Quaternary pollen records from the Archipiélago de Chiloé in the context of glaciation and climate
Calvin J. Heusser Clinton Woods, Tuxedo, Ne.,., York 10987, U.S.A.
George H. Denton Inslltute lor Quatemary Studles, UniversHy 01 Maine, Orono, Main3 04469·0110, U.S.A.
Arturo Hauser Servicio Nacional de Geologla y Minerla, Casilla 10465, Santiago, Chile
Bjarn G. Andersen Institute lor Geology, UniversHy 01 Oslo, P.O. Box 1047, Blindern N·0316, Oslo 3, Norway
Thomas V. Lowell Department 01 Geology, University 01 Cincinnati, Cincinnal~ Ohio 45221, U.S.A.
ABSTRACT
Quate mary vegetation, climateand glaciation oflhe Archipiélago de Chiloéare interpretedfrom five fossilpollen sequences, chronologically controlled by 35 radiocarbon dates. The ear1iest one from Punta Tentén, representing open Subantarctic North Patagonian Rain Forest and Magellanic Moor1and during a cold interstade is dated >49,700 yr B.P. The late-glacial and Holocene sequences at Mayol, Estero Huitanque, Dichán, and Puchilco postdate recession of the Castro lobe of the Chiloé piedmont glacier before 14,350 yr B.P. These sites at 14,350-12,000 yr B.P., at first, reflect cold, t-umid Subantarctic Paridand, followed by warming and forest development; later, at 12,000-10,000 yr B. P. cooling is inferrad by changing taxa belonging to North Patagonian Rain Forest communities. Holocene sequences, indicating moderatad conditions with Valdivian-type forest and later cooling with North Patagonian-type, are of vegetation considerably disturbad by Paleoindian burning and by European settlement. Holocene sites consistently contain a tephra layervariously dated between 9,760 and 8,820 yr B.P. Data from the late-glacial of this study and from Ihe full-glacial studied previously at Dalcahue show two glacial maxima and final multistep wastage of the Castro lobe. The first step follows a maximum of the ice, dat3d at close 21,000 yr B.P., during late Llanquihue glaciation; a second step follows another maximum dated at between 14,700 and 14,350 yr S.P., and a third step is implied from pollen data after 12,000 yr B.P. Each step, following long-term coo ing on a millennial time scale, is recognized in other geographic regions in the polar hemispheres and may be globally imprinted.
Key words: Quaterna/}' fossil palien, Vegetation, Clima te, Glacial events, Chiloé, Chile.
RESUMEN
Registros de polen cuaternario del Archipiélago de Chiloé en el contexto de glaciación y clima. Basado en cinco secuencias de polen fósil controladas cronológicamente por 35 edades de radiocarbono, se presenta una interpretación de la vegetación, el clima y las glaciaciones cuaternarias del Archipiélago de Chiloé. La más antigua de Punta Tentén, que representa selva pluviosa Subantártica Norpatagónica y tundra Magallánica durante un in:erestadio frío, fue datada en más de 49.700 a AP. Las secuencias tardiglaciales y holocenas de Mayol, Estero Huitanque, Dichán y Puchilco son posteriores a la recesión del lóbulo Castro del glaciarpedemontano de Chiloé, antesde 14.350 a A.P. Estas localidades de 14.350-12.000 a A.P. reflejan, primero, Parque Subantártico frío y húmedo, seguido por calentamiento y desarrollo de bosque; posteriormente, entre 12.000 y 10.000 a A.P., se infiere un enfriamiento por cambios de taxe pertenecientes a comunidades de selva pluvial norpatagónica. Las secuencias holocénicas, que indican condiciones moderadas con selva de tipo Valdiviano y posterior enfriamiento con selva tipo norpatagónica, están compuestas por vegetación considerable-
Revista Geol6gica da Chile. Vol. 22, No. 1, p. 25·46. 10 Figs, 5 Tables, Ju/y1995. 26 QUATERNARY POLLEN RECORDS FROM THE ARCHIPIÉLAGO DE CHILOÉ •••
mente perturbada por quemas paleo indias y por la colonización europea. Las localidades holocenas contienen consistente mente una capa de tefra datada entre 9.760 y 8.820 a A.P. Los datos del tardiglacial en este estudio y aquéllos acerca del glacial estudiado anterionnente en Oalcahue muestran dos máximos glaciares y una destrucción en varias etapas del lóbulo de Castro. La primera etapa sigue a un máximo del hielo, datado en cerca de 21.000 a A.P. durante la glaciación Llanquihue tardía; una segunda etapa sigue a otro máximo glaciar datado entre 14.700 y 14.500 a A.P; y una tercera etapa ocurrió depués de los 12.000 a A.P. según se deduce de los datos palinológicos. Cada etapa, que sigue a enfriamientos de largo plazo en una escala de milenios, se reconoce también en otras regiones geográficas de los hemisferios polares, y podrían tener un origen en causas globales.
Palabras claves: Polen fósil, Vegetación, Clima y glaciación, Cuatemario, Chiloé, Chile.
INTRODUCTION
Mid-latitude southern Chile, by virtue of its exten the GISP and GRIP ice cores from Greenland have siveQuaternary stratigraphic sequences, is recognized indicated a remarkable degree of rapidly-changing as one of the most formidable locations in the Southern stades and interstades (Dansgaard et al. ,1993), simi Hemisphere for tne study of c1imatic changes related lar Dansgaard-Oeschger cycles in ice cores from to past ice ages. As part of an ongoing, long-term Antarctica, however, are notclearly expressed (Jouzel undertaking to develop a detailed account of Quater et al., 1987b). Our studies in the Southern Andes seek nary climatic events in the region, fossil pollen records to establish additional sources of evidence that can reported in this paper derive from deposits studied in demonstrate the timing and abruptness of climatic 1991 during reconnaissance mapping of the glacial shifts in the polar hemispheres. geology of the Archipiélago de Chiloé. This work, a The project in 1995 completed its fifth year of field continuation of previous studies (Heusser and Flint, work including mapping of glacial drift deposited in the 1977; Heusser, 1990), parallels the paleoecological lowland duringthe last (L1anquihue) glaciation between work done on Isla Grande de Chiloé by Godley and Lago Puyehue in the southern part of the lake district Moar (1973) and Villagrán (1985, 1988a, 1988b, and northeastern Isla Grande de Chiloé (40°30'- 1990, 1991a, 1991b, 1993). 42°25'S). Maps were drawn at a scale of 1 :50,000 Significant with respect to the current set of fossil from aerial photographs with features checked by poli en data of the last approximately 14,000 years is ground reconnaissance. Numerous stratigraphic sec the need to assess the late-glacial and full-glacial tions of exposures and lake/mire deposits studied, paleoenvironment and examine the nature of regional resulting in poli en records with chronologies reaching glaciation and deglaciation. Evidence from geogra >50,000 yr B.P., form the basis for interpretation of phically-diverse places in the Southern Hemisphere, vegetation sequences and paleoclimate relative to Antarctica (Lorius et al., 1979; Jouzel et al., 1987a) each of four glacial lobes: L1anquihue, Reloncaví, and New Zealand (Denton and Hendy, 1994), for Ancud, and Castro. Chronological data indicate example, has shown that climate and glaciers maxima ofthe lobes at 14,500-14,700,21,000,23,100, underwent broadly-comparable, stepwise fluctuations 26,900, and at or before 35,000 yr B.P. (Lowell et al., during the full-glacial and the late-glacial. In the in press).ltwasfoundthat inthe case ofthe L1anquihue Northern Hemisphere, the latest ice-rafting episodes lobe, the maximum at 21,000 was greater than the at 2,000-3,000 year intervals observed in marine one at 14,500-14,700 yr B.P., whereas forthe Castro sediments of the North Atlantic Ocean (Bond et al., lobe, the maximum at 14,500-14,700 yr B.P. was 1993; Bond and Lotti, 1995), which are related to most extensive. Latitudinal shifting of storm tracks, behavior of the Laurentide ice sheet, indicate a meas differentially affectingthesnow accumulation regimes ure of correspondence with mountain glacier maxima of the lobes at these times of maxima, possibly ac in New Zealand and southern South America. While counts for this contrast. C. Heusser. George H. Denton. A. Hauser. B. G. Andersen and T. V. Lowell 27
ARCHIPIELAGO DE CHILOE
PHYSICAL SETTlNG ANO GLACIATION Corcovado and Golfo de Ancud (Fig. 1). The archipe lago is the northernmost of the insular network that The Archipiélago de Chiloé (41 °46'-43°28'S, 72°55'- extends only with limited interruption to the southern 74°23' W) is made up by Isla Grande de Chiloé, 185 extremity of Chile at Cabo de Hornos(56°S). Altitudes km long and as much as 65 km wide, and dozens of on Isla Grande, mostly <200 m, rise to 700-800 m in smaller islands, the largest of which, Quinchao, Lemuy, the Cordillera de Piuchén,located in :he northwestern Tranqui, and San Pedro, are situated in or about Golfo sector of the island.
lO o
ID 'O ..., ID
'O o.. .. O Mlchlnmahuida Grande
de
Chlloé Cueata Moraga FIG. 1. Map 01 Ihe Archi .. piélago de Chiloé Vantelea - emphaslzing Foaal! Pollen Sltea _ physical fealures Volcanoes .. and 10caUons re ferred lo In Ihe 10 O SQkm lexl. Insel deline I ales Ihe sludy area (Fig. 4). 28 QUATERNARY POLLEN RECORDS FROM THE ARCHIPIÉLAGO DE CHILOÉ •••
Pleistocene glaciers originating in the Cordillera lakes. Wastageof ice later was extensive, taking place de los Andes on multiple occasions coalesced to form at Cuesta Moraga in the glacial source region at 700 piedmont lobes that pushed onto the northeastern m in the Andes (Fig. 1) before 12,300 yr B. P. (Heusser part of Isla Grande (Fig. 1); the southern part, from et al., 1992). No subsequent late-glacial readvance of roughlythe latitude ofChonchi, was apparently entirely ice has been established. overridden by ice (Heusser and Flint, 1977; Heusser, Glacial geological mapping by B.G. Andersen 1990). Atthe time ofthe late Llanquihue glaciation, ice from aerial photographs in the vicinity of Chonchi (Fig. on Isla Grande reached close to the mountain front 1) in the southwestern sector of the Castro lobe shows (Fig. 1). Arcuate deployment of the moraines and of a dominance of weak morainalfeatures and meltwater drift 10rming island loops offshore delineates lobes 01 channels (Fig. 2). The best developed ice-contact the Chiloé piedmont glacier as it spread westward slopes connected with fairly weak marginal moraines from the Andes. occur in a zone near the coast to the north and south During the first 01 two known advances 01 the of Chonchi. Several of the largest drainage channels Castro lobe, the Llanquihue ice 1ront at about 22,000 start in this zone. The gradient ofthe marginal moraines yr B.P. extended to the vicinity 01 Teguaco (Fig. 1). and channels is in generallow, suggesting that 1airly Later, the lobe continued to advance, reaching a flat glacier lobes occupied the valleys. The lack of well maximum, receded and, subsequently, readvanced developed end moraines indicates that the glaciers beyond Dalcahue at about 14,700 yr B.P. (Lowell et were less active; however, no typical dead-ice topog al., in press); Mercer(1984) datedthissecondadvance raphy occurs in the area. Somewhat more distinctive at 15,000-14,500 yr. Recession 01 the Castro lobe marginal moraines and channels occur on the moun afterward was accompanied along the eastern border tain slopes within the northwest comer 01 the area 01 Isla Grande by the 10rmation at 1irst 01 ice-front mapped.
L E G E N o @ Morainic hill ~ and ridge
@ Morainic hill and ridge with ice ~ conteet slopes
~ Ice-contaet alope
o Morainic terraln :::=. Fluted surface
~ Scarp
...... _. Marginal meltwater channel
~ Ou,twash plain or flat valley lIoor
,...- Roed
• Secllon site
73 50' I
FIG. 2. Glacial geologlc map 01 lhe vicinily 01 Chonchi prepared by B. G. Andersen Irom aerial pholographs. c. Heusser, Gearge H. Dentan, A. Hauser, B. G. Andersen and T. V. Lawell 29
eL/MATE ANO VEGETATION
Under the dominant control 01 the polar maritime Eucryphia cordifolía, Gevuina avellana, Caldcluvia air mass over the South Pacilic Ocean and 01 cold panículata, Laurelía philíppiana, and several myrta Humboldt Current ollshore, the southern coast 01 ceous species, Amomyrtus luma, A melí, Myrceuge Chile in the latitude 01 the Archipiélago de Chiloé is nia planipes, M. ovata varoovata and Luma apiculata. subject to humid, cool-temperate climate throughout North Patagonian Rain Forest ébove 200-250 m the year (Miller, 1976; Prohaska, 1976). Cyclonic in altitude is first dominated by LaL:relía phílippíana, depressions associated with the southern westerlies Amomyrtus luma, and M. ovata varo ovata. Above cross the islands Irom off the ocean with considerable 350-450 m, communities are a manifestation ollorest Irequency, causing heavy precipitation, strong wind, at lower altitudes in the southern part 01 Isla Grande. and cloudiness. Annual precipitation averages be Tree species include broad-Iealed Nothofagus_dom tween 2,000-3,000 mm with mean temperatures at beyí, N. nitida, Weinmannia trichosperma, and Pseu sea level close to 14°C in January (summer) and 8°C dopanax laetevirens, together with the gymnosperms, in July (winter). On the Pacilic slope 01 Isla Grande Podocarpus nubígena, Saxe-gothaeaconspícua, and aboye 600 m altitude, precipitation values are estima Fitzroya cupressoides; tall shrub/small tree species ted to be >3,000 mm and temperatures as much as are Desfontainía spinosa, Myrceugenia chrysocarpa, 3°C lower. Somewhat drier and warmer conditions and Tepualía stípularís. are obtained on the inland side 01 the island, as air Ocean-Iacing slopes and platforms higher than crossing the cordillera descends the leeward slope. 600 m are a patchwork of Subantarctic Rain Forest This contrast influences the abundance and altitudinal communities, identified principally by Nothofagus distribution 01 plant species (Villagrán, 1985). betuloídes, Pilgerodendron uvíferum, and Drímys Vegetation, originally described in the works 01 wínterí, interspersed with Magellanic Moorland. Skottsberg (1910) and Espinosa (1917), is compre Moorland on Isla Grande is the discontinuous, moun hensively covered by Godley (1968); Godley and tainous counterpart to widespread distribution 01 the Moar (1973); Troncoso and Torres (1974); Veblen et wetland complex at low altitudes on coastal islands to al. (1983); Donoso et al. (1984, 1985); Villagrán the south. Species present have adapted to the (1985, 1988a, 1988b, 1990, 1991 b, 1993); Villagrán et prevailing conditions 01 heavy rainlaU, poor drainage, al. (1986a, 1986b); Armesto and Figueroa (1987); and a relatively lowtemperature regime. Ombrotrophic Armesto and Fuentes (1988) and Ruthsatz and cushion bogs 01 Donatía fascícularís contrast min Villagrán (1991). Evergreen rain lorest, the prevailing erotrophic lens characterized by distínct communities natural vegetation belowan altitude 01 600-650 m, is 01 Astelía pumíla and Schoenus antarctícus (Ruthsatz classilied as Valdivian, North Patagonian, and and Villagrán, 1991). Subantarctic (Schmithüsen, 1956); Magellanic It should be notedthat tree species that character Moorland (Godley, 1960), mostly at altitudes aboye ize each type 01 rain lorest olten exhibit wide ecological 600 m, is constituted by wet, peaty ground, which is amplitudes and are, thus, present over a range 01 covered by cushion bogs and by lens 01 grass/tussock altitudes/latitudes in a variety 01 communities. For sedge, among scattered enclaves 01 woodland 01 example, Nothofagus dombeyi, Weinmannía trícho• subantarctic species. sperma, and Pseudopanax laetevírens 01 the North Vegetation 01 Isla Grande is taken into account by Patagonian Rain Forest may also be important in a transect (Fig. 3) at altitudes >100 m across the Valdivian-type lorest. The status 01 species in each Cordillera de Piuchén in the north-central part 01 the community, as pointed out by Villagrán (1988a), is island (Villagrán, 1985, 1988a, 1988b). Valdivian Rain dictated, largely, according to a combination 01 Forest, increasingly reduced in extent since the arrival temperature and moisture adaptations, shade and settle ment by E uropeans >400 yr ago, is distributed tolerance levels, and topography. at <200-250 m. Communities contain the trees, 30 QUATERNARY POLLEN RECOROS FROM THE ARCHIPIÉLAGO DE CHILOÉ ...
;.
- p 0'00 0 0 E? ~ ES ~ tOO - ¡¡= D" c::: ' = E?' b B ¡:¡:='.l D I i r r i r r r-r ,--r ¡-r- r--r- -,.-r--T I r r--r- ,.--r-r,...... - r r r ,...,.-r = w.. t Slop. o 50~ Cordillera de Piuchén = eut Slope
FIG. 3. Frequency dlstributlon 01 arboreaVsubalboreal species on west and east slopes aloog a transect across the Cordillera de Pluchéo, shown lo relalloo to rain loresl and moorland vegetal Ion (redrawn Irom Villagrán, 1985).
METHODS
Stratigraphic samples from a measured section at Unidentifiable grains usually constituted 1-2%. Punta Tentén and from cores taken at four mire sites Most pollen and spores are morphologically distinct at Mayol, Estero Huitanque, Dichán, and Puchilco, all (Heusser, 1971; Villagrán, 1980) at generic orfamilial located in relation to drift of the Castro lobe in or about levels. Types are designated for certain intractable the east-central part of Isla Grande (Fig. 4), were genera, as in the case of Nothofagus, which is distin processed for pollen and spores (Heusser and Stock, guishable only as N. dombeyi and N. obliqua types, 1984), charcoal particulates (total area in microns2 and Pilgerodendrontype, which in the Archipiélago de cm3 in the 7-150 micron size range), percentage 1055 Chiloé is represented by both Pilgerodendron uviferum on ignition (Aaby, 1986), and radiocarbon ages. and Fitzroya cupressoides. Frequency diaqrams are Fossil pollen and spores were identified and divided stratigraphically into pollen asserrblage zones, counted underthe microscope (analyses C.J.H.) and based on peak amounts of key taxa. taxa grouped in "requency ("lo) diagrams (Fig. 5-9), as Plant nomenclature follows Marticorena and Que upland trees and shrubs/herbs (n = 300 pollen grains) zada (1985), except in the instance ofthe gymnosperm, and as aquatics/cryptogams (n =>300 total pollen and Lepidothamnus fonckiiPhil. [= Dacrydiumfonckii(Ph il.) spores). Specimens were also scanned to include the Florin]. presence of anytaxon not found in the sums counted. C. Heusser, George H. Denton, A. Hauser, B. G. Andersen and T. V. Lowel/ 31
1 .1.
O'lnde
d.
eh 11 o é
DlehAn• 7885 ~ 110 • Chonchl• (TUI-257'" e.t.Hultanque '4,3501240 (8.,.-1170211) • Mayol .4,270 t 110 (8"'-1170311)
FIG. 4. Mapo ~ lhestudyareawhere o !5km ~I = =='_..... ' sHes 'Nllh lhe Ir rasped ive radlocarbon ages are al MayoL Estero HuHanque, Dicha"!, Puchilco and PUf} ta Tentén.
SITES, STRATIGRAPHY, PALYNOLOGY, AND RADIOCARBON CHRONOLOGY
MAYOL, ISLA GRANDE DE CHILOE of error of each other; the tephra layer is dated between 9,500 and 9,380 yr S.P. The Sphagnum-Empetrum rubrum mire at Mayol The basin at Mayol was originally asmall freshwater (42°38'35"8, 73°45'35"W; 75 m altitude) is situated lake that became converted to mire. Aquatics in the approximately 2.5 km south of Chonchi (Fig. 4). A 5.7- gyttja include considerable amounts of the vascular m section of ¡he mire (Fig. 5) shows a sequence from cryptogam Isoetes savatieri and the green alga toptobottorr of unhumified Sphagnummoss, detritus Pediastrum, while overlying deposits are principally of peat, and gyttja overlying coarse sand. The detritus Sphagnum, Cyperaceae, Ericaceae, and Empetrum peat contains pieces of wood in the lower part, rubrum. The percentage 1055 on ignit on curve follows indicative of past arboreal plant cover, and contains a the change in residual organic matter overthe course thin tephra layer at 2.5-2.6 m depth. Thirteen radio of deposition and clearly marks the location of the carbon-dated levels provide chronological control for tephra layer at 2.5-2.6 m. the section. Maximum ages at two levels 1rom the Pollen assemblage zones M-8 through M-5 base 01 the section, 14,270 and 13,935 yr S.P., approximate the late-glacial; the Holocene is covered although stratigraphically inverted, are within the limits by the zones M-4 through M-1 (Table 1). Chronostra- w / T' ... ---- - ,.., /!,.':/A//./ ~ ./ ~,~ 7/ - ,.. _..
po.... D.. th "'.. emblql' m %on .. .. 0- / .. _·· (../:M4?. / / ~ lJi",lU.d I r '~ I '-""' ~_' ''H / . ••noo""," .r .l ~.L.:' I ",,-"-"-F·.!.· y,'- '- -,:·-' ·- ···í'-·(-b·!.'-·L í-.L:,-.. L .'-.r •.L::'- rO "c,,&.P. ~h M'
:2780 .t ea .. . O_trltu. M-' ., .... ._-_. __ a070 t 80 .. 2 - ._~ -. M- 3 8::1.110 t eo . _ 8600.1110 .. :T,*pbra :-.: 8860 !,120 .. 3 - de.,tl..,.... • M- 4 10..270 t. 10 .. UO",.ou. Inp.t. M-5 1 o,aoo:!: 220 .. I 4 - .. 1 1,7G0.1 1ao .. ~~:~;g::n: -1 G~'UJ. u,oeo .t 200 .. 5- 14,270t 170. M-8 f3.035 '1 270 .. ·'_ ... _.. _ ...... -l 'Sand rr rrrrr- rr-r-r rr rrr~ rrrr-rrrrrrrrrrrrrrrrrrrrrr r rr r r , ' O • rr-r-r ~ft\2(;:M-3)( 100 o 76 ... C,yp.ogom. r::-o"" · Mayol o la la Grande de Chiloe e ~ 1/ ~'.'q, "'JO 7 Z Doo1h ~~,,~,~~~~Z.,· .../' "'o.- ~(../qO / 6~!~~ ~~ .'.. P*n ~ , I ·_ .. ·-(f· (. ..1. -é~_ . _.. ,,l._." .. _.. _ ,1;/ ....- z...... L . , "l.... _.....; _. - o •• On ,. "1 " ._ ._LI .... _._' I I~ .I ' ...... _.. _, n o. F "'Z L __ 7"· " JO rr ~ 1 ~___ ---- :~ - , "'o M- 2 O oJO ¡e::;:r- -_.- -'--_.. _ ._. __.. _ ... I I - 2 (JO -n .-- M-3 , el ~ 3 - -" - 3 -< I " · ==:====FL _~~=~::~ = , / I , M- 5 "' ~o 4--1 - 4 I 'ii _.. ~ .• " ",-e m. _.. ":.:::=:::::::::::=::..ltc· i¡; G- J - 5 8 M-8 o r I : "'() I - 1 rrr r rr rr"...... ,.,.-r-r- ~ I o 50 '0011 ~. 5['1. FIG. 5. Palien and spore dlagram 01 lhe core 'rom Mayal, Isla Grande de Chlloé_ c. Heusser, George H. Den/on, A. Hauser, B. G. Andersen and T. V. LowelJ 33
tigraphy (Fig. 5) is emphasizedforthe late-glacial and afterward the rate increases to 23 yr :::m'. The low rate early Holocene between 14,270 and 9,070 yr B.P. between 9,070and 2,760yr B.P. appears relatedto a (zones M-8 - M-3), where the sedimentation rate continuous succession of fires, as revealed by the averages 14 yr cm'. Later, unti12,760 yr B.P. (zone charcoal record over the 6,300 year interval. M-2), the rate at 79 yr cm' is exceedingly low, while
TABlE 1. POllEN ASSEMBlAGE ANO CHRONOSTRATIGRAPHIC DATA FOR MAYOl,lSlA GRArmE DE CHllOE.
POllan PoIlan 8888mblaga Aga a898mblage zona (14 C yr B.P.) o M-l Gramlneae - Empe/rum- (0-0.9 m) Ericaceae - Plan/ago- Plnus - No/hofagus >400 M-2 No/hofagus - Podocalpus- 2760±60 (0.9-2.0 m) Gramineae (1.2 m, Bela -67034) 9000 M-3 No/hofagus - Myrtaceae- 9070±60 (2.0-2.6 m) Gramineae (2.0 m, Bela-61855) 9380±90 (2.5 m, Bela-618056) 9500 M-4 Welnmann/a - No/hofagus- 9500±110 (2.6-3.0 m) Hydrangea - Erlcaceae (2.6 m, Bela -67(35) 985O±120 (2.8 m, Bela-67036) 10,000 M-5 Podocalpus - No/hofagus- 10,270±70 (3.0-4.3 m) Myrtaceae - Gramineae- (3.3 m, Bela·61867) Tubulillorae 10,800+..220 (3.7 m, Bela-67037) 11 ,750±190 (4.2 m, Bela-61869) 11,500 M-6 Pseudopanax - Myrtaceae- (4.3-4.6 m) No/hofagus 12,000 M-7 Myrtaceae - Maytenus- 11,950±200 (4.6-4.8 m) No/hofagus (4.6 m, Bela-61868) 12,750 M-8 No/hofagus - Loma/la- 12,730±410 (4.8-5.7 m) PIlgerodendron Iype· (4.8 m, Bela-67038) Gramlneae - Ericaceae 13,090±200 (5.0 m, Bela-62440) 14,270±170 (5.4 m, Bela-67039) 13,935±270 (5.7 m, T-9660A)
Late-glacial vegetation (14,270-10,000 yr B.P.), communities, which consisted of Gramineae and indicated by the pollen and spore record during Ericaceae together with Gunnera and a few other approximately the first millennium of deposition, is minor, but distinctivetaxa. While arboreal components essentially Subantarctic Parkland of Nothofagus other than Nothofagus are present initially (Pi/gero dombeyí type. Frequency of Nothofagus at the dendron type, Lomatía, Myrtaceae, Maytenus), their beginning (34%) reaches a maximum (66%) late in frequencies only begin to rise shortly befo re 13,000 yr zone M-8, following displacement of nonarboreal B.P. , indicating incipient diversificat on of species in 34 QUATERNARY POLLEN RECORD S FROM THE ARCHIPIELAGO DE CHILOE •••
the flora under moderated conditions su itable for plant disturbance taken near Castro (Fig. 1l, interpreted invasion. By approximately 12,OOOyrB.P. (zone M-l), Holocene paleoenvironments from pollen data. She frequency of Notfoofagus dombeyítype (10%) is greatly found a major early Holocene prominence of Valdivian reduced largely by Myrtaceae (46%) of the developing type EucryphíalCaldcluvía, which was preceded and North Patagon an Rain Forest. Subsequently, followed by North Patagonian Myrtaceae (cf. Myr Pseudopanax laetevírens (zone M-6) is prominent for ceugenía and Amomyrtus) and Drímys, among other an estimated 200 yr, followed for some 1,500 yr by taxa. The broad implication of data from the core is of Podocarpusnub.gena(22-31%), which underacooler relativelycool/wetclimate atthe late-glacial- Holocene climate against a backdrop of Nothofagus and boundary and during the late Holocene, interrupted by Myrtaceae is manifest until1 0,270 yr B.P. the warmer/drier early Holocene. Onset of the warml Vegetation during the first millennium of the dry interval is dated at about 9,580 yr B. P., which at Holocene at Mayol (1 O,OOO-Oyr B.P.) is given overfor Mayol, Estero Huitanque, and Puchilco (Figs. 5, 6, 8) the most part t,::> Nothofagus dombeyí type and falls close to the age of a tephra layer bracketed by Myrtaceae (zones M-4 and M-3). Burning at around dates of between 9,760 and 8,820 yr S.P. 10,000 yr B.P., e'¡ident fromthe presence of charcoal Settlement by Europeans during the past >400 yr and ascribable to Paleoindians, may account for the resulted in the loss of forest cover on Isla Grande and short episode of Weínmannía tríchospermalHydran• brought about the introduction of exotic taxa. These gea serratífolía (zone M-4) between 9,850 and 9,500 centuries of change created an increase in open yrB.P. The pollen record after 9,OOOyr B.P. shows no space shown by the conspicuous increase in Grami clear evidence of Valdivian Rain Forest, which has neae and decrease of Nothofagus dombeyí type been described for the Holocene elsewhere on Isla (zone M-1). Openness made possible the spread of Grande (Villagrá:1, 1985, 1988a). The noticeably high light-demanding plants, including exotics (Pínus, Ru incidence of fire, shown by charcoal (zone M-2) may mex, Spergula aNensís, cf. Trífolíum, Umbelliferae, explain the apparent exclusion of Valdivian-forest Plantago, Liguliflorae, Tubuliflorae). Low incidence of indicator species. Late in the Holocene at around charcoal during the period of settlement, following 2,760 yr B.P., North Patagonian Rain Forest is ex high frequency/intensity of Paleoindian burning, infers pressed by the high proportion of Nothofagus (80%) that clearing was predominantly through tree cutting, coupled with Podocarpus nubígena (zone M-2). probably because of the need of lumber for construc Villagrán (1935), working with a core with minimal tion.
ESTERO HUITANQUE, ISLA GRANDE DE CHILOE
The site of Ihe freshwater mire at the head of detritus peat (Myríophy/lum, Azo/la fílículoídes, Isoetes Estero Huitanque (43°37'30"S, 73°48'OO"W; 52 m savatíen) were deposited during a lake stage prior to altitude) is on the east side of Route 5, less than 3 km replacement by mire. The presence of massulae southwest of Chonchi (Fig. 4). A 4.8 m section of the containing microspores of Azolla at Estero Huitanque, mire, taken be lo .... mounds of Sphagnum overrun by and also at Puchilco (Fig. 8), is unusual and is the first Empetrum rubrum, covers a sequence of unhumified report of this plant in the Quaternary deposits of Sphagnum, detritus peat, gyttja, and sand (Fig. 6). A southern Chile. According to Gunckel (1984), the tephra layer at 1.57-1.73 m, limited in age by radio species ranges from Arica to Magallanes, and Looser carbon dates of 3,200 and 8,820 yr B.P. and marked (1961) recorded it from Isla Lemuy, the location of by a distinct decrease in percentage loss on ignition, Puchilco, one of two modern collections recorded in is interbedded irn the upper detritus peat. Values for the Province of Chiloé. loss on ignition show a sharp rise in organic content at The section at Estero Huitanque is divided into 3.9-3.8 m, just abovethe gyttja, markingthe beginning four pollen assemblage zones, their time spans of shoa ing at the core site, coincident with reduction ascertained by nine radiocarbon dates and, in the in extent of open water. Peat higher in the section is case of the uppermost zone (EH-1), by the centuries contributed chiefly by Sphagnum, Cyperaceae, of European settlement (Table 2). Late-glacial veg Ericaceae, and Empetrum rubrum. etation (14,350-10,000 yr B.P.) commenced as Sub Aquatics present in the gyttja and lower part of the antarctic Parkland of Nothofagus dombeyí type and / Tr... /J Shrub••• d Hub. 7 ~ .¡¡ " oo.. ~,-<¡ ...f' ~of'~.f' /1' ..+ - ~q Q~ ~ e,·!\.q¡; ~ ~.. ~ -,,' .§'~o Ji...... ~ .., ," ..."., •• .t. ,§ ~. ..," ,f.... '!<.'fJ" (j~ .,+ ~/ e C; v- I I - 1 I I 2 - ~-"." , r. I EH- 2 - 2 - 3 1~ I" , -.1I---.:,.... J ...... I ----...... -. rrr-r I EH- 4 rrrrrrrr r rr 1--'-" - I o 50 100'" ["'7[.. FIG. 6. Pollen and spore dlagram 01 the eore lrom Estero HuH.anque, Isla Grande de ChRoé. ~ 36 QUATERNARY POllEN RECORDS FRO M THE ARCH IPIElAGO DE CHll OÉ ... Gramineae (zone EH-4). The episode covers the time Holocene vegetation (10,000-0 yr S. P.) is charac of deposition befo re 12,750 yr S.P. There follows an terized by the increase of Nothofagus dombeyitype interval of Gramineae-Tubuliflorae, averaging 62% of (79%), despite incidences of fire indicated by abun the pollen sum (zone EH-3), extending for ca. 2,700 yr dances of charcoal (zone EH-2). Growth of the mire until about 1O,OOJ yr S.P. Over this time span, North stagnated at this time, possibly as a result of burning; Patagonian Rain Forest elements, except for rates of sedimentation before 8,820 and after 1,940 yr Nothofagus, are comparatively minoro The G ramineae S.P. average respectively, 17 and 24 yr cm-', while Tubuliflorae assemblage infers principally grassland, during intervening millennia the rate at 98 yr cm' is containing small, scattered stands of trees. Dominance conspicuously low. Later arrival by Europeans and of Gramineae at this site compared with arboreally clearing of the land with settlement of Chonchi (zone dominated Mayol suggests a local late-glacial veg EH-I) coincide with the decrease of Nothofagus, rise etation mosaico Charcoal in uppermost late-glacial of Gramineae, introduction of foreign adventives, levels is from the earliest major fires at Estero Hui including Pinus, Rumex, and Plantago, and cessation tanque. of Paleoindian burning. TABLE 2. POLLEN ASSEMBLAGE ANO CHRONOSTRATIGRAPHIC DATA FOR ESTERO HUITANQUE, ISLA GRANDE DE CHILOE. PoIlen assemblage Palien assemblage Age zone (1' C yr B.P.) o EH-1 Gramineae - Empetrum (0-0.6 m) Plantago - Rumex - Pínus - Podocarpus - Nothofagus ------~OO EH-2 Nothofagus - Gramineae 1940±90 (0.6-2.0 m) Erlcaceae (0.8 m, 6ela -67025) 8820±100 (1 .5 m. 6ela-61948) 9200±80 (1 .8 m, 6ela-61947) ------10,000 EH-3 Gramineae - Tubuliflorae 10,160±60 (2.0-3.9 m) Valeriana - POdocarpus - (2.0 m, 6ela-61861) Myrtaceae - Maytenus 11,430±150 Nothofagus (2.5 m, 6ela-67026) 11 ,690±400 (3.5 m, 6ela-67028) --:-:----:-__--: ______12,750 EH-4 Nothofagus - Lomatía- 12,750±130 (3.9-4.8 m) Gramineae (3.9 m. 6ela-61862) 14 ,350±240 (4 .6 m, 6ela-67029) 13,345±105 (4 .8 m, TUa-259a) DICHAN, ISLA GRANDE DE CHILOE The mire at Dichán (42°31 OO"S, 73° 49' 40"W; 50 the most part of detritus peat underlain by interbedded m altitude), located 4.5 km west of Chonchi (Fig_ 4), peat and sand and overlain by unhumified Sphagnum. is developed on a recent meander scar in the floodplain Mounds of Sphagnum at the surface are covered in of Estero Huenué, which accounts for its Holocene part by Empetrum rubrum (Fig, 7). age of 7,885 yr S.P. The deposit atthe site consists for T'eo. ~ S.,ub. an4 Horb. !="l ~ ~,¡; ~~ ,~/.,. Do ~ 3080:!. 80 2 - Q.elrllus I "'( I",'j c:: , ,."', b, .. " ...... b ..·.. • .. · ,·- ~. 1- 2 p ••• • ."'_1"': .. .=:::::::: 1·:::::::::::::,_ .. __ ¡g ~ '·'·T "':~~:~::~~:':: :: ~~~: -=:~:~-~::.:!::,-":-- : ~ : ':::',::" ,:'.:'~.:':::::: ,:.:::'.:=~~~ ~:::"·"-O:3 '-"' -- ..... 0-4 3- f ~ 4900!80D> r ,_o : ~ ---- ~ -- ¡ 1: - ~ --_ : _-_:;:':" - -- o --_.-- o [r -- b 1>-5 4 - r '"~ 611Ot80. ~ --_ .... _--_. ~ _ .., .._.- ..l-.. ,... ,-,-~" ... ~. ~ I (jJ .. r·J·· L.. ::___ '_ ' _ 1~ 4 <11 I 11 , I .,~,_. Sand '·'-- ¡ ~ , '" 7885180. 5 -1,::::' peot::::;.;; b l ' , , , I , - 5 '"Q. ...nd r . rr"T"" rr"T"" • r r r r rrrrrrr rrrrrr rr-r rr-r-r-r r r rrrrrrr r rrrrr ~ '" 0 2 • :-i ¡-ro-r- --. O 15"4 AQUOlfCs J.lm 2 cm-3 "-107 :-::: r o I r ";.eryP 70l1am. Dichán ~./" A" ~ A..,. • • .l4r§-,... . Isla Grande de Chiloé ,¡-' r:.";/;,""e"li" O.pt" A",¡,...... ~ .df.~':.&.~~ .. j' m '1&t"./ .;:.... ;~,,?;;:~~. /' Pollen o - ,:: .. f, ...... ;:..,(.>.. , ~'%~ J. A••• mblag_ ... ,+...... """''''''''' ~/ .. _.,,_._ ...... Zone _...... s Lo .. On Ignlllan m h I ,_.f ------.---_.'_:' ' -, - 1 I 1 j I 0-2 2 - " :::'::'"::::::::::::::,, .... ; ',:::.::::·:,:::::::: :::::::: ?::~~~~:_.I 1-2 3 - , I 1 " 0 - 4 - 3 ·'···L··_·· .... r'-"" .. ~·"- .. ·- l D-S f------j\ - 4 4l I 1'-" +---:"· ------"u ~: "· 6-, ~ b' l;;=:I - 5 r ¡-rT rrrr.-.- rrr ,i i i i , o 50 100"4 f'76...... <.o> FIG. 7. Palien and spore dlagram 01 lhe core trom Dichán, Isla Grande de ChKoé 38 QUATERNAAY POLLEN AECOROS FROM THE ARCHIPIÉLAGO DE CHILOÉ... Sedimentation began in a backwater of the be the cause initially for the high trequency 01 meander in what was apparently a sluggish drainage Gramineae (38%). Vegetation, otherwise, contained course occupied by Cyperaceae with Isoetes savatieri. variable quantities of taxa associated with Valdivian Following initially-interrupted, organic deposition, forest: Weinmannia trichosperma (zones D-5 and D- percentage loss 00 ignition records a steady sequence 4), Myrtaceae (centered on zone D-3), and Hydrangea ofvalues elose to 100% overthe remainder of the 5.0- serratifolía (zones D-4 and D-2). The occurrence of m section of the deposito Sedimentation during the peak Myrtaceae, typically an inhabitant of low ground time of record, a'¡eraging 9-16 yr cm' between five along rivers, may derive 1rom disturbance during radiocarbon-dated levels and the surface, reveals no periods of flooding. Disturbance may also be a factor striking irregularities that reflect protracted, low-water related to the variable 1requency 01 Weinmannia and stages of the river. Hydrangea, both of which are light dependent and Six pollen assemblage zones are recognized for require open communities in order to endure. the nearly 8,OOO-year account of vegetational change Land clearance during European settlement is at Dichán (Fig. 7; Table 3). Rain forest dominated by substantiated in the uppermost part of the section by Nothofagus, inferred by N. dombeyi type assemblages the reduction in Nothofagus frequencies (zone D-1) (zones D-6, D-5, and D-2), was subject to tire both at and presence of alien Pinus, Rumex, and Plantago. the start and later, which created openness and may TABLE 3. POLLEN ASSEMBLAGE ANO CHRONOSTRATIGRAPHIC DATA FOR DICHAN, ISLA GRANDE DE CHILOE. Pollen assemblage Pollen assemblage zone o 0·1 Empetrom • Gramlneae- (0·0.6 m) Rumex· Plantago • Plnus >400 D-2 Nothofagus • Myrtaceae- 680±70 (0.6-2.1 m:. Hydrangea - Empetrom (0.8 m, Bela -67030) 3100 D-3 Myrtaceae 3080±80 (2.1-2.4 m:. (2.1 m, Bela-67031) 3500 0-4 Weinmannia - Hydrangea (2.4-3.2 m:· 4900 0-5 Nothofagus - Myrtaceae- 4900±80 (3.2-4.3 m: Empetrom (3.2 m. Bela-67032) 6700 0-6 Nothofagus - Gramlneae 6710±80 (4.3-5.0 m: (4 .3 m. Bela-67033) 7885+80 (5.0 m. TUa257A) PUCHILCO, ISLA LEMUY The site 01 the Sphagnum mire at Puchilco Isoetes savatieri attests to the presence of open water (42°36'45"S, 73°36'15"W; 110m altitude) is in the at the start of detritus peat deposition; later, detritus northeastern sector of Isla Lemuy, ca. 2 km inland contributed in the main by other aquatics is from fromthe shore ot Canal Quehui (Fig. 4). The mire rests Cyperaceae and Sphagnum, along with Potamogeton/ in a drainageway connecting the basins of Lagunas Tetroncium, Myriophyllum, and Azolla filiculoides. A de Puchilco. A 4.1-m section of the 11 ,440-yr B.P. tephra layer, emplaced in the peat at 3.10-3.1 5 m and deposit (Fig. 8) shows detritus peat, which ineludes dated between 9,760 and 8,880 yr S.P., is elearly some wood, res1ing on sand, overlain, in turn, by registered by the percentage loss on ignition curve. layers of humifiedand unhumified Sphagnum. Aquatic Divisible in the section are seven pollen assem- Tr..... ~ Shtul>. ond Hub. 7 ~ "..( 1I· FIG. 6. Pollen and spore dlaQfam 01 lhe core Irom PUchilco, Isla Lemuy. ~ 40 QUATERNARY POLLEN RECOROS FROM THE ARCHIPIÉLAGO DE CHILOÉ ••• blage zones, the chronostratigraphy of which is es B.P. (zone PU-4), Myrtaceae afterward until4, 150 yr tablished from seven radiocarbon dates and from B.P. (zone PU-3), and later, both Myrtaceae and exotic pollen incicators related to the presence of Pseudopanax laetevírens (zone PU-2), extending to European man h recent centuries (Table 4). Late the beginning ofthe European era. Openness, inferred glacial zones (FU-7-PU-5) trace the initial rise of by quantities ofGramineae and by intolerantValdivian Myrtaceae and LDmatía at the expense of Nothofagus type Hydrangea serratífolía and Weínmannía (zone dombeyítype in r'¡orth Patagonian Rain Forest (zone PU -4), probably resu Ited f ro m fire disturbance, which PU-7, >11,440-11,400 yr B.P.), followed by peaks of is seen in the amounts of charcoal deposited during Pseudopanax laetevírens (zone PU-6, 11,400 -11,350 the interval. As recorded elsewhere on Isla Grande, yr B.P.) and of Podocarpus nubígena (zone PU-5, Gramineae are noticeably abundant (60%) following 11,350-10,020yrB.P.). Holocenecommunitiescontain the arrival of Europeans (zone PU-1), and occur with varying amounts of Nothofagus in association with the adventives, Pínus, Rumex, and Plantago. Weínmannía tríchosperma until an estimated 6,500 yr TABLE 4. POLLEN ASSEMBLAGE ANO CHRONOSTRATIGRAPHIC DATA FOR PUCHILCO, ISLA LEMUY. PoIlen assemblage Palien assemblage Age zone (u C yr B.P.) O PU-1 Gramineae - Plantago- (0-1.2 m) Rumex - Nothofagus- Podocarpus - Pínus >400 PU-2 Pseudopanax - Myrtaceae- (1.2-1 .6 m) Eucryphia/Caldcluvla- Nothofagus 4150 PU-3 Nothofagus - Myrtaceae- 4150±60 (1.6-2.3 m) Gramineae - Empetrum- (1.6 m, Bela-61863) Tubuliflorae 6500 PU-4 Nothofagus - Welnmannía- 8880±160 (2.3-3.3 m) Gramineae - Hydrangea- (2 .9 m, Bela -61864) 9760±90 (3.2 m, Bela-50718) 10,000 PU-5 Nothofagus - Podocarpus 10,020±120 (3.3-3.5 m) (3.3 m, Bela-50719) 11,350 PU-6 Nothofagus - Myrtaceae- 11,350±150 (3.5-3.9 m) Pseudopanax - Griselinia (3 .5 m, Bela-50721) 11.400 PU-7 Myrtaceae - Lomatía- 11,400±100 (3.9-4.1 m) Nothofagus (3.9 m, Bela-50720) 11 ,440±170 (4 .0 m, Bela 50722) PUNTA TENTEN, ISLA GRANDE DE CHILOE A measured section >163 cm thick at Punta to top; the peat bed higher in the section is much Tentén (42°28'20"S,73°44'45"W), an intertidal site compacted and contains, at upper levels, remains of along upper Estero Castro approximately 1 km east of treetrunks as much as 10 cmthick. An age of >49,700 the town of Castro (Fig. 4), consists of beds of sand, yrB.P. on thewood predatesthe age ofthe lastglacial peat, silty peat, énd tephra, which are underlain by a maximum. The site has been subject to tectonism, diamicton and overlain by colluvium (Fig. 9). Both whereby the upper of the two silty peat beds is tilted beds of silty peat are increasingly organic from bottom and dips 5-10° to the north. c. Heusser, George H. Denton, A. Hauser, B. G. Andersen and T. V. Lowell 41 Pollen and spore stratigraphy, divided into four From its stratigraphic position and its content poli en assemblage-zones (Fig. 9; Table 5), shows predominantly of Nothofagus pollen, the deposit is Nothofagus dombeyi type (>50%) dominant and considered to be interstadial and most probably of Gramineae subdominant. The implication of the data Pleistocene age, but may be older. Kinds and quantities is of openness within or beyond mostly tree-covered of taxa in the record are largely irdicative of cold upland. In the sequence of beds, a successional temperate Subantarctic-North Patagonian Rain Forest component is inferred by the early abundance of (Nothofagus, Embothriumcoccineum, Drimys winteri, Lycopodium (PT-1). Subsequent quantities of Cype Podocarpus nubigena, Saxe-gothaea conspicua) with raceae and Myriophy/lum are, in turn, indicative of restricted presence of Magellanic Moorland (Lepido progressive paludification with increasingly aquatic thamnus fonckii. Donatia fascicularis, Gramineae). conditions (PT-2 and PT-3) and, ultimately, change T axa indicative of relatively moderated climatic regimes toward a subaerial type site (PT-4). Present-day (Myrtaceae, Hydrangea, Gevuina, Eucryphia, intertidal relations at Punta Tentén were apparently Aextoxicon) are not in evidence. Generalrelationships established at some time following deposition of the can be seen in the modern distribution of species in uppermost peat, as there is no indication of marine the Cordillera de Piuchén (Fig. 3). submergence earlier in the measured section. ~ Treea 7 r- Shrubl and H.rb2~ Aquatlc."and C·lPtavaml Me ...... ed 4...... 4" oS> '/ .. D:,lh Secllon ,.A ~' ~ ~"T ..,. ...~ , 0- ·Ob.cured- ~"{".~"'" ,,(jI.~ • ,¡ :~~: Sand 13 ] r·r···,····Ir·········I····,····r·········1r ¡·····:···············I····'··········¡ ·· ·.,..·············l···f·······r··· ···· ~ ··· l···I····~·······r······r ··· ...... :~;: ...... SlIly [ 18 ro r ----,---,..'1- peat rr~~ ~rríT~rrrr~rrrrrrrrrr r~rrr- ~ o 1 1113- 18 ó"1'i.. jJt112cm-3'1011 DI_clon -obacured- Punta Tentén FIG. 9. Palien and spore diagram 01 Ihe measured section al Punla Tenlén, Isla Grande de Chiloé. TABLE 5. POLLEN ASSEMBLAGE ANO CHRONOSTRATIGRAPHIC DATA FOR PUNTA TENTEN, ISLA GRANO: DE CHILOE. Pollen assemblage Palien a&semblage Age zone (14C yr B.P.) PT-1 Nothofagus - Lepidothamnus >49,700 (40-55 cm) Gramineae (40 cm, A-6184) PT-2 Nothofagus - Gramineae (55-120 cm) PT-3 Nothofagus - Saxe-golhaea (120-145 cm) Gramineae PT-4 Nothofagus - Gramineae (145-163 cm) 42 QUATERNARY POUEN RECORDS FROM THE MCHIPIELAGO DE CHIlOÉ... Fires are possibly the cause 01 openness in the 1rom volcanoes, which may serve as other vectors 01 vegetation, as charcoal occurs virtually throughout burning (Heusser, 1994). The charcoal sequence the deposit, except where 1requency 01 Nothofagus thus, may imply antiquity 01 human presence in Chile dombeyi type (83%) is highest and wet conditions at > 49,700 yr B.P., considerably beyond the oldest maximal (zone PT -2). Fires on Isla Grande are attribu known, Paleoindian age 0113,000 yr B.P. (Dillehay, table to Paleoincians, as the island is not subject to 1989). lightning strikes, and is isolated, distantly removed OISCUSSION ANO CONCLUSIONS The sequence of events surrounding late Llanqui when climate grew warmer, enabling Nothofagus to hue 11uctuations of the Castro lobe in a paleoenviron expand both at Mayol (zone M-8; Fig. 5) and Estero mental context are summarized in figure 1 O. Following Huitanque (zone EH-4; Fig. 6). The interval of milder the glacial maximum near Teguaco (close to climate that followed was marked by arboreal diver 21 ,690±120 yr B P., A-7729), the full-glacial reported si1ication beginning befo re 13,000 yr B.P., including in this paper deri'Jes from the intertill site at Dalcahue peak Myrtaceae at Mayol close to 12,000 yr B.P. (Fig. 1; Heusser, 1990; Lowell et al., in press), shown (zone M-7; Fig. 5). Afterward at Mayol (zones M-6 and bracketed by radiocarbon dates of 19,630±180 and M-5), and also at Puchilco (zones PU-6 - PU-5; Fig. 8), 14,720±100 yr B.P. (QL-4324 and A-6189, respec peak percentages of Pseudopanax laetevírens and tively); the mires at Mayol and Estero Huitanque (Fig. Podocarpus nubigena imply colder conditions and 4) are sources 01 data 10rthe late-glacial dated between reversal of the warming trend. A colder setting is 14,350 and approximately 10,000 yr B.P. Mean apparent from the modern altitudinal distribution of summertemperature duringthefull-glacial is estimated these species with reference to species 01 Myrtaceae at ~4 OC (Villagr¿n, 1988b) and as much as 6-6SC in the Cordillera de Piuchén (Fig. 3). At Estero Hui (Heusser, 1991) below the present; an estimate of 2- tanque (zone EH-3; Fig. 6), the colder interval dated 3°C of temperature depression compared with today later than 12,750 yr B.P. is reflected by the high at the close 01 the late-glacial, when Podocarpus proportion of Gramineae and Tubuli110rae and by the nubigena was important in the pollen record, results comparatively poor display 01 arboreal species. 1rom the applicétion 01 a lapse rate 01 -0.55°C 100 Initial late-glacial expansion and subsequent m-1 to the in1erred 300-500 m lower altitudinal zone 01 diminution 01 Nothofagus on Isla Grande, as climate P. nubigena in the Cordillera de Piuchén (Fig. 3). at first became milder and later colder, can be seen in Uncovering sites of this study, the Castro lobe other data from the 80uthern Andes. The 11uctuation pulled back 1rom its latest maximum be10re approxi 1rom >50 to <30% Nothofagus occurs on the Penínsu• mately 14,350 ~'r B.P., which at Estero Huitanque la de Taitao at 46°25'8 after 14,335±145 yr B.P., and (Fig. 4) is the earliest deglacial age on Isla Grande. ineludes peak Podocarpus nubígena (>35%) between Earlier after 14.720 yr B. P., the Castro lobe had 11,000 and 10,000 yr B.P. (Lumley and 8witsur, advanced at Dalcahue (Fig. 1), ca. 40 km to the 1993); in Tierra del Fuego at 54°52' 8 after 14,640 ± northeast, making duration 01 the maximum on the 260 yr B.P., values of > 75% Nothofagus decrease to order of severaf hundred years. While increase of <2% between 11,160 and 10,200 yr B.P. (Heusser, Gramineae and decrease 01 Nothofagus at Dalcahue 1989, 1993). after an estimated 16,500 yr B.P. in1ers progressive Repetition 01 a sudden reversal 01 trend with cooling 10r two millennia prior to overriding 01 the site subsequently milder climate is best shown at the late by the ice (Fig. 10), the duration 01 the glacier at its glacial-Holocene boundary at Puchilco (zone PU-4; outermost stand was comparatively short. The onset Fig_ 8), where the profile 01 Weinmannía trichosperma, 01 cooling is estimated based on AM8 radiocarbon unimportant in the late-glacial, 101l0ws Podocarpus dates of 17,000=145 and 15,975±145 yr B. P. (UGA- nubigena in <300 yr. The shi1t during similar short 7056 and UGA-7053, respectively). periods is also noted at Mayol (zones M-5 - M-4; Fig. Termination 01 the maximum occurred abruptly 5) and Estero Huitanque (zones EH-3 - EH-2; Fig. 6), C. Heusser, George H. Denton, A. Hauser, B. G. Andersen and T. V. Lowel/ 43 but has been subdued in each case, apparently, by from Myrtaceae to Podocarpus nub;gena in the pollen fire. assemblages, for example, suggests concordant alti Late-glacial Chiloé vegetation over the roughly tudinal lowering of vegetation belts in the cordillera. 4,000 yr of record underwent transition from open Open grassland at Estero Huitanque (zone EH-3; Fig. Subantarctic Parkland (probably containing Nothofa 6) possibly reflects the spread of high-cordilleran/ gus betuloides) to mostly closed North Patagonian high-Iatitudecommunities. No clearnodern analogue, Rain Forest. Internal changes in the North Patagonian however, exists for either Subantarctic Parkland or communities during the latest two millennia, the shift grassland in Pacific coastal southern Chile. CHILOE PIEDMONT GLACIER CASTRO LOBE VEGETATION GLACIATION CLIMATE ., lO- -10 ., o North Patagonlan Rain Foreat Glacial rejuvenatlon Cool tempera te, humld .1 0.3 ~ and readvanee (?) Est. summer T; 2' C )( ..: (Podoearpus, Pseudopanax, lower than presant (Younger Oryaa Chron) .. 10.8 a.: ai 11- Notholagus, Myrtaeeae) - 11 ai ... Coollng North Patagonlan Rain Foreat .. 11.8 ~ O 12 - -12 O ;! locally elosed (Myrtaeeae) .. Oeglaclatlon In the Andes Modaratlng condltlona at 700 m.12.300 yr B.P. 412.7 13- Arboreal dlverslllcatlon - 13'13.1 (PlIgerodendron type, Lomatla, Maytenus, Myrtaceae) Subantaretlc Parkland 1.- Glacial retreat Cool, humld (Notholagua, Gramlneae) -1. 111111111111111111111111111111111111111111111111111111111111 11 G L A C I A L M A X I M U M 11111111111111111111111111111111111111111111111111111111111 11 1111 ::::~ 15 - Subantaretle Parkland Glacial rejuvenatlon Cold, humld -15 (Gramlneae, Caryophyllaeeae, and readvance Eat. summer T = .... C Lepldothamnua, Huperzla, lowsr than presant Notholagua) Coollng 16- Arboreal expanalon Glacial retreat Moderatlng condltlona (Notholagua) 17 - - 17.17.0 18- - 16 -19 19- Subantarctlc Parkland Glacial ratreat Cold, humld (Gramlneae, Empetrum, Eat. summer T=~4·C Erleaceae, Lapldothamnua, lower than presant '19.6 Orapetea, Notholagua, 20- Orlmya) - 20 21- -21 11111111111111111111111111111111111111111111111111111111111111 G L A C I A L M A X I M U M 11111111111111111111111111111111111111111111111111111111111111111 • 21.7 FIG. 10. Summary 01 vegetational, glacial, and climatic events related to fluctuations 01 the Castro lobe during late Uanquihue glaciation. Late-glacial at Mayol (Rg. 6) is combined with the lull-glaclal at Dalcahue (Heusser, 1990; Lowell el al., In press). Magellanic Moorland elements are not evident in yr B.P., and have become isolated both on Isla these or in otherlowland, late-glacial records (Villagrán, Grande (Villagrán, 1991 b) and in Chiloé Continental 1985, 1988a). Elements appear to have migrated to (Heusser et al., 1992). Earlier, during the full-glacial the cordillera, following the glacial advance of 1 4,700 under colder conditions, moorland communities were 44 QUATERNARY POLLEN RECORDS FROM THE ARCHIPIÉLAGO DE CHILOÉ ••• widely distributec at low altitudes beyond the ice front tions during the last glacial maximum (Heusser and on northeastern Isla Grande (Villagrán, 1988b, 1990, van de Geer, 1994); in the Northern Hemisphere, ice 1993). Their pres:nce at Taiquemó (Fig. 1) extends to rafting events (YO, H 1, and H2) that punctuate the approximately 43,000 yr B.P. (Heusser, 1990). behavior of the Laurentide ice sheet (Bond et al., In conclusion, stepwise deglaciation, following a 1993; Bond and Lotti, 1995) follow the cycling of maximum stand ofthe late Llanquihue Castro lobe on glacial advances/cooling discernible in the Southern Isla Grande at close to 21,000 yr B.P., included a Hemisphere. second maximum at approximately 14,700 yr B.P. Cooling relatedtothe Younger Dryas Chron seen Climatic interpretation ofthe radiocarbon-dated pollen in the Chiloé records, despite a source of controversy records covering the full-glacial and late-glacial in southern South America(Heusser, 1993), is reported suggests cycles oIlong-termcooling andcomparatively from northern South America (Kuhry et al., 1993), rapid warming, respectively, leading up to and northwestern North America (Mathewes, 1993), succeeding times of maxima. This order of events Atlantic Canada (Mott et al., 1986) and Scandinavia centers on the 14,700-yr B.P. maximum, but is also (Paus, 1989), among other geographic regions. implied by evidence for cooler climate at the time of Although Chiloé pol!en zones show shifts with an the Younger Dryas Chron (11,000-10,000 yr B.P.) . inferred drop of temperature at the time of the Younger Cooling preceding maxima appears to have been Dryas, the Southern Andes have yet to yield evidence millennial in extent, whereas successive warming of corresponding glacial activity. The converse of this was of shorter duration, apparently, accountable in situation exists in New Zealand, where pollen data centuries. (McGlone, 1988) provide noclearindication ofclimatic Paleoenvironments and times of maxima of the change during glacial advance of Younger Dryas age, Castro lobe bear a close relationship to other records which most recently has been demonstrated for the on a global scale (Lowell et al., in press). The emerging Franz Josef Glacier in the Southern Alps of South pattern is recogrizable in marine sediments that are Island (Denton and Hendy, 1994). The variable nature tied to oxygen isotope stratigraphy in both polar of the evidence, or lack of it, for colder climate of hemispheres. In the Southwest Pacific at oxygen iso Younger Dryas age is possiblycaused by low intensity/ tope stage 2, pollen of grasses and other herbs short duration forcing factors, linked to the irregular reflects the mostly treeless vegetation that dominated ecophysiological responses of different plant species. South Island, New Zealand under subantarctic condi- ACKNOWLEDGEMENTS This study in collaboration with the Servicio Nacio laboratory processing of samples, C.T. Porter for nal de Geología y Minería (SERNAGEOMIN) was showing the authors the site at Punta Tentén, the supported by the National Science Foundation, Radiological Dating Laboratory, Trondheim, Norway National Geographic Society, National Oceanic and for radiocarbon dates, and C. Villagrán and M. Pino Atmospheric Administration, and Norwegian Research (Universidad de Chile and Universidad Austral de Council. The authors thank L. E. Heusser, (Lamont Chile, respectively) for reviewing the manuscript. Doherty Earth Observatory, Palisades, New York), for REFERENCES Aaby, B. 1986. Paleoecological studyofmires./nHandbook Archipelago, Chile. Jouma/of8íogeography, Vol. 14, p. of Paleoecology and Paleohydrology (Berglund, S.E.; 367-376. editor). Wi/ey, p. 145-164. New York. Armesto,J.J.; Fuentes, E.A. 1988. Treespeciesregeneration Armesto, J.J.; Figueroa, J. 1987. 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