ELSEVIER Palaeogeography, Palaeoclimatology, Palaeoecology 155 (2000) 155–176

The last glacial cycle from the humid tropics of northeastern Australia:comparison of a terrestrial and a marine record

Patrick T. Moss, A. Peter Kershaw *

Centre for Palynology and Palaeoecology, Department of Geography and Environmental Science, Monash University,Clayton, Vic. 3168, Australia

Received 26 January 1998; accepted 28 April 1999

Abstract

A detailed pollen record from the Ocean Drilling Program Site 820 core, located on the upper part of the continentalslope off the coast of northeast Queensland, was constructed to compare with the existing pollen record from Lynch’sCrater on the adjacent Atherton Tableland and allow the production of a regional picture of vegetation and environmentalchange through the last glacial cycle. Some broad similarities in patterns of vegetation change are revealed, despite thedifferences between sites and their pollen catchments, which can be related largely to global climate and sea-level changes.The original estimated time scale of the Lynch’s Crater record is largely confirmed from comparison with the morethoroughly dated ODP record. Conversely, the Lynch’s Crater pollen record has assisted in dating problematic parts of theODP record. In contrast to Lynch’s Crater, which reveals a sharp and sustained reduction in drier araucarian forest around38,000 yrs BP, considered to have been the result of burning by Aboriginal people, the ODP record indicates, most likely, astepwise reduction, dating from 140,000 yrs BP or beyond. The earliest reduction shows lack of a clear connection betweenAraucaria decline and increased burning and suggests that people may not have been involved at this stage. However, afurther decline in araucarian forest, possibly around 45,000 yrs BP, which has a more substantial environmental impact andis not related to a time of major climate change, is likely, at least partially, the result of human burning. The suggestion,from the ODP core oxygen isotope record, of a regional sea-surface temperature increase of around 4ºC between about400,000 and 250,000 yrs BP, may have had some influence on the overall decline in Araucaria and its replacement bysclerophyll vegetation. 2000 Elsevier Science B.V. All rights reserved.

Keywords: Australia; tropics; late Quaternary; climate change; terrestrial palynology; marine palynology; rainforest history

1. Introduction

The long, continuous palynological record fromLynch’s Crater on the Atherton Tableland (Kershaw,1976, 1986) has, for many years, provided the stan-dard for late Quaternary environmental change in

Ł Corresponding author. Tel. C61-3-9905-2927; Fax: C61-3-9905-2948; E-mail: peter.kershaw@arts.monash.edu.au

northeastern Australia. The record indicates sub-stantial vegetation variation in response to climaticoscillations as well as sustained changes in taxonand community distributions. However, this smallvolcanic crater provides a limited spatial picture andone which may be unrepresentative of the broaderregion due to the steep altitudinal and rainfall gradi-ents of the Tableland area. Of special interest is anyregional expression of the decline of drier araucarian

0031-0182/00/$ – see front matter 2000 Elsevier Science B.V. All rights reserved.PII: S 0 0 3 1 - 0 1 8 2 ( 9 9 ) 0 0 0 9 9 - 1

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forest in association with increased burning aroundLynch’s Crater about 38,000 yrs BP which has beententatively attributed to the activities of Aboriginalpeople. Furthermore, that part of the record be-yond the effective limit of radiocarbon dating, about40,000 yrs BP, has no firm age control.

The opportunity to produce a more regional andbetter dated record was provided by the retrieval ofmarine cores on the continental slope adjacent to theAtherton Tableland by the Ocean Drilling Program,Leg 133 (Davies et al., 1991). Preliminary palyno-logical results indicated good pollen representationthrough much of the 1.4 Ma core sequence (Ker-shaw et al., 1993) with age control provided by adetailed oxygen isotope record for the last 700,000years (Peerdeman et al., 1993), radiocarbon dates forthe most recent sediments (Peerdeman and Davies,1993), and marine microfossil stratigraphy (Peerde-man et al., 1993; Wei and Gartner, 1993). The pollenrecord suggests that the initiation of the declinein araucarian forest occurred some time betweenabout 150,000 and 100,000 yrs BP, much earlierthan around Lynch’s Crater but the record resolu-tion was too coarse to allow further comparisons.Subsequently, one of us (PTM) has been producinga detailed palynological record from the upper partof this marine sequence to provide a much firmerbasis for comparative study. This paper provides acomparison for the period covering at least the lastglacial cycle.

2. Regional setting

The location of sites in relation to major envi-ronmental features is shown in Fig. 1. Major phys-iographic features are aligned approximately north–south. From the coast inland there is a low coastalrange, separated by a coastal plain from the graniticEastern Highlands which rise to 1600 m and containthe highest mountains in Queensland. The MulgraveRiver valley partly separates the Eastern Highlandsfrom the basaltic Atherton Tableland, an undulatingplateau ranging between 700 and 800 m elevation,which is flanked by the ‘Great Dividing Range’ onits western side. The region is drained largely bythe Barron and Mulgrave=Russell river systems. Offthe coast there is the continental shelf, some 40–80

km in width, that supports islands of the Great Bar-rier Reef. The shelf margin slopes steeply into theQueensland Trough.

The variable physiography has resulted in markedclimatic gradients. Rainfall is high along the coastand in the Eastern Highlands, and falls dramat-ically inland. Weather patterns are dominated bythe southeasterly trades that produce much of therain, although this is supplemented by monsoonalnorthwesterlies and occasional cyclones. Most rainfalls in summer but almost continuous cloud covermaintains moist conditions throughout the year onthe higher ranges. Mean annual temperatures exceed24ºC along the coast and fall to below 21ºC on theTableland and to below 17ºC on the highest ranges.

Natural vegetation is dominated by a variety ofrainforest types (Tracey, 1982) existing under rainfalltotals >1500 mm. These give way abruptly or acrossa narrow ecotone of wet sclerophyll forest to openforest or woodland characterised by species of Eu-calyptus or Casuarinaceae in the drier western partof the region. Variations of this pattern relate largelyto topography with Melaleuca woodland and cyper-aceous swamp communities replacing rainforest inlowland areas with impeded drainage. Diverse man-grove communities with extensive areas dominatedby species of Rhizophoraceae occur within estuariesand around the mouths of major rivers. Araucarianrainforest has a very restricted distribution, largelyconfined to dry, fire-protected stream gullies androcky outcrops particularly along the coast and onsome offshore islands.

3. Sites

Lynch’s Crater (17º220S, 145º420E) occurs at analtitude of 760 m within the southeastern part ofthe Atherton Tableland. The vegetation around thesite, prior to clearance this century, was complexmesophyll vine forest or lowland tropical rainforest.The high-altitude occurrence of this rainforest typearound the crater is due to the high nutrient statusof basaltic soils which compensates for reduced tem-peratures. From BIOCLIM (Busby, 1991) estimates,the mean annual temperature is 20.4ºC while meanannual precipitation is 2570 mm. Because of regulardrizzle associated with frequent cloud cover during

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Fig. 1. Location of Lynch’s Crater and ODP Site 820 in relation to major environmental features of the humid tropics region.

the winter months, rainfall is less seasonal than atlower altitudes and an average of 61 mm falls duringthe driest month.

The cores from ODP site 820 (16º380S, 146º180E)were collected from 280 m of water on the continen-tal slope, seaward of the Grafton Passage. The siteis approximately 8 km east of the nearest reef andabout 45 km from the present shoreline.

4. Site records

The records presented (Figs. 2 and 3) most likelyextend from the present to the later part of marineoxygen isotope stage 6 (Martinson et al., 1987). Apreliminary chronology for the ODP record is pro-vided by one of the two original interpretations of theisotope record undertaken on the core (Peerdeman etal., 1993). Dating of the Lynch’s Crater record isbased on extrapolation beyond the limit of radiocar-bon dating, taking into account the moisture content

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of the sediments (Kershaw, 1980), and curve match-ing with the marine isotope record (Kershaw, 1986).On the basis of these chronologies, the two coreshave relatively rapid and similar average sedimentaccumulation rates and the similar sampling interval,some 20 or 40 cm for the ODP core and predom-inantly 20 cm for the Lynch’s Crater core, makesfor realistic comparisons. The Lynch’s Crater coreis composed of organic lake mud from the base toabout 10 m depth where it is succeeded by detritusderived from herbaceous swamp (Kershaw, 1985).The ODP core sediments consist predominantly ofa variable mixture of marine-derived carbonates andterrigenous clays, silts and fine sands (Glenn et al.,1993; Feary and Jarrard, 1993). The input of ter-rigenous material is generally higher during periodsof less negative oxygen isotope values, i.e. duringinterglacial and interstadial periods.

Samples for pollen and charcoal analysis wereprepared by standard KOH, acetolysis and HF pro-cedures for Lynch’s Crater but this methodology wasnot successful on the ODP core material. Instead, acombination of sodium pyrophosphate and heavy liq-uid separation using a bromoform–alcohol mixturewith a density of 2.0 produced the desired results.

A pollen sum of arboreal rainforest and sclero-phyll taxa was selected as the most appropriate forcomparative purposes (Figs. 2 and 3). This excludedmangroves, which are confined almost exclusivelyto the marine record, and Poaceae, which, althoughgenerally a regional indicator of open vegetation, hasformed a major component of the swamp vegetationwithin the upper part of the Lynch’s Crater record.Values for Poaceae are included on both diagramsand those for mangroves appear on the ODP dia-gram, but percentages for both plant groups werecalculated outside the sum. Only those arboreal taxawhich have relatively high representation in bothdiagrams or are diagnostic are shown on Figs. 2and 3. These are the rainforest conifers Araucaria,Agathis, Podocarpus and Dacrydium, the rainforestangiosperm trees Macaranga, Trema, Celtis, Cunon-iaceae, Elaeocarpus and Olea, and the sclerophylltaxa Casuarinaceae and Eucalyptus type. They in-clude almost all the identifiable major arboreal taxaof ODP site 820 but exclude a number of major taxarecorded at Lynch’s Crater. However, the majorityof these exclusions, notably Syzygium complex, Ra-

panea, Oraniopsis and Archontophoenix, were dis-covered from a recent study of the marginal sedi-ments of Lynch’s Crater (Bohte and Kershaw, 1999)to represent predominantly local swamp forest ratherthan regional vegetation. Dacrydium was also iden-tified as a component of this swamp forest but hasbeen retained in the sum because of its stratigraphicvalue. In addition to the individual pollen taxa, sum-mary diagrams of the rainforest conifers, rainforestangiosperms, and sclerophyll trees are also shown.

Other graphed features include the radiometricdates, the oxygen isotope record and biostratigraphicmarkers for the ODP Site 820 diagram, and charcoalparticle concentrations, determined on counts of par-ticles greater than 10 µm maximum diameter, as anindicator of fire activity.

The diagrams have been stratigraphically dividedin a way that may facilitate comparison with eachother and with records from other regions. The basisof the classification is the marine isotope record.However, due to uncertainties in the relationshipbetween the isotope stratigraphy (Martinson et al.,1987) and the isotope record of ODP 820, and inthe timescale of Lynch’s Crater beyond the limit ofradiocarbon dating, individual divisions are referredto as phases rather than isotopic stages or pollenzones.

5. Modern vegetation–pollen–environmentalrelationships

To provide some basis for interpretation of therecords, it is valuable to examine major present-daydistributional features of the selected taxa.

From the comprehensive rainforest data set (644sites ð1422 species) of Webb et al. (1984) and thepredicted climatic ranges of species incorporated inthe selected taxa (Busby, 1991), the ranges of therainforest taxa in relation to mean annual tempera-ture and rainfall, as well as mean annual precipitationof the driest month, which is an indication of sea-sonality critical to survival of many taxa, are plottedon Fig. 4. For the sake of clarity and to emphasisethe primary areas of plant taxon distributions, themedian and 25–75 percentile values are shown forthe annual parameters and the median is shown forthe precipitation of the driest month.

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Fig. 2. Selected features from that part of the pollen diagram from Lynch’s Crater which is considered to cover over the last glacialcycle. Different shadings for rainforest gymnosperm, rainforest angiosperm and sclerophyll tree taxon curves are designed to facilitatecomparisons both within this diagram and between his diagram and that portrayed in Fig. 3. See Table 1 for details and complete listingof radiocarbon dates.

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Fig. 3. Selected features of the pollen record and chronostratigraphy from ODP Site 820. Dotted lines indicate positions of possiblehiatuses within the record. Different shadings for rainforest gymnosperm, rainforest angiosperm and sclerophyll tree taxon curves aredesigned to facilitate comparisons both within this diagram and between this diagram and that portrayed in Fig. 2. See Table 2 for detailsof radiocarbon, isotopic and biostratigraphic ages.

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Fig. 4. Median and 25–75 percentile ranges for mean annual precipitation and temperature and median for precipitation of the driestmonth of major rainforest taxa recorded in the Lynch’s Crater and ODP Site 820 pollen diagrams. Estimates are derived from thebioclimatic analysis of Australian rainforest site data. Bioclimatic data for Lynch’s Crater are also included.

The mean values of taxa cover a temperaturerange from about 18º to 25ºC and a precipitationrange from about 1270 to 2050 mm. The inclu-sion of 25 to 75 percentile values extends theseranges to almost 15–27ºC and about 1000 to 2500mm, respectively. Median precipitation of the driestmonth varies from about 28 to 85 mm. Althoughthe ranges are broad, taxon ranges overlap. OnlyTrema and Macaranga at one extreme and Araucariaand Olea at the other, fail to, or only just, over-lap in both precipitation and temperature. A majorpart of the explanation for lack of overlap in Trema,Olea and Araucaria is that they contain only one ortwo species while most of the remainder have manyspecies with very different biogeographic patterns.

In general terms, Trema, Macaranga and Celtisindicate warmest rainforest climates whereas Cunon-iaceae, Olea and perhaps Araucaria indicate thecoolest forest zone. Araucaria and Olea indicate thedriest conditions. Celtis is most tolerant of dry win-ters and Cunoniaceae, and Elaeocarpus to a lesserdegree, are least tolerant of dry winters. Values forLynch’s Crater have also been included on Fig. 4 and

it is clear that present-day precipitation is at or abovethe percentile ranges of the selected taxa.

A more direct relationship between taxa and cli-mate from the study area can be examined from themodern pollen data set collected from a range ofrainforest and rainforest margin environments withinthe wet tropics region (Kershaw, 1976; Kershaw andBulman, 1994). Plotting the location of these 14samples against BIOCLIM-generated estimates oftemperature and precipitation (Fig. 5) shows a re-duced temperature range in comparison with that inFig. 4, consistent with the limited latitudinal spread.The plot also shows higher precipitation values thanthose in Fig. 4, a reflection of both high rainfall inthe area relative to that of Australian rainforest gen-erally, and the truncated nature of rainforest alongthe drier margin. Pollen samples, which were takenfrom vegetation plots incorporated within the Webbet al. (1984) rainforest data set, are concentrated inthe more accessible lowland and plateau areas. Thelack of modern pollen samples from lowland areasdrier than about 2000 mm reflects the lack of suchenvironments within the study region at present.

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Fig. 5. Climatic ranges for highest representation of major rainforest taxa in the Lynch’s Crater and ODP Site 820 pollen diagrams inrelation to bioclimatic estimates for modern pollen samples from northeast Queensland rainforests. The extent of penetration of highvalues for the sclerophyll taxon Casuarinaceae along the temperature and precipitation gradients, and the bioclimatic values for Lynch’sCrater are also shown.

Pollen taxon ranges reflect the major occurrenceof poorly represented pollen taxa and the highest per-centage values of common taxa. Pollen of Trema isabundant in lowland rainforest, Elaeocarpus pollenhas high values in low-altitude, high-rainfall rain-forests, Cunoniaceae pollen is prevalent in high-alti-tude forests and pollen of Olea, Podocarpus andAgathis are found together in the fairly dry middle-altitude site samples. Macaranga pollen is abundantin driest-forest samples at middle elevations. Insuf-ficient pollen of Celtis was recorded to determine apreferred distribution, possibly because of a lack ofdry warm conditions. As expected from the rare oc-currences of plants in the region, no Araucaria pollenwas found. The distribution of high pollen values forthe sclerophyll taxon Casuarinaceae is also shown. Itindicates significant pollen representation in samplesfrom drier and cooler rainforest sites although plantsare restricted to open forests. The other major scle-rophyll pollen taxon, Eucalyptus, is well representedin many of the rainforest samples but reveals no clearspatial pattern. The position of Lynch’s Crater is againplotted. Here the site falls usefully within the generalclimatic range of the plot samples but outside the ma-jor distributions of any of the selected taxa.

In comparison with plant taxon ranges, many ofthe pollen taxa exhibit predicted distributions in rela-tion to temperature. Trema pollen is characteristic ofthe warmest sites, Cunoniaceae pollen is dominant inthe coolest, Elaeocarpus pollen has a broad low- tomid-temperature distribution, and Agathis pollen hasa narrow representation within the middle part of thetemperature gradient. Relationships with respect toprecipitation are not as close, but the higher rainfalldistributions of Trema, Elaeocarpus and Cunoni-aceae in comparison with the other taxa is reflectedin their abundance in pollen samples. The least satis-factory patterns are for Olea and Macaranga pollen.A possible explanation with Macaranga is, that be-ing predominantly a successional plant, its pollenabundance is greatest in the more disturbed forestsclose to drier rainforest margins. Overall, consider-ing the great differences in data sets, one being basedon presence and absence of plants at a continentalscale and the other on modern pollen representationin a limited number of sites within a restricted area,comparisons are very satisfactory. It is relevant alsothat the selected pollen taxa are only 8 out of 140recorded in the modern pollen data set, and that over-representation by poorly dispersed taxa in samples

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taken from beneath the rainforest canopy will havedistorted the relative representation of the selectedtaxa.

Other modern pollen data from northeastern Aus-tralia have established that there is little aerial dis-persal of rainforest pollen beyond rainforest marginsbut have confirmed that taxa of more open vegeta-tion, particularly Eucalyptus, Casuarinaceae and, toa certain extent Poaceae, have much wider dispersalability (Kershaw, 1976; Crowley et al., 1994). Sur-face samples from mangroves and araucarian forestshave been shown to be dominated by pollen of theirmajor components, Rhizophoraceae and Araucaria,respectively (Kershaw, 1976; Grindrod, 1988; Crow-ley et al., 1994). In both cases, aerial pollen dispersalis restricted.

6. Fossil pollen representation

6.1. Taxon abundance

In terms of relative abundance of the selectedtaxa, there are marked similarities between theLynch’s Crater (Fig. 2) and ODP (Fig. 3) pollen di-agrams despite major differences in location, pollencatchment area, and most likely means of pollentransport. Pollen of Araucaria, Olea, Cunoniaceae,Elaeocarpus and Eucalyptus comp. have high val-ues, at least during some phases, while Trema,Macaranga and Celtis have low representation. Ex-ceptions to this pattern are the mangroves which areconfined to the marine record, and differential rep-resentation of Podocarpus, Casuarinaceae, Agathis,Dacrydium and Poaceae. Casuarinaceae is well rep-resented in the modern pollen samples from higheraltitudes and it could be that, in the past, as welltoday, component species have been excluded fromthe coastal lowlands. However, Cunoniaceae, whichhas a similar high-altitude distribution, achieves highpollen values in the marine record.

The much higher representation of Dacrydium, ataxon no longer present in Australia, in the Lynch’sCrater than the ODP record can be explained by itspast occurrence in swamp forest which was aroundthe margins of the site until at least the early part ofthe last glacial period (Bohte and Kershaw, 1999).The only extant species with a similar pollen mor-

phology to the Dacrydium is D. guillauminii whichhas a very restricted distribution in New Caledo-nia. The species occurs only in four localities onthe swampy margins of rivers and lakes and is con-sidered relict and vulnerable due to human burning(Jaffre, 1995). Such an ecology for the AustralianDacrydium could also explain why the taxon wasalso represented in the ODP record in addition to itsgeneral demise.

Higher values of Agathis within the marine coremay provide a better indication of the regional im-portance of the taxon as component species tendto avoid the basaltic soils which surround Lynch’sCrater. There may also have been some confusion inidentification of poorly preserved specimens betweenclosely related Agathis and Araucaria. As previouslymentioned, there is a relationship between the gen-eral increase in Poaceae pollen percentages and theestablishment of swamp vegetation at Lynch’s Crater.Therefore, although Poaceae values in the upper partof this record are similar to those in the marinerecord, the regional component, as indicated in theolder part of the record, is much lower than in themarine record.

The reason for low levels of Podocarpus pollen inthe ODP record relative to those at Lynch’s Crateris difficult to explain but may relate to the pollenpreparation technique. Pollen of Podocarpus, as wellas Casuarinaceae, achieved much higher proportionsin the original study of ODP 820 (Kershaw et al.,1993). One contributing factor may be that, in the1993 study, the larger 8 µm sieve size together withtogether with the use of an ultrasonic needle, ap-peared to eliminate most of the smaller grains, par-ticularly Elaeocarpus and Cunoniaceae, effectivelyincreasing the percentages of the larger grains.

6.2. Taxon relationships

Although there are similarities in the general rep-resentation of many taxa in Figs. 2 and 3, a morecritical feature of the diagrams for environmentalreconstruction and stratigraphic comparison is thepattern of temporal changes. In order to investigatetaxon relationships, principal components analysisusing the correlation coefficient option in the statis-tical package MINITAB was employed to comparethe relative abundance of taxa in all samples from

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Fig. 6. Plot of first two axes from principal components analysisbased on percentage values of major taxa recorded in the Lynch’sCrater pollen diagram. Taxa are: Ag D Agathis, Ar D Araucaria,Ca D Casuarinaceae, Ce D Celtis, Cu D Cunoniaceae, DaD Dacrydium, E D Elaeocarpus, Eu D Eucalyptus, Ma DMacaranga, Ol D Olea, P D Poaceae, Po D Podocarpus, Tr DTrema.

Fig. 7. Plot of first two axes from principal components analysisbased on percentage values of major taxa recorded in the ODPSite 820 pollen diagram. Taxa are: Ag D Agathis, Ar D Arau-caria, Ca D Casuarinaceae, Ce D Celtis, Cu D Cunoniaceae,Da D Dacrydium, E D Elaeocarpus, Eu D Eucalyptus, Ma DMacaranga, Ol D Olea, P D Poaceae, Po D Podocarpus, Tr DTrema.

the Lynch’s Crater and ODP 820 diagrams. The firsttwo components from these analyses are shown onthe ordination diagrams of Figs. 6 and 7.

In the Lynch’s Crater PCA (Fig. 6), the first axis(which explains 27% of the variance) relates to pre-cipitation with the sclerophyll taxa Casuarinaceae

and Eucalyptus at one extreme and the wet rainfor-est indicators Cunoniaceae, Elaeocarpus and Tremaat the other. The first axis origin clearly separatesPoaceae, Podocarpus and Araucaria with Casuari-naceae and Eucalyptus as a ‘drier’ assemblage withPodocarpus and Araucaria separated from the scle-rophyll taxa along axis 2. All taxa on the positiveside of axis 1 are components of rainforest and theirpositions along the axis relate fairly well to theirpredicted positions along a rainfall gradient frommodern data. The second axis (explaining 17% of thevariance) separates Elaeocarpus and Cunoniaceae asthe dominant taxa of ‘wet’ forest from Macaranga,Celtis and Trema, which characterised pollen assem-blages from warmer rainforest in Fig. 4, and Agathisand Olea, which occur in relatively dry forest. The‘extinct’ Dacrydium species falls between these lat-ter two groupings.

The PCA ordination diagram for taxa from the ma-rine core provides less differentiation of taxa. How-ever, the first axis (which explains 20% of the vari-ance) separates taxa from wetter and=or warmer rain-forests, which include Elaeocarpus, Cunoniaceae,Celtis and Trema, from those of drier middle altitudeforests such as Olea, Podocarpus, and Agathis. Maca-ranga is included with the ‘wetter’ taxa in line withthe BIOCLIM estimate rather than the surface sam-ple data, although, unlike in the Lynch’s Crater ordi-nation, it is separated from Celtis and Trema alongthe second axis. Araucaria and Poaceae are part ofthe dry element group on axis 1. All contained taxaare separated along axis 2 (which explains 19% ofthe variance) except for Agathis and Araucaria whichlie close together. It is interesting that on both theLynch’s Crater and ODP PCA diagrams, pollen ofthe rainforest conifers Agathis, Araucaria and Podo-carpus are at the positive extreme of the second axis,and that of Dacrydium is also close to this extreme(Figs. 6 and 7). This pattern may suggest that theconifers have had a distinctive response to environ-mental change. Certainly all have suffered a generaldecline through time in at least one of the records. Un-like the Lynch’s Crater record, Eucalyptus and Casua-rinaceae, both found close to the axis origins, appearto have played little part in the construction of the first2 axes. However, both are clearly separated from allother taxa along the third axis of the PCA on the ODPdata set which explains 14% of variance.

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7. Vegetation and environmental reconstructions

7.1. Lynch’s Crater

Although the Lynch’s Crater pollen record has beeninterpreted previously and climate conditions havebeen quantified from BIOCLIM estimates of inferreddominant community types (Kershaw, 1986) andoverlapping ranges of selected taxa (Kershaw and Nix,1989), the modern data presented here allow some re-finement of palaeovegetation and palaeoclimatic esti-mates. It is also important to provide reconstructionsthat can be compared with those from ODP 820.

The earliest period, phase L6, is characterisedby high values for the rainforest gymnosperms andtaxa of open-canopied vegetation, suggesting a mixof araucarian and sclerophyll forest or woodlandaround the site. It is likely that the araucarian forestexisted on the basaltic soils with open Casuarinaceaeand eucalypt forest or woodland on poorer metamor-phic soils. From the present-day distribution of thesevegetation types, it has been estimated that rainfallwould have been at least 1000 mm lower than today(Kershaw, 1986). The modern pollen data presentedsupport this estimate and also suggest that the sea-sonal distribution of rainfall was equal to or less thantoday. Temperature estimates are difficult to makebut the presence of Araucaria, Olea and Podocar-pus suggests that temperatures may have been sim-ilar to, or marginally lower than, present. However,within phase L6, there are minor pollen peaks inrainforest angiosperms, particularly Trema, Cunoni-aceae (tricolpate) and Elaeocarpus and a decrease inAraucaria pollen suggesting a temporary expansionof complex rainforest under increased rainfall andtemperature. The increase in precipitation may havebeen limited, from about 1400 to 1600 mm, but theabundance of Araucaria and Trema pollen indicatethat temperatures may have exceeded those of today.The highest values for both Eucalyptus and Poaceaeoccur in the upper part and suggest that this mayhave been the driest part of the phase.

Phase L5 is characterised by high pollen valuesof rainforest angiosperms indicating a predominanceof complex rainforest around the site. The boundarybetween phases L6 and L5 is very abrupt and marksa change from dry to very wet conditions initiallywith dominance of Cunoniaceae, Elaeocarpus and

Trema pollen, and the almost complete exclusion ofmost drier rainforest elements including the gym-nosperms as well as sclerophyll taxa. High valuesfor Celtis suggest that precipitation may have beenno higher than about 1800 mm and, in combinationwith Trema, that temperatures may have been up to4ºC higher than today. These estimates are consistentwith those from the bioclimatic analysis of Kershawand Nix (1989). However, high values of Cunoni-aceae indicate that temperature levels did not exceedthose of today by much and, in combination withabundant Elaeocarpus pollen, that precipitation wasat least near and possibly above that of today.

After this initial rainforest-dominated part ofphase L5, at a core depth of 37.5 m, there areincreases in sclerophyll taxa which, together withincreases in Olea and conifers and substantial de-clines in Cunoniaceae and Eleaocarpus, indicatea reduction in precipitation. Lower percentages ofTrema and Celtis suggest also a reduction in temper-ature. The BIOCLIM estimates of Kershaw and Nix(1989) of 1500–2000 mm, combined with tempera-tures some 2ºC lower than today seem reasonable.The strong representation of Casuarinaceae duringthis mid-phase L5 period (between depths of 37and 32 m) indicates even lower temperatures, ratherthan a decrease in rainfall, as there is no similarresponse in either the Poaceae or Eucalyptus records.Close to the end of phase L5, at a depth of 27 m,the complex rainforest pollen component increasesagain although not to the same level as in the earlypart of phase L5 and did not affect Trema and Celtis.Climatic conditions were similar to those of today aspredicted by BIOCLIM (Kershaw and Nix, 1989).

The phase L5=L4 boundary is characterised by asharp increase in pollen of sclerophyll trees relativeto those of rainforest. It is also marked by a briefsharp peak in Olea pollen at the end of phase L5 anda similar peak in Casuarinaceae at the beginning ofphase L4. These taxa suggest that a fall in tempera-ture was the predominant cause of the abrupt changeas both Eucalyptus and Poaceae, indicative of drierconditions, increase only gradually. After the tran-sition, phase L4 is marked by dominance of pollenof sclerophyll taxa, Araucaria and Podocarpus, withonly Olea pollen within the rainforest angiospermsshowing a consistent representation. The inferredclimate is the same as that for phase L6.

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The base of phase L3 is distinguished by a peakin pollen of rainforest angiosperms, of which Elaeo-carpus pollen is a major contributor and Trema isinvolved, although proportions of rainforest gym-nosperms and sclerophyll taxa are still high. Thelack of Cunoniaceae and decline in Casuarinaceaesuggest that the response was largely temperaturerelated to a warming to above present-day levels.Subsequently, a pollen assemblage similar to thatof phase L4 returns. The return is also marked bya gradual increase in Poaceae percentages and thisheralds the development of a swamp cover over thelake surface. The degree to which this change in de-positional environment influenced pollen depositionis unknown, but it may have contributed to the rel-ative increase in the obligate wind-dispersed taxonPodocarpus.

There are abrupt changes in the latter part of phaseL3 radiocarbon dated to about 38,000 BP. Pollen ofrainforest conifers declines sharply and then contin-ues to decline to the end of the phase when Dacry-dium appears to become extinct and Araucaria be-comes ‘relictual’. It is likely also that there was areduction in species of Podocarpus. The apparent re-placement of the araucarian forest by sclerophyll veg-etation and perhaps also the extinction of Dacrydiumand other components of swamp forest, most notablythe myrtaceous genus Xanthomyrtus (Bohte and Ker-shaw, 1999), have been attributed to an increase inburning, indicated by a substantial rise in charcoalparticles. The preferred explanation for this burninghas been the additional ignition resulting from the ar-rival and impact of Aboriginal people. A decreasedprecipitation is possible. Dry conditions would haveplaced the araucarian forest and swamp forest undergreater moisture stress, and facilitated their destruc-tion and replacement by fire-promoting sclerophyllcommunities and swamp grasses respectively.

The area around Lynch’s Crater was surroundedby sclerophyll vegetation during the whole of phaseL3 extending into phase L2. From initial high valuesat the end of phase L3, Poaceae falls to levels similarto those of phase L6 suggesting a regional source.It is likely that only an ephemeral lake was presentin the crater preventing the development of a con-tinuous swamp cover. From the present position ofthe rainforest–sclerophyll boundary on basalt soilswithin the region, and the nature of swamp envi-

ronments (Kershaw, 1976), precipitation is likely tohave been less than 1400 mm. There is insufficientrainforest pollen in phase L2 to suggest survivalaround Lynch’s Crater but regular occurrences ofPodocarpus, Olea and Macaranga are enough to in-dicate a regional presence. The increase in Poaceaepollen towards the end of the phase and into phaseL1 suggests a local response to increasing precipita-tion, not registered by the re-emergence of rainforestuntil well into phase L1. A second major phase ofburning accompanies the Poaceae increase suggest-ing more intense human impact, denser vegetationcover regionally and on the swamp surface to carryfire, or a combination of these factors.

The condensed nature of the phase L1 sequenceprevents full elucidation of the vegetation but themiddle section indicates the development of com-plex rainforest very similar to that of the laterpart of phase L5 although sclerophyll trees main-tained higher percentages, perhaps due to ecologicaldrift (Jackson, 1968) with regionally more frequentfires. Locally, however, burning was almost excludedand swamp forest, now lacking some elements, re-invaded the swamp surface (Bohte and Kershaw,1999). This swamp forest was subsequently de-stroyed by fire, about 4500 yrs BP due to humanimpact perhaps combined with increased activity ofthe Southern Oscillation (McGlone et al., 1992). Thesurrounding rainforest was little affected by peopleuntil the arrival of Europeans.

7.2. ODP 820

The vegetation and climate can only be recon-structed in qualitative terms due to the broad catch-ment area and changing proximity of the site toland. During glacial periods of low sea level, thesite would have been as close as 8 km to the coast,some 40 km closer than during high sea-level phases,and water depth would have been as low as 150 m.Consequently, the extent as well as the nature of thepollen catchment is likely to have changed substan-tially through time. Most of the pollen is likely tohave derived via water transport from the Barron andperhaps Mulgrave=Russell rivers through the GraftonPassage, a river system itself during low sea-level pe-riods, to the core site, as the predominant winds arefrom the ocean (Kershaw et al., 1993).

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The first part of the oldest phase (phase P6) ischaracterised by very high values of Araucaria andAgathis pollen, indicating the regional importanceof araucarian forest. Pollen of sclerophyll trees ispoorly represented although grass pollen, perhapsderived largely from lowland swamp environments,has high values. Rainforest angiosperms, of whichCunoniaceae and Elaeocarpus are the most conspic-uous, are poorly represented. Values for charcoalindicate continuous burning and show a rising trend.

In the later part of phase P6 the charcoal curverises more steeply to a pronounced peak just beforethe end of the phase. A reduction in Araucariaceaepollen and its partial replacement by pollen of euca-lypts, which reach highest percentages with the char-coal, may be direct responses to this burning. De-spite this burning and associated increase in pollenof sclerophyll vegetation, there is some increase inthe pollen of rainforest angiosperms, with Celtis andOlea consistently present and Cunoniaceae peakingclose to the end of the phase. The latter two taxa mayhave joined the lowland-distributed Celtis as a resultof a decrease in temperature.

The transition from phase P6 to P5 is markedby a sharp decline in both Eucalyptus pollen andcharcoal, a continuation of the declining trend forAraucaria pollen, and the achievement of highestlevels of pollen of rainforest angiosperms for thediagram. All evidence points to the attainment, inthe early part of phase P5, of highest effective pre-cipitation levels recorded for the period covered bythe diagram, and that, from the importance of Celtis,Trema, Macaranga and Elaeocarpus, these levelswere achieved under highest recorded temperatures.The transition also sees a major peak in mangrovepollen. Both late Quaternary records from coastaltropical environments (Grindrod, 1988) and longtropical marine records (e.g. Wang et al., 1999; vander Kaars et al., 1999) indicate that peaks in man-grove pollen accompany marine transgressions. Con-sequently, it would appear that a major sea-level riseaccompanied and was probably implicated in the in-crease in precipitation during the transition. There is,however, no indication from the pollen data, that thistransgression, which would have drowned a greatdeal of the pollen catchment area, eliminated anycoastal communities which might have characterisedthe continental shelf during the glacial period.

After the initial peak in rainforest, Elaeocarpusand Celtis pollen drop to lower percentages throughthe remainder of the phase, Macaranga pollen virtu-ally disappears and there is some return of Araucariaand Poaceae pollen, but, although Poaceae valueshave increased, sclerophyll tree values remain rela-tively low and Cunoniaceae continues to dominatethe pollen sum. Conditions are clearly somewhatdrier and cooler. There is some indication of a sec-ond peak in rainforest angiosperm pollen in the latterpart of the phase which may indicate some increasein temperature and precipitation. This period is alsomarked by a second peak in charcoal but burningappears to have had little influence on the vegetation.

At the very end of phase P5 a significant de-crease in precipitation and perhaps also temperatureis suggested by reductions in pollen of all remain-ing rainforest angiosperms except for Olea, whichmaintains high values through most of phase P4 andPodocarpus, which attains its highest values for thediagram. A small peak in mangrove pollen, whichmay be indicative of some exposure of the continen-tal shelf with sea-level lowering, accompanies thetransition. Apart from steadily increasing Poaceaevalues, there are no other characteristic features ofthe phase P5=P4 transition or phase P4.

The early part of phase P3 shows a large mangrovepeak indicative of a significant marine transgression,consistent with the decrease in δ18O values of the iso-tope record, but there is little accompanying change indry land pollen taxa apart from a continued increasein Poaceae values. It is possible that sea level roseto a position optimal for the development of exten-sive coastal grassland communities on the continentalshelf. A subsequent decline in Poaceae percentagesis accompanied by an increase in percentages of bothrainforest taxa and sclerophyll tree pollen, but littlechange in representation of the Araucariaceae whichhave remained relatively stable since the middle ofphase P5. It is possible that phase P3 is reflectingvegetation changes associated with the expansion ofterrestrial environments with sediment build-up alongthe coast under relatively stable climatic conditions. Ifthis is the case, then it suggests that the Araucariaceaewere divorced from the coastal lowlands, probablygrowing, like today, on elevated ground. The periodalso witnessed an increasing incidence of fire basedon higher charcoal particle concentrations.

170 P.T. Moss, A.P. Kershaw / Palaeogeography, Palaeoclimatology, Palaeoecology 155 (2000) 155–176

Towards the end of phase P3, there are dramaticchanges in the pollen record. The previously sta-ble record of Araucariaceae undergoes a dramaticand, in the case of Araucaria, sustained decline.Conditions appear to have been relatively dry as an-giosperm rainforest taxa have low representation butit is likely that fire was the major agent of araucarianforest destruction as charcoal values achieve theirhighest levels for the diagram. It is probable thatfire worked in association with fire-promoting euca-lypts which also peak at this time. These changesin dry land pollen coincide with high mangrovevalues. Although no consistent relationship betweenprevious mangrove peaks and dry land vegetationand environments has been established, this peak isclearly different in being prolonged and embracingboth high burning levels and the peak in Eucalyp-tus pollen. It is also not accompanied by a changein oxygen isotope values which would indicate theexistence of a marine transgression. As suggestedby Kershaw et al. (1993), such a major upheavalwithin the regional vegetation as a result of increasedburning would have resulted in massive soil erosionwhich could have choked the river systems and es-tuaries along the existing coastline, substantially in-creasing substrates available for mangrove colonisa-tion.

At the very end of phase P3, conditions appearto return to those experienced around the middleof the phase although mangroves maintain a sig-nificant presence, and eucalypts replaced Araucaria.The peak in Cunoniaceae percentages indicates someincrease in precipitation and, without significant rep-resentation of lowland forest pollen indicators, rela-tively cool conditions. The transition between phasesP3 and P2 sees the last occurrence of Dacrydium.

Phase P2 shows total dominance of Poaceaepollen, moderate values of Eucalyptus and notablepercentages of only Cunoniaceae, Agathis and Oleafrom the rainforest pollen component. There is a ma-jor increase in mangrove pollen percentages withinthe latter part of the phase which, following the peakin Poaceae as in the phase P6=P5 mangrove peak,probably represents the last major marine transgres-sion. The maintenance of high Poaceae levels, duringthis period of changing coastal environments sug-gests a major regional development of grassland orvery open woodland vegetation under low rainfall.

The low charcoal values suggest that the vegetationwas too open to carry frequent or intense fires.

Mangrove values peak at the base of phase P1 andthere is a lag before an increase in percentages ofpollen taxa, particularly Cunoniaceae and Elaeocar-pus, indicating an expansion of rainforest vegetation.Rainforest angiosperm values reach as high as thoseat the base of phase P5, and indicate high rainfall.Low percentages of lowland rainforest taxa suggestcooler conditions than those of phase P5. In themiddle of the phase there are significant reductionsin Agathis and Poaceae pollen percentages suggest-ing maximum expansion in the phase of complexrainforest.

8. Establishment of a regionalchronostratigraphy

Radiocarbon dates on the upper parts of both se-quences (Tables 1–2) indicate chronologic integrityback to the effective limit of radiocarbon dating.Some parts of the Lynch’s Crater sequence are verycondensed and it is possible that there may havebeen short hiatuses in the upper part, particularlyat the very end of the Pleistocene (oxygen isotopestage 2) and in the late Holocene. However, the freshnature of swamp and lake sediments suggests contin-uous sedimentation beyond the dating limit of about40,000 yrs BP. With the ODP record, the Holoceneappears to have a more rapid sedimentation rate thanthe Late Pleistocene although the sequence is consid-ered to be continuous back to about 43,000 yrs BP

Table 1Radiocarbon dates from Lynch’s Crater (Kershaw, 1976)

Depth Radiocarbon age Lab. number(cm) (14C yrs BP)

65–80 6,850 š 90 ANU-95880–100 7,090 š 100 ANU-959

140–160 10,390 š 130 ANU-960200–220 15,510 š 195 ANU-961430–440 19,670 š 320 ANU-962529–540 25,700 š 800 ANU-738

32,100C1360�1160 ANU 963

840–860 37,940C1870�1520 ANU-964

1000–1020 >37,300 ANU-965

P.T. Moss, A.P. Kershaw / Palaeogeography, Palaeoclimatology, Palaeoecology 155 (2000) 155–176 171

Table 2Age determinations for the ODP 820 core; AMS radiocarbondates from University of Waikato, New Zealand (from Peerde-man and Davies, 1993)

Depth Radiocarbon age(cm) (14C yrs BP)

243–248 4,944 š 64325–327 6,304 š 60365–367 6,968 š 65393–398 7,396 š 67425–427 7,475 š 71564–568 8,954 š 88605–607 9,365 š 83693–698 14,780 š 130725–727 31,000 š 1100745–747 41,200 š 1300773–780 43,600 š 1600

(Peerdeman and Davies, 1993). From sedimentolog-ical evidence, these authors interpret this part of therecord as indicating a sea-level regression (41,000–18,000 yrs BP), a lowstand centred on 18,000 yrs BP,an early (18,000–9400 yrs BP) and late (9400–4900yrs BP) transgression, and a highstand (4900 yrsBP to present). The higher sedimentation rate duringthe Holocene is attributed to increased input of ter-rigenous mud. The ODP pollen record reflects thispattern of sea-level change with reduced rainforestand increased Poaceae representation during the re-gression to a lowstand at the Last Glacial Maximumand then a reversal of these trends after about 9000yrs BP to the mid-Holocene. There is also a strongpeak in mangrove pollen during the transgressivephase. The pollen data, exhibiting highest rainfor-est percentages in the Holocene and high values ofsclerophyll tree or Poaceae pollen during the laterpart of the Pleistocene, suggest a positive relation-ship between precipitation and sea level, and thatthe increased input of terrigenous material during theHolocene is a result of higher rainfall within the area.

There are sufficient similarities between inferredpatterns of vegetation change in the ODP andLynch’s Crater records over much of this radiocar-bon-dated period to provide a basis for stratigraphiccorrelation of older parts of the records. In partic-ular, rainforest, with low representation during theLast Glacial Maximum (phase 2) and the earliestHolocene then increases substantially with the dom-

Table 3Age determinations for the ODP 820 core; biostratigraphic hori-zons from Wei and Gartner (1993)

Datum Depth Age(m) (yrs BP)

LO Emiliani huxleyi acme 11.32–12.82 75,000HO Globigerinoides ruber pink 32.35–31.55 120,000LO Bolliela calida calida 38.45–40.11 140,000 or

200,000HO Emiliani huxleyi 34.82–36.82 275,000

LO D lowest occurrence; HO D highest occurrence.

inance of Cunoniaceae and Elaeocarpus. In bothrecords, Dacrydium has its last occurrence around25,000 to 30,000 yrs BP, according to the radiocar-bon dates. However, there is some age discrepancybetween what is a major feature of both diagramswithin phase L3 and P3 — the sustained declineof Araucaria and associated increases in sclerophylltaxa and a major peak in charcoal. This event isdated to about 38,000 yrs BP at Lynch’s Crater andis clearly beyond the 43,600 yrs BP date from theODP core. However, this discrepancy is not as greatif the statistical errors on the dates are taken intoaccount and the sedimentation rate increased belowthe dated section of the ODP core. Two standard de-viations would give an overlap between the Lynch’sCrater date (34,900 to 41,700 yrs BP) and the ODPdate (40,400 to 46,800 yrs BP).

Beyond the limit of radiocarbon dating, two agemodels have been proposed for the ODP recordbased on a comparison of the detailed oxygen iso-tope record with those of western equatorial Pacificdeep-sea core records (Peerdeman et al., 1993) (seeFig. 3). The first age model, utilising the graphiccorrelation concepts of Prell et al. (1986), identifiedall stage boundaries and almost all isotopic events,and is consistent with the date for the highest occur-rence of Globigerinoides ruber pink and the 140,000yrs BP age option for Bolliela calida calida (seeTables 3–4). With this option the phases identifiedon the ODP pollen diagram (Fig. 3) are equivalent tothe last six isotope stages.

The second model of Peerdeman et al. (1993)is based largely on other biostratigraphic indicators,particularly the lowest occurrence of Emiliani hux-leyi acme and the highest occurrence of Emiliani

172 P.T. Moss, A.P. Kershaw / Palaeogeography, Palaeoclimatology, Palaeoecology 155 (2000) 155–176

Table 4Age determinations for the ODP 820 core; oxygen isotope stageboundaries according to the age models of Peerdeman et al.(1993) (ages from Martinson et al., 1987)

Stage boundary Model Depth Age(m) (yrs BP)

1–2 1 and 2 6.45 12,0002–3 1 and 2 7.78 24,0003–4 1 21.45 59,0004–5 1 23.55 74,0003–5 2 8.02–12.1 <58,000 to ½74,0005–6 1 32.10 130,0006–8 2 34.55–35.8 <186,000 to >245,000

huxleyi. In this model, there appear to be two hia-tuses, an early one between 34.55 and 35.8 m depthwhich covers at least the time interval for stage 7(186,000 to 245,000 yrs BP), and a late one be-tween 8 and 12 m depth that incorporates stage 4(58,000–74,000 yrs BP) and possibly some of stage3. Peerdeman et al. (1993) consider that this secondmodel is more compatible with the biostratigraphicnannofossil ages for the core commonly used inglobally related isotope studies. However, the valid-ity of the use of the last occurrence of E. huxleyimust be open to question as this species occurs inyounger sediments in the Wanganui stratigraphy ofNew Zealand (Naish et al., 1998).

Both the first and second models and all datesindicate that the bulk of the record covers muchof the last glacial cycle and there is little questionthat the transitions from the height of the glacialto the ‘peak’ of the interglacial are represented forboth stages 6 to 5 and stages 2 to 1. These transi-tions are also clearly marked in the phases of bothpollen diagrams with changes from domination bydrier araucarian and=or sclerophyll taxa to highestrepresentation of rainforest. In the ODP record, thesubstantial peaks in mangrove pollen clearly indicatethat there were accompanying major marine trans-gressions. In both diagrams the transitions are fairlyabrupt and conditions during the last interglacialwere more conducive for the spread of rainforestthan the Holocene. From these comparisons, theoriginally proposed time span of the Lynch’s Craterrecord is confirmed.

With regard to the degree of continuity of theODP record, a broad comparison of pollen propor-

tions with highest rainforest representation duringphases 5 and 1 in both diagrams is in general ac-cord with the first age model. However, consideringthe fact that sedimentation rates in the ODP recordappear to be higher at times of increased precip-itation, the duration of phase P5 seems too shortto accommodate the whole of isotope stage 5. Inaddition there is little evidence of the double rain-forest peak recorded in phase L5. Consequently itis considered that isotope stage 5 extends to at leastthe position of the lowest occurrence of Emilianihuxleyi acme, in accordance with the second agemodel. This identifies almost the whole of phaseP5 as equivalent to the Last Interglacial (stage 5e),an interpretation consistent with the oxygen isotoperecord where values are similar to those of stage1. Phase P4 and much of phase P3 are then coolerand relatively warmer and wetter phases respectivelywithin stage 5. The palynological comparisons withLynch’s Crater are reasonable with high percentagesof Cunoniaceae and Elaeocarpus dominating the tworainforest-dominated phases and high Olea percent-ages important within the intervening period and alsoincreasing at the end.

In contrast to the deep-sea core isotope stratigra-phy, both the pollen and isotope data suggest thatonly 3 rather than 5 substages during stage 5 arepresent in the ODP record. One possibility is thatthe hiatus extends into stage 5. However, a similarpattern in the continuous record from Lynch’s Cratersuggests that this may be a regional feature.

Acceptance of the second age model has bearingon the timing of the Araucaria decline. In contrastto the first age model, the event may have occurredwithin the hiatus, suggesting an earlier date possi-bly from about 74,000 yrs BP to at least 58,000yrs BP. However, much of the activity consideredto have been associated with this event, such asthe peaks in Eucalyptus and mangroves, occur afterthe most likely break in sedimentation, identified bysharp changes in representation of rainforest gym-nosperms, rainforest angiosperms, mangroves andthe isotope record. In this case, an age around orafter 58,000 yrs BP is indicated. The absence ofa rainforest peak equivalent to that at the base ofphase 3 in the Lynch’s Crater record might suggestthat the early part of stage 3 is missing and thatthe Araucaria decline is most likely to have been

P.T. Moss, A.P. Kershaw / Palaeogeography, Palaeoclimatology, Palaeoecology 155 (2000) 155–176 173

Fig. 8. Comparison of best estimate chronologies for the ODPSite 820 and Lynch’s Crater pollen records.

substantially later than 58,000 yrs BP, and similar inage to that proposed in model 1.

With respect to the possible earlier hiatus, cov-ering at least stage 7, there are few abrupt changesin pollen representation to support such a proposal.However, there is a marked decrease in Araucari-aceae. This decrease, like the later one in Araucariaat least, is sustained and suggests a stepwise reduc-tion in representation of the family. It also occursduring a steep increase in charcoal values indicating

the possibility of a burning cause, although, becauseof a lack in response of mangroves and a much laterand less pronounced response in Eucalyptus, fireswere not as environmentally damaging or were moreremote from the ODP core site. There is no suchreduction in the Lynch’s Crater record, even withinthat part of the record which probably extends tostage 7 (Kershaw, 1986) so, consequently, the pos-sibility of a regional decline in between or withinstages 8 or 6 remains.

Based on this analysis of the various forms ofdating and the pollen data, tentative chronostratigra-phies for the two pollen records are provided for thetwo records on Fig. 8.

9. Decline of araucarian forest

Refinement of the ODP record has provided someunexpected results relating to the possible role ofpeople in the decline of Araucaria forest. The orig-inal proposal of Kershaw et al. (1993) and Kershaw(1994), based on the Lynch’s Crater and preliminaryODP records, was that Aboriginal people may havearrived about 140,000 yrs BP, during the height ofthe penultimate glacial period and, with their use offire, caused the progressive elimination of araucarianforest and its replacement with fire promoting scle-rophyll vegetation dominated by Eucalyptus. Thisproposal can be questioned with the two-step declineindicated in the ODP record presented here.

An alternative proposal involving people is thateither there were two colonisation phases, the secondby a technologically more advanced people, or thatthere was a change in technology or a sharp increasein population levels during this early period of res-idence. This proposal, however, assumes some tem-poral relationship between the second event in theODP core and that at Lynch’s Crater. It is interestingto note here that if the oxygen isotope record is as-sumed to be continuous, and a timescale constructedsimply on the dates of the isotope boundaries thenthe second step in the decline of Araucaria in theODP record comes out with a date almost exactlythe same as that at Lynch’s Crater (Fig. 8). Tak-ing the ODP radiocarbon dates into account though,the event may have been up to 10,000 years earlierin the ODP record than the Lynch’s record, but it

174 P.T. Moss, A.P. Kershaw / Palaeogeography, Palaeoclimatology, Palaeoecology 155 (2000) 155–176

has to be borne in mind that older dates from bothcores are close to the radiocarbon limit and possiblyunreliable. The apparent difference in the timing ofpresumed human impact at the two sites may not beas great if an earlier decline in another fire-sensi-tive, coniferous genus, Callitris, around 45,000 yrsBP at Lynch’s Crater is taken into account (Ker-shaw, 1976). This dramatic and sustained decline,probably in the rainforest margin species, Callitrismackleyana, has not been emphasised previously be-cause the decline is not accompanied by an increasein burning and corresponds closely with the changein the core from lake to swamp sediments whichmay have not been conducive to the preservation ofthis delicate Cupressaceae pollen type. However, ifthe decline is real, it may reflect earlier alterationof vegetation some distance from the site and aburning signal from the well-dispersed pollen is notaccompanied by one from charcoal.

There is also some concern about the age of theearliest araucarian decline in the ODP record. A min-imum date of about 140,000 yrs BP is much olderthan established archaeological ages for the presenceof people in Australia of around 40,000 yrs BP basedon radiocarbon dating (Allen and Holdaway, 1995)and about 60,000 yrs BP based on optically stim-ulated thermoluminescence (OSL) dating (Robertsand Jones, 1994). The date is consistent, though,with that proposed from increased burning at LakeGeorge in New South Wales (Singh et al., 1981;Singh and Geissler, 1985) and from thermolumines-cence dating of the archaeological site of Jinmiumin the Northern Territory (Fullagar et al., 1996).However recent radiocarbon and OSL dating of theJinmium site have suggested that the true age ismuch younger, probably no more than 10,000 yrs BP(Roberts et al., 1998). If the age of the ODP eventwas any older, as may be suggested in age model 2,then there are real difficulties in proposing a humancause, even though it is now suggested that people,in the form of Homo sapiens, managed to make shortsea crossings to the Indonesian Island of Flores tothe north of Australia by 700,000–800,000 yrs BP(Sondaar et al., 1994; Morwood et al., 1998).

It is very possible that the two-step araucariandecline is more apparent than real. Both steps relateto proposed hiatuses in the ODP core and mayreflect accumulated change over many thousands of

years. This is more likely to be the case with theolder step which is somewhat divorced from thesubsequent peaks in charcoal and Eucalyptus. Thedirect role of people may also be questioned becausethese peaks are clearly associated with the heightof the penultimate glacial when very dry conditionsmay have been sufficient to induce increased burningand promotion of sclerophyll vegetation. The recentaraucarian decline is closely linked with increasedcharcoal and eucalypt values, at least towards the endof the event, has had a larger general environmentalimpact, and is not associated with a time of majorclimate change. These features, together with theirsimilarity to those in the Lynch’s Crater record,make this event more likely to have had a humancause or at least human involvement. The demise ofthe Dacrydium species occurs at a later date but thesensitivity of this, or closely related, species on NewCaledonia to human-induced fire suggests a similarcause. It is probable that Dacrydium survived longerdue to its swamp and riverine habitat but succumbedwhen there was a general landscape drying towardsthe Last Glacial Maximum.

The postulation of a climatic cause for at least theinitial phase of replacement of drier araucarian forestby sclerophyll vegetation is problematic in that thereis little evidence for systematic climate change overthis period globally. However, the oxygen isotoperecord from ODP 820 does show a marked shiftin average values between stages 11 and 8 which,if interpreted in terms of local temperature, couldindicate an increase in sea-surface temperatures ofabout 4ºC (Peerdeman et al., 1993). Such a changeon the adjacent land may have led to increases inboth temperature and precipitation both of whichare likely to have disadvantaged Araucaria relativeto other major taxa recorded in the pollen records.Unfortunately, the actual influence of these changeson the vegetation of the region cannot be gaugeduntil the extension of the ODP pollen record hasbeen completed.

10. Conclusions

The analysis of the onshore and offshore pollenrecords, in relation to modern pollen samples andclimatic ranges of extant taxa, has produced an in-

P.T. Moss, A.P. Kershaw / Palaeogeography, Palaeoclimatology, Palaeoecology 155 (2000) 155–176 175

terpretable pattern of vegetation and environmentalchange over the last glacial cycle. Dates availablefrom the marine core have confirmed previous ageestimates on the terrestrial Lynch’s Crater record forkey periods of time. Conversely, the continuous na-ture of the Lynch’s Crater pollen record has helpedresolve some dating uncertainties in the offshorerecord.

There is a clear relationship between climate, sealevel and vegetation with driest conditions duringglacial periods and highest rainfall and temperaturelevels during the interglacials. Superimposed on thiscyclical pattern are reductions in drier araucarianforest and general increases in sclerophyll vegeta-tion and associated biomass burning. In contrast tothe Lynch’s Crater record which shows one markedchange around 38,000 yrs BP, the offshore recordindicates that this reduction has been either continu-ous or stepwise. If stepwise, changes occurred sometime between 240,000 and 140,000 yrs BP and about45,000 yrs BP. A regional increase in temperature ofsome 4ºC around 400,000 yrs BP may have triggeredthese trends but the later changes, at least, probablyalso involved burning by Aboriginal people.

Acknowledgements

We thank the Ocean Drilling Program Labora-tory at College Station for providing core samples,Sander van der Kaars for advice on preparation ofmarine pollen samples, Chris Turney and particularlyBill Watts and Cathy Whitlock for their extremelyhelpful comments on the originally submitted manu-script, and Gary Swinton for drafting illustrations.The research was facilitated by a Monash Gradu-ate Scholarship to Patrick Moss and an AustralianResearch Council grant to Peter Kershaw.

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