The Holocene 134 (2003) pp 581ndash591

Holocene palaeoclimates of southernPatagonia limnological andenvironmental history of Lago CardielArgentinaVera Markgraf1 J Platt Bradbury2 Antje Schwalb3

Stephen J Burns4 Charles Stern5 Daniel Ariztegui6 AdrianGilli6 Flavio S Anselmetti6 Scott Stine7 and Nora Maidana8

(1Institute of Arctic and Alpine Research University of Colorado BoulderColorado 80309ndash0450 USA 25784 Horseradish Gulch Golden Colorado80403 USA 3Institut fur Umwelt-Geochemie Universitat Heidelberg ImNeuenheimer Feld 236 D-69120 Heidelberg Germany 4Department ofGeosciences University of Massachusetts Amherst Massachusetts 01003ndash5820USA 5Department of Geological Sciences University of Colorado BoulderColorado 80309ndash0399 USA 6Geological Institute Swiss Federal Institute ofTechnology ETHZ Sonneggstrasse 5 CH-8092 Zurich Switzerland7Department of Geography and Environmental Studies California StateUniversity Hayward California 94542 USA 8Departamento de CienciasBiologicas Laboratorio de Morfologia Vegetal Universidad de Buenos AiresFacultad de Ciencias Exactas y Naturales 1428 Buenos Aires Argentina)

Received 25 February 2002 revised manuscript accepted 5 August 2002

Abstract Multiproxy palaeoenvironmental and palaeolimnological analyses of two Holocene-age sedimentcores from the margin of Lago Cardiel a 76 m deep closed-basin lake in southern Patagonia (latitude 49degS)provide information on lake-level changes that can be related to regional palaeoclimate scenarios Sedimentol-ogic (magnetic susceptibility organic and inorganic carbon content) and environmental indicators (pollen dia-toms ostracodes and stable isotopes on ostracodes) show lake levels markedly higher than today during theearly Holocene following a rapid lake-level rise after a desiccation phase prior to 11000 BP After about 6000BP lake levels were generally lower but underwent repeated uctuations These inferred changes support thepreviously proposed view that the southern westerly stormtracks were focused (zonal) north of latitude 50degSduring the early Holocene allowing for Antarctic cold fronts to bring easterly moisture to southern Patagoniawhereas during the late Holocene the stormtracks shifted seasonally with an overall more meridional behaviourresulting in less and more variable moisture at these latitudes

Key words Environmental history multiproxy approach palaeolimnology palaeoclimates lake levels storm-tracks Patagonia Lago Cardiel Argentina South America Holocene

IntroductionLago Cardiel located in the Patagonian region of Santa Cruzprovince in Argentina (Figure 1) lies at an elevation of 276 m

Author for correspondence (e-mail markgrafspotcoloradoedu)Present address Institut Forel and Department of Geology and PaleontologyUniversity of Geneva Rue des Maraichers 13 CH-1211 Geneva 4 Switzerland

Oacute Arnold 2003 1011910959683603hl648rp

asl beyond the reach of past and present Andean glaciers andtheir meltwaters The heart-shaped lake of about 370 km2 and alake drainage area of about 4500 km2 has a present maximumwater depth of 76 m Cretaceous sediments and Tertiary basaltsoutcrop in the watershed (Feruglio 1950 Hensheimer 1959) RioCardiel is the principal perennial in owing river Several smallerpermanent and ephemeral streams originate within the perimeter

582 The Holocene 13 (2003)

of the basin Present-day mean annual precipitation falling prim-arily during the winter months (May to August) ranges fromabout 160 mm near the lake to a maximum of 500 mm in thewestern and northwestern mountainous area (1300 to 1700 melevation) where the Rio Cardiel originates (Heinsheimer 1959)Mean annual air temperature is about 8degC and prevailing windsespecially strong and persistent during summer are from the westLike many closed lakes in Patagonia Lago Cardiel has beenreceding since 1940 (Stine and Stine 1990) Present-day veg-etation is Patagonian steppe-scrub with patches of tall shrubs inthe valley bottoms (Schinus patagonicus Berberis empetrifoliaLycium chilense and Verbena tridens) Exposed mud ats aroundthe lake margin are covered by dense growth of Chenopodiaceaeand other weedy taxa some of European origin SubantarcticNothofagus antarctica woodland and Nothofagus pumilio forestgrow on the higher-elevation mountains about 50 km to thenorthwest beyond the lake catchment

In studying fossil shoreline tufas and sediments dissected byRio Cardiel and other streams Galloway et al (1988) and sub-sequently in far greater detail Stine and Stine (1990) identi edand radiocarbon dated former Lago Cardiel highstands Stine andStine (1990) measured and dated lake-transgressive and lake-regressive deposits exposed in the walls of stream cuts as wellas numerous strandlines that encircle the lake The highest strand-line at +75 m above the 1990 lake surface (273 m) is deeplydissected by numerous arroyos and is characterized by a subduedmorphology and by wind-polished stone pavements Its age isbeyond radiocarbon dating At +55 m is a littoral embankment(beachridge) that has been dissected by only the largest of thelakersquos in owing streams and whose surface clasts lack notablepolish In cross-sections exposed in stream cuts this embankmentcan be seen to conformably overlie a lake-transgressive sequenceof upwardly ning littoral gravels and sands intercalated with thinplates of cemented tufa near the base Fossil oogonia and stemsof Chara near the top of the deposits represent a lagoon that sub-sequently developed behind the embankmant Radiocarbon dateson calcareous plates of tufa and Chara yield ages of 9780 and9480 BP respectively demonstrating an early-Holocene age forthis high stand (Stine and Stine 1990) Thoroughly tufa-cementedlittoral gravel at the +43 m level forms a beachrock that dates at8620 BP indicating that the lake had fallen at least 12 m fromits early-Holocene highstand by that time A sequence of veradiocarbon dates on thin plates of tufa that lie within a strati-graphic section of deltaic bottomset beds at the +28 m level indi-cate that the lake remained above that elevation until 7690 BPafter which it declined to an unde ned lowstand Since then thelake has undergone at least ve transgressionsand regressions allof which have been dated by radiocarbon analyses of buried soilsand peats and rooted stumps Only the rst of these ve trangres-sions which peaked at 5130 BP exceeded a level of +20 m Thefour other late-Holocene lake-level highstands of +3 to +10 mwere dated between 4540 and 3070 BP around 2000 1450 and800 BP At least two of the late-Holocene regressions took thelake to levels below that of 1990 though the precise elevationsof these lowstands could not be determined In 1990 the lakestood by Holocene standards at a very low level

In 1998 a renewed interdisciplinaryeffort was undertaken withfunding from the US and Swiss National Science foundationsto provide a more complete history of palaeoenvironmental andpalaeolimnologicalchanges for this basin The co-operative inter-national project included present-day limnological data collection(Schwalb et al 2002) analysis of data based on seismic mappingof the basin sediment ll (Gilli et al 2001) collection of sedi-ment cores analysis of sediment stratigraphy and palaeoenviron-mental indicators in sediment cores Here we report on the multi-proxy study of two Holocene-age cores taken at the present-dayshoreline in the Bahacutea Pescaderia on the north coast of Lago

Cardiel The analyses included radiocarbon dating of the sedi-ments chemical ngerprinting of distinct tephra layers usingtrace element analysis diatom pollen and stable isotope analyseson ostracodes and total organic (TOC) and inorganic (TIC) car-bon

Methods

Two sediment sections were cored with a square-rod Livingstonepiston corer in 1998 and 1999 Magnetic susceptibility (102 5 SI)was measured prior to opening the cores using a multisensor corelogger at the Paleolimnology Laboratory ETH Zurich Switzer-land Subsequently the cores were photographed and subsampledfor different analyses Total inorganic carbon (TIC) and total car-bon (TC) were measured on the 2 mm sediment fraction groundto 500 mm using a coulometer in the Sedimentologic Labora-tory of INSTAAR Ostracodes were separated according to amodi ed version of Forester (1988) One to 12 g of wet sedimentwere placed in wide-mouth plastic bottles and shaken with 250mL of 90degC deionized water and one teaspoon of baking sodaTo promote full dispersal the sample sat for several more hoursThe sample was then frozen allowed to thaw and sit for severalhours The disaggregated sediment was slowly sieved by handthrough a 63 mm sieve rinsed with deionized water and air-driedWell-preserved valves of Eucypris sp aff E fontana the mostabundant ostracode species in the lake were selected for stableisotopic analyses (d18O and d13C) Two samples from the lower-most levels were analysed on valves from Ilyocypris ramireziOne to four valves per sample were analysed for oxygen and car-bon isotopes on a VG Prism ratio mass spectrometer (UniversitatBern) using an online automated carbonate preparation Analyti-cal reproducibility for standards is 008permil for d18O and 004permilfor d13C All analyses are reported relative to the VPDB standardand were corrected using the phosphoric acid fractionation factorfor calcite at the appropriate temperature Pretreatment for pollenanalysis consisted of hydro uoric acid to eliminate inorganicmatter followed by acetolysis to reduce dispersed organic matterPollen was counted on a Leitz Ortholux microscope with 3400to 31000 magni cation Pretreatment for diatom analysis con-sisted of digesting the sample in concentrated HNO3 at 100degC for30 minutes in a hot water bath to eliminate carbonates and labileorganic compounds Diatom concentration was determined bymounting similar volumes of diatom residue and determining thenumber of frustules per mm2 on the microscopic coverslip Tephrasamples were washed with distilled water and dilute HCl groundto a powder and analysed for trace elements (Rb Sr Zr Y andNb) concentrations by energy-dispersive X-ray uorescence

Results

Core lithology and chronologyThe 1062 cm long sediment core CAR-98ndash2L was retrieved inJanuary 1998 on the north side of Lago Cardiel (48deg4859S71deg139W) at the present-day shoreline in Bahacutea Pescaderia at 276m elevation (Figure 1) The core site lies at the mouth of anincised drainage channel which carries water and sediment attimes of heavy rainfall In the upper 520 cm the sediment is com-posed of ne grey light and dark banded clay interbedded with ne black sand bands especially between 100 and 300 cm Plantdetritus (probably Ruppia) is abundant at 175ndash190 cm 257ndash300cm 380ndash400 cm and 500ndash520 cm Below 520 cm the sedimentis more uniform compact clay with increasing amounts of sandbelow 950 cm One major black sandy layer at 838ndash839 cm wasidenti ed by petrochemical analysis as volcanic tephra derivedfrom a mid-Holocene (|6700 BP) eruption of the Hudson

582 The Holocene 13 (2003)

of the basin Present-day mean annual precipitation falling prim-arily during the winter months (May to August) ranges fromabout 160 mm near the lake to a maximum of 500 mm in thewestern and northwestern mountainous area (1300 to 1700 melevation) where the Rio Cardiel originates (Heinsheimer 1959)Mean annual air temperature is about 8degC and prevailing windsespecially strong and persistent during summer are from the westLike many closed lakes in Patagonia Lago Cardiel has beenreceding since 1940 (Stine and Stine 1990) Present-day veg-etation is Patagonian steppe-scrub with patches of tall shrubs inthe valley bottoms (Schinus patagonicus Berberis empetrifoliaLycium chilense and Verbena tridens) Exposed mud ats aroundthe lake margin are covered by dense growth of Chenopodiaceaeand other weedy taxa some of European origin SubantarcticNothofagus antarctica woodland and Nothofagus pumilio forestgrow on the higher-elevation mountains about 50 km to thenorthwest beyond the lake catchment

In studying fossil shoreline tufas and sediments dissected byRio Cardiel and other streams Galloway et al (1988) and sub-sequently in far greater detail Stine and Stine (1990) identi edand radiocarbon dated former Lago Cardiel highstands Stine andStine (1990) measured and dated lake-transgressive and lake-regressive deposits exposed in the walls of stream cuts as wellas numerous strandlines that encircle the lake The highest strand-line at +75 m above the 1990 lake surface (273 m) is deeplydissected by numerous arroyos and is characterized by a subduedmorphology and by wind-polished stone pavements Its age isbeyond radiocarbon dating At +55 m is a littoral embankment(beachridge) that has been dissected by only the largest of thelakersquos in owing streams and whose surface clasts lack notablepolish In cross-sections exposed in stream cuts this embankmentcan be seen to conformably overlie a lake-transgressive sequenceof upwardly ning littoral gravels and sands intercalated with thinplates of cemented tufa near the base Fossil oogonia and stemsof Chara near the top of the deposits represent a lagoon that sub-sequently developed behind the embankmant Radiocarbon dateson calcareous plates of tufa and Chara yield ages of 9780 and9480 BP respectively demonstrating an early-Holocene age forthis high stand (Stine and Stine 1990) Thoroughly tufa-cementedlittoral gravel at the +43 m level forms a beachrock that dates at8620 BP indicating that the lake had fallen at least 12 m fromits early-Holocene highstand by that time A sequence of veradiocarbon dates on thin plates of tufa that lie within a strati-graphic section of deltaic bottomset beds at the +28 m level indi-cate that the lake remained above that elevation until 7690 BPafter which it declined to an unde ned lowstand Since then thelake has undergone at least ve transgressionsand regressions allof which have been dated by radiocarbon analyses of buried soilsand peats and rooted stumps Only the rst of these ve trangres-sions which peaked at 5130 BP exceeded a level of +20 m Thefour other late-Holocene lake-level highstands of +3 to +10 mwere dated between 4540 and 3070 BP around 2000 1450 and800 BP At least two of the late-Holocene regressions took thelake to levels below that of 1990 though the precise elevationsof these lowstands could not be determined In 1990 the lakestood by Holocene standards at a very low level

In 1998 a renewed interdisciplinaryeffort was undertaken withfunding from the US and Swiss National Science foundationsto provide a more complete history of palaeoenvironmental andpalaeolimnologicalchanges for this basin The co-operative inter-national project included present-day limnological data collection(Schwalb et al 2002) analysis of data based on seismic mappingof the basin sediment ll (Gilli et al 2001) collection of sedi-ment cores analysis of sediment stratigraphy and palaeoenviron-mental indicators in sediment cores Here we report on the multi-proxy study of two Holocene-age cores taken at the present-dayshoreline in the Bahacutea Pescaderia on the north coast of Lago

Cardiel The analyses included radiocarbon dating of the sedi-ments chemical ngerprinting of distinct tephra layers usingtrace element analysis diatom pollen and stable isotope analyseson ostracodes and total organic (TOC) and inorganic (TIC) car-bon

Methods

Two sediment sections were cored with a square-rod Livingstonepiston corer in 1998 and 1999 Magnetic susceptibility (102 5 SI)was measured prior to opening the cores using a multisensor corelogger at the Paleolimnology Laboratory ETH Zurich Switzer-land Subsequently the cores were photographed and subsampledfor different analyses Total inorganic carbon (TIC) and total car-bon (TC) were measured on the 2 mm sediment fraction groundto 500 mm using a coulometer in the Sedimentologic Labora-tory of INSTAAR Ostracodes were separated according to amodi ed version of Forester (1988) One to 12 g of wet sedimentwere placed in wide-mouth plastic bottles and shaken with 250mL of 90degC deionized water and one teaspoon of baking sodaTo promote full dispersal the sample sat for several more hoursThe sample was then frozen allowed to thaw and sit for severalhours The disaggregated sediment was slowly sieved by handthrough a 63 mm sieve rinsed with deionized water and air-driedWell-preserved valves of Eucypris sp aff E fontana the mostabundant ostracode species in the lake were selected for stableisotopic analyses (d18O and d13C) Two samples from the lower-most levels were analysed on valves from Ilyocypris ramireziOne to four valves per sample were analysed for oxygen and car-bon isotopes on a VG Prism ratio mass spectrometer (UniversitatBern) using an online automated carbonate preparation Analyti-cal reproducibility for standards is 008permil for d18O and 004permilfor d13C All analyses are reported relative to the VPDB standardand were corrected using the phosphoric acid fractionation factorfor calcite at the appropriate temperature Pretreatment for pollenanalysis consisted of hydro uoric acid to eliminate inorganicmatter followed by acetolysis to reduce dispersed organic matterPollen was counted on a Leitz Ortholux microscope with 3400to 31000 magni cation Pretreatment for diatom analysis con-sisted of digesting the sample in concentrated HNO3 at 100degC for30 minutes in a hot water bath to eliminate carbonates and labileorganic compounds Diatom concentration was determined bymounting similar volumes of diatom residue and determining thenumber of frustules per mm2 on the microscopic coverslip Tephrasamples were washed with distilled water and dilute HCl groundto a powder and analysed for trace elements (Rb Sr Zr Y andNb) concentrations by energy-dispersive X-ray uorescence

Results

Core lithology and chronologyThe 1062 cm long sediment core CAR-98ndash2L was retrieved inJanuary 1998 on the north side of Lago Cardiel (48deg4859S71deg139W) at the present-day shoreline in Bahacutea Pescaderia at 276m elevation (Figure 1) The core site lies at the mouth of anincised drainage channel which carries water and sediment attimes of heavy rainfall In the upper 520 cm the sediment is com-posed of ne grey light and dark banded clay interbedded with ne black sand bands especially between 100 and 300 cm Plantdetritus (probably Ruppia) is abundant at 175ndash190 cm 257ndash300cm 380ndash400 cm and 500ndash520 cm Below 520 cm the sedimentis more uniform compact clay with increasing amounts of sandbelow 950 cm One major black sandy layer at 838ndash839 cm wasidenti ed by petrochemical analysis as volcanic tephra derivedfrom a mid-Holocene (|6700 BP) eruption of the Hudson

Vera Markgraf et al Holocene palaeoclimates of southern Patagonia a multiproxy study from Lago Cardiel 583

volcano The base at 1062 cm is composed of bluish dry claywith reworked clay granules

A second 704 cm long sediment core (CAR-99ndash2L) wasretrieved in March 1999 c 1 km west of core CAR-98ndash2L (Figure1) also at the present-day shoreline but distant from anyin owing stream channel The stratigraphy resembles core CAR-98ndash2L showing a higher frequency of sandy layers in the upper260 cm more compact clays between 260 and 480 cm sandyclays between 480 and 620 cm and compact clays below 620 cmPlant remains (probably Ruppia) are abundant at 210ndash216 cm and620ndash645 cm At 100 cm 550 cm and between 620 and 638 cmthe sediment contains snails Wood pieces are found at 626 cmand Chara detritus at 627ndash632 cm At 683 cm there is a sharptransition to mottled red and green dry reworked clay granules

AMS radiocarbon dates were obtained for both cores on woodsnails Ruppia plant remains and Chara detritus (Table 1) Totest for potential dating problems caused by hard-water effectsoriginating from occasional Cretaceous-age oyster shells indeposits surrounding the lake three samples of living green algaeand Ruppia were also dated All three samples were reported aspostmodern (108 to 117 of modern) suggesting that the fossilaquatic organic materials should yield reasonable ages

Both cores CAR-98ndash2L and CAR-99ndash2L represent a fairlycomplete record of near-shore Holocene sedimentation Althoughthe base of core CAR-98ndash2L could not be dated it was correlatedwith core CAR-99ndash2L based on the characteristic stratigraphy ofthe diatom Epithemia argus and the calcareous green alga Phac-otus Presence of Phacotus at 1050 cm in CAR-98ndash2L can berelated to the level of 645 cm in CAR-99ndash2L The initial increaseof Epithemia argus occurring at 645 cm depth in core CAR-99ndash2L and dated to 9880 6 85 BP correlates to the depth of 1020cm in CAR-98ndash2L The end of the Epithemia argus interval at627 to 632 cm depth in CAR-99ndash2L dating 9590 6 65 correlatesto the depth of 1000 cm in core CAR-98ndash2L

Chronologic evaluation of the cores was aided by identi cationof distinct volcanic ashes Geochemical ngerprinting of ashdeposits from cores and outcrops in southern Patagonia and Tierradel Fuego indicate that just ve eruptions of four different vol-

Table 1 Radiocarbon and tephra dates from Lago Cardiel coresCAR-98ndash2L and CAR-98ndash2L

Sample Depth (cm) Age (BP) Laboratory Datedno material

Ruppia 117 modern NSRL-10767 Living Ruppialeaves

Green algae in 108 modern LDGO-1714Y Living greenRio Cardiel algaeGreen algae in 108 modern LDGO-1714Z Living greenLago Cardiel algaeCAR-98ndash2L 257ndash258 1630 6 40 CAMS-59501 Ruppia

stemsleavesCAR-98ndash2L 383ndash384 3100 6 40 CAMS-59592 Ruppia

stemsleavesCAR-98ndash2L 5185ndash5195 4460 6 30 CAMS-59593 Ruppia

stemsleavesCAR-98ndash2L 837ndash838 6700 Hudson H1

tephraCAR-99ndash2L 460ndash615 6700 Hudson H1

tephraCAR-99ndash2L 550ndash551 8610 6 75 NSRL-11432 snailCAR-99ndash2L 626 10230 6 65 NSRL-11433 woodCAR-99ndash2L 627ndash632 9590 6 65 NSRL-12507 Chara hash

carbonateCAR-99ndash2L 645 9880 6 85 NSRL-12508 Ruppia ()

rootlets ()

canos are responsible for the most important and regionally wide-spread volcanic tephra deposits in this region (Stern 1991 19922000) Only two of these eruptions are known to have depositedash in the area of Lago Cardiel one produced by the Hudsonvolcano (46degS latitude) and another from one of three volcanos(Aguilera Viedma or Lautaro located between 49 and 50degSlatitude) in the Northern Austral Volcanic Zone (NAVZ) For theHudson H1 tephra found both north and south of Lago Cardiel(Stern 1991 Naranjo and Stern 1998) an age of |6700 BP wasdetermined and for the ash derived from one of the NAVZvolcanos the age is |3345 BP (Tables 2 and 3) A tephra layerwith the same petrochemical characteristics as the NAVZ stan-dards found in a peat outcrop within the Lago Cardiel drainagehas been dated to 3010 6 45 BP We use this latter age ratherthan the |3345 BP age proposed by Stern (1991 1992 2000)Other widespread tephra in southernmost Patagonia produced byexplosive eruptions of Reclus (51degS) and Mt Burney (52degS)volcanos are found only south of Lago Cardiel

All Hudson tephra samples are characterized by olive-greenglass with relatively high amounts of zirconium (Zr 200 ppm)(Figure 2) and other high- eld-strength elements such as titaniumhafnium yttrium and niobium Green Hudson-derived tephrafound at Lago Cardiel both in cores and in one outcrop are com-positionally similar to tephra formed by explosive eruption H1 ofthe Hudson volcano at 6700 BP In contrast all tephra from thethree NAVZ volcanos are characterised by clear glass the pres-ence of biotite and relatively low zirconium (Zr 150 ppm) andother high- eld-strength elements Mt Burney and Reclus tephraare also characterized by clear glass but lack biotite and haverelatively low rubidium (Rb 5ndash15 ppm for Mt Burney and 25ndash40 ppm for Reclus) compared to tephra derived from the NAVZvolcanos (Rb 55ndash90 ppm) (Figure 2) White biotite-bearingtephra found at Lago Cardiel both in cores and outcrops are com-positionally similar to the tephra formed by the |3345 BP erup-tion from one of the three NAVZ volcanos

Whereas both volcanic ashes are well distinguished in the open-water cores (Gilli et al 2001) the correlation of the volcanicashes in the shore cores is problematic The 6700 BP Hudson H1ash is found as a distinct tephra layer at 838 cm depth in coreCAR-98ndash2L but in core CAR-99ndash2L volcanic glass shardscharacteristic of Hudson H1 ash are found in variable concen-trations between 615 and 460 cm depth Extrapolating from thedates of 9590 BP at 627ndash632 cm depth directly underlying the rst occurrence of Hudson H1 volcanic shards and 8610 BP at550 cm depth suggests the 6700 BP Hudson H1 ash should occur

Table 2 Petrographic data from regionally widespread tephra in southernPatagonia (Stern 1990 1991 1992 2000 Stern and Kilian 1996 Naranjoand Stern 1998)

Standards Number of Rb Sr Zr Y Identitysamples

Hudson 6720 6625 green tephraAverage 10 50 374 360 40 H1Range 10 44ndash54 351ndash412 324ndash393 36ndash43 H1

Hudson 3670 3495 green tephraAverage 10 75 243 424 49 H2Range 10 68ndash80 218ndash328 396ndash466 46ndash51 H2

AguileraLautaro volcanos 3345 white tephra with biotiteAverage 6 60 390 137 12 NAVZRange 6 52ndash67 301ndash450 121ndash150 9ndash15

Reclus volcano 12060 12010 white tephra no biotiteAverage 9 28 400 123 9Range 9 22ndash35 303ndash544 84ndash158 7ndash11

584 The Holocene 13 (2003)

Table 3 Petrographic data from Lago Cardiel samples cores and outcrops

Samplecoreoutcrop Rb Sr Zr Y Identity

CAR-98ndash2L core 838 cm 51 360 320 42 H1green tephraDuplicate 48 357 342 41 H1

CAR-98ndash11 core 124 cm 56 368 328 40 H1green tephraDuplicate 59 382 319 37 H1Duplicate 64 346 341 41 H1

CAR-99ndash2L core 463ndash464 55 399 363 38 H1cm green tephraDuplicate 62 409 330 43 H1

PCAR-99ndash7ndash4 core 59ndash605 46 391 330 45 H1cm green tephraDuplicate 48 378 350 41 H1

PCAR-99ndash9ndash11 core 3655ndash 60 410 349 45 H13755 cm green tephra

Arroyo Cerro Bajo outcrop 48 377 344 40 H1green tephraDuplicate 53 358 359 43 H1

CAR-98ndash8 core 121 cm 101 280 111 16 NAVZwhite tephra w biotiteDuplicate 98 282 121 14 NAVZDuplicate 99 279 105 15 NAVZ

CAR-98ndash12 core 23 cm 120 297 110 13 NAVZwhite tephra w biotiteDuplicate 95 318 120 15 NAVZDuplicate 110 309 111 12 NAVZ

PCAR-99ndash7ndash0B core 16ndash17 79 373 135 13 NAVZcm white tephra with biotite

PCAR-99ndash9ndash6 core 32ndash33 88 304 127 15 NAVZcm white tephra with biotite

Bahacutea Puntudo outcrop white 80 295 128 13 NAVZtephra with biotite

Ea La Colorada Meseta 68 307 147 12 NAVZStrobel white tephra withbiotite dated 3010 6 45(Table 1)

Ruta 40 excavation LC40 70 364 117 10 NAVZwhite tephra with biotite

in core CAR-99ndash2L around 460 cm depth The presence of Hud-son H1 ash over 155 cm depth in core CAR-99ndash2L might beexplained by reworking of ash into desiccation cracks or by post-depositional intrusion of the ash into the deeper soft clay levels(eg Anderson et al 1984 Beierle and Bond 2002) In eithercase the well-de ned diatom stratigraphy suggests that there wasno sediment mixing

Volcanic glass shards of the younger light-coloured ashascribed petrochemically to a volcanic eruption in the NorthernAustral Volcanic Zone (NAVZ) are found in very small amountsin core CAR-99ndash2L at 370 cm depth Absence of this tephra layerat the levels in core CAR-98ndash2L dated 3100 BP (383 cm) is dueeither to the dilution of the sediments by sand or to erosion duringa lacustrine lowstand although discrete layers of this ash arefound in outcrops of littoral bedded sand at several locationsaround Lago Cardiel at about 1 m above the 19981999 shorelinelevel (276 m)

49 00rsquoS

48 50rsquoS

71 05rsquoW71 20rsquoW

Rio Cardiel

Rio Bayo

0 5km

N98-2L

99-2L

0

0

00

50m

Lago Cardiel

Hudson

Lautaro

AguileraReclus

M Burney

75 W 65 W 60 W

Cari Laufquen Grande

Figure 1 Map of southern South America with location of Lago Cardieland volcanos mentioned in text (upper panel) Map of Lago Cardiel withlocation of shore cores CAR-98ndash2L and CAR-99ndash2L (lower panel) Waterdepth in area within dotted line is between 50 m and 76 m

Zr p

pm

450

400

350

300

250

200

150

100

50

0

0 20 40 60 80 100 120

Rb ppm

H1 (6700 BP)

Mt Burney

A ustra l V olcanic Zone (A V Z)

Reclus (clear glass w ithout biotite)

Northern A V Z (clear glass w ith biotite)

Hudson (green glass)

H2 (3600BP)

Figure 2 Rubidium (Rb) versus zirconium (Zr) concentrations in partsper million (ppm) for samples of tephra from Lago Cardiel cores (soliddiamonds) compared to elds for the compositions of Patagonian tephraderived from the Hudson (Stern 1991 Naranjo and Stern 1998) andAustral Volcanic Zone (AVZ) volcanos (Stern 1990 1992 2000 Sternand Kilian 1996) in the southern Andes

Vera Markgraf et al Holocene palaeoclimates of southern Patagonia a multiproxy study from Lago Cardiel 585

SedimentologySedimentologic changes are based on macroscopic sedimentcharacteristics trends and shifts in magnetic susceptibility andtotal inorganic carbon (TIC) and total organic carbon (TOCcalculated as the difference between TIC and TC) Palaeo-environmental changes are interpreted from changes in ostracodeassemblages stable carbon and oxygen isotope ratios on ostra-codes diatoms green algae and pollen

Magnetic susceptibility and TICTOC (Figure 3) show morestable conditions below 520 cm (c 4500 BP) and 560 cm (c 4700BP) respectively and more variable changes above those depthsThe peak in magnetic susceptibility at 832 cm represents the Hud-son H1 ash Throughout core CAR-98ndash2L TIC and TOC uctuateinversely TIC shows relatively higher levels between 1040 and1000 cm (9500ndash9000 BP) followed by a decreasing trend to 620cm depth At the same time TOC shows an increasing trendAbove 620 cm primarily TIC but also TOC to a minor degreeshow ve uctuations of relatively higher and lower values Thehigh TIC values often correspond to high values in magnetic sus-ceptibility represented by sandy layers in the sediment includingostracode and mollusc remains The high TOC values correspondto levels with high amounts of macroscopic plant detritus prim-arily Ruppia

Ostracodes and stable isotopesThe ostracode species assemblages of core CAR-98ndash2L consistof only four species Eucypris sp aff E fontana Limnocytherepatagonica L rionegroensis and Ilyocypris ramirezi Changes inthe assemblage composition divide the core into ve ostracodezones (Figure 3) The lowermost zone 1 (below 1055 cm c 9500 BP) is characterized by Ilyocypris ramirezi a speciescharacteristic of seeps spring pools and small streams It suggeststhat there was signi cant input of stream water at the core locationandor that the core site was close to the site where the streamentered Between 1055 and 1005 cm (zone 2) Eucypris sp affE fontana and Limnocythere rionegroensis are dominant and Lpatagonica is present at most levels This suggests moderate sal-inity and shallow lake conditions Zone 3 (1005 to 765 cmc 9000 to 6000 BP) is characterized by Eucypris sp aff E fon-tana and Limnocythere patagonica This is the only zone in thecore where L rionegroensis is absent attesting to fresher water

0 1 0 1 0 3 -3 0 20 1 0500 50100 200

1000

900

800

700

600

500

400

300

200

100

4460

6700

~10000

3100

1630

Pediastrum

Botryoco

ccus

sandy clay Ruppia Hudson H1 tephra desiccated clay

0

0

Radiocarb

on yr B

P

0 0

mm2mm 2SI x 10 -5wt wt

Depth (cm)

Inorganic ca

rbon

Organic

carbon

Magnetic

su

sceptib

ility

d13 C (o

straco

des)

d18 O (o

straco

des)

Diatoms

Phytolith

s

5

4

3

21

Ostraco

de zones

clay

Figure 3 Selected sedimentologic and palaeoenvironmental records from core CAR-98ndash2L See text for discussion of ostracode zones

and high lake levels Between 765 and 485 cm (c 6000 to 4000BP zone 4) Eucypris sp aff E fontana is again the dominantspecies accompanied by variable occurrences of Limnocytherepatagonica Limnocythere rionegroensis is present in mostsamples This suggests a return to more concentrated lake chemi-cal conditions and lower lake levels The uppermost 485 cm ofsediment (zone 5) contain uctuating abundances of Eucypris spaff E fontana and variable numbers of Limnocythere patagonicaLimnocythere rionegroensis is present in 50 of the samplehorizons indicating repeated changes between more saline andfresher phases

A present-day ostracode calibration set helps interpret palaeo-limnological conditions for data derived from core studies(Schwalb et al 2002) Modern ostracode species assemblagesand ostracode and water isotope compositions from sites in theLago Cardiel area at 48deg to 49degS and 70deg to 71degW as well as inthe Laguna Cari Laufquen area at 41degS and 68deg to 69degW can beassigned to three groups (I) springs spring-fed pools and streams(II) permanent ponds and lakes fed by a combination of surfacewater and runoff and (III) ephemeral ponds and lakes Group Iis characterized by Ilyocypris ramirezi Amphycypris nobilisHeterocypris incongruens and Eucypris sp aff E fontana withoxygen isotope (d18O) values between ndash11 and ndash5permil and carbonisotope (d13C) values between ndash13 and ndash7permil Ostracodes frompermanent ponds and lakes (group II) are characterized by Limno-cythere patagonica Eucypris labyrinthica Limnocythere sp andEucypris sp aff E fontana with d18O values between ndash8 and+2permil and d13C values between ndash6 and +4permil Ostracodes ofephemeral ponds (group III) are dominated by Limnocythererionegroensis with values between ndash1 and +3permil for d18O and ndash5and +2permil for d13C

The d18O values of Lago Cardiel waters show small seasonalvariation of about 03permil between ndash38permil (January) and ndash41permil(October) (VSMOW) These values are approximately 8 to 9permilenriched compared to the primary source waters of the lake RioCardiel (ndash123permil January ndash119permil March ndash141permil October)and Rio Bayo (ndash134permil January ndash124permil March ndash132permilOctober) Both input rivers are fed by snowmelt with a similarisotopic composition of ndash126permil

Modern ostracode d18O values from surface sediments in LagoCardiel show no clear trend with water depth varying by

586 The Holocene 13 (2003)

09permil (of the mean values between 7 m and 35 m water depth)and show a positive offset from equilibrium (at measuredtemperatures) of up to 2permil This difference is consistent with theobservations by Xia et al (1997) von Grafenstein et al (1999)and Keatings (2000) The d18O values from Eucypris sp aff Efontana do not show any marked differences between dead andliving animals consistent with the small seasonal difference inlake-water d 18O Thus the isotopic signatures from Eucypris spaff E fontana specimens record annual averages of lake waterd18O composition

In contrast to the d18O values the d13C values for Eucypris spaff E fontana show a clear trend in the transect samples fromLago Cardiel ranging from +18permil (7 m) to +2permil (145 m)+29permil (18 m) +30permil (19 m) and +17permil (35 m) This increasingand subsequently decreasing trend appears to relate to productivitywhich for diatoms and green algae increases from near-shore sedi-ments to a maximum between 10 and 20 m water depth Theisotopic values are comparable to the range documented in thecore

Overall neither carbon nor oxygen isotope ratios vary greatlyover the length of the core d13C values range from +1 to + 3permiland d18O values from ndash3 to ndash1permil Downcore changes for oxygenand carbon ratios analysed on Eucypris sp aff E fontana in theLago Cardiel shore core do not co-vary (Figure 3) Below 520cm (c 4500 BP) the d18O record is overall less negative (ndash1 tondash2permil) whereas d13C values are less positive (+1 to +2permil) above520 cm the reverse is true with more negative values of d18O(ndash2 to ndash3permil) and more positive values for d13C (+2 to +3permil) IfLago Cardiel remained a closed lake over the entire period ofdeposition recorded in our cores then the fraction of water lostto evaporation was always 100 For such a system changes inlake-water d18O values are driven solely by changes in humiditywhich determine the kinetic fractionation factor (Gon antiniet al 1986) In terms of regional climate humidity changes prob-ably correlate to changes in the evaporation to precipitation ratio(EP) If interpreted in terms of changing EP then the shiftupcore at 520 cm depth from less negative to more negative oxy-gen isotope values would suggest a shift from higher to lowerevaporation which should be accompanied by a shift frominitially shallower to relatively deeper water levels This scenariois however inconsistent with the results from the ostracode spec-ies assemblages that indicate higher water levels below 485 cmand shallower levels above that depth Another way to interpretthe isotopic and ostracode species assemblage data sets wouldsuggest a change in temperatures instead Below 520 cm bottom-water temperatures would have been lower related to higher lakelevels while above 520 cm water temperatures would have beenhigher as lake levels fell bringing the littoral zone where theostracodes were living closer to the core site A relatively smallaverage increase in temperature of 4degC at the lake bottom woulddecrease ostracode calcite d18O values by about 1permil as observed

Carbon isotopes are controlled by the isotopic composition ofthe lake-water DIC which can be affected by external sources thatinclude groundwater dissolved old carbonates and soil DIC Thelatter is in uenced by the vegetation in the catchment anddepends strongly on the ratio of plants with C3 or C4 photosyn-thetic pathways In Lago Cardiel however these external sourcesfor DIC remained relatively unchanged (according to the pollenrecord) over the time period under consideration and changes ind13C are thus probably affected by photosynthetic activity in thelake Plankton preferentially take up the lighter carbon isotope 12Cleading to an enrichment of 13C in the residual dissolved inorganiccarbon (DIC) pool of the epilimnion (Stuiver 1975 McKenzie1985) Organic matter depleted in 13C may be oxidized duringdecay to release 13C depleted CO2 that is taken up by benthicostracodes More positive d13C values of ostracodes could there-fore suggest a decrease in surface water productivity However

the more positive d13C values above 520 cm in the Lago Cardielrecord might indicate shallower-water littoral environmentswhere photosynthetic activity was high and 12C enriched macro-phyte and algal organic matter were buried This interpretationseems supported by the modern data In this scenario overlyingwaters would have become enriched in 13C that subsequentlywould be taken up by ostracodes growing in the littoral zone

Pollen recordThe pollen record (Figure 4) is dominated (60 to 70) by non-arboreal taxa including Poaceae (oscillating around 20)Asteraceae subfamily Asteroideae (between 5 and 10) Cheno-podiaceae (20 to 40) and a great diversity of other herbaceoustaxa (10 to 20) Arboreal taxa are represented by Nothofagusdombeyi-type (10 to 20) Podocarpus (1 to 8) and traces ofDrimys Maytenus and Cupressaceae (probably Pilgerodendron)all of which most likely represent long-distance transport fromthe west Also Dryopteris-type fern spores probably re ect long-distance sources Shrub taxa include Ephedra (5 to 15) Schinus(1 to 10) Berberis (1 to 2) Rhamnaceae (1 to 2)Asteraceae subfamily Mutisieae (10 throughout) and traces ofVerbena Botryococcus and Pediastrum both green algae areabundant in the record with values up to 60 (Botryococcus) andover 400 (Pediastrum) (calculated relative to the sum of pollen)

Modern pollen spectra from surface sediment samples from RacuteoCardiel and Lago Cardiel are generally similar to the fossil spectrain terms of taxa composition and proportions re ecting theregional vegetation Some differences are evident in the modernpollen proportions however For instance Chenopodiaceae aremore abundant near shore (100 to 300 m) in shallow-water (2 to10 m) surface sediments where they range from 20 to 30 thanat greater distance from shore (400 m) and in greater waterdepths (20 m) where the percentages decrease to less than 10Similarily the green algae Botryococcus and Pediastrum showdifferent relative proportions in surface samples from LagoCardiel depending on water depths Percentages are lowest(Pediastrum 10 to 30 Botryococcus 3 to 10) in samples nearshore (100 m) and at shallow depth (5 m) percentagesincrease to 100 to 300 (Pediastrum) and 20 to 30

(Botryococcus) at intermediate distances from shore (100 to 400m) and intermediate depths (6 to 15 m) and percentages decreaseagain to 50 to 80 (Pediastrum) and 10 to 20 (Botrycoccus) atdistances 400 m and water depths 20 m The intermediatezone of high green algae abundance is also the zone where Rup-pia grows

Whereas the fossil pollen spectra of CAR-98ndash2L show onlyminor proportional changes in the regional pollen input majorproportional changes characterize the input of local taxa primarilyChenopodiaceae and green algae spectra (Figure 4) From 1020cm to about 900 cm (c 9500 to 7500 BP) regional pollen spectraare dominated by Poaceae followed by Asteraceae and steppeherbs and scrub taxa Nothofagus is present with only 10 andPodocarpus with less than 5 re ecting low levels of polleninput from long distance Among the herbaceous taxa Calan-drinia is present with 10 and among the steppe scrub taxaespecially Ephedra is abundant with percentages of 15 to 18The abundance of Calandrinia and Ephedra both found today onrocky and gravelly substrates especially along shorelines orexposed deltas suggests proximity to an active shoreline at thattime Between 900 and 750 cm (7500 to 6000 BP) Ephedradecreases but continues with proportions above present-dayvalues Chenopodiaceae and other herbs increase slightly to 20

each (with almost 10 of the herbs represented by Caryophylla-ceae replacing Calandrinia) and the green alga Pediastrumincreases to over 50 The Chenopodiaceae increase might sug-gest seasonal drying of many of the small lakes within the Cardielbasin and seasonally uctuating lake levels The Pediastrum

Vera Markgraf et al Holocene palaeoclimates of southern Patagonia a multiproxy study from Lago Cardiel 587

0

100

200

300

400

500

600

700

800

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1000

Depth

(cm

)

1000

2000

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5000

6000

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Radio

carb

on A

ge (BP)

20

Notho

fagu

s

Podoc

arpu

s

othe

r tre

es

20 40

Poace

ae

20

Astera

ceae

Mut

isiea

e

20

Astera

ceae

subf

Aste

roidea

e

Astera

ceae

subf

Cich

orio

idea

e

Acaen

a

Calan

drin

ia

Caryo

phyl

lacea

e

20

othe

r her

bs

20 40

Cheno

podi

acea

e

20

Cyper

acea

e

20

Ephed

ra

20

Schi

nus

20

other sh

rubs

20 40 60

Botryoco

ccus

100 200 300 400 500

Pedia

strum

fern

s

100 200 300 400

sum

Lago Cardiel core CAR-98-2Lpollen ()

Trib

0

(Exc

luded f

rom polle

n sum)

(Exclu

ded f

rom polle

n sum

)

Figure 4 Pollen diagram of core CAR-98ndash2L (in ) showing major taxa including ferns and green algae (Pediastrum and Botryococcus in of totalpollen sum)

increase might imply increased turbulence characteristic of con-ditions closer to the shore with shallower water than before At750 cm (c 6000 BP) Ephedra declines to less than 5 Schinusincreases up to 10 and herbaceous taxa the major componentamong them again Calandrinia increase to near 30 Poaceaedecrease only slightly However pollen preservation during thisinterval especially of herbaceous taxa is poor SimultaneouslyPediastrum increases from about 50 to over 100 Higheramounts of pollen of Schinus which today grows primarily alongthe watercourses together with higher proportions of other shrubsand lesser proportions of herbs may indicate overall drier con-ditions The higher values of Pediastrum suggesting furtherincrease in turbulence and thus further lowering of lake levelswould support this interpretation Above 580 cm (c 5000 BP)long-distance components Nothofagus and Podocarpus increaseto 20 and 10 respectively both showing high variability Thissuggests either that both taxa increased in abundance growingcloser to Lago Cardiel than before or possibly that increasedwinds enhanced pollen transport The increase in forest density athigher latitudes related to a decrease in re frequency (Huber2001) supports the rst explanation The green alga Botryococcus(maximum 40) and Pediastrum (maximum 400) increasemarkedly and show repeated uctuations during the remainder ofthe record All this suggests uctuating environmental conditionsin terms of turbulence and lake levels At 350 cm (c 3000 BP)Schinus decreases and remains at 2 for the remainder of therecord whereas shrubs as well as Chenopodiaceae increase sug-gesting further increased regional dryness and lower lake levels

Changes in pollen spectra probably re ect regional climaticvariability speci cally changing moisture conditions althoughthe concomitant changes of Chenopodiaceae and green algae indi-cate that changing lacustrine conditions in part in uenced shiftsin pollen proportions

Diatom recordLittoral benthic diatom taxa dominate cores CAR-98ndash2L andCAR-99ndash2L Today in Bahacutea Pescaderia the productive littoral

habitat lies about 200 m offshore in water 7 to 10 m deep whereaquatic macrophytes (eg Ruppia cirrhosa) grow within thephotic zone (Lucchini 1975) Diatoms other algae snails ostra-codes amphipods and sh inhabit this zone and oxidation of theorganic production here causes underlying sediments to becomeanoxic The distribution of submerged macrophytes elsewhere inthe lake is not known and the comparatively protected water ofBahacutea Pescaderia may represent a special case Although plankticdiatoms (Cyclostephanos sp and Thalassiosira patagonica) arepresent and may dominate in surface sediment samples at greaterdepths these small diatoms do not appear to contribute substan-tially to the overall productivity of Lago Cardiel because of thegenerally low numbers of all diatoms in deep-water sedimentsLarge quantities of suspended clay and occasionally CaCO3

whitings give the lake a turquoise blue colour and may curtailphytoplankton production through nutrient (P) removal by sorp-tion or by co-precipitation with calcite (Otsuki and Wetzel 1972)

Low uctuating diatom abundance and poor preservationcharacterize the shoreline cores CAR-98ndash2L and CAR-99ndash2L(Figures 5 and 6) This probably re ects dilution by clay-rich sedi-ment entering Bahacutea Pescaderia from Cretaceous outcrops in thebasin along with breakage and diatom dissolution in the turbulentand high pH water (~9) of the lake Such uctuations may nothave large-scale limnologic signi cance The greatest concen-tration and best preservation of diatoms coincides approximatelywith sandy or silty intervals identi ed by magnetic susceptibilityand often with higher concentrations of phytoliths Phytoliths aresilt-sized silica deposits in terrestrial plant cells Both the phyto-liths and detrital silt and sand are concentrated in the shallowhigh-energy depositional environments in the littoral zone of LagoCardiel which also supports beds of subaquatic macrophytes andtheir epiphytic and benthic diatom communities within the photiczone This productive zone coupled with higher sedimentationrates linked to sediment trapping by aquatic macrophytes helpsaccount for the preservation of diatoms in this lacustrine setting

The diatom stratigraphy of both lake margin cores begins about10000 BP with high percentages of Epithemia argus a benthic

588 The Holocene 13 (2003)

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

Radioc

arbon

Age

(BP)

0

100

200

300

400

500

600

700

800

900

1000

Depth

(cm)

20 40

Epithe

mia ad

nata

20 40 60 80

Epithe

mia ar

gus

20

Cocco

neis

place

ntula

20 40 60 80

Diplon

eis sm

ithii

20

Diplon

eis pa

rma

20 40

Calone

is sp

p

20

Surir

ella o

vata

v ut

ahen

sis

20

Surir

ella f

ortii

20

Cratic

ula cu

spida

ta

20 40 60 80 100

Hyalod

iscus

20

Frag

ilario

id ta

xa

Cyclot

ella m

eneg

hinian

a

20

Cyclos

tepha

nos

20 40

Dmm

benthic attached benthic motile benthic loose planktic

Lago Cardiel core CAR-98-2Ldiatoms ()

2

Figure 5 Diatom diagram of core CAR-98ndash2L (in ) showing major taxa and their limnological af nities

8500

9000

9500

10000

Radio

carb

on A

ge (BP)

540

560

580

600

620

640

Depth

(cm)

20 40

Epithe

mia arg

us

20 40 60

Epithem

ia adnata

Cocco

neis

placentu

la

20 40

Diplone

is sm

ithii

Diplon

eis pa

rma

Calone

is sp

p

20

Surire

lla sp

p

Cratic

ula cusp

idata

20 40 60 80

Hyalo

discu

s

20 40 60

Frag

ilario

id ta

xa

Cyclo

tella

men

eghi

nian

a

20 40

Cyclos

tepha

nus

Phaco

tus

phyto

liths

200 400 600 800

dmm2

benthic attached benthic motile benthic loose planktic

Lago Cardiel core CAR-99-2Ldiatoms ()

Figure 6 Diatom diagram of core CAR-99ndash2L (in ) showing major taxa and their limnological af nities

diatom living attached to aquatic macrophytes and thereforeindicative of shallow water within the photic zone of the lake Theage of this interval in core CAR-98ndash2L is based on correlationof the diatom stratigraphy with core CAR-99ndash2L where the rst

increase of Epithemia argus is dated 9880 6 85 BP and the endof the E argus zone 9590 6 65 BP (Figure 6) Hence by thebeginning of the Holocene water level in Lago Cardiel rose tosomewhat above the current shoreline elevation of 276 m The

Vera Markgraf et al Holocene palaeoclimates of southern Patagonia a multiproxy study from Lago Cardiel 589

diatom assemblage (Epithemia argus) suggests generally fresh(3 gL TDS) if alkaline water with signi cant magnesium andsulphate concentration

A small undescribed species of Hyalodiscus characterizes thefollowing interval from 950 cm to 750 cm (9600 to 6800 BP) ofcore CAR-98ndash2L Today this diatom is found between 15 m and20 m depth in Lago Cardiel although it is not especially commonIt probably lives loosely attached to available substrateswithin the lower part of the photic zone but may enter theplankton if turbulence is suf cient The co-occurrence of smallnumbers of planktic diatoms (Cyclostephanos sp and Cyclotellameneghiniana) between 9600 and 8400 BP could testify to sig-ni cantly higher water levels above the core site at this time thatmay relate to highstand deposits (+45 to +55 m) recorded on themargins of the Lago Cardiel basin about 9800 to 9400 BP (Stineand Stine 1990)

The zone dominated by Hyalodiscus sp encompasses a discretelayer of olive-brown tephra at 838 cm identi ed as the HudsonH1 ash dated to 6700 BP By interpolation between the age ofthe tephra layer and the overlying radiocarbon date (4460 BP at520 cm) the end of the Hyalodiscus zone and the inferred inter-mediate lake stage occurred about 6100 BP

The remainder of the core is dominated by large but uctuatingpercentages of a motile benthic diatom Diploneis smithii Themotile benthic diatom community that includes Diploneis smithiiand several other bilaterally symmetrical raphid diatoms (such asCraticula cuspidata and Caloneis spp) typically lives on lake-bottom sediments where light is suf cient for growth Beingmotile these diatoms can move among the sediment grains toposition themselves optimally for light and nutrients Their abilityto move to the sediment surface after episodic burial enables themto take advantage of habitats where currents repeatedly alter lake-bottom sediment surfaces Consequently in Lago Cardiel this dia-tom community is most common at shallow water depths gener-ally less than 15 m Nevertheless because of their exposure tohigh-energy environments benthic motile diatoms often becomeshort-term members of the plankton when turbulence is high Thisis especially true for species of Surirella whose at leaf- ordisc-like shapes enables these diatoms to remain in the planktonfor longer periods so long as wind-generated turbulence can sup-port them

The uctuating dominance of Diploneis smithii after 6000 BPindicates that water levels of Lago Cardiel uctuated around 10ndash15 m above the 1990 level Strong uctuations in relative abun-dance of this and other species may track rapid changes in lakelevel although similar uctuations could be caused by diatomdestruction or dilution in this high-energy depositional environ-ment The stratigraphy of Surirella ovata var utahensis (sensuSylvestre 1997) a benthic motile species whose at shapeenables it to easily become planktic may indicate episodes ofsomewhat greater water depth The relative abundance of this dia-tom along a transect of sur cial sediments in Lago Cardiel peaksat water depths between 40 and 45 m indicating that Surirellaovata var utahensis may be able to take advantage of a deepturbulent water-column

Discussion and conclusion

The following Holocene palaeoenvironmental history of LagoCardiel sediments integrates the information from the analysis ofsediment characteristics ostracode assemblages pollen greenalgae diatoms and stable isotopes on ostracodes (Figure 3) Fol-lowing the desiccation phase dated 11200 BP in deep-water coreCAR-99ndash7P at ndash76 m (Gilli et al 2001) the lake rose rapidly andreached the present-day shoreline shortly after 10000 BP Domi-nance of benthic diatoms and the green alga Phacotus as well as

of the stream ostracode Ilyocypris ramirezi in the basal levels ofboth lake margin cores represents the initial lake transgressionabove the present-day shoreline After about 9500 BP the lakewas relatively deep as suggested by the abundance of benthicloosely attached diatoms and the presence of planktic diatomslow proportions of Pediastrum and Botryococcus dominance ofEucypris sp aff E fontana and Limnocythere patagonica andabsence of L rionegroensis This interpretation of an early-Holocene phase of a relatively deep turbid lake inferred pre-viously by Stine and Stine (1990) on the basis of shoreline evi-dence is also supported by the relatively low stable magneticsusceptibility during that time After 6100 BP lake levels fell toless than 15 m above present-day shoreline judging from thedominance of motile and attached benthic diatoms increased pro-portions of Chenopodiaceae Pediastrum and Botryococcus andpresence of Limnocythere rionegroensis Since that time the lakedid not fall for extensive periods more than a few metres belowthe 1990 lowstand and judging from the ostracode and diatomassemblages water chemistry did not change signi cantly Asre ected by the pollen record the regional vegetation experiencedno major changes After 4900 BP all palaeoenvironmental indicatorsanalysed in core CAR-98ndash2L show generally more variable almostcyclic changes This mid- and late-Holocene interval is interpretedto represent changes between more and less turbulent lake conditionsrelated to lake-level uctuations Intervals of increased lake turbu-lence represented by sandy sediment higher amounts of inorganiccarbon higher proportions of Chenopodiaceae Pediastrum andBotryococcusand of the motile benthic diatom Diploneis smithii indi-cate lower lake levels when the core site was closer to the shorelineIntervals of relatively more quiet and deeper-water conditions whenthe core site was at some greater distance from the shore arecharacterized by presence of Ruppia layers in the sediment higherorganic carbon content higher proportions of loosely attachedbenthic diatoms (eg Fragilaria spp and Hyalodiscus sp) andhigh diatom and phytolith abundances

With respect to the palaeoenvironmental interpretation of theostracode stable isotope record it appears that the d18O signalprimarily re ects water-temperature changes related to lake vol-ume Relatively positive d18O values during the early Holocenecould relate to lower water temperatures associated with greaterlake volume The shift to more negative d18O values after 6100BP would re ect higher water temperatures associated with thegenerally lower lake volume The ostracode d13C record shows acomparable history in terms of palaeoproductivity lower in theearly Holocene when the lake was deep and higher in the lateHolocene when the water was shallower and the coring site closerto shore

The earlier reconstruction of lake-level uctuations (Stine andStine 1990) based on dating geomorphic features and lacustrinedeposits above the 1990s lowstand level generally agrees withthe lake-level chronology interpreted from the shoreline coresThe +55 m early-Holocenehighstand probably relates to the early-Holocene deeper-water phase in core CAR-98ndash2L although thecore dates suggest that the transgression above the shoreline didnot begin until after 9600 BP Outcrop ages of 8620 BP (+49 m)and of 7690 BP (+28 m) are in keeping with data from the corepointing to a persistence of high water levels (relative to thoseof modern time) throughout the early Holocene A mid-Holocenehighstand (+215 m) dated 5130 BP is followed by outcroprecords of ve lake regressions and four relatively minor (to +10m) lake transgressions This lake-level variability may correspondto the repeated uctuations seen also in the core record but thelow resolution of both the outcrop and core chronologies cannotcon rm the contemporaneity of the uctuations

The last of Lago Cardielrsquos regressions began around ad 1940and culminated about 1990 Since then the lake has risen approxi-mately 4 m (S Stine unpublished data) with most of the rise

Vera Markgraf et al Holocene palaeoclimates of southern Patagonia a multiproxy study from Lago Cardiel 589

diatom assemblage (Epithemia argus) suggests generally fresh(3 gL TDS) if alkaline water with signi cant magnesium andsulphate concentration

A small undescribed species of Hyalodiscus characterizes thefollowing interval from 950 cm to 750 cm (9600 to 6800 BP) ofcore CAR-98ndash2L Today this diatom is found between 15 m and20 m depth in Lago Cardiel although it is not especially commonIt probably lives loosely attached to available substrateswithin the lower part of the photic zone but may enter theplankton if turbulence is suf cient The co-occurrence of smallnumbers of planktic diatoms (Cyclostephanos sp and Cyclotellameneghiniana) between 9600 and 8400 BP could testify to sig-ni cantly higher water levels above the core site at this time thatmay relate to highstand deposits (+45 to +55 m) recorded on themargins of the Lago Cardiel basin about 9800 to 9400 BP (Stineand Stine 1990)

The zone dominated by Hyalodiscus sp encompasses a discretelayer of olive-brown tephra at 838 cm identi ed as the HudsonH1 ash dated to 6700 BP By interpolation between the age ofthe tephra layer and the overlying radiocarbon date (4460 BP at520 cm) the end of the Hyalodiscus zone and the inferred inter-mediate lake stage occurred about 6100 BP

The remainder of the core is dominated by large but uctuatingpercentages of a motile benthic diatom Diploneis smithii Themotile benthic diatom community that includes Diploneis smithiiand several other bilaterally symmetrical raphid diatoms (such asCraticula cuspidata and Caloneis spp) typically lives on lake-bottom sediments where light is suf cient for growth Beingmotile these diatoms can move among the sediment grains toposition themselves optimally for light and nutrients Their abilityto move to the sediment surface after episodic burial enables themto take advantage of habitats where currents repeatedly alter lake-bottom sediment surfaces Consequently in Lago Cardiel this dia-tom community is most common at shallow water depths gener-ally less than 15 m Nevertheless because of their exposure tohigh-energy environments benthic motile diatoms often becomeshort-term members of the plankton when turbulence is high Thisis especially true for species of Surirella whose at leaf- ordisc-like shapes enables these diatoms to remain in the planktonfor longer periods so long as wind-generated turbulence can sup-port them

The uctuating dominance of Diploneis smithii after 6000 BPindicates that water levels of Lago Cardiel uctuated around 10ndash15 m above the 1990 level Strong uctuations in relative abun-dance of this and other species may track rapid changes in lakelevel although similar uctuations could be caused by diatomdestruction or dilution in this high-energy depositional environ-ment The stratigraphy of Surirella ovata var utahensis (sensuSylvestre 1997) a benthic motile species whose at shapeenables it to easily become planktic may indicate episodes ofsomewhat greater water depth The relative abundance of this dia-tom along a transect of sur cial sediments in Lago Cardiel peaksat water depths between 40 and 45 m indicating that Surirellaovata var utahensis may be able to take advantage of a deepturbulent water-column

Discussion and conclusion

The following Holocene palaeoenvironmental history of LagoCardiel sediments integrates the information from the analysis ofsediment characteristics ostracode assemblages pollen greenalgae diatoms and stable isotopes on ostracodes (Figure 3) Fol-lowing the desiccation phase dated 11200 BP in deep-water coreCAR-99ndash7P at ndash76 m (Gilli et al 2001) the lake rose rapidly andreached the present-day shoreline shortly after 10000 BP Domi-nance of benthic diatoms and the green alga Phacotus as well as

of the stream ostracode Ilyocypris ramirezi in the basal levels ofboth lake margin cores represents the initial lake transgressionabove the present-day shoreline After about 9500 BP the lakewas relatively deep as suggested by the abundance of benthicloosely attached diatoms and the presence of planktic diatomslow proportions of Pediastrum and Botryococcus dominance ofEucypris sp aff E fontana and Limnocythere patagonica andabsence of L rionegroensis This interpretation of an early-Holocene phase of a relatively deep turbid lake inferred pre-viously by Stine and Stine (1990) on the basis of shoreline evi-dence is also supported by the relatively low stable magneticsusceptibility during that time After 6100 BP lake levels fell toless than 15 m above present-day shoreline judging from thedominance of motile and attached benthic diatoms increased pro-portions of Chenopodiaceae Pediastrum and Botryococcus andpresence of Limnocythere rionegroensis Since that time the lakedid not fall for extensive periods more than a few metres belowthe 1990 lowstand and judging from the ostracode and diatomassemblages water chemistry did not change signi cantly Asre ected by the pollen record the regional vegetation experiencedno major changes After 4900 BP all palaeoenvironmental indicatorsanalysed in core CAR-98ndash2L show generally more variable almostcyclic changes This mid- and late-Holocene interval is interpretedto represent changes between more and less turbulent lake conditionsrelated to lake-level uctuations Intervals of increased lake turbu-lence represented by sandy sediment higher amounts of inorganiccarbon higher proportions of Chenopodiaceae Pediastrum andBotryococcusand of the motile benthic diatom Diploneis smithii indi-cate lower lake levels when the core site was closer to the shorelineIntervals of relatively more quiet and deeper-water conditions whenthe core site was at some greater distance from the shore arecharacterized by presence of Ruppia layers in the sediment higherorganic carbon content higher proportions of loosely attachedbenthic diatoms (eg Fragilaria spp and Hyalodiscus sp) andhigh diatom and phytolith abundances

With respect to the palaeoenvironmental interpretation of theostracode stable isotope record it appears that the d18O signalprimarily re ects water-temperature changes related to lake vol-ume Relatively positive d18O values during the early Holocenecould relate to lower water temperatures associated with greaterlake volume The shift to more negative d18O values after 6100BP would re ect higher water temperatures associated with thegenerally lower lake volume The ostracode d13C record shows acomparable history in terms of palaeoproductivity lower in theearly Holocene when the lake was deep and higher in the lateHolocene when the water was shallower and the coring site closerto shore

The earlier reconstruction of lake-level uctuations (Stine andStine 1990) based on dating geomorphic features and lacustrinedeposits above the 1990s lowstand level generally agrees withthe lake-level chronology interpreted from the shoreline coresThe +55 m early-Holocenehighstand probably relates to the early-Holocene deeper-water phase in core CAR-98ndash2L although thecore dates suggest that the transgression above the shoreline didnot begin until after 9600 BP Outcrop ages of 8620 BP (+49 m)and of 7690 BP (+28 m) are in keeping with data from the corepointing to a persistence of high water levels (relative to thoseof modern time) throughout the early Holocene A mid-Holocenehighstand (+215 m) dated 5130 BP is followed by outcroprecords of ve lake regressions and four relatively minor (to +10m) lake transgressions This lake-level variability may correspondto the repeated uctuations seen also in the core record but thelow resolution of both the outcrop and core chronologies cannotcon rm the contemporaneity of the uctuations

The last of Lago Cardielrsquos regressions began around ad 1940and culminated about 1990 Since then the lake has risen approxi-mately 4 m (S Stine unpublished data) with most of the rise

590 The Holocene 13 (2003)

coming in association with El Nino-induced precipitation Thispoints to a modern climatic pecularity in this portion of Patagoniawhich appears to be very dry by Holocene standards

The multiproxy Holocene palaeoenvironmental history fromLago Cardiel helps to ne-tune the regional palaeoclimate evol-ution in southern South America There are numerous recordsfrom temperate southern South America between 36 and 55degSshowing different histories for different latitudinal bands(Markgraf 1991) The differences are related to different timingof maximum moisture interpreted as re ecting differences in lati-tudinal position and intensity of the southern westerlies The earlyHolocene between 10000 BP and 8500 BP at both the northern(36deg to 43degS) and at the southern latitudinal bands (52deg to 56degS)are characterized by markedly drier environments (Villagran1991 Markgraf 1991 Huber and Markgraf 2003) whereas dur-ing that time the intermediate latitudes (43deg to 52degS) includingLago Cardiel show maximum moisture levels (Lumley and Swit-sur 1993 Bennett et al 2000 Massaferro and Brooks 2002)The westerlies must have been focused at the intermediatelatitudes perhaps in response to the small seasonal contrast ininsolation at that time (Markgraf et al 1992) Such focusingcould allow for higher frequency of Antarctic cold air incursionswhich would bring easterly moisture to southern Patagonia(Bradbury et al 2001) After 8500 BP moisture increased bothin the northern and high southern temperate latitudes (Villagran1991 McCulloch and Davies 2001) whereas intermediate lati-tudes became drier and warmer (Massaferro and Brooks 2002Ashworth et al 1991) The inferred intermediate lake levels ofLago Cardiel would support this scenario To explain this latitudi-nal distribution of moisture the westerly stormtracks probablybecame more meridional shifting seasonally across the whole lati-tudinal band (Markgraf et al 1992) For about 1000 years after6000 BP aridity affected the whole temperate region of southernSouth America including Lago Cardiel There is no climatologicexplanation for this mid-Holocene widespread aridity that evenincludes northern South America Central America and portionsof North America (Grimm et al 2001) After c 5000 BP modernenvironmental conditions (and climates) characterized byincreased variability became established throughout the southerntemperate latitudes In addition to the establishment of the season-ality shift of the westerly stormtracks poleward in summer andequatorward in winter the in uence of El NinoSouthern Oscil-lation (ENSO) was undoubtedly contributing to this variability(McGlone et al 1992) It is not surprising that Lago Cardiel withits repeated lake-level uctuations illustrates this variabilityespecially well because ENSO very strongly affects this inter-mediate latitude east of the Andes (Villalba et al 1997)

Acknowledgements

This study is supported by the US National Science Foundationgrants NSF-EAR-9709145 NSF-ATM-008267 and NSF-ATM-0081279 to Vera Markgraf and Kerry Kelts and the a SwissNational Science Foundation grant Nr 21ndash5086297 to the ETHLimnogeology group For his enthusiastic help with carbon con-tent analyses we thank Adrian Clark Jocelyn Turnbull is thankedfor her valuable suggestions and excellent preparation of the AMSradiocarbon targets We thank Mark Brenner and Andrew Cohenfor their constructive and thoughtful reviews

References

Anderson RY Nufer E and Dean WE 1984 Sinking of volcanicash in uncompacted sediment in Williams Lake Washington Science 225505ndash508

Ashworth AC Markgraf V and Villagran C 1991 Late Quaternaryclimatic history of the Chilean Channels ased on fossil pollen and beetleanalyses with an analysis of the modern vegetation and pollen rain Jour-nal of Quaternary Science 6 279ndash91Beierle B and Bond J 2002 Density-induced settling of tephra throughorganic lake sediments Journal of Paleolimnology 28 433ndash40Bennett KD Haberle SG and Lumley SH 2000 The last glacialndashHolocene transition in southern Chile Science 290 325ndash28Bradbury JP Grosjean M Stine S and Sylvestre F 2001 Full andlate glacial lake records along the PEP 1 transect their role in developinginterhemispheric paleoclimate interactions In Markgraf V editorInterhemispheric climate linkages San Diego Academic Press 265ndash89Feruglio E 1950 Descripcion geologica de la Patagonia v III DireccionNacional de Yacimientos Fiscales Buenos Aires Argentina 431 ppForester RM 1988 Nonmarine calcareous microfossil sample prep-aration and data acquisition procedures United States Geological SurveyTechnical Procedure HP-78 RI 1ndash9Galloway RW Markgraf V and Bradbury JP 1988 Dating shore-lines of lakes in Patagonia Argentina Journal of South American EarthSciences 1 195ndash98Gilli A Anselmetti FS Ariztegui D Bradbury JP Kelts KRMarkgraf V and McKenzie J 2001 Reconstructing late Quaternarylake level changes in Patagonia seismic stratigraphic analysis of LagoCardiel Argentina (49S) Terra Nova 13 443ndash48Gon antini R 1986 Environmental isotopes in lake studies In Fritz Pand Fontes J-Ch editors Handbook of environmental isotope geochem-istry volume 2 (the Terrestrial Environment B) Amsterdam Elsevier113ndash68Grimm EC Lozano-Garcia S Behling H and Markgraf V 2001Holocene vegetation and climate variability in the Americas In MarkgrafV editor Interhemispheric climate linkages San Diego Academic Press325ndash70Heinsheimer JJ 1959 El Lago Cardiel Anales de la AcademiaArgentina de Geograa 3 86ndash132Huber UM 2001 Linkages among climate vegetation and re in Fuego-Patagonia during the late-glacial and Holocene PhD dissertationUniversity of Colorado Boulder USAHuber UM and Markgraf V 2003 Holocene re frequency and cli-mate change at Rio Rubens Bog southern Patagonia In Veblen TTBaker WL Montenegro G and Swetnam TW editors Fire andclimatic change in temperate ecosystems of the western Americas NewYork Springer Verlag 357ndash80Keatings KW 2000 The basis for ostracod shell chemistry in paleocli-mate reconstruction PhD Thesis Kingston University UKLucchini L 1975 Estudio ecologico preliminar de las diatomeas perifacutet-icas y bentonicas como alimento de anfacutepodos lacustres (Lago CardielProv Santa Cruz) Physis sec B Buenos Aires 34 85ndash97Lumley SH and Switsur R 1993 Late Quaternary chronology of theTaitao Peninsula southern Chile Journal of Quaternary Science 8161ndash65Markgraf V 1991 Late Pleistocene environmental and climatic evol-ution in southern South America Bamberger Geographische Schriften 11271ndash82Markgraf V Dodson JR Kershaw AP McGlone MS and Nich-olls N 1992 Evolution of late Pleistocene and Holocene climates in thecircum-South Paci c land areas Climate Dynamics 6 193ndash211Massaferro J and Brooks SJ 2002 Response of chironomids to LateQuaternary environmental change in the Taitao Peninsula southern ChileJournal of Quaternary Science 17 101ndash11McCulloch RD and Davies SJ 2001 Late-glacial and Holocenepalaeoenvironmental change in the central Strait of Magellan southernPatagonia Palaeogeography Palaeoclimatology Palaeoecology 173143ndash73McGlone MS Kershaw AP and Markgraf V 1992 ElNinoSouthern Oscillation climatic variability in Australasian and SouthAmerican paleoenvironmental records In Diaz HF and Markgraf Veditors El Nino historical and paleoclimatic aspects of the SouthernOscillation Cambridge Cambridge University Press 345ndash462McKenzie JA 1985 Carbon isotopes and productivity in the lacustrineand marine environment In Stumm W editor Chemical processes inlakes Chichester Wiley 99ndash118Naranjo JA and Stern CR 1998 Holocene explosive activity of theHudson volcano southern Andes Bulletin of Volcanology 59 291ndash306

Vera Markgraf et al Holocene palaeoclimates of southern Patagonia a multiproxy study from Lago Cardiel 591

Otsuki A and Wetzel RG 1972 Coprecipitation of phosphate withcarbonates in a marl lake Limnology and Oceanography 17 763ndash67Schwalb A Burns SJ Cusminsky G Kelts K Markgraf V andPatagonian Lake Drilling Team 2002 Assemblage diversity and isotopicsignals of modern ostracodes and host waters from Patagonia ArgentinaPalaeogeography Palaeoclimatology Palaeoecology 187 323ndash40Stern CR 1990 Tephrochronology of southernmost Patagonia NationalGeographic Research 6 110ndash26mdashmdash 1991 Mid-Holocene tephra on Tierra del Fuego (54degS) derived fromthe Hudson volcano (46degS) evidence for a large explosive eruption Revi-sta Geologica de Chile 18 139ndash46mdashmdash 1992 Tefrocronolog a de Magallanes nuevos datos e implicacionesAnales del Instituto de la Patagonia 21 129ndash41mdashmdash 2000 The Holocene tephrochronology of southernmost Patagoniaand Tierra del Fuego Actas IX Congreso Geologico Chileno Puerto Varas2 77ndash80Stern CR and Kilian R 1996 Role of the subducted slab mantlewedge and continental crust in the generation of adakites from the AndeanAustral Volcanic Zone Contributions to Mineralogy and Petrology 123263ndash81Stine S and Stine M 1990 A record from Lake Cardiel of climatechange in southern South America Nature 345 705ndash707

Stuiver M 1975 Climate versus changes in C13 content of the organiccomponent of lake sediments during the late Quaternary QuaternaryResearch 5 251ndash62Sylvestre F 1997 La derniere transition glaciairendashinterglaciaire (18 00014C ans BP) des Andes tropicales sud (Bolivie) drsquoapres lrsquoetude des diato-mees PhD Dissertation Museum National drsquoHistorie Naturelle Paris245 ppVillalba R Cook ER DrsquoArrigo RD Jacoby GC Jones PDSalinger JM and Palmer J 1997 Sea-level pressure variability aroundAntarctica since ad 1750 inferred from subantarctic tree-ring records Cli-mate Dynamics 13 375ndash90Villagran C 1991 Historia de los bosques templados del sur de Chiledurante el Tardiglacial y Postglacial Revista Chilena de Historia Natural64 447ndash60von Grafenstein U Erlenkeuser H and Trimborn P 1999 Oxy-gen and carbon isotopes in modern fresh-water ostracod valvesassessing vital offsets and autoecological effects of interest for palaeo-climate studies Palaeogeography Palaeoclimatology Palaeoecology148 133ndash52Xia J Ito E and Engstrom DR 1997 Geochemistry of ostracodecalcite part I An experimental determination of oxygen isotope fraction-ation Geochimica et Cosmochimica Acta 61 377ndash82