preliminary analysis. Rev. Paleobot. Palynol. 79, 113–119. Larocque, I., 2001. How many chironomid head capsules are enough? Daly, C., Neilson, R.P., Phillips, D.L., 1994. A statistical-topographic A statistical approach to determine sample size for palaeoclimatic model for mapping climatological precipitation over mountainous reconstructions. Palaeogeogr. Palaeoclimatol. Palaeoecol. 172, terrain. J. Appl. Meteorol. 33, 140–158. 133–142. Danks, H.V., 1981. Arctic Arthropods: a Review of Systematics and Larocque, I., Hall, R.I., 2003. Chironomids as quantitative indicators Ecology with Particular Reference to the North American Fauna. of mean July air temperature: validation by comparison with Entomological Society of Canada, Ottawa. 608 pp. century-long meteorological records from northern Sweden. Foit, F.F., Gavin, D.G., Hu, F.S., 2004. The tephra stratigraphy of two J. Paleolimnol. 29, 475–493. lakes in south-central British Columbia, Canada and its implica- Levesque, A.J., Cwynar, L.C., Walker, I.R., 1997. Exceptionally steep tions for mid–late Holocene volcanic activity at Glacier Peak north–south gradients in lake temperature during the last and Mount St. Helens, Washington, USA. Can. J. Earth Sci. 41, deglaciation. Nature 385, 423–426. 1401–1410. Livingstone, D.M., Lotter, A.F., Walker, I.R., 1999. The decrease in Gandouin, E., Franquet, E., 2002. Late Glacial and Holocene summer surface water temperature with altitude in Swiss alpine lakes: chironomid assemblages in ‘Lac Long Inférieur’ (southern France, a comparison with air temperature lapse rates. Arct. Antarct. Alp. 2090 m): palaeoenvironmental and palaeoclimatic implications. Res. 31, 341–352. J. Paleolimnol. 28, 317–328. Lotter, A.F., Walker, I.R., Brooks, S.J., Hofmann, W., 1999. An Gavin, D.G., Hu, F.S., 2006. Spatial variation of climatic and non- intercontinental comparison of chironomid palaeotemperature infer- climatic controls on species distribution: the range limit of Tsuga ence models: Europe vs North America. Quat. Sci. Rev. 18, 717–735. heterophylla. J. Biogeogr. 33, 1384–1396. Luckman, B.H., 2000. The Little Ice Age in the Canadian Rockies. Gavin, D.G., Hu, F.S., Lertzman, K., Corbett, P., 2006. Weak climatic Geomorphology 32, 357–384. control of stand-scale fire history during the late Holocene. Ecology Luckman, B.H., Holdsworth, G., Osborn, G.D., 1993. Neoglacial glacier 87, 1722–1732. fluctuations in the Canadian Rockies. Quat. Res. 39, 144–153. Grimm, E.C., 1987. CONISS: a FORTRAN 77 program for stratigra- Massey, N.W.D., MacIntyre, D.G., Desjardins, P.J., Cooney, R.T., phically constrained cluster analysis by the method of incremental 2005. Digital Geology Map of British Columbia. B.C. Ministry of sum of squares. Comput. Geosci. 13, 13–35. Energy and Mines, Geofile 2005–7. Grimm, E.C., 1993. TILIA 2.0b.4 (Computer Software). Illinois State Mathewes, R.W., 1985. Paleobotanical evidence for climatic change in Museum, Research and Collections Center, Springfield, Il. southern British Columbia during late-glacial and Holocene time. Grimm, E.C., 2004. TGVIEW 2.0.2 (Computer Software). Illinois Syllogeus 55, 397–422. State Museum, Research and Collections Center, Springfield, Il. Mathewes, R.W., 1993. Evidence for Younger Dryas—age cooling on Grootes, P.M., Stuiver, M., White, J.W.C., Johnsen, S., Jouzel, J., the North Pacific coast of America. Quat. Sci. Rev. 12, 321–331. 1993. Comparison of oxygen isotope records from the GISP2 and Mathewes, R.W., Heusser, L.E., Patterson, R.T., 1993. Evidence for a GRIP Greenland ice cores. Nature 366, 552–554. Younger Dryas-like cooling event on the British Columbia coast. Hebda, R.J., 1995. British Columbia vegetation and climate history Geology 21, 101–104. with focus on 6 ka BP. Géogr. Phys. Quat. 49, 55–79. Mosteller, F., Tukey, J.W.,1977. Data Analysis and Regression: a Second Heegaard, E., Lotter, A.F., Birks, H.J.B., 2006. Aquatic biota and the Course in Statistics. Addison-Wesley, Reading (MA). 608 pp. detection of climate change: are there consistent aquatic ecotones? Nyman, M., Korhola, A., Brooks, S.J., 2005. The distribution and J. Paleolimnol. 35, 507–518. diversity of Chironomidae (Insecta: Diptera) in western Finnish Heinrichs, M.L., Walker, I.R., 2006. Fossil midges and palaeosalinity: Lapland, with special emphasis on shallow lakes. Global Ecol. potential as indicators of hydrological balance and sea-level change. Biogeogr. 14, 137–153. Quat.Sci.Rev.25,1948–1965. Oliver, D.R., Roussel, M.E., 1983. The Insects and Arachnids of Heinrichs, M.L., Wilson, S.E., Walker, I.R., Smol, J.P., Mathewes, R.W., Canada, Part 11: the Genera of Larval Midges of Canada (Diptera: Hall, K.J., 1997. Midge- and diatom-based palaeosalinity reconstruc- Chironomidae). Canadian Government Publishing Centre, Ottawa. tions for Mahoney Lake, Okanagan Valley, British Columbia, Osborn, G., Karlstrom, E.T., 1988. Holocene history of the Bugaboo Canada. Internat. J. Salt Lake Res. 6, 249–267. Glacier, British Columbia. Geology 16, 1015–1017. Heinrichs, M.L., Walker, I.R., Mathewes, R.W., Hebda, R.J., 1999. Palmer, S., Walker, I., Heinrichs, M., Hebda, R., Scudder, G., 2002. Holocene chironomid-inferred salinity and paleovegetation recon- Postglacial midge community change and Holocene palaeotem- struction from Kilpoola Lake, British Columbia. Géogr. Phys. perature reconstructions near treeline, southern British Columbia Quat. 53, 211–221. (Canada). J. Paleolimnol. 28, 469–490. Heinrichs, M.L., Walker, I.R., Mathewes, R.W., 2001. Chironomid- Pisaric, M.F.J., Holt, C., Szeicz, J.M., Karst, T., Smol, J.P., 2003. based paleosalinity records in southern British Columbia, Canada: Holocene treeline dynamics in the mountains of northeastern a comparison of transfer functions. J. Paleolimnol. 26, 147–159. British Columbia, Canada, inferred from fossil pollen and stomata. Heiri, O., Lotter, A.F., 2001. Effect of low count sum on quantitative Holocene 13, 161–173. environmental reconstructions: an example using subfossil chir- Ponel, P., Gandouin, E., Coope, G.E., Andrieu-Ponel, V., Guiter, F., onomids. J. Paleolimnol. 26, 343–350. Van Vliet-Lanoë, V., Franquet, E., Brocandel, M., Brulhet, J., 2007. Heiri, O., Lotter, A.F., Lemcke, G., 2001. Loss on ignition as a method for Insect evidence for environmental and climate changes from Youn- estimating organic and carbonate content in sediments: reproducibility ger Dryas to Sub-Boreal in a river floodplain at St-Momelin (St-Omer and comparability of results. J. Paleolimnol. 26, 101–110. basin, northern France), Coleoptera and Trichoptera. Palaeo- Juggins, S., 1997. CALIBRATE Version 0.82 (Computer Software). geogr. Palaeoclimatol. Palaeoecol. 245, 483–504. Kurek, J., Cwynar, L.C., Spear, R.W., 2004. The 8200 cal yr BP Porinchu, D.F., MacDonald, G.M., Bloom, A.M., Moser, K.A., 2003. cooling event in eastern North America and the utility of midge Late Pleistocene and early Holocene climate and limnological Author's personal copy

M. Chase et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 257 (2008) 244–259 259

changes in the Sierra Nevada, California, USA inferred from midges Verschuren, D., Eggermont, H., 2006. Quaternary paleoecology of (Insecta: Diptera: Chironomidae). Palaeogeogr. Palaeoclimatol. aquatic Diptera in tropical and Southern Hemisphere regions, with Palaeoecol. 198, 403–422. special reference to the Chironomidae. Quat. Sci. Rev. 25, Quinlan, R., Smol, J.P., 2001. Setting minimum head capsule 1926–1947. abundance and taxa deletion criteria in chironomid-based inference Walker, I.R., 1995. Chironomids as indicators of past environmental models. J. Paleolimnol. 26, 327–342. change. In: Armitage, P.D., Cranston, P.S., Pinder, L.C.V. (Eds.), Reasoner, M.A., Osborn, G., Rutter, N.W., 1994. Age of the Crowfoot The Chironomidae: Biology and Ecology of Non-biting Midges. advance in the Canadian Rocky Mountains: a glacial event coeval Chapman and Hall, London, pp. 405–422. with the Younger Dryas oscillation. Geology 22, 439–442. Walker, I.R., 2000. The WWW Field Guide to Subfossil Midges. Reimer, P.J., Baillie, M.G.L., Bard, E., Bayliss, A., Beck, J.W., Bertrand, http://www.paleolab.ca/wwwguide/ Accessed 2004–2006. C.J.H., Blackwell, P.G., Buck, C.E., Burr, G.S., Cutler, K.B., Damon, Walker, I.R., 2001. Midges: Chironomidae and related Diptera. In: P.E., Edwards, R.L., Fairbanks, R.G., Friedrich, M., Guilderson, T.P., Smol, J.P., Birks, H.J.B., Last, W.M. (Eds.), Tracking Environ- Hogg, A.G., Hughen, K.A., Kromer, B., McCormac, G., Manning, mental Change Using Lake Sediments. Zoological Indicators, S., Ramsey, C.B., Reimer, R.W., Remmele, S., Southon, J.R., vol. 4. Kluwer Academic Publ., Dordrecht, pp. 43–66. Stuiver, M., Talamo, S., Taylor, F.W., van der Plicht, J., Walker, I.R., 2006. Chironomid overview. In: Elias, S.A. (Ed.), Weyhenmeyer, C.E., 2004. IntCal04 terrestrial radiocarbon age Encyclopedia of Quaternary Science, vol. 1. Elsevier, Amsterdam, calibration, 0–26 cal kyr BP. Radiocarbon 46, 1029–1058. pp. 360–366. Rosenberg, S.M., Walker, I.R., Mathewes, R.W., 2003. Postglacial Walker, I.R., Cwynar, L.C., 2006. Midges and palaeotemperature spread of hemlock (Tsuga) and vegetation history in Mount reconstruction — the North American experience. Quat. Sci. Rev. Revelstoke National Park, British Columbia, Canada. Can. J. Bot. 25, 1911–1925. 81, 139–151. Walker, I.R., Mathewes, R.W., 1987. Chironomidae (Diptera) and late- Rosenberg, S.M., Walker, I.R., Mathewes, R.W., Hallett, D.J., 2004. glacial climate at Marion Lake, British Columbia, Canada. Quat. Midge-inferred Holocene climate history of two subalpine lakes in Res. 27, 89–102. southern British Columbia, Canada. Holocene 14, 258–271. Walker, I.R., Mathewes, R.W., 1988. Late-Quaternary fossil Chir- Schmid, P.E., 1993. A key to the larval Chironomidae and their instars onomidae (Diptera) from Hippa Lake, Queen Charlotte Islands, from the Austrian Danube Region, streams and rivers. Wasser British Columbia, with special reference to Corynocera Zett. Can. Abwasser Suppl. 3. Entomol. 120, 739–751. Smith M.J., 1997. Postglacial changes in chironomid communities and Walker, I.R., Mathewes, R.W., 1989. Early postglacial chironomid inferred climate near treeline at Mount Stoyoma, Cascade succession in southwestern British Columbia, Canada, and its Mountains, Southwestern British Columbia. M.Sc. Thesis, paleoenvironmental significance. J. Paleolimnol. 2, 1–14. Simon Fraser University, Burnaby, Canada. Walker, I.R., Pellatt, M.G., 2003. Climate change in coastal British Smith, M.J., Pellatt, M.G., Walker, I.R., Mathewes, R.W., 1998. Columbia — a paleoenvironmental perspective. Can. Water Resour. Postglacial changes in chironomid communities and inferred climate J. 28, 531–566. near treeline at Mount Stoyoma, Cascade Mountains, southwestern Walker, I.R., Smol, J.P., Engstrom, D.R., Birks, H.J.B., 1991. An British Columbia, Canada. J. Paleolimnol. 20, 277–293. assessment of Chironomidae as quantitative indicators of past climatic Spooner, I.S., Barnes, S., Baltzer, K.B., Raeside, R., Osborn, G.D., change. Can. J. Fish. Aquat. Sci. 48, 975–987. Mazzucchi, D., 2003. The impact of air mass circulation dynamics Weckström, J., Korhola, A., 2001. Patterns in the distribution, on Late Holocene paleoclimate in northwestern North America. composition and diversity of diatom assemblages in relation to Quat. Internat. 108, 77–83. ecoclimatic factors in arctic Lapland. J. Biogeogr. 28, 31–45. Stepanovic', L., 2006. 12500 years of midge-inferred climatic history for Whitney, B.S., Vincent, J.H., Cwynar, L.C., 2005. A midge-based late- interior Alaska. M.Sc. Thesis, Simon Fraser University, Burnaby, glacial temperature reconstruction from southwestern Nova Scotia. Canada. Can. J. Earth Sci. 42, 2051–2057. Thompson, R.S., Whitlock, C., Bartlein, P.J., Harrison, S.P., Spaulding, Wiederholm, T. (Ed.), 1983. Chironomidae of the Holarctic region. Keys W.G., 1993. Climatic changes in the western United States since and Diagnoses: Part 1. Larvae. Entomol Scand, suppl. 19. 457 pp. 18,000 years BP. In: Wright J.R., H.E., Kutzbach, J.E., Webb III, T., Woodward, C.A., Shulmeister, J., 2007. Chironomid-based recon- Ruddiman, W.F., Street-Perrott, F.A., Bartlein, P.J. (Eds.), Global structions of summer air temperature from lake deposits in Lyndon Climates Since the Last Glacial Maximum. University of Stream, New Zealand spanning the MIS 3/2 transition. Quat. Sci. Minnesota Press, Minneapolis, pp. 468–513. Rev. 26, 142–154. ter Braak, C.J.F., Juggins, S., 1993. Weighted averaging partial least Wright Jr., H.E., 1967. A square-rod piston sampler for lake sediments. squares regression (WA-PLS): an improved method for reconstructing J. Sediment. Petrol. 27, 957–976. environmental variables from species assemblages. Hydrobiologia Yamaguchi, D.K., 1983. New tree-ring dates for recent eruptions of 269/270, 485–502. Mount St. Helens Quat. Res. 20, 246–250. ter Braak, C.J.F., Juggins, S., Birks, H.J.B., van der Voet, H., 1993. Zdanowicz, C.M., Zielinski, G.A., Germani, M.S., 1999. Mount Weighted averaging partial least squares regression (WA-PLS): Mazama eruption: calendrical age verified and atmospheric impact definition and comparison with other methods for species-envi- assessed. Geology 27, 621–624. ronment calibration. In: Patil, G.P., Rao, C.R. (Eds.), Multivariate Environmental Statistics. Elsevier, Amsterdam, pp. 525–560. Velle, G., Brooks, S.J., Birks, H.J.B., Willassen, E., 2005. Chironomids as a tool for inferring Holocene climate: an assessment based on six sites in southern Scandinavia. Quat. Sci. Rev. 24, 1429–1462.