Qua Ternary Fossil Insect From Patagonia

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Quaternary Fossil Insects from Patagonia

Julieta Massaferro1, Allan Ashworth2 and Stephen Brooks3

1CONICET – Laboratorio de Ecotono, CRUB/Universidad del Comahue, 8400 – Bariloche, Argentina2Department of Geosciences, North Dakota State University, Fargo, 58105-5517 North Dakota, US

3Department of Entomology, Natural History Museum, SW7 5BD London, UK

1. Introduction: The Importance of Patagoniafor Climatic Studies

Patagonia is the region of Argentina and Chile thatextends from 39� to 55� S. In the last 20 yrs Patagoniahas become increasingly important in paleoclimaticresearch due to its exceptional geographic locationbetween the South Pacific, Atlantic and Antarctic oceansand the abundance of lakes and bogs from which climateindicators can be easily obtained.

The Andean region of Patagonia is ideal for monitoringLate Quaternary climate at mid-latitudes because it is one ofthe few areas sustaining a suite of rainforest communitiesalong altitudinal and latitudinal gradients within the belt ofthe southern westerlies (Moreno, 1997; Whitlock et al.,2001). Such a location is a key for investigations relatedto the reorganization of climate during the Late Pleistoceneand Holocene, especially for testing the synchroneity ofclimate changes in the Northern and Southern Hemispheres.

Patagonia is also a key place for the study of inter-annual and decadal climate variations such as the El NinoSouthern Oscillation (ENSO) that affect the Pacific Oceanand leaves paleoecological evidence in lake records.Furthermore, Patagonia also provides evidence of pastclimate changes from regions located in the same latitudeand climate as those in the Northern Hemisphere whereclimate has been extensively studied (Denton, 1999).

Finally, neo-ecological work developed in this part ofSouth America has emphasized the strong need for thestudy of catastrophic disturbances such as earthquakes,volcanic activity, insect outbreaks, windstorms and firesthat affected flora and fauna in Patagonian rainforest inthe past (Szeicz et al., 2003).

2. Paleoclimatic Proxies

So far, most of the evidence for climate change in southernSouth America has been derived from abiotic climateproxies and a few biotic proxies, especially pollen records.Extensive mapping and dating of glacial and fluvio-glacialfeatures has produced a detailed history of glacial behaviorin the Chilean Lake District (Denton et al., 1999) and atother 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 beretrieved from long lake-sediment cores, bogs or marine

sediments, is that they offer a continuous record of cli-mate change. The study of these records combined withphysical and chemical parameters can provide a compre-hensive array of information for climate change studies.

Recent palynological studies from southern SouthAmerica have provided a thorough overview of pastvegetation and climate change, specially those changesassociated with shifts in the latitudinal position of thewesterlies in southern temperate ecosystems (Markgraf,1987; Heusser, 1989, 2003; Markgraf et al., 1995; Moreno,1997; Moreno et al., 1999, 2001; Moreno and Leon, 2004).

Fossil insects are often abundant in a wide range ofQuaternary deposits. Several orders of insects can befound in fluvial and lacustrine sediments such as speciesfrom the Order Hemiptera including Gerridae, Corixidaeand Notonectidae. The larvae of caddisflies (Trichoptera)are aquatic and their sclerites can be found in lacustrinesediments. Caddisfly larvae provide valuable informationabout the water quality they inhabit, as many species arestenothermic and are sensitive to changes in pH and trophy(Elias, 1994). Another group that has recently proved to beuseful in paleolimnology, especially in fluvial sediments,is the Family Simuliidae. Simuliids have been studied byCurrie and Walker (1992) in North America who demon-strated they were useful indicators of precipitationchanges. However, to date, most of the paleoenvironmen-tal 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 comesfrom late Tertiary and early Quaternary assemblages inAlaska. However, those records are generally poorly pre-served, laid down in bedrock, full of spatial and temporalgaps and lacking in continuity (Elias, 1994).

For this reason, this chapter focuses on midges andbeetles from the Quaternary period, especially the LatePleistocene and Holocene, with which, to date, most ofthe fossil insect studies have dealt.

The use of fossil insects in Quaternary studies at mid-latitude South America is relatively limited, and themajor reason is the lack of taxonomical informationavailable from these remote areas. Many of these studieshave been conducted in the southern part of SouthAmerica, in Argentina and Chile (Ashworth andHoganson, 1987, 1993; Hoganson et al., 1989; Ashworthet al., 1991; Hoganson and Ashworth, 1992; Massaferroand Brooks, 2002; Massaferro et al., 2004).

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3. Chironomids

Chironomidae belong to the Order Diptera: Nematocera andthey are colloquially known as non-biting midges. Thelarvae of the majority of these species are aquatic andconstitute one of the most abundant bottom-dwelling macro-invertebrates of freshwaters (Cranston, 1995) (Fig. 1a).

The distribution of the different chironomid taxa isrestricted by environmental conditions. Most species arestenotopic (i.e., able to adapt only to a narrow range ofenvironmental conditions) and respond rapidly to envir-onmental change. The sensitivity of chironomids to dif-ferent environmental variables such as dissolved oxygen,nutrient and organic content, pH and salinity has led totheir use as indicators of lake quality and in other ecolo-gical studies (Porrinchu and MacDonald, 2003).

Midges began to be used in paleoecological studiesduring the 1980s and 1990s. Excellent reviews of chir-onomids as paleoindicators can be found in Frey (1964,1988), Hofmann (1971, 1988) and Walker (1990, 1995,2001). Their remains are of special interest in paleolim-nology because their strongly sclerotized larval headcapsules are preserved in sediment deposits (Fig. 1b).There are several reasons why chironomids are consid-ered important in paleolimnology: (i) they are sensitive to

environmental variables such as temperature, pH, trophicconditions, dissolved oxygen; (ii) they have relativelyshort life cycles; (iii) the adult are mobile; (iv) the larvaepossess chitinous head capsules that are well preserved inlake sediments and (v) they are abundant, diverse andreadily identifiable to generic and species-group level,enabling high resolution studies. Past chironomid strati-graphies can be reconstructed and readily used to inferenvironmental conditions at the time of deposition.

Chironomids are now well established as paleoecolo-gical proxy indicators and have been used effectively todocument changes in salinity (Walker et al., 1995), lakeproductivity (Lotter et al., 1997, 1998; Brodersen andLindegaard, 1999; Brodersen and Anderson, 2000) andhypolimnetic anoxia (Quinlan et al., 1998). However,perhaps the most successful use of chironomids is toquantify past climate changes during the Late Glacialand Holocene in the Northern Hemisphere (Levesqueet al., 1996; Lotter et al., 1999; Brooks, 2000; Korholaet al., 2000; Brooks and Birks, 2001).

3.1. Methodology

The volume of sediment required to recover a sufficientnumber (50–150) of chironomid head capsules variesfrom lake to lake, but usually 1–3 g of wet sediment isplenty. However, in Late Glacial inorganic clayish sedi-ments or volcanic sediments sometimes this amount ofsediment is not enough. The methodology involved inprocessing and identification of chironomid remainsgenerally follows standard procedures (Warwick, 1980;Hofmann, 1986; Walker, 1995). Although the approachesin individual laboratories vary slightly, the concept remainsthe same: a careful separation of the subfossil head cap-sules from the sediment matrix using mild chemical treat-ment and sieving (Porrinchu and MacDonald, 2003).

The procedure involves deflocculating the sedimentsample using 10% KOH solution at 50�–70�C for10 minutes. The warm KOH serves to break up colloidalmatter without damaging the remains. The next steprequires sieving the sediment and a mesh size of 95 mmshould retain most of the heads. Sorting the samplerequires a grooved counting tray. The chironomid headsare then handpicked with forceps or micropipettes into80% ethanol using a stereo dissection microscope(25–50�). Finally, chironomid remains are dehydratedby transfer from 80% ethanol to 100% ethanol to Euparalessence and finally to Euparal�, which is a permanentmounting medium for permanent slides.

3.2. Applications of Chironomids inPaleoenvironmental Reconstructions

Subfossil chironomids have been used extensively as qua-litative indicators of past environmental conditions. Sincethe earliest days of modern limnology, chironomids havebeen used in lake typologies to indicate trophic status ofwaters (Thienemann, 1918; Brundin, 1949; Saether, 1979;Wiederholm, 1984). Late Glacial sediments from littoraland profundal lake zones in the Northern Hemisphere

Lake

Sedimentcore

Head capsule PupaeLarval instars

Adult

AdultswarmsEgg masses

Mandible

Mentum

Antenna

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(b)

Fig. 1. (a) Chironomidae life cycle (modified fromPorrinchu and MacDonald, 2003). (b) Fossilchironomid head capsules from Laguna Stibnite, Chile,showing taxonomical useful features (Massaferro andBrooks, 2002).

394 Julieta Massaferro et al.

include cold stenothermic, ultraoligotrophic taxa such asHeterotrissocladius spp. and Tanytarsus lugens (Brundin,1949). In mesotrophic lakes, those assemblages arereplaced by taxa more tolerant to oxygen depletion suchas Sergentia coracina and Stictochironomus. Finally,warm-adapted Chironomus spp. are characteristic of pro-fundal zones in eutrophic lakes. This faunistic systemapplies in the Northern Hemisphere and has been usedextensively to develop transfer functions (TF), whichrelate the modern chironomid distribution to a particularenvironmental variable such as temperature, oxygen con-centration or total phosphorous. These TF allow quantita-tive reconstructions of particular environmental variables(see ‘‘Quantitative temperature reconstructions using fossilinsects’’ in this chapter).

In an expedition to the southern Andes in SouthAmerica, Brundin (1958) collected and described muchof the chironomid fauna of the area demonstrating thatthe fauna had a great resemblance to the Holarctic fauna.He recognized taxa with similar ecological requirementsin both hemispheres. For example, Tanytarsus rothi-community replaces T. lugens; Lenzia (Sergentia) coracinainstead of Sergentia coracina and Parachironomus speciesreplacing the northern Paracladopelma species. Later on,Brundin (1966) published an extensive study of the midgesubfamilies Podonominae and Aphroteniinae. This invalu-able work also shows evidence of chironomid biogeogra-phical relationships between the separated Gondwana landmasses of Australia and southern South America.

Little has been done on larval chironomid taxonomyin Patagonia since Brundin’s work (Gonser and Spies,1997; Andersen and Contreras-Ramos, 1999; Cranstonand Edwards, 1999; Cranston, 2000). Recently,Massaferro and Brooks (2002) and Massaferro et al.(2005) described specimens from the subfossil chirono-mid fauna and identified additional taxonomic groupsthat could be ecologically related to European taxa.However, more ecological work is needed especiallyregarding the distribution and habitat requirements ofthis group of insects in South America.

3.3. Eutrophication

Increase in lake productivity is accompanied by oxygendepletion in the hypolimnium. Certain chironomid larvaesuch as Chironomus spp. can tolerate very low oxygenlevels that commonly exist in eutrophic and hyper-eutrophic lakes. They contain invertebrate haemoglobinenabling respiration in sites with low oxygen concentra-tions. There are many studies that have used chironomidsas indicators of the trophic status of lakes (Hofmann, 1978;Warwick, 1980; Wiederholm, 1983) and there have alsobeen several quantitative reconstructions estimating pastchanges in productivity based on chironomids (Lotteret al., 1998; Quinlan et al., 1998; Brooks et al., 2001;Quinlan and Smol, 2001). In Patagonia a few qualitativestudies have been done on this subject, especially relatedto human activities, the impact of building developments,fish introduction and increase of nutrients in lakes(Bianchi et al., 1997, 2000; Massaferro et al., 2004).

3.4. Acidification

The effects of acid rain on ecosystems have had animportant impact in North America and Europe duringthe 19th and 20th centuries. The immediate consequenceof acid rain is lowered pH that affects the function ofecosystems. In aquatic systems, there are some speciesof chironomids that can tolerate low pH such as speciesof Chironomus, Zavrelia, Zalutschia and Psectrocladius.In the Northern Hemisphere there are a number of studiesdealing with pH and chironomids (e.g., Wiederholm andEriksson, 1979; Henrikson and Oscarson, 1985; Brodinand Gransberg, 1993). Lake acidification can alsobe caused by natural factors, usually induced by devel-opment of soils related to vegetational succession.However, in southern South America there have beenno studies related to acidification.

3.5. Lake-level Changes

Changes in lake level can influence the proportion andvolume of the littoral and profundal zones causingchanges in the composition and distribution of the chir-onomid assemblages. Strongest impacts may be detectedin a littoral core where deepening may cause an increasein profundal taxa. When lake level falls, the proportion ofprofundal taxa is likely to decline. The influence of depthon the distribution of chironomids has long been known(Hofmann, 1998; Korhola et al., 2000; Massaferroand Brooks, 2002; Marchetto et al., 2004) and there isa clear differentiation between littoral taxa such asDicrotendipes, Glyptotendipes and Polypedilum, whichare associated with macrophytes, semi-terrestrial taxasuch as Limnophyes, Smittia and Gymnometriocnemusand profundal taxa such as Chironomus, T. lugens andProcladius (Armitage et al., 1995).

3.6. Climate

Chironomid distribution is significantly affected by tem-perature, albeit in different ways. For instance, egg andlarval development are influenced directly by water tem-perature (Tokeshi, 1995), but also water and air tempera-tures affect midges in an indirect way. In general, anincrease in water temperature leads to an increase inproductivity, which, in turn, increases food supply anddecreases oxygen availability.

Since the 1990s the use of fossil midges as indicatorsof climate change has proliferated and there is plenty ofevidence concerning the significance of temperature incontrolling chironomid distribution and abundance, espe-cially during Late Glacial times. These studies were firstdeveloped in arctic and alpine lakes (Walker andMathewes, 1987; Walker et al., 1991) sediments andshowed that cold-stenothermic taxa such as Heterotrisso-cladius spp. and T. lugens dominate the Late Glacialperiod and that these taxa disappear with climate warm-ing at the beginning of the Holocene, when they arereplaced by a diverse, thermophilic chironomid assem-blage dominated by Chironomini.

Quaternary Fossil Insects from Patagonia 395

4. Beetles

Coleoptera or beetles are a diverse (more than 300,000known species) and abundant order of insects. This highdiversity makes them an important group in the fossilrecord. They are ubiquitous occurring from arctic polardeserts to the Subantarctic islands and at elevations ashigh as 5600m in the Himalayas. There are species withphysiologies adapted to survive periodic below freezingtemperatures and other littoral species adapted to survivedaily tidal inundations by burrowing in sand. Like otherinsects, they are ectotherms and are dependent on environ-mental temperatures during all phases of their life cycle.

Most beetles are small organisms, ranging in lengthfrom 0.25 mm to several centimetres. Average length isestimated to be in the range of 4–5 mm. Because of theirabundance, beetles are important food items for numer-ous 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

stored products. Their most important beneficial roles, aspollinators and as recyclers of nutrients, are activities thatensure the health of ecosystems.

Species in many families of beetles are susceptibleto environmental change. In general, predators andscavengers receive the most attention in paleoenviron-mental reconstructions because they are able to respondmore rapidly to climate change, since they are not tied tospecific types of vegetation (Elias, 1994).

Beetles respond to Quaternary climate change mostlyby dispersal to track a favourable climate envelope,which ultimately led to large-scale changes in geographi-cal distribution. Quaternary beetle fossils consist mostlyof disarticulated exoskeletons; setae and scales are fre-quently preserved in unconsolidated sediments from shal-low lacustrine, paludal and fluvial environments. Internalstructures such as the male genitalia also occur as fossils.However, for practical purposes, the parts most studiedby paleoentomologists are heads, pronota (thoraces) andelytra (wing cases) (Ashworth, 2001) (Fig. 2a, b).

Diacheila polita Fald. (Coleoptera: Carabidae)

S.E.M.'s of head, pronotum, andelytra.

Conklin Quarry Site, Iowa City,Iowa, U.S.A.

Cerroglossus sp.(Coleoptera: Carabidae)

Pair of elytra (wing covers) inpeat.

Rio Caunahue Site, southernChile. Ca. 10,000 yr BP

Anisosticta bitriangularis (Say)(Coleoptera: Coccinellidae)

Left elytronWinter Gulf Site, North Collins,

New York, U.S.A.Ca. 12,700 yr BP

Elytra

Character: Frontangle and Lateral stria

Character: Latero-BasalFovea

Character:Microsculpture

Character: Hind angle andLatero-basal puncture

(b)

(a)Head capsule

Pronotum

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


4.1. Methodology

Fossils of beetles for Quaternary studies are usuallyobtained from stratigraphic sections exposed in cut-bankson rivers, in road cuts and by excavating pits in bogs. Thequantities of sediment used in the studies vary but typi-cally are 10 kg for each 5 cm stratigraphic interval.

Organic sediments are wet sieved and the fractionlarger than 300 mm is further processed using a keroseneflotation technique (Elias, 1994). This technique concen-trates large numbers of insect skeletal parts, mostly theheads, pronota and elytra of beetles. The fragments tendto be very well preserved, with setae and scales andstructural colours intact. The details preserved on thefossils facilitate their identification. Data from fossilbeetle analysis are usually presented in the form ofspecies abundance lists showing the number of indivi-duals occurring within a particular sample. Occasionally,further information about specific parts of the body suchas elytra or pronotum is provided (Lowe and Walker,1997).

As with their counterparts in North America andEurope, the fossils of Patagonian Coleoptera are identicalto extant species. The beetle fauna of South America isnot as well known as that of Europe or North America buteven so large numbers of species are identifiable fromtheir fossils.

4.2. Applications of Beetles for PaleoenvironmentalReconstructions

Coleoptera are very useful in paleoecological reconstruc-tions because they are such an important element interrestrial ecosystems. They are relatively abundant andhighly diverse in a wide range of deposits. Speciation andextinction is extremely rare, at least during the Pleisto-cene (Elias, 1994). The common response is for speciesto survive by dispersal. In consequence, beetle geo-graphic distributions shrink and expand constantly. Inthis respect, the South American fauna at temperate lati-tudes is no different from that in the northern Hemi-sphere. Therefore, beetle species constancy over the lastmillion years allows us to make use of ecological anddistributional data drawn from modern populations(Elias, 1994).

In addition to that, beetles are stenotopic, whichmeans that they show a marked preference for a veryrestricted number of environments. A large number ofbeetles are associated with aquatic habitats, for exampleflowing water is indicated by Esolus, Limnius volckmariand Ochthebius pedicularis whereas Potamonectes andHalyplus live in still waters with sandy or silty bottoms.Other beetles indicate the presence of particular plants oranimals. A profusion of dung beetles, for example, wouldindicate the presence of mammals (Lowe and Walker,1997). Beetle assemblages can therefore provide valuableinformation on a diverse range of contemporaneous habi-tats with differences in vegetation, soils, water quality,forest composition and health, and may provide environ-mental insights that are difficult to obtain from otherlines of evidence (Elias, 1994).

5. Quantitative Temperature ReconstructionsUsing Fossil Insects

The analysis of fossil insects can be used for both qualitativeand quantitative environmental reconstructions. Althoughthe qualitative approach is long established, recent advancesin statistical techniques have allowed paleoecologicalresearch to undergo a quantitative revolution.

Temperature reconstructions using fossil insectassemblages have played an important role in NWEurope in recent attempts to reconstruct timing, magni-tude and rates of climate changes during the LateGlacial–Interglacial transition and Holocene (Brooks,2003). The close relationship between temperatureand the distribution and abundance of fossil assem-blages has been used to develop temperature inferencemodels that can produce quantitative environmentalreconstructions.

5.1. Chironomids

One of the advantages of temperature reconstructionusing chironomids is that many hundred of head capsulescan be obtained from as little as 1 cm3 of sediment givinga higher resolution record than other methods such as forbeetles, where large amounts of sediments are required.

Pioneering work using chironomids for quantitativereconstructions was done in Canada by Levesque et al.(1993) and Walker et al. (1997) who produced tempera-ture models that have been used successfully numeroustimes in eastern and western Canada. Further chironomidtemperature quantitative models were developed in North-ern 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 fromNorway, Brooks and Birks (2001) applied the inferencemodel to Late Glacial chironomid assemblages fromWhitrig Bog in Scotland for a high-resolution quantitativeclimate reconstruction. The correlation between thechironomid-inferred temperature and the GRIP oxygenisotope stratigraphy shows striking similarities (Fig. 3).

Relatively few quantitative reconstructions have beencarried out in the Southern Hemisphere. In Australia,Dimidiatris and Cranston (2001) developed a chironomidtemperature model based on the MCR method (seebelow) that has been applied to a Holocene sequencefrom a maar lake in Queensland.

In an attempt to explore the potential of chironomidsas quantitative indicators of past temperatures inPatagonia, Gilchrist (2005) developed a statisticalmodel to infer paleoenvironmental changes in two lakesin southern Chile: Laguna Leta (41� S, 73� W) andLaguna Boal (44� S, 73� W). Records from both lakesindicated that climate changes occurred during the LateGlacial–Holocene transition and give evidence of theexistence of a reversal event at the time of the YoungerDryas (YD) between 13,300 and 12,000C yr BP.Concomitant with this cooling event, there is evidenceof an increase of moisture that potentially caused a risein lake levels. These promising results highlight theimportance of continuing this kind of investigations.


This approach is yet to be fully exploited in investiga-tions at mid-latitudes in the southern Hemisphere.

The power of chironomids to infer past temperaturescan be validated against other climatic reconstructions suchas ice core records, marine micropaleontological records,isotopic records and evidence from other biotic proxiessuch as pollen, beetles, cladocera and diatoms. Good exam-ples are the comparison of the Late Glacial isotopic andpollen records from Hawes Water, ostracods from Ammer-see, the chironomid temperature curve from Whitrig Bog toGRIP ice core isotope records (Jones and Marshall, 2002)and the multiproxy study developed in Krakenes (Norway)that present a comparison of temperature reconstructionsfrom different groups of fossil organisms including beetlesand midges (Birks et al., 1999) (Fig. 4).

5.2. Beetles

The most important factor driving beetle distributionduring the Quaternary has been climate (Coope, 1990).In Europe, modern distribution maps show that the geo-graphical range of many species corresponds with well-defined climate zones. Coope (1977) demonstrated thatduring the Quaternary, extremely rapid climate changesmay have allowed Coleoptera to colonize new habitatsrelatively quickly and in most of the cases where therange limit of the coleopteran species coincides with aclimatic boundary, this relationship has been used toapply quantitative paleotemperature reconstructions(Lowe and Walker, 1997).

In the Holarctic region, beetles have been widely usedfor quantitative temperature reconstructions (Coope,1977; Elias, 1994; Ashworth, 2001).

The Mutual Climate Range method (MCR) (Atkinsonet al., 1986, 1987) is used to infer temperatures from fossilbeetle assemblages. In this method, the geographic rangesof species are plotted within a climatic framework, usually

Fig. 3. (a) Chironomid reconstruction of mean Julyair temperature at Whitrig Bog, Scotland. (b) TheGRIP oxygen isotope record. Vedde Ash was includedin both plots to show synchronicity between bothreconstructions (modified from Brooks and Birks,2001).

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


mean January (T min) and mean July temperature (T max).In a fossil assemblage the overlapping climate envelopes ofeach species provide the mutual climate range, or theclimate space between T max and T min that the assem-blage was most likely to inhabit. The method depends ondetailed modern distributional information for species. TheMCR method has been used to reconstruct climatic condi-tions in Europe during the Late Glacial–Interglacialtransition (Ponel and Coope, 1990; Lemdahl, 1991; Walkeret al., 1993). MCR beetle curves are strongly supported byother climatic reconstructions such as Greenland ice corerecords and marine evidence (Lowe and Walker, 1997).

Due to little knowledge of modern species compositionand distribution in South America the MCR method andthe climatic summary it provides cannot be used at present.

6. Fossil Insects and Climate Studiesin South America

The current knowledge of insect paleoecology in Pata-gonia is relatively limited. In the Neotropics, there are

only two studies dealing with fossil insects available atpresent. In Venezuela, an investigation of fossil chiro-nomids from a sediment core from Lake Valencia indi-cated lake-level changes and trophic changes during thelast 12,000 14C yrs (Binford, 1982). The other studywas developed in Peru (Churcher, 1966) using insectremains from Talara. However, despite there beinggood information about the ecology of the differentgroups of Coleoptera in Peru, no specific identifica-tions, essential for paleoenvironmental reconstructions,were made.

6.1. Fossil Midges

There are currently few chironomids paleoecologicalstudies from Patagonia. There have been some investiga-tions carried out in Argentine Patagonia, within the limitsof the Nahuel Huapi National Park (41� S, 71�300 W)(Ariztegui et al., 1997; Bianchi et al., 1997, 2000; Corleyand Massaferro, 1998; Massaferro and Corley, 1998;Massaferro et al., 2004) (Fig. 5).

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


The research conducted by Ariztegui et al. (1997) is amultiproxy study in which changes in pollen, chironomidand geochemistry in Lago Mascardi during the LateGlacial were interpreted as a response to a reversal coin-cident with the timing of the YD. Between 11,400 and10,200 14C yr BP, there was a decrease in the total polleninflux as a consequence of an increase in inorganic sedi-mentation. A sharp decrease in the hydrogen index wasalso recorded. These results were interpreted as a coolingaccompanied by an increase in subglacial erosion due toan advance of the Tronador icecap that feeds proglacialLago Mascardi. The disappearance of the warm-adaptedChironomus and the decline in the total chironomidabundance at this time also suggests a climaticdeterioration.

Bianchi et al. (1997, 2000) show the results from amultiproxy study of a sediment core from Lago El Trebol.Although the site was suitable for paleolimnologicalstudies, the sampling resolution was not enough to discernclimatic changes during the Late Glacial period.

Corley and Massaferro (1998) and Massaferro andCorley (1998) also studied subfossil chironomid assem-blages from Lago Mascardi. However, the results focusedmostly on the importance of paleolimnological studies inunderstanding the role of natural disturbance and diver-sity patterns of biological communities in the past.

Massaferro et al. (2004) studied geochemical andchironomid records from a short core from LagoMorenito, near San Carlos de Bariloche. The results

show the response of chironomids to natural (volcanic)and non-natural (human) environmental disturbancesduring the last 200 yrs. The study also demonstrated theimportance of the multiproxy approach for paleoenviron-mental reconstructions.

There have not been other detailed studies of theresponse of chironomid assemblages to Late Quaternaryclimate change in other areas of Argentina. The reasonfor this is the lack of information on chironomid taxon-omy due to the small number of researchers working onthe subject. The first high-resolution environmentalreconstruction using chironomids in Chile was publishedrecently by Massaferro and Brooks (2002) (Fig. 6).Changes in the chironomid assemblages at Laguna Stib-nite (46� S) in the Taitao Peninsula in Chile suggest thatthe climate in southern Chile was at it coolest during theYD (Fig. 7). In addition, during this period, chironomidhead capsule concentrations fall suggesting low lakeproductivity, which would be consistent with lowtemperatures during this event. The specific chironomidassemblage during this period also indicates that theclimate was cooler and drier. Between 11,300 and9,400 14C yr BP (13,000–11,200 cal. yr BP), the cold-stenothermic Podonominae were consistently present inevery sample attaining a peak abundance during thisperiod. This suggests that the lake waters were cool andoligotrophic during the YD. The low concentration ofhead capsules also reflects low lake productivity. Duringthe Holocene, chironomids from Laguna Stibnite show

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CIF

IC O

CE

AN

AdventureBay

I. ChiloéL. Yelcho

L. Verde

L. De la Plata

L. Rosselot

Puerto Aguirre

Mount Hudson

Penins

ula T

aitao

L. Buenos Aires

North PatagonianIce Field

L. PresidenteRios

L. Elena

L. San Rafael

Glaciar San Rafael

LagunaStibnite

44° S

45° S

46° S

80° W 70°

0 200 400

50°

40° S

60°

Km

Pac

ific

ocea

n

Chi

le

AtlanticOcean

Argentina

CHILE

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


a response to cyclical precipitation patterns. Results frombeetles from Puerto Eden (Ashworth et al., 1991) located300 km south of Taitao Peninsula also suggest thatchanges in precipitation occurred during the Holocene;however, they are almost out-of-phase with thoseinferred at Laguna Stibnite. If these interpretations areboth correct, changes in precipitation patterns may becaused by a latitudinal shift of the westerlies (Massaferroand Brooks, 2002).

Pollen records from Laguna Stibnite (Lumley andSwitsur, 1993; McCulloch et al., 2000) could find noevidence of cooling during the Late Glacial–Interglacialtransition. At other sites in Patagonia, changes in pollenassemblages at the end of the Late Glacial have beeninterpreted as a response to climatic cooling (Heusser andRabassa, 1987; Heusser, 1989, 1993; Rabassa et al.,1990; Heusser et al., 1996; Moreno, 1997). On the con-trary, palynological studies performed in seven otherlakes located in this area of Chile bear no evidence of areversal during the Late Glacial period (Bennett et al.,2000; Haberle and Bennett, 2004). In addition, Bennettet al. (2000) found no changes in lithology or magneticsusceptibility that might indicate periods of cooling insouthern Chile.

Recently, Massaferro et al. (2005) carried out a studyon pollen and fossil chironomids in Laguna Facil, locatedin the Chonos Archipelago in Chile. The results showedthat no response to a cooling event coinciding with the

YD is apparent at this lake. Instead, chironomids seem tobe responding to local rather than regional environmentalchanges, perhaps in response to the gradual migrationand colonization of trees in the lake catchment (Fig. 8).Pollen records from Laguna Facil and Laguna Oprasa(separated by 50 km) also showed no cooling during theYD (Haberle and Bennett, 2004). Despite the similaritiesof fauna and the proximity between them, the morenortherly location of Laguna Facil means that it is lesslikely than Laguna Stibnite to have been influenced byany resurgence of Andean glaciers during the YoungerDryas Chronozone (YDC). Glacial resurgence could berelated 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). Geographicvariability in glacial activity would indicate that climaticconditions were possibly insufficiently intense and/orof insufficient duration to effect uniform regionalpaleobiotic changes; therefore a response during the YDmay be recognizable at some sites but not at others.

Results from a chironomid study (Massaferro,unpublished) carried out on samples from Lago Mascardinot previously examined by Ariztegui et al. (1997) pro-vide new evidence of climatic cooling during LateGlacial times. The improved radiocarbon chronologyspans the interval between 12,000 and 9,500 14C yr BPand allows changes in chironomids in response to

300500

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17,300 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 0 50 150 –100 0 100 200300

Zone

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kief

ferie

lla

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kief

ferie

lla fe

nnic

a

Apse

ctro

tany

pus

Mac

rope

lopi

a

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noph

yes

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undi

nia

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nops

ectra

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chiro

nom

us

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rono

mus

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ladi

usLa

uter

boni

ella

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nom

ectri

onem

us

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rote

ndip

es

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ynon

eura

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psec

trocl

adiu

sPo

lype

dilu

mAb

labe

smyi

aC

lado

pelm

a

Pseu

doch

irono

min

i

Tany

tars

ini A

Tany

tars

ini C

Tany

tars

ini B

Tota

l hea

d ca

psul

es

Tany

tars

ini D

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d ca

psul

es/g

PCA

axis

1

PCA

axis

2

% Abundance

LL

L Blue gray clay grading to organic clay Dark brown gyttja Silty gyttja T = Tephra layer

YD

Age

(cal

. yr B

P)Po

dono

min

ae

–50

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).


climatic variability to be pinpointed, and also a compar-ison with the well-established Late Glacial chronologyfrom Greenland and Antarctic ice core records. Chirono-mids indicate a cooling during the YD but of a longerduration than in the Northern Hemisphere (Fig. 9). Theseresults are in agreement with Hajdas et al. (2003) andMassaferro et al. (submitted) who demonstrated theoccurrence of a cold event in the mid-latitudes of SouthAmerica known as the Huelmo Mascardi Cold Reversal(HMCR) that encompasses the North Atlantic YD andthe Gerzensee/Killarney Oscillation. Similar results havebeen found in Kaipo Bog in New Zealand from pollenrecords. These results indicate a cooling of ca. 600 14C yrBP before the YD (Newnham and Lowe, 2000).

6.2. Fossil Beetles

Fossil beetle faunas have been investigated from severallowland sites in Chile, in the Chilean Lake District (seeFig. 5) (Hoganson et al., 1989; Hoganson and Ashworth,1992; Ashworth and Hoganson, 1993) and further south,in the Chilean Channels (Fig. 10) (Ashworth andMarkgraf, 1989; Ashworth et al., 1991).

To develop reliable information about the moderndistribution and ecological requirements of the coleop-teran fauna, Ashworth and Hoganson (1987) carried outan extensive collecting programme for several years.They identified 462 species of beetles belonging to 48families 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 demon-strates significant differences between the low and highelevation fauna, especially between those of the forestedand treeless Andean tundra habitats. The study clearlydemonstrated a relationship between beetles and climatewithin the region.

Hoganson and Ashworth (1992) and Ashworth andHoganson (1993) reported on several fossil beetleassemblages from Puerto Octay, Puerto Varas and RıoCanahue in the Chilean Lake Region (40�–41� S,72�–73� W) that spans the interval from the Last Glacialmaximum to the Holocene. They showed that fullglacial assemblages were species-poor, containing onlyabout 20% of the species of the Holocene assemblage.They inferred that the full-glacial beetle assemblagesrepresented a Magellanic moorland environment whichexisted in a climate with mean January temperatures4�–5�C cooler than present (Fig. 11a, b). What wasparticularly striking was the rapidity and timing of thechange to the postglacial fauna. The change startedbefore 14,000 14C yr BP and was completed by 12,50014C yr BP. Moreno (1997), based on a high resolutionstudy of pollen, confirmed that the full glacial flora wasMagellanic moorland and that the transition to forestoccurred between 15,000 and 14,000 14C yr BP. Thesechanges are similar in timing to changes marking theend of the Pleistocene in the Pacific Northwest of NorthAmerica. These results also show that the time of thetransition from glacial to interglacial conditions in theSouthern Hemisphere occurred earlier than in the NorthAtlantic Ocean.

Brown gyttja TephraSilt/clay gyttja Olive grey clay

20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 100 2004040 40 6040 40

Fa-c4

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% Abundance

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id zo

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ieffe

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rsus

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trota

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s

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smya

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omus

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undin

ia

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omus

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phye

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ochir

onom

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omina

e

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rsus

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ernb

oniel

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rsus

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ius

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rope

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us

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rsus

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Age (c

al yr

BP)

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)

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11,30012,30013,30014,300

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0.2

2.8

7.2

11.1

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15.9

Fa-p2

10,300

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


11,0

00

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arct

ica

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ICA

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OD Bo

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enla

ndG

ISP

2

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S

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δ18

O

Cal 14C ages

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00

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Radiocarbon agesCal yr BPParakiefferiellaPhaenopsectra Parachironomus PodonominaeChironomus Parapsectrocladius Tanytarsini D Tanytarsini A PolypedilumLimnophyes DicrotendipesCricotopus Orthocladiinae JPseudochironomusTotal number

Fig.9.Chironomid

stratigraphic

diagram

from

LagoMascardishowingYounger

Dryas(YD),Huelmo-M

ascardiCold

Reversal(H

MCR)andAntarcticCold

Reversal(ACR).

Dark

profilesrepresentcold

species(P

arak

ieffer

iellaincludemixed

cold

andwarm

species).EPICA(Antarctica)andGISP2(G

reenland)icecore

recordsare

shownto

allow

comparisons(originaldata

from

NOAAweb

page)

(Massaferro,unpublished).


However, the lack of a response of the beetle fauna tocooling at the time of the YD contradicted the results ofHeusser (1974, 1997)andHeusser andStreeter (1980)whichshowed a change in the vegetation that was interpreted as aresponse to a temperate depression up to 6�C lower thanpresent. Moreno (1997) has also subsequently reported cli-matic cooling in the Lake District at the time of the YD.

Further south in the Chilean Channels, Ashworth andMarkgraf (1989) and Ashworth et al. (1991) reported onfossil beetle and pollen assemblages fromGlaciar Tempano(48� S, 72� W) and from Puerto Eden (49� S, 74� W) thatshowed an excellent correlation indicating that regional andlocal biotic changes were in phase (Fig. 12). The interpreta-tion of the fossil beetle assemblages was aided by studies of

PA

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IC O

CE

AN

ARGENTINAL. Cardiel

L. Argentino

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I. Wellington

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Punta Bandera

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Punta Arenas

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L. Yehuin

Puerto Harberton

Puerto delHambre

Canal Beagle

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South PatagonianIce Field

ATLANTICOCEAN

74° 70° 66°

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80° W 70°

0 200 400

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Km

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ific

ocea

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le

AtlanticOcean

Argentina

N

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

0.1

18,000 16,000 14,000 12,000 10,000

20

60

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Forest

Age 14C yr BP

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ber

of ta

xa

(a)

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40

80

120

16 14 12 10

Num

ber

of ta

xa

Age 14C yr BP × 103

Total taxaObligate arborealtaxa

(b)

Fig. 11. (a) Change in composition of the beetle fauna in the Chilean Lake District during the interval between 18,000 and10,000 14C yr BP. The dashed line represents the total number of taxa. The solid line represents the ratio of the threedependent 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 interglacialtransition (modified from Hoganson and Ashworth, 1992; Ashworth and Hoganson, 1993).


the modern beetle fauna reported in Ashworth et al. (1991).The results suggest that in Puerto Eden, prior to 13,000 14Cyr BP, the climate was probably windier than today;between 13,000 and 9,500 14C yr BP the Nothofagus forestexpansion and the presence of aquatic beetles were inresponse to an increase in the precipitation that lasted till5,500 14C yr BP. From 5,500 to 3,000 14C yr BP theprecipitation declined and, after 3,000 14C yr BP, precipita-tion increased again to the present-day levels. The authorsconclude that the cyclical wet/dry periods were in responseto latitudinal shifts of the westerlies. These results show noevidence of cold reversal in the area at the time of the YD.These results also demonstrate that in a heavily glaciatedenvironment 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 thediscovery, in the basal deposits of the bog at PuertoEden, of the remains of relatively large flightless beetles.If this discovery can be substantiated, it will require amajor revision of our current understanding of the extentof the Patagonian Ice Sheet. For a flightless beetle to occurin the basal deposits it would require that some parts of thearchipelago were unglaciated and the climatic conditionssufficiently moderate to support a refuge for the biota. Thestandard biogeographic interpretation is that the currentbiota of the archipelago was derived by dispersal fromboth the north and the south during postglacial times.

Fossil beetles and pollen from Glaciar Tempano comefrom an exposed section in the walls of a meltwater channellocated 2 km from the margin of the South Patagonian IceCap. Ashworth and Markgraf (1989) reported a flora andbeetle fauna for the time of the YD that was very similar tothatof present day.The implicationwas that at the timeof theYD, the margin of the South Patagonian Ice Cap was insimilar position as it is todayand that the climatewas similar.This site was revisited in April 2005 and the basal depositswill be re-dated at the Climate Change Institute of the Uni-versity of Maine. If the radiocarbon dates obtained in 1989are confirmed, then the evidence from certain areas of wes-ternmost southern South America will indicate that therewas no glacier advance at the time of the YD in this portionof the continent. These studies indicate that the transition

fromglacial to postglacial conditionswas themajor regionalclimate change in the last 15,000 yrs and that coleopteranevidence fromChileanPatagonia doesnot support the occur-rence of climate reversals during the Late Glacial period.

Although pollen and beetle records show no evidencefor temperature changes during the LateGlacial–interglacialtransition, they all indicate alternating dry and wet periodsdue to changes in the precipitation pattern during this period.They interpret these changes as being caused by latitudinalshifts in the position of storm tracks in the belt of southernwesterlies. Markgraf (1989, 1991, 1993a, b) indicated thatvegetation changes in this area were successional, edaphicor in response to disturbance by fire.

Throughout the Holocene, the beetle fauna of mid-latitude South America was not affected by any majorclimate change (Hoganson and Ashworth, 1992). For theperiod 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 and3,000 14C yr BP suggests that conditions then becamedrier than today.

6.3. Inter-Hemispheric linkages

Synchronicity of climate change and comparability ofclimate signals, both temporal and spatial, are the princi-pal parameters for evaluating inter-hemispheric linkages.Today, due to the many uncertainties in the absolutetiming and magnitude of the events recorded in the twohemispheres, the relationship between Late Glacial andInterglacial transition climate change in the Northernand Southern Hemispheres remains clouded. Differenthypotheses, relying on different lines of evidence, pointvariously to the Northern Hemisphere leading the South-ern Hemisphere and vice versa, or to synchrony betweenhemispheres (Glasser et al., 2004).

A large body of data from ice core, sedimentary,geomorphological and paleoecological investigations sup-ports the argument that during the Late Glacial climatechange was globally synchronous (Denton and Hendy,1994, 1995; Lowell et al., 1995; Denton et al., 1999;

5630

11,59012,960 X

X

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14 C age

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Depth

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)

Notho

fagu

s poll

en

Tree/

shru

b be

etles

Heath

/ope

n po

llen

types

Open

grou

nd b

eetle

s

Moo

rland

poll

en

Potam

oget

on

Aquat

ic be

etles

Assem

blage

zone

s

Inte

rpola

ted 14 C yr

BP

Percentage

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


Moreno et al., 1999; Steig et al., 1998). To investigate thecauses for the inter-hemispheric synchroneity, Whitlocket 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 South-ern Hemispheres. The paleoclimatic simulations were thencompared to pollen and beetle records from both hemi-spheres and showed that Glacial–Interglacial climaticoscillations during the Quaternary affected both regionssynchronously but the extent of ice cover was different.However, the mechanisms that link glacial cycles in thetwo hemispheres were not completely explained.

Chironomid assemblages from Lago Mascardi inArgentina (Massaferro, unpublished) show excellentagreement with both EPICA Antarctica and GISP2Greenland ice core records giving evidence of out-of-phase Late Glacial climatic events in both hemispheres(see Fig. 9). These results support the anti-phased north–south deglacial patterns and the relationship to theTHC (thermohaline circulation) changes that producesa ‘‘seesaw’’ transfer of ocean heat between the hemi-spheres (Broecker, 1998). Recent studies of Antarcticice cores added to the discussion but did not resolve thecontroversy (Lamy et al., 2004). The discrepancies in thedifferent chronologies in the various Antarctic ice corerecords make it difficult to arrive at any conclusion.

Summarizing, the existence of the cold reversals dur-ing the Late Glacial–Interglacial transition in the south-ern Hemisphere is still controversial (Ashworth et al.,1991; Markgraf, 1993a, b; Heusser et al., 1996; Arizteguiet al., 1997; Bennett et al., 2000; McCulloch et al., 2000;Massaferro and Brooks, 2002). Some studies indicate acooling in South America that is more coincident with theAntarctic Cold Reversal (ACR) than the YD (Newnhamand Lowe, 2000; Turney et al., 2003) whereas Bennettet al. (2000) looking at pollen studies suggest gradualwarming with no reversals in the Southern Hemisphere.

In New Zealand, the evidence of climate reversalduring the YD is also problematic. Many pollen studiesindicate progressive forest development implyingthat deglacial temperatures and precipitation increasedgradually without significant reversal (McGlone, 1995;Vandergoes and Fitzsimons, 2003). In the South Island ofNew Zealand, Shakau (1986, 1990) developed a moderntraining set using chironomids; nevertheless, these resultsdid not focus on climatic reconstructions. New attemptsto infer temperature using chironomid-temperature mod-els have been recently carried out at the University ofMaine (USA) with the aim to produce a reliable datasetfor quantitative reconstruction of past temperatures.

7. Future Investigations in Patagonia

This chapter has provided evidence that the location ofPatagonia in combination with the study of insects is idealfor testing hypotheses related to climate change during theQuaternary. It highlights the importance of southern SouthAmerica as one of the most important regions in the worldfor testing whether climate changes are global or not.

The studies presented in this chapter clearly show thepotential of chironomids and beetles as proxy indicators of

climate change. However, there is still a lack of informa-tion about insect taxonomy, ecology and modern distribu-tion in the Southern Hemisphere that is indispensable foraccurate inferences. In addition, a better knowledge ofinsect taxonomy would allow development of transferfunctions and quantitative reconstructions of past tempera-ture which, in turn, would provide new approaches forunderstanding the synchronicity of climatic events inboth hemispheres. Summarizing, the use of fossil insectsas independent quantitative indicators could be key to anew approach for future paleoclimatic work.

Although there have been an increasing number ofpaleoecological studies in Patagonia there is also muchwork to be done to fully understand and interpret the regio-nal Quaternary scenarios, involving changes in biodiversity,tree refugia, species dispersion, successional changes andmigration patterns since the last ice age.

Acknowledgments

The authors want to thank Andrea Rizzo for her assistanceduring the fieldtrips in Patagonia and Sarah Gilchrist forproviding them access to her unpublished PhD Thesis.Thanks also to Pat Haynes for helping in the preparationof samples.

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