Quaternary Fossil Insects from Patagonia

20 Quaternary Fossil Insects from Patagonia Julieta Massaferro1, Allan Ashworth2 and Stephen Brooks3 1

CONICET – Laboratorio de Ecotono, CRUB/Universidad del Comahue, 8400 – Bariloche, Argentina 2 Department of Geosciences, North Dakota State University, Fargo, 58105-5517 North Dakota, US 3 Department of Entomology, Natural History Museum, SW7 5BD London, UK

sediments, is that they offer a continuous record of climate change. The study of these records combined with physical and chemical parameters can provide a comprehensive array of information for climate change studies. Recent palynological studies from southern South America have provided a thorough overview of past vegetation and climate change, specially those changes associated with shifts in the latitudinal position of the westerlies in southern temperate ecosystems (Markgraf, 1987; Heusser, 1989, 2003; Markgraf et al., 1995; Moreno, 1997; Moreno et al., 1999, 2001; Moreno and Leo´n, 2004). Fossil insects are often abundant in a wide range of Quaternary deposits. Several orders of insects can be found in fluvial and lacustrine sediments such as species from the Order Hemiptera including Gerridae, Corixidae and Notonectidae. The larvae of caddisflies (Trichoptera) are aquatic and their sclerites can be found in lacustrine sediments. Caddisfly larvae provide valuable information about the water quality they inhabit, as many species are stenothermic and are sensitive to changes in pH and trophy (Elias, 1994). Another group that has recently proved to be useful in paleolimnology, especially in fluvial sediments, is the Family Simuliidae. Simuliids have been studied by Currie and Walker (1992) in North America who demonstrated they were useful indicators of precipitation changes. However, to date, most of the paleoenvironmental studies available have focused on the remains of beetles (Order Coleoptera, Families Carabidae, Scarabaeidae, Cydnidae, Chrysomelidae, Coccinellidae) and midges (Order Diptera, Family Chironomidae). Some of the earliest evidence for beetle species comes from late Tertiary and early Quaternary assemblages in Alaska. However, those records are generally poorly preserved, laid down in bedrock, full of spatial and temporal gaps and lacking in continuity (Elias, 1994). For this reason, this chapter focuses on midges and beetles from the Quaternary period, especially the Late Pleistocene and Holocene, with which, to date, most of the fossil insect studies have dealt. The use of fossil insects in Quaternary studies at midlatitude South America is relatively limited, and the major reason is the lack of taxonomical information available from these remote areas. Many of these studies have been conducted in the southern part of South America, in Argentina and Chile (Ashworth and Hoganson, 1987, 1993; Hoganson et al., 1989; Ashworth et al., 1991; Hoganson and Ashworth, 1992; Massaferro and Brooks, 2002; Massaferro et al., 2004).

1. Introduction: The Importance of Patagonia for Climatic Studies Patagonia is the region of Argentina and Chile that extends from 39 to 55 S. In the last 20 yrs Patagonia has become increasingly important in paleoclimatic research due to its exceptional geographic location between the South Pacific, Atlantic and Antarctic oceans and the abundance of lakes and bogs from which climate indicators can be easily obtained. The Andean region of Patagonia is ideal for monitoring Late Quaternary climate at mid-latitudes because it is one of the few areas sustaining a suite of rainforest communities along altitudinal and latitudinal gradients within the belt of the southern westerlies (Moreno, 1997; Whitlock et al., 2001). Such a location is a key for investigations related to the reorganization of climate during the Late Pleistocene and Holocene, especially for testing the synchroneity of climate changes in the Northern and Southern Hemispheres. Patagonia is also a key place for the study of interannual and decadal climate variations such as the El Nin˜o Southern Oscillation (ENSO) that affect the Pacific Ocean and leaves paleoecological evidence in lake records. Furthermore, Patagonia also provides evidence of past climate changes from regions located in the same latitude and climate as those in the Northern Hemisphere where climate has been extensively studied (Denton, 1999). Finally, neo-ecological work developed in this part of South America has emphasized the strong need for the study of catastrophic disturbances such as earthquakes, volcanic activity, insect outbreaks, windstorms and fires that affected flora and fauna in Patagonian rainforest in the past (Szeicz et al., 2003).

2. Paleoclimatic Proxies So far, most of the evidence for climate change in southern South America has been derived from abiotic climate proxies and a few biotic proxies, especially pollen records. Extensive mapping and dating of glacial and fluvio-glacial features has produced a detailed history of glacial behavior in the Chilean Lake District (Denton et al., 1999) and at other latitudes in Argentinean and Chilean Patagonia (Clapperton et al., 1995; Marden and Clapperton, 1995; Strelin and Malagnino, 2000; Kaplan et al., 2004). The advantage of biological proxies, which can be retrieved from long lake-sediment cores, bogs or marine

 2008 ELSEVIER B.V. ALL RIGHTS RESERVED

DEVELOPMENTS IN QUATERNARY SCIENCES VOLUME 11 ISSN 1571-0866 393

394

Julieta Massaferro et al.

3. Chironomids Chironomidae belong to the Order Diptera: Nematocera and they are colloquially known as non-biting midges. The larvae of the majority of these species are aquatic and constitute one of the most abundant bottom-dwelling macroinvertebrates of freshwaters (Cranston, 1995) (Fig. 1a). The distribution of the different chironomid taxa is restricted by environmental conditions. Most species are stenotopic (i.e., able to adapt only to a narrow range of environmental conditions) and respond rapidly to environmental change. The sensitivity of chironomids to different environmental variables such as dissolved oxygen, nutrient and organic content, pH and salinity has led to their use as indicators of lake quality and in other ecological studies (Porrinchu and MacDonald, 2003). Midges began to be used in paleoecological studies during the 1980s and 1990s. Excellent reviews of chironomids as paleoindicators can be found in Frey (1964, 1988), Hofmann (1971, 1988) and Walker (1990, 1995, 2001). Their remains are of special interest in paleolimnology because their strongly sclerotized larval head capsules are preserved in sediment deposits (Fig. 1b). There are several reasons why chironomids are considered important in paleolimnology: (i) they are sensitive to

(a) Adult Adult swarms

Egg masses

Lake Sediment core

Head capsule

Pupae

Larval instars

(b)

Antenna Mandible

environmental variables such as temperature, pH, trophic conditions, dissolved oxygen; (ii) they have relatively short life cycles; (iii) the adult are mobile; (iv) the larvae possess chitinous head capsules that are well preserved in lake sediments and (v) they are abundant, diverse and readily identifiable to generic and species-group level, enabling high resolution studies. Past chironomid stratigraphies can be reconstructed and readily used to infer environmental conditions at the time of deposition. Chironomids are now well established as paleoecological proxy indicators and have been used effectively to document changes in salinity (Walker et al., 1995), lake productivity (Lotter et al., 1997, 1998; Brodersen and Lindegaard, 1999; Brodersen and Anderson, 2000) and hypolimnetic anoxia (Quinlan et al., 1998). However, perhaps the most successful use of chironomids is to quantify past climate changes during the Late Glacial and Holocene in the Northern Hemisphere (Levesque et al., 1996; Lotter et al., 1999; Brooks, 2000; Korhola et al., 2000; Brooks and Birks, 2001).

3.1. Methodology The volume of sediment required to recover a sufficient number (50–150) of chironomid head capsules varies from lake to lake, but usually 1–3 g of wet sediment is plenty. However, in Late Glacial inorganic clayish sediments or volcanic sediments sometimes this amount of sediment is not enough. The methodology involved in processing and identification of chironomid remains generally follows standard procedures (Warwick, 1980; Hofmann, 1986; Walker, 1995). Although the approaches in individual laboratories vary slightly, the concept remains the same: a careful separation of the subfossil head capsules from the sediment matrix using mild chemical treatment and sieving (Porrinchu and MacDonald, 2003). The procedure involves deflocculating the sediment sample using 10% KOH solution at 50–70C for 10 minutes. The warm KOH serves to break up colloidal matter without damaging the remains. The next step requires sieving the sediment and a mesh size of 95 mm should retain most of the heads. Sorting the sample requires a grooved counting tray. The chironomid heads are then handpicked with forceps or micropipettes into 80% ethanol using a stereo dissection microscope (25–50). Finally, chironomid remains are dehydrated by transfer from 80% ethanol to 100% ethanol to Euparal essence and finally to Euparal, which is a permanent mounting medium for permanent slides.

3.2. Applications of Chironomids in Paleoenvironmental Reconstructions Mentum

Fig. 1. (a) Chironomidae life cycle (modified from Porrinchu and MacDonald, 2003). (b) Fossil chironomid head capsules from Laguna Stibnite, Chile, showing taxonomical useful features (Massaferro and Brooks, 2002).

Subfossil chironomids have been used extensively as qualitative indicators of past environmental conditions. Since the earliest days of modern limnology, chironomids have been used in lake typologies to indicate trophic status of waters (Thienemann, 1918; Brundin, 1949; Saether, 1979; Wiederholm, 1984). Late Glacial sediments from littoral and profundal lake zones in the Northern Hemisphere

Quaternary Fossil Insects from Patagonia include cold stenothermic, ultraoligotrophic taxa such as Heterotrissocladius spp. and Tanytarsus lugens (Brundin, 1949). In mesotrophic lakes, those assemblages are replaced by taxa more tolerant to oxygen depletion such as Sergentia coracina and Stictochironomus. Finally, warm-adapted Chironomus spp. are characteristic of profundal zones in eutrophic lakes. This faunistic system applies in the Northern Hemisphere and has been used extensively to develop transfer functions (TF), which relate the modern chironomid distribution to a particular environmental variable such as temperature, oxygen concentration or total phosphorous. These TF allow quantitative reconstructions of particular environmental variables (see ‘‘Quantitative temperature reconstructions using fossil insects’’ in this chapter). In an expedition to the southern Andes in South America, Brundin (1958) collected and described much of the chironomid fauna of the area demonstrating that the fauna had a great resemblance to the Holarctic fauna. He recognized taxa with similar ecological requirements in both hemispheres. For example, Tanytarsus rothicommunity replaces T. lugens; Lenzia (Sergentia) coracina instead of Sergentia coracina and Parachironomus species replacing the northern Paracladopelma species. Later on, Brundin (1966) published an extensive study of the midge subfamilies Podonominae and Aphroteniinae. This invaluable work also shows evidence of chironomid biogeographical relationships between the separated Gondwana land masses of Australia and southern South America. Little has been done on larval chironomid taxonomy in Patagonia since Brundin’s work (Gonser and Spies, 1997; Andersen and Contreras-Ramos, 1999; Cranston and Edwards, 1999; Cranston, 2000). Recently, Massaferro and Brooks (2002) and Massaferro et al. (2005) described specimens from the subfossil chironomid fauna and identified additional taxonomic groups that could be ecologically related to European taxa. However, more ecological work is needed especially regarding the distribution and habitat requirements of this group of insects in South America.

3.3. Eutrophication Increase in lake productivity is accompanied by oxygen depletion in the hypolimnium. Certain chironomid larvae such as Chironomus spp. can tolerate very low oxygen levels that commonly exist in eutrophic and hypereutrophic lakes. They contain invertebrate haemoglobin enabling respiration in sites with low oxygen concentrations. There are many studies that have used chironomids as indicators of the trophic status of lakes (Hofmann, 1978; Warwick, 1980; Wiederholm, 1983) and there have also been several quantitative reconstructions estimating past changes in productivity based on chironomids (Lotter et al., 1998; Quinlan et al., 1998; Brooks et al., 2001; Quinlan and Smol, 2001). In Patagonia a few qualitative studies have been done on this subject, especially related to human activities, the impact of building developments, fish introduction and increase of nutrients in lakes (Bianchi et al., 1997, 2000; Massaferro et al., 2004).

395

3.4. Acidification The effects of acid rain on ecosystems have had an important impact in North America and Europe during the 19th and 20th centuries. The immediate consequence of acid rain is lowered pH that affects the function of ecosystems. In aquatic systems, there are some species of chironomids that can tolerate low pH such as species of Chironomus, Zavrelia, Zalutschia and Psectrocladius. In the Northern Hemisphere there are a number of studies dealing with pH and chironomids (e.g., Wiederholm and Eriksson, 1979; Henrikson and Oscarson, 1985; Brodin and Gransberg, 1993). Lake acidification can also be caused by natural factors, usually induced by development of soils related to vegetational succession. However, in southern South America there have been no studies related to acidification.

3.5. Lake-level Changes Changes in lake level can influence the proportion and volume of the littoral and profundal zones causing changes in the composition and distribution of the chironomid assemblages. Strongest impacts may be detected in a littoral core where deepening may cause an increase in profundal taxa. When lake level falls, the proportion of profundal taxa is likely to decline. The influence of depth on the distribution of chironomids has long been known (Hofmann, 1998; Korhola et al., 2000; Massaferro and Brooks, 2002; Marchetto et al., 2004) and there is a clear differentiation between littoral taxa such as Dicrotendipes, Glyptotendipes and Polypedilum, which are associated with macrophytes, semi-terrestrial taxa such as Limnophyes, Smittia and Gymnometriocnemus and profundal taxa such as Chironomus, T. lugens and Procladius (Armitage et al., 1995).

3.6. Climate Chironomid distribution is significantly affected by temperature, albeit in different ways. For instance, egg and larval development are influenced directly by water temperature (Tokeshi, 1995), but also water and air temperatures affect midges in an indirect way. In general, an increase in water temperature leads to an increase in productivity, which, in turn, increases food supply and decreases oxygen availability. Since the 1990s the use of fossil midges as indicators of climate change has proliferated and there is plenty of evidence concerning the significance of temperature in controlling chironomid distribution and abundance, especially during Late Glacial times. These studies were first developed in arctic and alpine lakes (Walker and Mathewes, 1987; Walker et al., 1991) sediments and showed that cold-stenothermic taxa such as Heterotrissocladius spp. and T. lugens dominate the Late Glacial period and that these taxa disappear with climate warming at the beginning of the Holocene, when they are replaced by a diverse, thermophilic chironomid assemblage dominated by Chironomini.

396

Julieta Massaferro et al. stored products. Their most important beneficial roles, as pollinators and as recyclers of nutrients, are activities that ensure the health of ecosystems. Species in many families of beetles are susceptible to environmental change. In general, predators and scavengers receive the most attention in paleoenvironmental reconstructions because they are able to respond more rapidly to climate change, since they are not tied to specific types of vegetation (Elias, 1994). Beetles respond to Quaternary climate change mostly by dispersal to track a favourable climate envelope, which ultimately led to large-scale changes in geographical distribution. Quaternary beetle fossils consist mostly of disarticulated exoskeletons; setae and scales are frequently preserved in unconsolidated sediments from shallow lacustrine, paludal and fluvial environments. Internal structures such as the male genitalia also occur as fossils. However, for practical purposes, the parts most studied by paleoentomologists are heads, pronota (thoraces) and elytra (wing cases) (Ashworth, 2001) (Fig. 2a, b).

4. Beetles Coleoptera or beetles are a diverse (more than 300,000 known species) and abundant order of insects. This high diversity makes them an important group in the fossil record. They are ubiquitous occurring from arctic polar deserts to the Subantarctic islands and at elevations as high as 5600 m in the Himalayas. There are species with physiologies adapted to survive periodic below freezing temperatures and other littoral species adapted to survive daily tidal inundations by burrowing in sand. Like other insects, they are ectotherms and are dependent on environmental temperatures during all phases of their life cycle. Most beetles are small organisms, ranging in length from 0.25 mm to several centimetres. Average length is estimated to be in the range of 4–5 mm. Because of their abundance, beetles are important food items for numerous species of reptiles, birds, small mammals and fish. Beetles are also important agricultural and forestry pests, with numerous species being injurious to crops, trees, and (a)

Head capsule Pronotum Elytra

Character: Front angle and Lateral stria

Character: Microsculpture

Character: Hind angle and Latero-basal puncture

Character: Latero-Basal Fovea

(b)

Diacheila polita Fald. (Coleoptera: Carabidae) S.E.M.'s of head, pronotum, and elytra. Conklin Quarry Site, Iowa City, Iowa, U.S.A.

Cerroglossus sp. (Coleoptera: Carabidae) Pair of elytra (wing covers) in peat. Rio Caunahue Site, southern Chile. Ca. 10,000 yr BP

Anisosticta bitriangularis (Say) (Coleoptera: Coccinellidae) Left elytron Winter Gulf Site, North Collins, New York, U.S.A. Ca. 12,700 yr BP

Fig. 2. (a) Generalized drawings of coleopteran sclerites frequently preserved as Quaternary fossils, showing a range of diagnostic features used in fossil identification (modified from Elias, 1994). (b) SEM and light microscope photographs of fossil beetles, showing structural and pigmented patterns (from http://www.ndsu.nodak.edu/instruct/schwert/qel/ images.htm).

Quaternary Fossil Insects from Patagonia 4.1. Methodology Fossils of beetles for Quaternary studies are usually obtained from stratigraphic sections exposed in cut-banks on rivers, in road cuts and by excavating pits in bogs. The quantities of sediment used in the studies vary but typically are 10 kg for each 5 cm stratigraphic interval. Organic sediments are wet sieved and the fraction larger than 300 mm is further processed using a kerosene flotation technique (Elias, 1994). This technique concentrates large numbers of insect skeletal parts, mostly the heads, pronota and elytra of beetles. The fragments tend to be very well preserved, with setae and scales and structural colours intact. The details preserved on the fossils facilitate their identification. Data from fossil beetle analysis are usually presented in the form of species abundance lists showing the number of individuals occurring within a particular sample. Occasionally, further information about specific parts of the body such as elytra or pronotum is provided (Lowe and Walker, 1997). As with their counterparts in North America and Europe, the fossils of Patagonian Coleoptera are identical to extant species. The beetle fauna of South America is not as well known as that of Europe or North America but even so large numbers of species are identifiable from their fossils.

4.2. Applications of Beetles for Paleoenvironmental Reconstructions Coleoptera are very useful in paleoecological reconstructions because they are such an important element in terrestrial ecosystems. They are relatively abundant and highly diverse in a wide range of deposits. Speciation and extinction is extremely rare, at least during the Pleistocene (Elias, 1994). The common response is for species to survive by dispersal. In consequence, beetle geographic distributions shrink and expand constantly. In this respect, the South American fauna at temperate latitudes is no different from that in the northern Hemisphere. Therefore, beetle species constancy over the last million years allows us to make use of ecological and distributional data drawn from modern populations (Elias, 1994). In addition to that, beetles are stenotopic, which means that they show a marked preference for a very restricted number of environments. A large number of beetles are associated with aquatic habitats, for example flowing water is indicated by Esolus, Limnius volckmari and Ochthebius pedicularis whereas Potamonectes and Halyplus live in still waters with sandy or silty bottoms. Other beetles indicate the presence of particular plants or animals. A profusion of dung beetles, for example, would indicate the presence of mammals (Lowe and Walker, 1997). Beetle assemblages can therefore provide valuable information on a diverse range of contemporaneous habitats with differences in vegetation, soils, water quality, forest composition and health, and may provide environmental insights that are difficult to obtain from other lines of evidence (Elias, 1994).

397

5. Quantitative Temperature Reconstructions Using Fossil Insects The analysis of fossil insects can be used for both qualitative and quantitative environmental reconstructions. Although the qualitative approach is long established, recent advances in statistical techniques have allowed paleoecological research to undergo a quantitative revolution. Temperature reconstructions using fossil insect assemblages have played an important role in NW Europe in recent attempts to reconstruct timing, magnitude and rates of climate changes during the Late Glacial–Interglacial transition and Holocene (Brooks, 2003). The close relationship between temperature and the distribution and abundance of fossil assemblages has been used to develop temperature inference models that can produce quantitative environmental reconstructions.

5.1. Chironomids One of the advantages of temperature reconstruction using chironomids is that many hundred of head capsules can be obtained from as little as 1 cm3 of sediment giving a higher resolution record than other methods such as for beetles, where large amounts of sediments are required. Pioneering work using chironomids for quantitative reconstructions was done in Canada by Levesque et al. (1993) and Walker et al. (1997) who produced temperature models that have been used successfully numerous times in eastern and western Canada. Further chironomid temperature quantitative models were developed in Northern and Central Europe (Lotter et al., 1997; Olander et al., 1999; Brooks and Birks, 2000, 2001; Larocque et al., 2001). Based on a calibration data set of 111 lakes from Norway, Brooks and Birks (2001) applied the inference model to Late Glacial chironomid assemblages from Whitrig Bog in Scotland for a high-resolution quantitative climate reconstruction. The correlation between the chironomid-inferred temperature and the GRIP oxygen isotope stratigraphy shows striking similarities (Fig. 3). Relatively few quantitative reconstructions have been carried out in the Southern Hemisphere. In Australia, Dimidiatris and Cranston (2001) developed a chironomid temperature model based on the MCR method (see below) that has been applied to a Holocene sequence from a maar lake in Queensland. In an attempt to explore the potential of chironomids as quantitative indicators of past temperatures in Patagonia, Gilchrist (2005) developed a statistical model to infer paleoenvironmental changes in two lakes in southern Chile: Laguna Leta (41 S, 73 W) and Laguna Boal (44 S, 73 W). Records from both lakes indicated that climate changes occurred during the Late Glacial–Holocene transition and give evidence of the existence of a reversal event at the time of the Younger Dryas (YD) between 13,300 and 12,000 C yr BP. Concomitant with this cooling event, there is evidence of an increase of moisture that potentially caused a rise in lake levels. These promising results highlight the importance of continuing this kind of investigations.

398

Julieta Massaferro et al. This approach is yet to be fully exploited in investigations at mid-latitudes in the southern Hemisphere. The power of chironomids to infer past temperatures can be validated against other climatic reconstructions such as ice core records, marine micropaleontological records, isotopic records and evidence from other biotic proxies such as pollen, beetles, cladocera and diatoms. Good examples are the comparison of the Late Glacial isotopic and pollen records from Hawes Water, ostracods from Ammersee, the chironomid temperature curve from Whitrig Bog to GRIP ice core isotope records (Jones and Marshall, 2002) and the multiproxy study developed in Krakenes (Norway) that present a comparison of temperature reconstructions from different groups of fossil organisms including beetles and midges (Birks et al., 1999) (Fig. 4).

5.2. Beetles

Fig. 3. (a) Chironomid reconstruction of mean July air temperature at Whitrig Bog, Scotland. (b) The GRIP oxygen isotope record. Vedde Ash was included in both plots to show synchronicity between both reconstructions (modified from Brooks and Birks, 2001).

The most important factor driving beetle distribution during the Quaternary has been climate (Coope, 1990). In Europe, modern distribution maps show that the geographical range of many species corresponds with welldefined climate zones. Coope (1977) demonstrated that during the Quaternary, extremely rapid climate changes may have allowed Coleoptera to colonize new habitats relatively quickly and in most of the cases where the range limit of the coleopteran species coincides with a climatic boundary, this relationship has been used to apply quantitative paleotemperature reconstructions (Lowe and Walker, 1997). In the Holarctic region, beetles have been widely used for quantitative temperature reconstructions (Coope, 1977; Elias, 1994; Ashworth, 2001). The Mutual Climate Range method (MCR) (Atkinson et al., 1986, 1987) is used to infer temperatures from fossil beetle assemblages. In this method, the geographic ranges of species are plotted within a climatic framework, usually

Fig. 4. Comparison of mean July air temperature reconstruction for different groups of organisms during the Late Glacial and Holocene in western Norway (Birks et al., 1999).

Quaternary Fossil Insects from Patagonia mean January (T min) and mean July temperature (T max). In a fossil assemblage the overlapping climate envelopes of each species provide the mutual climate range, or the climate space between T max and T min that the assemblage was most likely to inhabit. The method depends on detailed modern distributional information for species. The MCR method has been used to reconstruct climatic conditions in Europe during the Late Glacial–Interglacial transition (Ponel and Coope, 1990; Lemdahl, 1991; Walker et al., 1993). MCR beetle curves are strongly supported by other climatic reconstructions such as Greenland ice core records and marine evidence (Lowe and Walker, 1997). Due to little knowledge of modern species composition and distribution in South America the MCR method and the climatic summary it provides cannot be used at present.

only two studies dealing with fossil insects available at present. In Venezuela, an investigation of fossil chironomids from a sediment core from Lake Valencia indicated lake-level changes and trophic changes during the last 12,000 14C yrs (Binford, 1982). The other study was developed in Peru (Churcher, 1966) using insect remains from Talara. However, despite there being good information about the ecology of the different groups of Coleoptera in Peru, no specific identifications, essential for paleoenvironmental reconstructions, were made.

6.1. Fossil Midges There are currently few chironomids paleoecological studies from Patagonia. There have been some investigations carried out in Argentine Patagonia, within the limits of the Nahuel Huapi National Park (41 S, 71300 W) (Ariztegui et al., 1997; Bianchi et al., 1997, 2000; Corley and Massaferro, 1998; Massaferro and Corley, 1998; Massaferro et al., 2004) (Fig. 5).

6. Fossil Insects and Climate Studies in South America The current knowledge of insect paleoecology in Patagonia is relatively limited. In the Neotropics, there are

72°

73°

74°

399

71°

N Valdivia

Rio Canahue

L. Rupanco

Chile

Pacific ocean

ARGENTINA

CHILE

PACIFIC OCEAN

40°

Argentina

L. Nahuel Huapi

Puerto Octay

41°

L. Llanquihue Puerto Montt

40° S

L. Trébol L. Morenito Puerto Varas

L. Mascardi Atlantic Ocean

L. Puelo

50°

Seno Reloncavi

I. Chiloé

Cordillera de Los Andes

Castro

42° 0 200 400 Km

80° W

70°

60°

Esquel L. Futalaufquen

43°

Fig. 5. Map of the Chilean and Argentinean Lake District showing chironomid and beetle sampling sites. Stars indicate sampling sites for the chironomid training set by Gilchrist (2005). On the right side, the map of Patagonia shows the location of the northern and southern Patagonian ice fields and the Cordillera Darwin Ice Field of Tierra del Fuego (modified from Haberle and Bennett, 2004).

Julieta Massaferro et al.

The research conducted by Ariztegui et al. (1997) is a multiproxy study in which changes in pollen, chironomid and geochemistry in Lago Mascardi during the Late Glacial were interpreted as a response to a reversal coincident with the timing of the YD. Between 11,400 and 10,200 14C yr BP, there was a decrease in the total pollen influx as a consequence of an increase in inorganic sedimentation. A sharp decrease in the hydrogen index was also recorded. These results were interpreted as a cooling accompanied by an increase in subglacial erosion due to an advance of the Tronador icecap that feeds proglacial Lago Mascardi. The disappearance of the warm-adapted Chironomus and the decline in the total chironomid abundance at this time also suggests a climatic deterioration. Bianchi et al. (1997, 2000) show the results from a multiproxy study of a sediment core from Lago El Tre´bol. Although the site was suitable for paleolimnological studies, the sampling resolution was not enough to discern climatic changes during the Late Glacial period. Corley and Massaferro (1998) and Massaferro and Corley (1998) also studied subfossil chironomid assemblages from Lago Mascardi. However, the results focused mostly on the importance of paleolimnological studies in understanding the role of natural disturbance and diversity patterns of biological communities in the past. Massaferro et al. (2004) studied geochemical and chironomid records from a short core from Lago Morenito, near San Carlos de Bariloche. The results

74° 17′ W

show the response of chironomids to natural (volcanic) and non-natural (human) environmental disturbances during the last 200 yrs. The study also demonstrated the importance of the multiproxy approach for paleoenvironmental reconstructions. There have not been other detailed studies of the response of chironomid assemblages to Late Quaternary climate change in other areas of Argentina. The reason for this is the lack of information on chironomid taxonomy due to the small number of researchers working on the subject. The first high-resolution environmental reconstruction using chironomids in Chile was published recently by Massaferro and Brooks (2002) (Fig. 6). Changes in the chironomid assemblages at Laguna Stibnite (46 S) in the Taitao Peninsula in Chile suggest that the climate in southern Chile was at it coolest during the YD (Fig. 7). In addition, during this period, chironomid head capsule concentrations fall suggesting low lake productivity, which would be consistent with low temperatures during this event. The specific chironomid assemblage during this period also indicates that the climate was cooler and drier. Between 11,300 and 9,400 14C yr BP (13,000–11,200 cal. yr BP), the coldstenothermic Podonominae were consistently present in every sample attaining a peak abundance during this period. This suggests that the lake waters were cool and oligotrophic during the YD. The low concentration of head capsules also reflects low lake productivity. During the Holocene, chironomids from Laguna Stibnite show

L. Yelcho

CHILE

nos Archi pel a

L. Rosselot

PACIFIC OCEAN

45° S

Laguna Facil Ad ve Ba ntu y re

L. Verde Isla Magdalena

L. De la Plata

Chile

C

ho

go

44° S

Pacific ocean

I. Chiloé

N

A RGENT INA

400

Argentina

40° S

Puerto Aguirre

Atlantic Ocean

Mount Hudson

50°

46° S

L. Buenos Aires

Laguna Stibnite L. Elena

North Patagonian Ice Field

0

200 400

Km

80° W

70°

60°

Glaciar San Rafael

Pe

ni ns ul a

Ta ita

o

L. Presidente Rios

L. San Rafael

Fig. 6. Map of the Taitao Peninsula in Chonos Archipelago, Chile, showing fossil chironomid sampling sites. Stars indicate sampling sites for the chironomid training set by Gilchrist (2005). On the right side, the map of Patagonia shows the location of the Patagonian and Fuegian Ice Fields, as in Fig. 5 (modified from Haberle and Bennett, 2004).

300

1

401

2 PC Aa xis

500

PC Aa xis

rB Po do P) no mi Pa n ae rak ief fer Pa iel rap la se ctr Ps oc eu lad do ius ch Po iro lyp no m e d ini Ab la ilum Cla besm d y Pa ope ia Aprakie lma se ffe Ma ctro riell cro tan a fe pe ypu nn lop s ica Ta ia ny tar sin iA Ta ny tar sin iB Ta ny tar sin iC Lim no ph ye s La bru nd ini a Ph ae Pa nop rac sec Ch hir t iro on ra Pr nom omu oc s u La ladi s u u Gy terb s m o Mi nomniella c Co rote ectri o r n Ta ynon dipe nem ny eu s us tar ra sin iD To tal he ad ca ps ule s He ad ca ps ule s/g

yr

Ag e

( 14 C Ag e

Lit ho log y

(ca l. y

BP )

Quaternary Fossil Insects from Patagonia

Zone Stib-7

T

1500

T

2500

1300

Stib-6

2300 3300

3500

Stib-5b 4300

4500

5300 6300

Stib-5a

5500 7300 8300

6500 7500

9300

Stib-4

8500

10,300

9500

11,300

10,500

12,300

T

11,500

T L L LL L L LL L L L L L L L L L LL L L LL L L L L L L L L L

12,500

Stib-3

YD

13,300

14,300

Stib-2 13,500 15,300

14,500

16,300

15,500

17,300

Stib-1 20

40

20

20

20

20

20

20

20

40

20

40

20

20

40

60

20

40

20

20

20

50 100 150 200

100

200

300 –150 –50 0 50 150

–100 0 100 200300

% Abundance L

L

L

Blue gray clay grading to organic clay

Dark brown gyttja

Silty gyttja

T = Tephra layer

Fig. 7. Chironomid percentage diagram showing selected taxa in the Late Quaternary sequence from Laguna Stibnite, Chile. Also shown are lithology and chironomid zones (Massaferro and Brooks, 2002).

a response to cyclical precipitation patterns. Results from beetles from Puerto Ede´n (Ashworth et al., 1991) located 300 km south of Taitao Peninsula also suggest that changes in precipitation occurred during the Holocene; however, they are almost out-of-phase with those inferred at Laguna Stibnite. If these interpretations are both correct, changes in precipitation patterns may be caused by a latitudinal shift of the westerlies (Massaferro and Brooks, 2002). Pollen records from Laguna Stibnite (Lumley and Switsur, 1993; McCulloch et al., 2000) could find no evidence of cooling during the Late Glacial–Interglacial transition. At other sites in Patagonia, changes in pollen assemblages at the end of the Late Glacial have been interpreted as a response to climatic cooling (Heusser and Rabassa, 1987; Heusser, 1989, 1993; Rabassa et al., 1990; Heusser et al., 1996; Moreno, 1997). On the contrary, palynological studies performed in seven other lakes located in this area of Chile bear no evidence of a reversal during the Late Glacial period (Bennett et al., 2000; Haberle and Bennett, 2004). In addition, Bennett et al. (2000) found no changes in lithology or magnetic susceptibility that might indicate periods of cooling in southern Chile. Recently, Massaferro et al. (2005) carried out a study on pollen and fossil chironomids in Laguna Fa´cil, located in the Chonos Archipelago in Chile. The results showed that no response to a cooling event coinciding with the

YD is apparent at this lake. Instead, chironomids seem to be responding to local rather than regional environmental changes, perhaps in response to the gradual migration and colonization of trees in the lake catchment (Fig. 8). Pollen records from Laguna Fa´cil and Laguna Oprasa (separated by 50 km) also showed no cooling during the YD (Haberle and Bennett, 2004). Despite the similarities of fauna and the proximity between them, the more northerly location of Laguna Fa´cil means that it is less likely than Laguna Stibnite to have been influenced by any resurgence of Andean glaciers during the Younger Dryas Chronozone (YDC). Glacial resurgence could be related to changing patterns of atmospheric moisture, from latitudinal movement of the southern westerlies, which resulted in a highly variable glacier system (Heusser, 2002; Glasser et al., 2004). Geographic variability in glacial activity would indicate that climatic conditions were possibly insufficiently intense and/or of insufficient duration to effect uniform regional paleobiotic changes; therefore a response during the YD may be recognizable at some sites but not at others. Results from a chironomid study (Massaferro, unpublished) carried out on samples from Lago Mascardi not previously examined by Ariztegui et al. (1997) provide new evidence of climatic cooling during Late Glacial times. The improved radiocarbon chronology spans the interval between 12,000 and 9,500 14C yr BP and allows changes in chironomids in response to

Julieta Massaferro et al.

0.2

Ag e

(c De al y rB pt h P) (c m Ps ) eu La do ut ch Po ern iron lyp bon om ed iel us ilu la Ta m ny ta Po rsu do s D Pa nom ra ps inae ec tro cla Li di m us no ph y Ta es ny ta rs us Ab A la be sm M ac ro ya pe Ch l iro opia no m Pa us ra ch ir o no Pa m us ra kie ffe Ha r ie rri lla si Ta us ny ta rs us Ta C ny t Ap arsu se s B c Ph trota ae ny pu n La op s s br un ectr a d G i ym nia n Co om ry ec no tri ne oc ur ne He m a ad us ca ps ul es /g Po lle n zo ne Ch s iro no m id zo ne s

402

300

300 350

1300

400

2.8

2300 450 500 3300 4300

550

Fa-p5

Fa-c4

Fa-p4

Fa-c3

Fa-p3

Fa-c2

5300 600

14.6

11.1

7.2

6300 650 7300 8300 700 9300 10,300 750 11,300 12,300 800 13,300 14,300 850

Fa-p2

900

Fa-p1

15,300

Fa-c1

15.9

950 1000 1050

20

20

20

20 40

20

20 40

20

20

20

20

20 40

20 40 60 20 20

20 20 40 20 20 100 200

% Abundance Brown gyttja

Silt/clay gyttja

Olive grey clay

Tephra

Fig. 8. Late Quaternary chironomid stratigraphy from Laguna Facil. Only the dominant taxa are shown. Solid horizontal lines indicate the position of chironomid zone boundaries identified by optimal partitioning and a brokenstick model. For comparison, pollen zone boundaries are indicated by dash-lines and show how some elements of the chironomid fauna show synchronous change with vegetation change (Massaferro et al., 2005).

climatic variability to be pinpointed, and also a comparison with the well-established Late Glacial chronology from Greenland and Antarctic ice core records. Chironomids indicate a cooling during the YD but of a longer duration than in the Northern Hemisphere (Fig. 9). These results are in agreement with Hajdas et al. (2003) and Massaferro et al. (submitted) who demonstrated the occurrence of a cold event in the mid-latitudes of South America known as the Huelmo Mascardi Cold Reversal (HMCR) that encompasses the North Atlantic YD and the Gerzensee/Killarney Oscillation. Similar results have been found in Kaipo Bog in New Zealand from pollen records. These results indicate a cooling of ca. 600 14C yr BP before the YD (Newnham and Lowe, 2000).

6.2. Fossil Beetles Fossil beetle faunas have been investigated from several lowland sites in Chile, in the Chilean Lake District (see Fig. 5) (Hoganson et al., 1989; Hoganson and Ashworth, 1992; Ashworth and Hoganson, 1993) and further south, in the Chilean Channels (Fig. 10) (Ashworth and Markgraf, 1989; Ashworth et al., 1991). To develop reliable information about the modern distribution and ecological requirements of the coleopteran fauna, Ashworth and Hoganson (1987) carried out an extensive collecting programme for several years. They identified 462 species of beetles belonging to 48 families in 41 locations of the Puyehue National Park, Chile (40–41 S, 71–72 W). Their collections were

the basis of a multivariate ordination study that demonstrates significant differences between the low and high elevation fauna, especially between those of the forested and treeless Andean tundra habitats. The study clearly demonstrated a relationship between beetles and climate within the region. Hoganson and Ashworth (1992) and Ashworth and Hoganson (1993) reported on several fossil beetle assemblages from Puerto Octay, Puerto Varas and Rı´o Canahue in the Chilean Lake Region (40–41 S, 72–73 W) that spans the interval from the Last Glacial maximum to the Holocene. They showed that full glacial assemblages were species-poor, containing only about 20% of the species of the Holocene assemblage. They inferred that the full-glacial beetle assemblages represented a Magellanic moorland environment which existed in a climate with mean January temperatures 4–5C cooler than present (Fig. 11a, b). What was particularly striking was the rapidity and timing of the change to the postglacial fauna. The change started before 14,000 14C yr BP and was completed by 12,500 14 C yr BP. Moreno (1997), based on a high resolution study of pollen, confirmed that the full glacial flora was Magellanic moorland and that the transition to forest occurred between 15,000 and 14,000 14C yr BP. These changes are similar in timing to changes marking the end of the Pleistocene in the Pacific Northwest of North America. These results also show that the time of the transition from glacial to interglacial conditions in the Southern Hemisphere occurred earlier than in the North Atlantic Ocean.

δ 18 O

Lim

edi

nop

lum

iD iA rsin

yta

lyp Po

rsin

Tan

yta Tan

hye s Dic ro Cri tendi cot pes o Ort p hoc us Pse ladiin ae udo J chi ron Tot om al n us um ber

us adi Ch iron Pa omus rap sec troc l

us ae

Po

don

om in

ctra

nom

ops e

hiro rac

Pa

aen Ph

rak

ieff erie

lla

age s car dio

l yr Ca

Ra

Pa

11,000

bon

–34 –35 –36 –37 –38 –39 –40 –41 –42 –43 –44 10,000

–38

–39

–39

–40

–40

11,000

–41

–41

–42 10,000

LITTORAL SPECIES

BP

δ 18 O

11,200 11,400 10,380 11,600 10,440 11,800 10,620

HMCR

YD

12,000

12,000

Cal 14C ages

11,000 9885

12,000 12,200 12,400

10,480 12,600 10,810 10,960 11,240 11,050 11,170 11,450

12,800 13,000 13,200 13,400

OD

14,000

13,800 11,720

Antarctica EPICA

12,770

15,000

15,000

14,000 14,200

12,650

Bo

13,600

14,400 14,600 14,800 15,000

Greenland GISP2

0 20 40 60 0 20

0 20 0

20

0

0

20 40

0

0 20 0

20

0 20 0

0

0

0 20 0 20 40 60 80 100

Fig. 9. Chironomid stratigraphic diagram from Lago Mascardi showing Younger Dryas (YD), Huelmo-Mascardi Cold Reversal (HMCR) and Antarctic Cold Reversal (ACR). Dark profiles represent cold species (Parakiefferiella include mixed cold and warm species). EPICA (Antarctica) and GISP2 (Greenland) ice core records are shown to allow comparisons (original data from NOAA web page) (Massaferro, unpublished).

Quaternary Fossil Insects from Patagonia

12,000 11,700

14,000

ACR

13,000

13,000

KO

403

404

Julieta Massaferro et al. Glaciar Témpano

ARGENTINA

N

L. Cardiel

Puerto Edén

South Patagonian Ice Field L. Argentino

50°

ATLANTIC OCEAN

Puerto Natales

Argentina

Chile

Punta Bandera

Pacific ocean

I. Wellington

52°

40° S

Estrecho de Magallanes

Atlantic Ocean

Punta Arenas

PACIFIC OCEAN

Puerto del Hambre

La Misión

50°

Tierra del Fuego

54° 0

200 400

L. Yehuin

Km

80° W

Puerto Harberton

70°

60°

Canal Beagle 74°

70°

66°

Fig. 10. Map of the Chilean Channels and Tierra del Fuego, Argentina, showing fossil beetle sampling sites. Stars indicate sampling sites for the chironomid training set by Gilchrist (2005). On the right side, the map of Patagonia shows the location of the Patagonian Ice Fields, as in Fig. 5 (modified from Haberle and Bennett, 2004).

(a)

(b)

0.5

Moorland 60

Forest

0.2

Total taxa Obligate arboreal taxa

80

40

20

0.1 18,000

Number of taxa

0.3

100

Number of taxa

120

0.4

16,000

14,000

12,000

10,000

Age 14C yr BP

0 18

16

14

12

10

Age 14C yr BP × 103

Fig. 11. (a) Change in composition of the beetle fauna in the Chilean Lake District during the interval between 18,000 and 10,000 14C yr BP. The dashed line represents the total number of taxa. The solid line represents the ratio of the three dependent taxa to total taxa. The zigzag dotted line marks the transition between moorland and forest assemblages. (b) Compositional and diversity changes in the beetle fauna of the Chilean Lake region during the last glacial to interglacial transition (modified from Hoganson and Ashworth, 1992; Ashworth and Hoganson, 1993).

However, the lack of a response of the beetle fauna to cooling at the time of the YD contradicted the results of Heusser (1974, 1997) and Heusser and Streeter (1980) which showed a change in the vegetation that was interpreted as a response to a temperate depression up to 6C lower than present. Moreno (1997) has also subsequently reported climatic cooling in the Lake District at the time of the YD.

Further south in the Chilean Channels, Ashworth and Markgraf (1989) and Ashworth et al. (1991) reported on fossil beetle and pollen assemblages from Glaciar Te´mpano (48 S, 72 W) and from Puerto Ede´n (49 S, 74 W) that showed an excellent correlation indicating that regional and local biotic changes were in phase (Fig. 12). The interpretation of the fossil beetle assemblages was aided by studies of

n

ty pe gr s ou M nd oo be rla et Po nd le po s ta m l l e og n Aq et o ua t ic n be As et se le m s In bl ag te rp e ol at zon ed e 14 s C yr BP

405

lle po

ea H

O pe n

th

/s

/o

hr

pe

ub

n

be

po s Tr

ee

ho ot

th N

ep D

fa

(c

m

gu

)

BP yr e ag C

14

et

lle

le

n

s

Quaternary Fossil Insects from Patagonia

0 5630

XX X X XX X

5 4 3

2000 4000 6000 8000 2 10,000 12,000

40 80

11,590 12,960

X XX X XX X

1

120

0

60

0

90

0

90

0 30 0 40 0 2 0

60

Percentage

Fig. 12. Pollen-beetle assemblage zones from the Puerto Ede´n peat profile (modified from Ashworth and Markgraf, 1989).

the modern beetle fauna reported in Ashworth et al. (1991). The results suggest that in Puerto Ede´n, prior to 13,000 14C yr BP, the climate was probably windier than today; between 13,000 and 9,500 14C yr BP the Nothofagus forest expansion and the presence of aquatic beetles were in response to an increase in the precipitation that lasted till 5,500 14C yr BP. From 5,500 to 3,000 14C yr BP the precipitation declined and, after 3,000 14C yr BP, precipitation increased again to the present-day levels. The authors conclude that the cyclical wet/dry periods were in response to latitudinal shifts of the westerlies. These results show no evidence of cold reversal in the area at the time of the YD. These results also demonstrate that in a heavily glaciated environment adjacent to the South Patagonian Ice Cap, deglaciation had begun by 13,000 14C yr BP. One of the surprising results of this study was the discovery, in the basal deposits of the bog at Puerto Ede´n, of the remains of relatively large flightless beetles. If this discovery can be substantiated, it will require a major revision of our current understanding of the extent of the Patagonian Ice Sheet. For a flightless beetle to occur in the basal deposits it would require that some parts of the archipelago were unglaciated and the climatic conditions sufficiently moderate to support a refuge for the biota. The standard biogeographic interpretation is that the current biota of the archipelago was derived by dispersal from both the north and the south during postglacial times. Fossil beetles and pollen from Glaciar Te´mpano come from an exposed section in the walls of a meltwater channel located 2 km from the margin of the South Patagonian Ice Cap. Ashworth and Markgraf (1989) reported a flora and beetle fauna for the time of the YD that was very similar to that of present day. The implication was that at the time of the YD, the margin of the South Patagonian Ice Cap was in similar position as it is today and that the climate was similar. This site was revisited in April 2005 and the basal deposits will be re-dated at the Climate Change Institute of the University of Maine. If the radiocarbon dates obtained in 1989 are confirmed, then the evidence from certain areas of westernmost southern South America will indicate that there was no glacier advance at the time of the YD in this portion of the continent. These studies indicate that the transition

from glacial to postglacial conditions was the major regional climate change in the last 15,000 yrs and that coleopteran evidence from Chilean Patagonia does not support the occurrence of climate reversals during the Late Glacial period. Although pollen and beetle records show no evidence for temperature changes during the Late Glacial–interglacial transition, they all indicate alternating dry and wet periods due to changes in the precipitation pattern during this period. They interpret these changes as being caused by latitudinal shifts in the position of storm tracks in the belt of southern westerlies. Markgraf (1989, 1991, 1993a, b) indicated that vegetation changes in this area were successional, edaphic or in response to disturbance by fire. Throughout the Holocene, the beetle fauna of midlatitude South America was not affected by any major climate change (Hoganson and Ashworth, 1992). For the period 9,500–5,500 14C yr BP Ashworth et al. (1991) concluded that the climate was as wet as present day, but an expansion in Empetrum heath between 5,500 and 3,000 14C yr BP suggests that conditions then became drier than today.

6.3. Inter-Hemispheric linkages Synchronicity of climate change and comparability of climate signals, both temporal and spatial, are the principal parameters for evaluating inter-hemispheric linkages. Today, due to the many uncertainties in the absolute timing and magnitude of the events recorded in the two hemispheres, the relationship between Late Glacial and Interglacial transition climate change in the Northern and Southern Hemispheres remains clouded. Different hypotheses, relying on different lines of evidence, point variously to the Northern Hemisphere leading the Southern Hemisphere and vice versa, or to synchrony between hemispheres (Glasser et al., 2004). A large body of data from ice core, sedimentary, geomorphological and paleoecological investigations supports the argument that during the Late Glacial climate change was globally synchronous (Denton and Hendy, 1994, 1995; Lowell et al., 1995; Denton et al., 1999;

406

Julieta Massaferro et al.

Moreno et al., 1999; Steig et al., 1998). To investigate the causes for the inter-hemispheric synchroneity, Whitlock et al. (2001) apply a Community Climate Model version (NCAR CCMI) using time-series of insolation and glacial, ice core, and ocean records from the Northern and Southern Hemispheres. The paleoclimatic simulations were then compared to pollen and beetle records from both hemispheres and showed that Glacial–Interglacial climatic oscillations during the Quaternary affected both regions synchronously but the extent of ice cover was different. However, the mechanisms that link glacial cycles in the two hemispheres were not completely explained. Chironomid assemblages from Lago Mascardi in Argentina (Massaferro, unpublished) show excellent agreement with both EPICA Antarctica and GISP2 Greenland ice core records giving evidence of out-ofphase Late Glacial climatic events in both hemispheres (see Fig. 9). These results support the anti-phased north– south deglacial patterns and the relationship to the THC (thermohaline circulation) changes that produces a ‘‘seesaw’’ transfer of ocean heat between the hemispheres (Broecker, 1998). Recent studies of Antarctic ice cores added to the discussion but did not resolve the controversy (Lamy et al., 2004). The discrepancies in the different chronologies in the various Antarctic ice core records make it difficult to arrive at any conclusion. Summarizing, the existence of the cold reversals during the Late Glacial–Interglacial transition in the southern Hemisphere is still controversial (Ashworth et al., 1991; Markgraf, 1993a, b; Heusser et al., 1996; Ariztegui et al., 1997; Bennett et al., 2000; McCulloch et al., 2000; Massaferro and Brooks, 2002). Some studies indicate a cooling in South America that is more coincident with the Antarctic Cold Reversal (ACR) than the YD (Newnham and Lowe, 2000; Turney et al., 2003) whereas Bennett et al. (2000) looking at pollen studies suggest gradual warming with no reversals in the Southern Hemisphere. In New Zealand, the evidence of climate reversal during the YD is also problematic. Many pollen studies indicate progressive forest development implying that deglacial temperatures and precipitation increased gradually without significant reversal (McGlone, 1995; Vandergoes and Fitzsimons, 2003). In the South Island of New Zealand, Shakau (1986, 1990) developed a modern training set using chironomids; nevertheless, these results did not focus on climatic reconstructions. New attempts to infer temperature using chironomid-temperature models have been recently carried out at the University of Maine (USA) with the aim to produce a reliable dataset for quantitative reconstruction of past temperatures.

7. Future Investigations in Patagonia This chapter has provided evidence that the location of Patagonia in combination with the study of insects is ideal for testing hypotheses related to climate change during the Quaternary. It highlights the importance of southern South America as one of the most important regions in the world for testing whether climate changes are global or not. The studies presented in this chapter clearly show the potential of chironomids and beetles as proxy indicators of

climate change. However, there is still a lack of information about insect taxonomy, ecology and modern distribution in the Southern Hemisphere that is indispensable for accurate inferences. In addition, a better knowledge of insect taxonomy would allow development of transfer functions and quantitative reconstructions of past temperature which, in turn, would provide new approaches for understanding the synchronicity of climatic events in both hemispheres. Summarizing, the use of fossil insects as independent quantitative indicators could be key to a new approach for future paleoclimatic work. Although there have been an increasing number of paleoecological studies in Patagonia there is also much work to be done to fully understand and interpret the regional Quaternary scenarios, involving changes in biodiversity, tree refugia, species dispersion, successional changes and migration patterns since the last ice age.

Acknowledgments The authors want to thank Andrea Rizzo for her assistance during the fieldtrips in Patagonia and Sarah Gilchrist for providing them access to her unpublished PhD Thesis. Thanks also to Pat Haynes for helping in the preparation of samples.

References Andersen, T. and Contreras-Ramos, A. (1999). First record of Antillocladius Sæther from continental South America (Chironomidae, Orthocladiinae). Acta Zoologica Academiae Scientiarum Hungaricae 45, 149–154. Ariztegui, D., Bianchi, M.M., Massaferro, J. et al. (1997). Interhemispheric synchrony of Late-glacial climatic instability as recorded in proglacial Lake Mascardi, Argentina. Journal of Quaternary Science 12, 333–338. Armitage, P.D., Cranston, P.S. and Pinder, L.C. (1995). The Chironomidae: the biology and ecology of nonbiting midges. Chapman and Hall, London. Ashworth, A.C. (2001). Perspectives on Quaternary beetles and climate change. In: Gerhard, L.C., Harrison, W.E. and Hanson, B.M. (eds), Geological Perspectives of Global Climate Change. American Association of Petroleum 47, Tulsa Oklahoma, US, 153–168. Ashworth, A.C. and Hoganson, J.W. (1987). Coleoptera bioassociations along an elevational gradient in the Lake Region of southern Chile, and comments on the postglacial development of the fauna. Annals of the Entomological Society of America 80, 865–895. Ashworth, A.C. and Hoganson, J.W. (1993). The magnitude and rapidity of the climate change marking the end of the Pleistocene in the mid-latitudes of South America. Palaeogeography, Palaeoclimatology, Palaeoecology 101, 263–270. Ashworth, A.C. and Markgraf, V. (1989). Climate of the Chilean channels between 11,000 to 10,000 yr BP based on fossil bettle and pollen analyses. Revista Chilena de Historia Natural 62, 61–74. Santiago.

Quaternary Fossil Insects from Patagonia Ashworth, A.C., Markgraf, V. and Villagra´n, C. (1991). Late Quaternary climatic history of the Chilean Channels based on fossil pollen and beetle analysis, with an analysis of the modern vegetation and pollen rain. Journal of Quaternary Science 6, 279–291. Atkinson, T.C., Briffa, K.R., Coope, G.R. et al. (1986). Climatic calibration of Coleopteran data. In: Berglund, B. (ed.), Handbook of Holocene Palaeoecology and Palaeohidrology 852–858. John Wiley, New York. Atkinson, T.C., Briffa, K.R. and Coope, G.R. (1987). Seasonal temperatures in Britain during the last 22,000 years, reconstructed using beetle remains. Nature 325, 587–592. Bennett, K.D., Haberle, S.G. and Lumley, S.H. (2000). The Last Glacial – Holocene transition in southern Chile. Science 290, 325–328. Bianchi, M.M., Massaferro, J., Roma´n Ross, G. et al. (1997). The Pleistocene-Holocene boundary from cores of Lake El Tre´bol, Patagonia, Argentina. Archiv fu¨r Limnologie 26, 805–808. Bianchi, M.M., Massaferro, J., Roma´n Ross, G. and Lami, A. (2000). Geochemical and biological tracers of climate fluctuations during Late Pleistocene and Holocene in Lake El Tre´bol, Northern Patagonia, Argentina. Journal of Paleolimnology 22, 137–148. Binford, M.W. (1982). Ecological history of Lake Valencia, Venezuela: interpretation of animal microfossils and some chemical, physical and geological features. Ecological Monographs 52, 307–333. Birks, H.H., Batarbee, R.W. and Birks, H.J.B. (1999). The development of the aquatic ecosystem at Kra˚kenes Lake, western Norway, during the late glacial and early Holocene: a synthesis. Journal of Paleolimnology 23, 91–114. Brodersen, K.P. and Anderson, N.J. (2000). Subfossil insect remains Chironomidae and lake water temperature inference in the Sisimiut-Søndre Strømfjord region, southern West Greenland. In: Dawes, P.R. and Higgins, A.K. (eds), Review of Greenland activities 1999. Geology of Greenland Survey Bulletin 186, 78–82. Brodersen, K.P. and Lindegaard, C. (1999). Mass occurrence and sporadic distribution of Corynocera ambigua Zetterstedt Diptera, Chironomidae in Danish lakes. Neo- and palaeolimnological records. Journal of Paleolimnology 22, 41–52. Brodin, Y.W. and Gransberg, M. (1993). Responses of insects, especially Chironomidae Diptera, and mites to 130 years of acidification in a Scottish lake. Hydrobiologia 250, 201–212. Broecker, W.S. (1998). Paleocean circulation during the last deglaciation: a bi-polar see-saw? Paleoceanography 13, 119–121. Brooks, S.J. (2000). Late-glacial fossil midge stratigraphies (Insecta: Diptera: Chironomidae) from the Swiss Alps. Palaeogeography, Palaeoclimatology, Palaeoecology 159, 261–279. Brooks, S.J. (2003). Chironomid analysis to interpret and quantify Holocene Climate Change. In: Mackay, A., Battarbee, R., Birks, J. and Oldfield, F. (eds), Global Change in the Holocene 328–341. Arnold, London. Brooks, S.J. and Birks, H.J.B. (2000). Chironomidinferred Lateglacial air temperature at Whitrig Bog,

407

south east Scotland. Journal of Quaternary Sciences 15, 759–764. Brooks, S.J. and Birks, H.J.B. (2001). Chironomidinferred air temperatures from Lateglacial and Holocene sites in north-west Europe: progress and problems. Quaternary Science Reviews 20, 1723–1741. Brooks, S.J., Bennion, H. and Birks, H.J.B. (2001). Tracing lake trophic history with a chironomid-total phosphorus inference model. Freshwater Biology 46, 413–533. Brundin, L. (1949). Chironomiden und andere Bodentiere der su¨dschwedischen Urgebirgsseen. Report of the Institute of Freshwater Research 30, 1–914. Drottningholm. Brundin, L. (1958). The bottom faunistical lake type system and its application to the Southern Hemisphere. Moereover, a theory of glacial erosion as a factor of productivity in lakes and oceans. Verhandlungen der Internationalen Vereinigung fu¨r Limnologie 13, 228–297. Brundin, L. (1966). Transantarctic relationships and their significance, as evidenced by chironomid midges, with a monograph of the subfamilies Podonominae and Aphroteniinae and the austral Heptagyiae. Kungl Svenska Vetenskapsakademiens Handlingar 11, 1–472. Churcher, C.S. (1966). The insect fauna from the Talara tar-seeps Peru. Canadian Journal of Zoology 44, 985–993. Clapperton, C.M., Sugden, D.E., Kaufman, D.S. and McCulloch, R.D. (1995). The Last Glaciation in central Magellan-Strait, Southermost Chile. Quaternary Research 42, 2, 133–148. Coope, G.R. (1977). Fossil coleopteran assemblages as sensitive indicators of climate change during the Devensian last cold age. Philosophical Transactions of the Royal Society of London B 280, 313–340. Coope, G.R. (1990). The invasion of northern Europe during the Pleistocene by Mediterranean species of Coleoptera. In: Di Castri, F., Hansen, A.J. and Debussche, M. (eds), Biological Invasions in Europe and the Mediterranean Basin, 203–215. Kluwer, The Netherlands. Corley, J.C. and Massaferro, J.I. (1998). Long term turnover of a fossil community of chironomids (Diptera) from Lake Mascardi (Patagonia, Argentina). Journal of the Kansas Entomological Society 71, 407–413. Cranston, P.S. (1995). Morphology of Chironomidae. In: Armitage, P., Cranston, P. and Pinder, L.V. (eds), The Chironomidae: the biology and ecology of non-biting midges, 11–30. Chapman and Hall, London. Cranston, P.S. (2000). Parapsectrocladius: a new genus of Orhocladiinae Chironomidae (Diptera) from Patagonia, the southern Andes. Insect systematics and evolution 31, 1, 103–120. Cranston, P.S. and Edwards, D.H.D. (1999). Botryocladius gen.n: a new transantarctic genus of Orthocladiinae midge (Diptera: Chironomidae). Systematic Entomology 24, 305–333. Currie, D. and Walker, I. (1992). Recognition and palaeohydrologic significance of fossil black fly larvae, with a key to the Nearctic genera (Diptera: Simuliidae). Journal of Paleolimnology 7, 37–54. Denton, G.H. (1999). Glacial and vegetational history of the southern Lake District of Chile-preface. Geografiska Annaler 81A, 2, 105–106.

408

Julieta Massaferro et al.

Denton, G.H. and Hendy, C.H. (1994). Younger Dryas age advance of Franz Josef Glacier in the Southern Alps of New Zealand. Science 264, 1434–1437. Denton, G.H. and Hendy, C.H. (1995). The age of the Waihoo Loop glacial event. Science 271, 669. Denton, G.H., Heusser, C.J., Lowell, T.V. et al. (1999). Interhemispheric linkage of paleoclimate during the last glaciation. Geografiska Annaler 81A, 107–153. Dimidiatris, S. and Cranston, P.S. (2001). An Australian Holocene climate reconstruction using Chironomidae from a tropical volcanic maar lake. Palaeogeography, Palaeoclimatology, Palaeoecology 176, 109–131. Elias, S.A. (1994). Quaternary insects and their environments. Smithsonian Institution Press, Washington, D.C., 284 pp. Frey, D.G. (1964). Remains of animals in Quaternary lake and bog sediments and their interpretation. Ergebnisse der Limnologie 2, 1–114. Frey, D.G. (1988). Littoral and offshore communities of diatoms, cladocerans and dipterous larvae, and their interpretation in Paleolimnology. Journal of Paleolimnology 1, 179–191. Gilchrist, S. (2005). Late Quaternary paleoclimatic reconstructions in Patagonia using chironomid analysis. Unpublished PhD Thesis, University of Edinburgh, Edinburgh. Glasser, N.F., Harrison, S., Winchester, V. and Masamu, A. (2004). Late Pleistocene and Holocene paleoclimate and glacier fluctuations in Patagonia. Global and Planetary Change 43, 79–101. Gonser, T. and Spies, M. (1997). Southern Hemisphere Symbiocladius (Diptera, Chironomidae) and their mayfly hosts (Ephemeroptera, Leptophlebiidae). In: Landolt, P. and Sartori, M. (eds), Ephemeroptera & Plecoptera. Biology – ecology – systematics, 455–466. MTL, Fribourg, Switzerland. Hajdas, I., Bonani, G., Moreno, P. and Ariztegui, D. (2003). Precise radiocarbon dating of Late-Glacial cooling in mid-latitude South America. Quaternary Research 59, 70–78. Haberle, S.G. and Bennett, K.D. (2004). Postglacial formation and dynamics of North Patagonian rainforest in the Chonos Archipelago, Southern Chile. Quaternary Science Reviews 23, 2433–2452. Henrikson, L. and Oscarson, H.G. (1985). History of the acidified Lake Ga˚rdsjo¨n: the development of chironomids. Ecological Bulletin 37, 58–63. Heusser, C.J. (1974). Vegetation and climate of the southern Chilean Lake District during and since the last interglaciation. Quaternary Research 4, 290–315. Heusser, C.J. (1989). Late Quaternary vegetation and climate of southern Tierra del Fuego. Quaternary Research 31, 396–406. Heusser, C.J. (1993). Late-glacial of southern South America. Quaternary Science Reviews 12, 345–350. Heusser, C.J. (1997). Deglacial setting of the Southern Andes following the last glacial maximum: a short review. Anales del Instituto de la Patagonia 25, 89–103. Punta Arenas. Chile. Heusser, C.J. (2002). On glaciation of the southern Andes with special reference to the Penı´nsula de Taitao and adjacent Andean cordillera (~46300 S). Journal of South American Earth Sciences 15, 577–589.

Heusser, C.J. (2003). Ice Age Southern Andes. A Chronicle of Paleoecological Events. Developments in Quaternary Science 3, 240 pp. Elsevier, Amsterdam. Heusser, C.J. and Rabassa, J. (1987). Cold climate episode of Younger Dryas age in Tierra del Fuego. Nature 328, 609–611. Heusser, C.J. and Streeter, S.S. (1980). A temperature and precipitation record of the past 16,000 years in southern Chile. Science 210, 1345–1347. Heusser, C.J., Lowell, T.V., Heusser, L.E. et al. (1996). Full-glacial – late-glacial palaeoclimate of the Southern Andes: evidence from pollen, beetle and glacial records. Journal of Quaternary Science 11, 173–184. Hofmann, W. (1971). Zur Taxonomie und Palo¨kologie subfossiler Chironomiden (Dipt.) in Seesedimenten. Ergebnisse der Limnologie 6, 1–50. Hofmann, W. (1978). Analysis of animal microfossils from the Grober Segeberger See (F.R.G). Archiv fu¨r Hydrobiologie 82, 316–346. Hofmann, W. (1986). Chironomid analysis. In: Berglund, B.E. (ed.), Handbook of Holocene Palaeoecology and Palaeohydrology 715–723. John Wiley, Chichester, New York. Hofmann, W. (1988). The significance of chironomid analysis (Insecta: Diptera) for paleolimnological research. Palaeogeography, Palaeoclimatology, Palaeoecology 62, 501–509. Hofmann, W. (1998). Cladocerans and chironomids as indicators of lake level changes in north temperate lakes. Journal of Paleolimnology 19, 55–62. Hoganson, J.W. and Ashworth, A.C. (1992). Fossil beetle evidence for climatic change 18,000 – 10,000 years BP in south-central Chile. Quaternary Research 37, 101–116. Hoganson, J.W., Gunderson, M. and Ashworth, A.C. (1989). Fossil beetle analysis. In: Dillehay, T.D. (ed.), Monte Verde, a Late Pleistocene Settlement in Chile, 1. Palaeoenvironment and Site Context, 215–226. Smithsonian Institute Press, Washington. Jones, R.T. and Marshall, J. (2002). Lacustrine Oxygen Isotopic Records from Temperate Marl Lakes. PAGES 10, 2, 17–19. Kaplan, M.R., Ackert, R.P., Singer, B.S. et al. (2004). Cosmogenic nuclide chronology of millennial-scale glacial advances during O-isotope stage 2 in Patagonia. Geological Society of America Bulletin 116, 3–4, 308–321. Korhola, A., Olander, H. and Blom, T. (2000). Cladoceran and chironomid assemblages as qualitative indicators of water depth in subarctic Fennoscandian lakes. Journal of Paleolimnology 24, 43–54. Lamy, F., Kaiser, J., Ninnemann, U. et al. (2004). Antarctic timing of surface water changes of Chile and Patagonian Ice Sheet Response. Science 304, 1959–1962. Larocque, I., Hall, R.I. and Grahn, E. (2001). Chironomids as indicators of climate change: a 100-lake training set from a subarctic region of northern Sweden (Lapland). Journal of Paleolimnology 26, 307–322. Lemdahl, G. (1991). A rapid climate change at the end of the Younger Dryas in South Sweden-Palaeoclimatic and palaeoenvironmental reconstructions based on fossil insect aseemblages. Palaeogeography, Palaeoclimatology, Palaeoecology 83, 313–331.

Quaternary Fossil Insects from Patagonia Levesque, A.J., Mayle, F.E., Cwynar, L.C. and Walker, I.R. (1993). A previously unrecognized late-glacial cold event in eastern North America. Nature 353, 423–426. Levesque, A.J., Cwynar, L.C. and Walker, I.R. (1996). Richness, diversity and succession of late-glacial chironomid assemblages in New Brunswick, Canada. Journal of Paleolimnology 16, 257–274. Lotter, A.F., Birks, H.J.B., Hofmann, W. and Marchetto, A. (1997). Modern diatom, cladocera, chironomid, and chrysophyte cyst assemblages as quantitative indicators for the reconstruction of past environmental conditions in the Alps. I. Climate. Journal of Paleolimnology 18, 395–420. Lotter, A.F., Birks, H.J.B., Hofmann, W. and Marchetto, A. (1998). Modern diatom, cladocera, chironomid and chrysophyte cyst assemblages as quantitative indicators forn the reconstruction of past environmental conditions in the Alps. II. Nutrients. Journal of Paleolimnology 19, 443–463. Lotter, A.F., Walker, I., Brooks, S. and Hofmann, W. (1999). An intercontinental comparison of chironomid paleotemperature inference models: Europe vs. North America. Quaternary Science Reviews 18, 717–735. Lowe, J.J. and Walker, M.J.C. (1997). Reconstructing Quaternary Environments. Longman, London. Lowell, T.V., Heusser, C.J., Andersen, B.G. et al. (1995). Interhemispheric correlation of Late Pleistocene glacial events. Science 269, 1541–1549. Lumley, S.H. and Switsur, R. (1993). Late Quaternary chronology of the Taitao Peninsula, southern Chile. Journal of Quaternary Science 8, 161–165. Marchetto, A., Lami, A., Musazzi, S. et al. (2004). Lake Maggiore (N. Italy) trophic history: fossil diatom, plant pigments, chironomids and comparison with longterm limnological data. Quaternary International 113, 97–111. Marden, C.J. and Clapperton, C.M. (1995). Fluctuations of the Southern Patagonia ice field during the last glaciation and the Holocene. Journal of Quaternary Science 10, 197–210. Markgraf, V. (1987). Palaeoenvironmental changes at the northern limit of the subantarctic Nothofagus forest. Quaternary Research 28, 119–129. Markgraf, V. (1989). Palaeoclimates in central and South America since 18,000 BP based on pollen and lakelevel records. Quaternary Science Reviews 8, 1–24. Markgraf, V. (1991). Younger Dryas in South America? Boreas 20, 63–69. Markgraf, V. (1993a). Younger Dryas in southernmost South America – an update. Quaternary Science Reviews 12, 351–355. Markgraf, V. (1993b). Paleoenvironments and paleoclimates in Tierra del Fuego and southern most Patagonia, South America. Palaeogeography, Palaeoclimatology, Palaeoecology 102, 53–68. Markgraf, V., McGlone, M. and Hope, G. (1995). Neogene palaeoenvironmental and palaeoclimatic change in southern temperate ecosystems – a southern perspective. Trends in Ecology 10, 143–147. Massaferro, J. and Brooks, S. (2002). The response of Chironomids to Late Quaternary environmental change

409

in the Taitao Peninsula, Southern Chile. Journal of Quaternary Science 17, 2, 101–111. Massaferro, J. and Corley, J. (1998). Environmental disturbance and chironomid paleodiversity: 15 kyr BP of history at Lake Mascardi (Patagonia, Argentina). Aquatic Conservation: Marine and Freshwater Ecosystem 8, 315–323. Massaferro, J., Ribeiro Guevara, S., Rizzo, A. and Arribere, M. (2004). Short term environmental changes in Lake Morenito (41 S, Patagonia, Argentina) from the analysis of subfossil chironomids. Aquatic Conservation: Marine and Freshwater Ecosystems 14, 123–134. Massaferro, J., Brooks, S. and Haberle, S. (2005). The dynamics of vegetation and chironomid assemblages during the Late Quaternary at Laguna Fa´cil, Chonos Archipelago, southern Chile. Quaternary Sciences Reviews 24, 2510–2522. Massaferro, J., Moreno, P., Denton, G. et al. Chironomid and pollen evidence for climate fluctuations during the Last Glacial Termination in NW Patagonia Quaternary Sciences Reviews (submitted). McCulloch, R.D., Bentley, M.J., Purves, R.S. et al. (2000). Climatic inferences from glacial and palaeoecological evidence at the last glacial termination, southern South America. Journal of Quaternary Science 15, 409–417. McGlone, M.S. (1995). Lateglacial landscape and vegetation change and the Younger Dryas climatic oscillation in New Zealand. Quaternary Science Reviews 14, 867–881. Moreno, A.I. (1997). Vegetation and climate near Lago Llanquihue in the Chilean Lake District between 20,200 and 9500 14C yr BP. Journal of Quaternary Science 12, 485–500. Moreno, P.I. and Leo´n, A. (2004). Abrupt vegetation changes during the last glacial to Holocene transition in mid-latitude South America. Journal of Quaternary Science 18, 1–14. Moreno, P.I., Jacobson, G.L., Andersen, B.G. et al. (1999). Vegetation and climate changes during the last glacial maximum and the last termination in the Chilean Lake District: A case study from Canal de la Puntilla (41 S). Geografiska Annaler 81A, 285–311. Moreno, P.I., Jacobson, G.L., Lowell, T.V. and Denton, G.H. (2001). Interhemispheric climate links revealed from a late-glacial cool episode in southern Chile. Nature 409, 804–808. Newnham, R.M. and Lowe, D.J. (2000). Fine-resolution pollen record of lateglacial climate reversal from New Zealand. Geology 28, 759–762. Olander, H., Birks, H.J.B., Korhola, A. and Blom, T. (1999). An expanded calibration model for inferring lakewater and air temperatures from fossil chironomid assemblages in northern Fennoscandia. The Holocene 9, 279–294. Ponel, P. and Coope, C.R. (1990). Lateglacial and early Flandrian Coleoptera from La Taphanel, Massif Central, France: Climatic and ecological implications. Journal of Quaternary Science 5, 235–249. Porrinchu, D.F. and MacDonald, G.M. (2003). The use and application of freshwater midges (Chironomidae: Insecta: Diptera) in geographical research. Progress in Physical Geography 27, 3, 378–422.

410

Julieta Massaferro et al.

Quinlan, R. and Smol, J.P. (2001). Setting minimum head capsule abundance and taxa deletion criteria in chironomid-base inference models. Journal of Paleolimnology 26, 327–342. Quinlan, R., Smol, J.P. and Hall, R.I. (1998). Quantitative inferences of past hypolimnetic anoxia in southcentral Ontario lakes using fossil midges (Diptera: Chironomidae). Canadian Journal of Fisheries and Aquatic Sciences 55, 587–596. Rabassa, J., Heusser, C.J. and Rutter, N. (1990). Lateglacial and Holocene of Argentine Tierra del Fuego. Quaternary of South America and Antarctic Peninsula 7, 327–351. A.A.Balkema Publishers, Rotterdam. Saether, O. (1979). Chironomid communities as water quality indicators. Holarctic Ecology 2, 65–74. Shakau, B.L. (1986). Preliminary study of the development of the subfossil chironomid fauna (Diptera) of Lake Taylor, South Island, New Zealand, during the younger Holocene. Hydrobiologia 143, 287–291. Shakau, B.L. (1990). Stratigraphy of the fossil Chironomidae (Diptera) from Lake Grassmere, South Island, New Zealand. Science 281, 812–814. Steig, E.J., Brook, E.J., White, J. et al. (1998). Synchronous climate changes in Antarctica and the North Atlantic. Science 282, 92–95. Strelin, J.A. and Malagnino, E.C. (2000). Late-glacial history of Lago Argentino, Argentina, and age of the Puerto Bandera moraines. Quaternary Research 54, 339–347. Szeicz, J., Haberle, S.G. and Bennett, K.D. (2003). Dynamics of North Patagonian rainforests from fine-resolution pollen, charcoal and tree-ring analysis, Chonos Archipelago, Southern Chile. Austral Ecology 28, 413–422. Thienemann, A. (1918). Untersuchungen uber die Beziehungen zwischen dem Sauerstoffgehalt des Wassers und der Zusammensetzung der Fauna in Norddeutschen Seen. Archiv fu¨r Hydrobiologie 8, 316–346. Tokeshi, M. (1995). Production Ecology. In: Armitage, P.D., Cranston, P.S. and Pinder, L.C. (eds), The Chironomidae: the biology and ecology of non-biting midges, 269–292. Chapman and Hall, London. Turney, C.S.M., McGlone, M.S. and Wilmshurst, J.M. (2003). Asynchronous climate change between New Zealand and the North Atlantic during the last glaciation. Geology 31, 223–226. Vandergoes, M.J. and Fitzsimons, S.J. (2003). The Last Glacial-Interglacial Transition (LGIT) in south Westland, New Zealand: Paleoecological insight into mid-latitude Southern Hemisphere climate change. Quaternary Science Reviews 22, 1461–1476. Walker, I.R. (1990). Modern assemblages of arctic and alpine Chironomidae as analogues for late-glacial communities. Hydrobiologia 214, 223–227.

Walker, I.R. (1995). Chironomids as indicators of past environmental change. In: Armitage, P., Cranston, P.S. and Pinder, L.V. (eds), The Chironomidae: the biology and ecology of non-biting midges, 405–422. Chapman and Hall, London. Walker, I.R. (2001). Midges: Chironomidae and related Diptera. In: Smol, J.P., Birks, H.J.B., Last, W.M. (eds), Tracking environmental change using lake sediments. Vol. 4. Zoological indicators. Kluwer Academic Publishers, Dordrecht. Walker, I.R. and Mathewes, R.W. (1987). Chironomidae (Diptera) and Postglacial Climate at Marion Lake, British Columbia, Canada. Quaternary Research 27, 89–102. Walker, I.R., Smol, J.P., Engstom, D.R. and Birks, H.J.B. (1991). An assessment of Chironomidae as quantitative indicator of past climate change. Canadian Journal of Fisheries and Aquatic Science 48, 975–987. Walker, M.J.C., Coope, G.R. and Lowe, J.J. (1993). The Devensian (Weichselian) Lateglacial palaeoenvironmental record from Gransmoor, East Yorkshire, England. Quaternary Science Reviews 12, 659–680. Walker, I.R., Wilson, S.E. and Smol, J.P. (1995). Chironomidae (Diptera): Quantitative palaeosalinity indicators for lakes of western Canada. Canadian Journal of Fisheries and Aquatic Science 52, 950–960. Walker, I.R., Levesque, A.J., Cwynar, L.C. and Lotter, A.F. (1997). An expanded surface-water palaeotemperature inference model for use with fossil midges from eastern Canada. Journal of Paleolimnology 18, 165–178. Warwick, W.F. (1980). Paleolimnology of the Bay Quinte, Lake Ontario: 2800 years of cultural influence. Canadian Bulletin of Fisheries and Aquatic Sciences 206, 1–117. Whitlock, C., Bartlein, P.J., Markgraf, V. and Ashworth, A. (2001). The Midlatitudes of North and South America during the Last Glacial Maximum and Early Holocene: similar paleoclimatic sequences despite differing large-scale controls. In: Markgraf, V. (ed.), Interhemispheric Climate Linkages, 391–416. Academic Press, New York. Wiederholm, T. (ed.) (1983). Chironomidae of the Holarctic region. Keys and diagnoses. Part 1. Larvae. Entomologica Scandinavica Suppl 19, 1–457. Wiederholm, T. (1984). Response of aquatic insects to environmental pollution. In: Resh, V.H. and Rosemberg, D.M. (eds), The Ecology of Aquatic Insects. Praeger Publishers, New York. Wiederholm, T. and Eriksson, O. (1979). Subfossil chironomids as evidence of eutrophication in Ekoln Bay, Central Sweden. Hydrobiologia 3, 283–302.