A late Quaternary marine palynological record (oxygen isotope stages 1 to 7) for the humid tropics of northeastern Australia based on ODP Site 820

Palaeogeography, Palaeoclimatology, Palaeoecology 251 (2007) 4 – 22 www.elsevier.com/locate/palaeo

A late Quaternary marine palynological record (oxygen isotope stages 1 to 7) for the humid tropics of northeastern Australia based on ODP Site 820 Patrick T. Moss a,⁎, A. Peter Kershaw b b

a School of Geography, Planning and Architecture, The University of Queensland, Brisbane Queensland 4072, Australia Centre of Palynology and Palaeoecology, School of Geography and Environmental Science, Monash University, Victoria 3800, Australia

Accepted 27 February 2007

Abstract A late Quaternary marine palynological record from the Ocean Drilling Program (ODP) site 820, adjacent to the humid tropics region of northeastern Australia, has demonstrated marked variation in orbital scale cyclicity, and also trends associated with both climate and human impact. However, some uncertainties in interpretation have resulted from concerns about the records chronology and continuity. Here we present, for the first time, the complete palynological data from detailed analysis of the top 67 m of sediment and examine it in relation to the marine isotope sequence from the core. It is proposed that the record is relatively continuous through the last 250,000 years although the latter part of oxygen isotope stage (OIS) 5, as well OIS 4 may be missing. Despite the variation on orbital scales, most palynological changes are not in phase with those from the marine isotope record suggesting a lack of direct Milankovitch forcing on vegetation. This lack of correspondence combined with major trends towards more open and sclerophyllous vegetation in association with increased burning supports a previous proposal that major control is being exercised by El Niño-Southern Oscillation variability whose influence may have been initiated by changes in oceanic circulation in the region within the mid Pleistocene. The lack of impact on the distribution of complex rainforest suggests that increased climate variability did not involve an overall decrease in total precipitation. © 2007 Elsevier B.V. All rights reserved. Keywords: Australia; Late Quaternary; Climate change; Human impact; Marine palynology; Rainforest history

1. Introduction The humid tropics region of northeastern Australia has provided a focus for Quaternary palynological research in Australia over the last 40 years. One component of this research has been the construction of long records for the late Quaternary (Kershaw, 1994) ⁎ Corresponding author. E-mail addresses: [email protected] (P.T. Moss), [email protected] (A.P. Kershaw). 0031-0182/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2007.02.014

with Lynch's Crater (Kershaw, 1986; this volume) being the most substantial. This record appears to demonstrate glacial–interglacial cyclicity through an estimated last 230,000 years with complex rainforest dominant during wetter interglacials and its partial replacement by drier araucarian rainforest, and sclerophyll woodland dominated by Eucalyptus and Casuarinaceae, during drier glacial periods. This pattern partly broke down during the last glacial period with the total replacement of araucarian forest by sclerophyll woodland in association with a major and sustained increase in charcoal

P.T. Moss, A.P. Kershaw / Palaeogeography, Palaeoclimatology, Palaeoecology 251 (2007) 4–22

suggesting that burning was the cause of this landscape transformation. It was further proposed, in the absence for significant climate change and lack of response in vegetation or charcoal to similar conditions in an earlier part of the record, that the increase in burning and vegetation change were associated with the arrival of Aboriginal people within the region. The original radiocarbon chronology dated this event to 38,000 years BP (Kershaw, 1986). Redating this event by radiocarbon dating using acid–base–acid stepped combustion (ABA-SC) pretreatment on swamp sediment has suggested an older date, about 45,000 years BP, for this significant environmental alteration (Turney et al., 2001). In order to provide a more robust chronology for the Atherton Tableland records beyond the limit of radiocarbon techniques, and to determine whether environmental changes had any broader regional expression, pollen analysis was undertaken on ODP site 820, a site subjected to detailed oxygen isotope and biostratigraphic analysis (Peerdeman et al., 1993) and located off the northeast Queensland coast almost adjacent to the Atherton Tableland. Preliminary palynological results, involving coarse sampling through the whole 1.4 Ma marine record, demonstrated similarities with the Lynch's Crater record in terms of gross pollen representation. It also indicated a similar loss of araucarian forest in the very late Pleistocene that was perhaps the most significant event within the whole recorded period (Kershaw et al., 1993; Kershaw, 1994). A more refined analysis of the upper part of the ODP 820 record revealed a more complex stepwise decline of the araucarian forest (Moss and Kershaw, 2000). Although some reduction occurred around 45,000 years BP, it was preceded by an initial step about 130,000 years ago, clearly beyond the earliest date for people on the Australian continent and not evident in the Lynch's Crater record. Both events could be related to peaks in charcoal. It has been proposed that these environmental changes could have been triggered by a 4 °C increase in sea surface temperature (SST) in the Coral Sea indicated by systematic shifts in oxygen isotope values and lithological evidence for carbonates indicating the formation of the Great Barrier Reef within the ODP 820 core and other records in the region between about 600,000 and 250,000 years BP (Davies and McKenzie, 1993; Peerdeman et al., 1993; Isern et al., 1996; Webster and Davies, 2003). It has been hypothesized that this temperature increase resulted from the development or expansion of the Indo-Pacific Warm Pool, centred to the east of New Guinea and to the north of this region. The Warm Pool formed as a consequence of the narrowing of the

5

Indonesian throughflow with the continued movement of the Australian continental plate northwards into that of Southeast Asia. Although plate movement is slow, changes may have been triggered by the crossing of a critical threshold or some specific tectonic event. The existence of the Warm Pool is an important prerequisite for operation of El Niño-Southern Oscillation (ENSO) variability that provides the drought conditions necessary for effective burning of vegetation. Consequently, it has been proposed that the major burning event around 130,000 years ago was a result of a combination of dry conditions at the end of the penultimate glacial period and a phase of high ENSO activity, while the event around 45,000 years ago was a result of human activity combined with high ENSO activity (Kershaw et al., 2003a,b). Results of past ENSO modeling (Clement et al., 1999) are not inconsistent with this interpretation. However, there are also uncertainties with aspects of the ODP 820 record and its interpretation. One concern is over the degree of continuity of the record. Two age models have been proposed based on comparison of the isotope record with those from other marine records in the region and on occurrences of selected biostratigraphic markers (Peerdeman et al., 1993). These models are shown in Fig. 4 together with a third model, for the last 140,000 years, based on the comparison of major features of the ODP 820 pollen record with that of Lynch's Crater (Moss and Kershaw, 2000). In terms of overall interpretation, recent results from alkenone palaeothermometry on the ODP 820 sediments have brought into question the trend towards higher temperatures. These results suggest that SSTs only changed by ∼ 1.5 °C or less over the last 800,000 years and the development of the Great Barrier Reef must be linked to factors other than increasing SSTs (Lawrence and Herbert, 2005). In this paper we present an extension to the length of the high resolution ODP site 820 record from 40 to 67 m, as well as provide complete pollen data for the whole period in order to provide further insights into the nature, timing and likely causes of environmental changes within the humid tropics region. 2. Regional setting ODP site 820 (16°38′S, 146°18′E, water depth — 280 m) is situated seaward of the Great Barrier Reef on the continental slope, about 40 km from the coast and about 100 km from Lynch's Crater (Fig. 1). The pollen and charcoal catchment for ODP site 820 has been suggested to cover an altitudinal range from sea level to about 1600 m (Moss et al., 2005). It includes lowland to

6

P.T. Moss, A.P. Kershaw / Palaeogeography, Palaeoclimatology, Palaeoecology 251 (2007) 4–22

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

montane rainforest (which occupy areas receiving about 1500 mm to in excess of 4000 mm of mean annual rainfall), sclerophyll vegetation (which dominates landscapes generally receiving a mean annual rainfall level of less than 1500 mm), small patches of araucarian forest (largely restricted to rainforest margins and continental islands), coastal swamps (on poorly drained soils) and mangrove areas (mainly around Trinity and Mutchero Inlets) (Tracey, 1982). Major components of pollen and charcoal are likely to have derived from the Russell/Mulgrave and Barron rivers systems (Kershaw, 1994; Moss, 1999; Moss et al., 2005) that drain a substantial part of the region (Fig. 1). Climatically, the region is largely controlled by the easterly trade winds that blow through most of the year and bring rainfall largely in summer when the intertropical convergence zone is at its most southerly extent (Gentilli, 1972). The importance of the Pacific Ocean for generating rainfall also means that the region is

sensitive to ENSO variability with significant annual reductions in rainfall during El Niño years when the activity of the trade winds is much reduced (Dai and Wigley, 2000). 3. Laboratory methods Samples for palynological investigation from the ODP 820A core, 5 cm3 in size, were provided by the Integrated Ocean Drilling Program Core Store at College Station in Texas, USA. Initially 181 samples were taken at approximately 40 cm intervals from the top 67 m and, subsequently, another 70 samples were provided at intervening 20 cm intervals from identified ‘interglacial’ stages to provide greater resolution for these periods. Preparation of samples for pollen and charcoal analysis followed the technique devised by van der Kaars (1991) for marine sediments. This method used

P.T. Moss, A.P. Kershaw / Palaeogeography, Palaeoclimatology, Palaeoecology 251 (2007) 4–22

sodium phyrophosphate to disaggregate the sediments, which were then further processed by acetolysis to darken the pollen grains and aid their visibility under a light microscope. Sodium polytungstate (with a specific gravity of 2.0) was then used to float the lighter organic fraction (including pollen) from the heavier minerogenic components. Prepared samples were mounted in silicon oil and pollen analysis was undertaken using a light microscope at × 650 magnification. At least 100 identifiable grains (or the total on 4 slides) were counted from the marine core. Charcoal was identified as black angular particles above 10 μm in maximum diameter and was counted using the point count method of Clark (1982). At least 200 points were recorded for determination of charcoal concentration. 4. The pollen diagrams Pollen taxa are divided into the following taxonomic, or ecological groupings for pollen diagram representation: rainforest gymnosperms that comprise trees from the southern hemisphere conifer families Podocarpaceae and Araucariaceae; rainforest angiosperms characterized by a diversity of taxa derived from trees, shrubs and vines; sclerophyll arboreal taxa dominated by members of the Myrtaceae family, particularly Eucalyptus and Melaleuca; sclerophyll herbs comprised mainly of grass species from the family Poaceae; pteridophytes; mangroves; and aquatics. The relative representation of these groups, expressed as percentages of the first four categories, i.e. dryland taxa, is displayed on the summary diagram of Fig. 2 along with charcoal and pollen concentrations, major lithological units (Feary and Jarrard, 1993) and the isotope record of Peerdeman et al. (1993). Individual taxa within these groupings are shown in Fig. 3A–C. Pollen diagrams were constructed using TGView Version 2.0.2 (Grimm, 2004). The pollen records are divided on the basis of stages as proposed in the first age model of Peerdeman et al. (1993) and pollen assemblages zones, based on pollen sum taxa. The first age model is used on the grounds that it allows scrutiny of all isotopes boundaries, and comparison with zone boundaries provides a basis for examination of potential leads and lags within the marine and terrestrial systems. Zonation has been facilitated by the use of the stratigraphically constrained classification of CONISS (Grimm, 1987) based on the pollen sum taxa and employing the Edwards and Cavalli-Sforza's chord distance as the sample similarity measure. The zonation is applied to non-arboreal as well as arboreal taxon diagrams to allow examination of any differences in response to outside forcing. Both the oxygen isotopes

7

stages and pollen zones are highlighted in the summary diagram (Fig. 2) while only the pollen zones are highlighted in the other diagrams (Fig. 3A–C). Fourteen zones have been selected on the basis of the CONISS classification diagram. Zone 14 (67.1 to 63.9 m) has highest values for rainforest conifers, largely Araucaria and Agathis, in the diagram, and significant representation of Olea paniculata and Ficus within the rainforest component. Sclerophyll taxa are generally poorly represented although the predominantly herbaceous taxa, Poaceae and Chenopodiaceae, have moderately high values. This zone also shows high values for pteridophyte taxa, particularly monolete fern spores, and moderate charcoal values. Zone 13 (63.9 to 60.8 m) is characterized by substantially lower values for the conifers Araucaria and Agathis, and the drier forest angiosperm O. paniculata, and there are sharp increases in abundance of wetter rainforest elements including Trema, Celtis, Sapotaceae, Arecaceae, Euphorbiaceae and Macaranga/Mallotus at the base of the zone, and Cunoniaceae, Elaeocarpus, Syzygium and Lonchocarpus comp. partway through the zone. Hamamelidaceae has clearly its best representation for the diagram in the zone. Within the sclerophyll taxa, Melaleuca increases in phase with the major wet rainforest canopy taxa Cunoniaceae and Elaeocarpus, Gyrostemonaceae peaks at highest values for the diagram while other sclerophyll taxa, apart perhaps from Casuarinaceae and Dodonaea, have very poor representation. Aquatics are relatively well represented with Triglochin and Potamogeton joining background levels of Cyperaceae, and the taxa of the dominant mangrove family, Rhizophoraceae, peak at highest levels for the core. Conversely, fern spores values have slumped and are barely recorded. Zone 12 (60.8 to 53.8 m) observes a sharp reversal of the decreases in Araucaria and Agathis values seen at the base of zone 13 and the values for these taxa are then maintained at high levels before some reduction in the latter part of the zone. The other major conifer, Podocarpus, has a notable peak in the middle of the zone. Rainforest angiosperms have generally reduced representation, at least in the lower half of the zone, but display several different patterns at the taxon level. Percentages of Trema, Celtis, Sapotaceae, Euphorbiaceae type and Hamamelidaceae have all declined with the latter disappearing from the record, values of Cunoniaceae, Elaeocarpus and Arecaceae are maintained while there is resurgence in Olea and Ficus values. The major sclerophyll responses are increases in Callitris and Pandanus to highest levels for the diagram

8 P.T. Moss, A.P. Kershaw / Palaeogeography, Palaeoclimatology, Palaeoecology 251 (2007) 4–22 Fig. 2. Comparison of the marine and terrestrial environmental evidence from the ODP 820 marine core for oxygen isotope stages 1 to 7. The solid lines represent the oxygen isotope stage (OIS) boundaries of the first age model (Peerdeman et al., 1993), while the hashed lines reflect the vegetation zones derived from the classification of the dryland pollen taxa.

P.T. Moss, A.P. Kershaw / Palaeogeography, Palaeoclimatology, Palaeoecology 251 (2007) 4–22

and near disappearance of Gyrostemonaceae, but Poaceae levels remain consistently high. The aquatic taxa have achieved highest representation for the diagram, mangrove representation has collapsed and, in the pteridophytes, monolete fern spores, Cyathea and Lycopodium percentages recover to levels observed in zone 14 although these values are not sustained through the zone with the latter two taxa. Charcoal values remain low in the lower half of the zone but peak in the upper half with the increase coinciding with overall decreases in gymnosperms and fern values. Zone 11 (53.8 to 49.1 m) is most clearly marked, although not defined, by the major representation of mangrove pollen and there are associated, but minor, decreases in pteridophytes and charcoal. Dryland taxa show marginal increases in Araucariaceae, Olea, Celtis and Sapotaceae, while Podocarpus, Cunoniaceae, Elaeocarpus and Arecaceae values are low. Dacrydium achieves highest values for the record mid-zone, and these levels are maintained to the middle of the succeeding zone. There is little change in sclerophyll taxa although Poaceae values are slightly lower and there is a second and final major peak in Gyrostemonaceae mid-zone. Zone 10 (49.1 to 43.8 m) observes the continued alternation between ‘wetter’ and ‘drier’ rainforest taxa with generally high values for Cunoniaceae, Elaeocarpus, and Arecaceae, joined also by Podocarpus and Dacrydium, while there are reduced percentages for Olea, Celtis, Sapotaceae and Ficus. Sclerophyll taxa are little changed and none, except for Poaceae, and Melaleuca in the topmost few samples, has notable values. There is a lack of mangroves, and aquatics apart from a late peak in Triglochin, while pteridophyte (monolete fern spores) and charcoal levels are relatively high. Zone 9 (43.8 to 35.9 m) is marked by a sharp increase in Poaceae and similar decreases in Arecaceae and pteridophytes, which are largely sustained through the remainder of the record. Araucariaceae values remain high, but variable and all other notable rainforest taxa are much reduced within the zone. Other taxa, apart from Melaleuca, Eucalyptus, and the Rhizophoraceae taxa, Rhizophora and Ceriops/Bruguiera, to a certain degree mid-zone, are poorly represented and charcoal values are relatively low. Zone 8 (35.9 to 32.3 m) is characterized by a sharp decline in Agathis and the beginning of a gradual decline in Araucaria that both result in a sustained reduction of representation of the taxa through subsequent zones. Values of rainforest angiosperms have increased, mainly due to a peak in Olea and a more

9

sustained increase in Cunoniaceae. There are marked increases in Melaleuca and Eucalyptus within the zone and these taxa peak at the very top in association with a major peak in charcoal. Poaceae values achieve very high levels and values for aquatics and ferns have increased slightly over those in the previous zone. Zone 7 (32.3 to 29.4 m) is most clearly identified by peaks in the Rhizophoraceae taxa and in the rainforest taxa Sapotaceae, Sapindaceae and Macaranga/Mallotus, as well as generally high values of the rainforest taxa Celtis, Cunoniaceae, Elaeocarpus and Ficus. Eucalyptus, Poaceae and pteridophytes have reduced percentages while charcoal values gradually fall after the peak at the top of the previous zone. Zone 6 (29.4 to 23.9 m) observes a fair degree of stability in representation of most taxa with Araucaria, Agathis, Celtis, Cunoniaceae, Elaeocarpus and Ficus continuing as the conspicuous rainforest taxa, though Podocarpus and Dacrydium do peak at the very top of this zone. Eucalypts generally maintain their representation, Melaleuca values decrease through the zone, while Poaceae percentages increase steeply through the zone from relatively low to high. Aquatics, mainly Cyperaceae, maintain low values while mangrove and pteridophyte values are also consistently low. Charcoal values are moderate apart from a minor peak within the zone. Zone 5 (23.9 to 18.3 m) observes Araucaria and Agathis maintaining consistent values, while those of Podocarpus decrease through the zone. Most rainforest angiosperms have very low representation or, in the case of Cunoniaceae and Elaeocarpus, decrease to low values in the zone centre. In contrast, O. paniculata increases sharply at the base of the zone and then declines through it. Poaceae peaks for the diagram in the middle of the zone while Melaleuca and Eucalyptus generally maintain similar values to those in zone 6. There is the first notable occurrence of Chenopodiaceae since zone 11 within the zone. Cyperaceae values are, on average, highest for the diagram and are accompanied by generally high mangrove values, especially in the upper part of the zone; these include the beginning of fairly consistent representation of Avicennia. Both pteridophyte and charcoal values are low. Zone 4 (18.3 to 11.8 m) has Araucaria and Agathis continuing to maintain moderate values, Elaeocarpus percentages have increased while Ficus, Cunoniaceae and Olea peak at the base, in the centre and at the top of the zone respectively. Values for Melaleuca and Eucalyptus generally increase while those of Poaceae generally decrease through the zone and Casuarinaceae displays rare consistent representation. Cyperaceae values are lower while mangrove and pteridophyte

10

P.T. Moss, A.P. Kershaw / Palaeogeography, Palaeoclimatology, Palaeoecology 251 (2007) 4–22

(both Cyathea and monolete fern spore) percentages gradually increase through the zone. Charcoal values also increase through the zone and incorporate two substantial peaks. Zone 3 (11.8 to 9.8 m) shows sharply lower values for Araucaria and Agathis as well as other major rainforest taxa except for Elaeocarpus, but strong peaks for the sclerophyll taxa Melaleuca and Eucalyptus, minor peaks for the Rhizophoraceae and the highest peak in the diagram for charcoal. Zone 2 (9.8 to 4.4 m) observes Araucaria, Agathis and O. paniculata values decreasing sharply at the base of the zone although Agathis recovers partially to the top. Dacrydium disappears completely (at 7.5 m) and Podocarpus displays a minor peak. Rainforest angiosperm taxa maintain relatively low values in this zone, except for Cunoniaceae, and to some extent Elaeocarpus, that have reasonable representation at each end of the zone and Sapotaceae that has a minor peak at the top. Melaleuca and Eucalyptus values are reduced but maintain generally higher values than in previous zones, while Poaceae values increase and a peak in Chenopodiaceae is also observed. Cyperaceae values are low except for a peak mid-zone that just precedes peaks in Rhizophoraceae taxa. Charcoal values are generally high apart from a dip mid-zone. Zone 1 (4.4 to 0 m) observes little representation of rainforest gymnosperms. By contrast, rainforest angiosperms probably have their highest values, due largely to high Cunoniaceae values but also supported by Trema, Elaeocarpus, Ficus, Arecaceae, Euphorbiaceae and Macaranga/Mallotus. Melaleuca, Eucalyptus and Poaceae maintain significant values, Triglochin and Potamogeton compete with Cyperaceae for highest, though very modest, aquatic representation, and mangroves are poorly represented. Pteridophyte values, particularly monolete fern spores, have their highest representation since zone 10. Charcoal maintains relative high and constant values. 5. General record chronology Three different chronologies, outlined in Fig. 4, have been proposed previously for the whole or part of this record based on the oxygen isotope record, biostratigraphic markers, radiocarbon dating and palynology. Models A and B were both proposed by Peerdeman et al. (1993) and are based on different interpretations of the nanofossil and foraminifera data from the record, as well as correlation of the ODP 820 isotope curve with deep-sea reference curves from the Pacific Ocean (Core V28-238, Hole 677A and Hole 607A). Model C, as

proposed by Moss and Kershaw (2000), utilizes this information but also incorporates a comparison of the ODP 820 and Lynch's Crater pollen records in the derivation of this age model, but extending only through the last glacial–interglacial cycle. It is considered that the pollen sequence shown here, extended in both time and taxon representation from that presented in Moss and Kershaw (2000), can resolve some chronological conflicts and uncertainties. Of significant benefit are the major peaks in mangrove taxa that have been demonstrated to be indicative of marine transgression phases from major sea level lows or transitions from glacial to interglacial periods (Terminations), with only minor mangrove responses to regressive sea level phases (Grindrod et al., 1999, 2002). The transgression at the Pleistocene–Holocene transition, which is dated from about 14,000 to 6000 years BP, provides a useful recent analogue for previous events. The mangrove peak extending from zone 8 into zone 7 provides good support for the OIS 6-5 division (Termination II), identified in all three age models, while the largest peak extending from the end of zone 14 through the whole of zone 13 provides support for a glacial–interglacial shift as indicated by transition from OIS 8-7 in model 1 (Termination III). General support for these glacial–interglacial transitions is provided by sediment variation, as well as changes in the δO18 values, which significantly decrease during each Termination event. In all three cases, mangrove increases begin within sandy sediment that appears to have been deposited during the periods of highest δO18 or lowest sea level in the diagram and in two cases, sand is succeeded by muds and, in one case, carbonate muds (Fig. 2). However, the major mangrove peak of zone 11 might be expected to be of similar glacial–interglacial status as the others and qualify as heralding the beginning of OIS 7 with the zone 13 peak relegated to the previous interglacial, OIS 9. Such a correlation, though, is unacceptable in relation to the biostratigraphic markers used by Peerdeman et al. (1993) and, consequently, allocation of the zone 11 peak to the major interstadial of OIS 7c appears much more appropriate. This mangrove peak also differs from those marking glacial terminations. Although it is the second largest, and is accompanied by a marked sedimentary response, the mangrove rise precedes a fall in δO18 by some 3 m and is actually in phase with a small rise in δO18 rather than a fall, and so is possibly related to a different set of environmental conditions. The mangrove record between Terminations I and II is less helpful, chronologically. There are two major mangrove phases, one peaking in zone 5 and the other in

P.T. Moss, A.P. Kershaw / Palaeogeography, Palaeoclimatology, Palaeoecology 251 (2007) 4–22

pp. 11–14

Fig. 3. (A) Classification of the rainforest gymnosperms and angiosperms component of the ODP 820 pollen record for oxygen isotope stages 1 to 7. The hashed lines reflect the placement of the oxygen isotope stages based on first age model of Peerdeman et al. (1993). (B) Classification of the sclerophyll component of the ODP 820 pollen record oxygen isotope stages 1 to 7. The hashed lines reflect the placement of the oxygen isotope stages based on first age model of Peerdeman et al. (1993). (C) Classification of the wetland component of the ODP 820 pollen record oxygen isotope stages 1 to 7. The hashed lines reflect the placement of the oxygen isotope stages based on first age model of Peerdeman et al. (1993).

15

Fig. 3 (continued ).

P.T. Moss, A.P. Kershaw / Palaeogeography, Palaeoclimatology, Palaeoecology 251 (2007) 4–22

P.T. Moss, A.P. Kershaw / Palaeogeography, Palaeoclimatology, Palaeoecology 251 (2007) 4–22

Fig. 3 (continued ).

16

P.T. Moss, A.P. Kershaw / Palaeogeography, Palaeoclimatology, Palaeoecology 251 (2007) 4–22

17

Fig. 4. Comparison of the three age models for the oxygen isotope results for ODP site 820: (A) reflects the first age model of Peerdeman et al., 1993; (B) reflects the second age model of Peerdeman et al., 1993; and (C) reflects the age model proposed by Moss and Kershaw (2000).

zone 3. The zone 5 peak is clearly related to a fall in δO18 values that indicate a marine transgression. Whether this represents the beginning of OIS 3 or a transgression within OIS 5 (i.e. OIS 5c or 5a) is uncertain from the

models. The zone 3 peak is even more problematic in that it is not accompanied by an isotope response and therefore its significance as a sea level indicator can be questioned. The presence of the two transgressions could

18

P.T. Moss, A.P. Kershaw / Palaeogeography, Palaeoclimatology, Palaeoecology 251 (2007) 4–22

support Model B if zone 5 represents OIS 5c and zone 3 represents OIS 5a. With this scenario, OIS 4 is missing and OIS 3 and 2 are very condensed or only partly represented. An alternative and preferred explanation for the zone 3 peak is that it owes its formation to a process other than sea level change. The peak is unusual in that it is much broader and flatter than the others as well as not relating to any alteration in the oxygen isotope curve. It also matches well the major phase of charcoal representation in the record and this is the only place in the record where mangroves and charcoal peak together. These relationships may support a previous suggestion (Kershaw et al., 1993) that mangrove development could have been enhanced by expansion of mud flats resulting from the deposition of eroded soil resulting from major burning of rainforest. The highest peaks in Melaleuca and Eucalyptus occur in this zone and suggest that large areas of soil may have their protective cover of rainforest removed for the first time within the Cenozoic period. Overall, the extension of the record and particularly the mangrove component has firmed up the chronology. It appears as though the major features of OIS 7 and OIS 6 are represented rather than missing as suggested in models B and C. There is still uncertainty though about record continuity, particularly during the last glacial period from OIS 5d to OIS 2, and consequently the positioning of isotope boundaries. However, it is considered that there is no compelling reason not to accept the boundaries as determined in Model A. 6. Trends in climate and vegetation Despite the dominant influence of Milankovitch forcing on mangroves, that can be attributed largely to ice cover variation operating through sea level variation, this influence is not as clearly expressed in other pollen attributes and hence in terrestrial vegetation. However, some attributes do demonstrate some cyclical variation on orbital timescales. This is most evident in the wetter elements including rainforest angiosperms, pteridophytes and aquatics, although these do not vary in phase. Rainforest angiosperms, predictably, tend to peak during interglacials and interstadials when conditions for high rainfall, including high sea surface temperatures and monsoon activity, are optimal, but aquatics have highest representation during glacials and stadials, perhaps the result of regionally lower water levels and reduced stream flow, as well as greater opportunities for swamp occurrence on a more extensive exposed continental shelf. Ferns, however, show little consistency in relation to major environmental conditions through the record. Charcoal representation also suggests

marked cyclicity but at a frequency that is not clearly associated with Milankovitch forcing. Orbital scale variability in gymnosperms and sclerophyll taxa is generally muted and instead their representation is characterized by decreasing and increasing trends, respectively. These trends have dominated previous interpretation of the record with the suggestion that the major peaks in burning, dated to about 130,000 and 45,000 years BP, led to the stepwise expansion of sclerophyll vegetation at the expense of fire sensitive, araucarian forest within the region (Moss and Kershaw, 2000; Kershaw et al., 2003a,b). However, evidence for additional changes within this extended record complicates interpretation. The major change revealed is the sharp increase in Poaceae and associated decreases in monolete fern spores and Arecaceae at the zone 10/9 boundary within the early part of OIS 6. It might be assumed either that there was some replacement of palm and fern components by grasses within some communities or that there was widespread community replacement, perhaps as a result of drier conditions. The lack of notable changes to rainforest canopies or of any response of sclerophyll woody taxa effectively excludes major regional community reorganization, suggesting more localized habitat changes effecting coastal environments. However, it would not be expected that localized impacts such as alteration of river channels, degree of exposure of the continental shelf or changing growth patterns of coral would override dramatic changes to coastal environments on glacial–interglacial timescales. Consequently, no feasible explanation can be offered. A similar unexplained and sustained increase in grasses is recorded in the marine Lombok Ridge record off northwestern Australia at about the same time (Wang et al., 1999). This increase, combined with the absence of a similar signal within the nearby terrestrial record of Lynch's Crater (Kershaw et al., 2007-this volume), does tend to favour a coastal explanation. The extended record also reveals possible long term changes in the importance of arboreal taxa in addition to the well-documented decline in Araucariaceae through the record (Moss and Kershaw, 2000). The angiosperm rainforest trees Trema, Celtis and Sapotaceae generally peak together in the lower part of the record and then show only low and sporadic representation after zone 6. Conversely, values of Cunoniaceae increase through the record. However, this appears not to represent direct replacement in that the former three taxa show distinct peaks at different times to those of Cunoniaceae, which varies in phase with the second most dominant angiosperm rainforest

P.T. Moss, A.P. Kershaw / Palaeogeography, Palaeoclimatology, Palaeoecology 251 (2007) 4–22

taxon, Elaeocarpus. Rainforest gymnosperms other than the Araucariaceae also decline within the record. Both Podocarpus and Dacrydium fail to peak from the end or close to the end of zone 10, with the latter becoming extinct regionally at the beginning of OIS 2 (Moss and Kershaw, 2000) and declines in these taxa appear more clearly related to charcoal peaks than those associated with the Araucariaceae. It is interesting to note that the sclerophyll conifer, Callitris, peaks only in the early part of the record and burning towards the end of zone 12 may also have been involved in its decline. It cannot be determined whether trends are totally the result of regional environmental changes or whether they are also reflecting localized alterations in pollen source areas and transport mechanisms due to physiographic changes on the continental shelf area associated with, for example, coral reef development. However, there is no doubt, from examination of suites of surface pollen samples in the area (Crowley et al., 1994; Kershaw and Bulman, 1994; Moss et al., 2005) in comparison with other pollen records extending back through the late Quaternary and into the late Tertiary (Kershaw et al., 2005), that the decline in Araucaria and expansion of Eucalyptus and Poaceae are major recent events.

19

ODP record clearly shows, from the pollen data associated with previous glacial–interglacial boundaries, that vegetation response is virtually immediate. Consequently, the lag can be most parsimoniously attributed to continuous burning by Indigenous people who, for some period, were able to retard rainforest advance. The impact of human influences on the ODP site 820 environmental record is further emphasized by the environmental alterations observed in zone 3, which have been previously discussed in relation to record chronology. There is also the question of potential for pollen contamination of the record from the movement of sediments accumulated on the continental shelf onto the continental slope, especially during sea level falls, and also turbidite movement on the slope itself. If substantial, these would complicate the record. In a broad sense, there is no evidence of major disruption to the sequence and, for the last 4000 years at least, the record is totally consistent with patterns of change in other late Holocene sequences from the area (Moss et al., 2005). Consequently, from available data, it appears as though contamination is minimal in the ODP 820 record, although it is acknowledged that a sediment loss from this mid-slope position is likely to have occurred. 8. Regional comparisons

7. Marine–terrestrial relationships The complexity of vegetation variation as reflected in the pollen and its uncertain relationships to Milankovitch forcing is reflected in the comparison of pollen zonation with isotope stage definition. Although there is a notable glacial–interglacial cyclicity, marked by the synchronicity between pollen zone and isotope boundaries at two sharp transitions from glacial to interglacial conditions (OIS 8/7 and OIS 6/5), only one other boundary shows coincidence between pollen zones and isotope stages (OIS 4/5). This indicates that either influences other than Milankovitch forcing are having a strong influence on the climate of this region, that there are significant vegetation lags to climate change, or that the vegetation/pollen assemblages are not responding predominantly to climate. The latter is almost certainly the case with the last glacial–interglacial (i.e. OIS 2/1) boundary where the change from sclerophyll to rainforest dominance in the vegetation lags the Holocene increase in precipitation. Although such a lag has been attributed previously, in relation to pollen records on the Atherton Tableland, to the time taken for rainforest to expand from retreats occupied during the last glacial period after climate change (Hopkins et al., 1993) the

Lack of synchronicity between oxygen isotope and pollen data is becoming an issue globally. Shackleton et al. (2002) suggest that there is a great deal of doubt on the fact that all proxy palaeoclimate records respond smoothly and in step with variations in insolation associated with orbital forcing. Support for assertion was provided by analysis of pollen data and deep sea oxygen isotope records from the Mediterranean region (Tzedakis et al., 1997) and southwestern Portugal (Tzedakis et al., 2004). Both studies observed a broad agreement between the foraminiferal oxygen isotope data and long pollen sequences. However, the pollen records, and thus the terrestrial sequence of vegetation events, contain a higher degree of climatic sensitivity than the oxygen isotope data. This suggests that the oxygen isotope record and/or a Milankovitch forced ice volume model may not be an appropriate template for fine-tuning the terrestrial record and that better terrestrial chronologies will depend on improved understanding of the role millennial variability plays in the specific duration of interglacial events (Tzedakis et al., 2004), as well as detailed knowledge of controls on sedimentation rates in individual sedimentary basins (Tzedakis et al., 1997).

20

P.T. Moss, A.P. Kershaw / Palaeogeography, Palaeoclimatology, Palaeoecology 251 (2007) 4–22

Several marine palynological studies from Africa have demonstrated broad agreement between vegetation change and Milankovitch forcing, but have also highlighted the importance of low latitude precessional influences (e.g. Van Campo et al., 1982; Lezine, 1991; Lezine and Casanova, 1991; Hooghiemstra et al., 1992; Dupont and Agwu, 1992; Dupont and Weinelt, 1996; Dupont et al., 1998; Jahns et al., 1998; Dupont et al., 1999; Shi et al., 2001). In addition, several of these studies have also observed vegetation alterations linked to other forcing mechanisms. For instance, Dupont and Weinelt (1996) suggested that the large modern extension of dry rainforest and savannah in West Africa could not be solely explained by climatic factors alone (i.e. humans play a significant role); Jahns et al. (1998) observed that late Pleistocene glacial stages were more arid than during the middle Pleistocene from their 400,000 year marine record off the Liberian coast; and Shi et al. (2001) observed a strong signal of intensification of southeasterly trade winds linked to Antarctic cooling over the last 135,000 years in palynomorphs from South Atlantic sediments. The results from the ODP site 820 record provide substantial support for the lack of synchronicity noted between the marine and terrestrial records in many parts of the world and that a variety of forcing mechanisms need to be systematically investigated. The most likely candidate is from a strong southern hemisphere precessional influence overriding northern hemisphere dominated orbital forcing. Such an influence is demonstrated to have overridden Milankovitch northern hemisphere forcing in a marine record from northwest Australia (Kershaw et al., 2006) covering a similar period of time and in an earlier Quaternary record from southeastern Australia (Sniderman et al., 2007). The precessional influence is also strong in the pollen, but not the isotope, record of the ODP 820, but the degree to which this is dominated by southern insolation has not been determined (Kershaw et al., 2003a). A major factor within the ODP record is the non-Milankovitch 30,000 year frequency that is present in most major attributes and dominates both gymnosperm and charcoal records (Kershaw et al., 2003a). It is considered to represent a modification of the precessional signal due to ENSO variability (Beaufort et al., 2003) and establish a good relationship with modeled ENSO variation at an orbital scale (Clement et al., 1999). The non-stationarity noted in pollen values within a number of records is nowhere expressed as strongly as in ODP 820, suggesting that the signal emanates from this geographical region. The pattern adds weight to the proposal that trends within the last few hundred years

have been triggered by changes in atmospheric and oceanic circulation related to development or expansion of the West Pacific Warm Pool and consequent operation of ENSO (Moss and Kershaw, 2000). If this is the case, it might be expected that similar trends would be evident in the nearby land record of Lynch's Crater. In this record vegetation alterations are present but much less pronounced apart from those within the last 40,000 years that have been attributed largely to human impact (Kershaw et al., 2007-this volume). It is possible that the ODP 820 record, with its broad pollen catchment incorporating a range of vegetation types including rainforest–non-rainforest boundaries, is more sensitive to regional climate-induced vegetation change than a small crater lake with a restricted catchment within the core area of rainforest distribution. 9. Conclusions Examination of the pollen data in relation to the oxygen isotope record from the site suggests that the record extends back to about 250,000 years, as proposed in the first age model of Peerdeman et al. (1993), although it may not be as continuous as proposed by this model, with a likelihood that parts of the last glacial period (OIS 5d-2) are missing. The sediments deposited during the heights of glacial periods are also condensed. Although major glacial–interglacial cyclicity is evident in the vegetation from correlation between isotope stage and pollen zone boundaries at glacial– interglacial transitions, at least prior to human impact, the lack of correlation elsewhere suggests that Milankovitch forcing on the vegetation is limited. It is possible that direct insolation forcing, with additional influences from ENSO variability operating largely through biomass burning, are exercising major control over cyclical patterns of vegetation change. Overriding orbital-scale cyclicity are strong trends or sustained alterations in components of the vegetation that have been considered as responses to periods of increased ENSO activity within the last few hundred thousand years with more recent superimposition of human impact. The identified mechanism for bringing about change has been biomass burning that could effectively have caused the replacement of relatively fire sensitive rainforest gymnosperms and open forest taxon Callitris by fire promoting eucalypts and other sclerophyll taxa during times of high climate variability. Conversely, average rainfall was not reduced sufficiently to reduce the extent of more complex rainforest dominated by angiosperms that exists under high precipitation. However, the recognition of changes that

P.T. Moss, A.P. Kershaw / Palaeogeography, Palaeoclimatology, Palaeoecology 251 (2007) 4–22

do not relate to times of major burning indicates attainment of critical thresholds independent of fire and perhaps also brings into the question the role of fire as an instigator of, rather than a response to, vegetation change. Acknowledgements We thank the Integrated Ocean Drilling Program Laboratory at College Station, Texas, USA for providing core samples from ODP site 820, Sander van der Kaars for advice on preparation of marine pollen samples, Gary Swinton for assistance with drafting illustrations, and Lydie Dupont and Dallas Mildenhall for very valuable comments on the originally submitted manuscript. This research was supported by a Monash University Graduate Scholarship to Patrick Moss and an Australian Research Council grant to Peter Kershaw. References Beaufort, L., de Garidel-Thoron, T., Linsley, B., Oppo, D., Buchet, N., 2003. Biomass burning and ocean primary production in the Sulu Sea area over the last 380 kyr and the East Asian monsoon dynamics. Mar. Geol. 201, 53–65. Clark, R.L., 1982. Point count estimation of charcoal in pollen preparations and thin sections of sediments. Pollen Spores 24, 523–535. Clement, A.C., Seager, R., Cane, M.A., 1999. Orbital controls on the El Niño/Southern Oscillation and the tropical climate. Paleoceanography 14, 441–456. Crowley, G.M., Grindrod, J., Kershaw, A.P., 1994. Modern pollen deposition in the tropical lowlands of northeast Australia. Rev. Palaeobot. Palynol. 83, 299–327. Dai, A., Wigley, T.M.L., 2000. Global patterns of ENSO-induced precipitation. Geophys. Res. Lett. 27, 1283–1286. Davies, P.J., McKenzie, J.A., 1993. Controls on the Pliocene– Pleistocene evolution of the northeastern Australian continental margin. Proc. Ocean Drill. Program Sci. Results 133, 755–762. Dupont, L.M., Agwu, C.O.C., 1992. Latitudinal shifts of forest and savanna in N. W. Africa during the Brunhes chron: further marine palynological results from site M 16415 (9°N 19°W). Veg. Hist. Archaeobot. 1, 163–175. Dupont, L.M., Weinelt, M., 1996. Vegetation history of the savanna corridor between the Guinean and the Congolian rain forest during the last 150,000 years. Veg. Hist. Archaeobot. 5, 163–175. Dupont, L.M., Marret, F., Winn, K., 1998. Land–sea correlation by means of terrestrial and marine palynomorphs from the equatorial East Atlantic: phasing of SE trade winds and the oceanic productivity. Palaeogeogr. Palaeoclimatol. Palaeoecol. 142, 51–84. Dupont, L.M., Schneider, R.R., Schmüser, S., Jahns, S., 1999. Marine– terrestrial interaction of climate changes in West Equatorial Africa of the last 190,000 years. Palaeoecol. Afr. 26, 61–84. Feary, D.A., Jarrard, R.D., 1993. Sedimentology and downhole log analysis of Site 820, Central Great Barrier Reef outer shelf: the factors controlling Pleistocene progradational and aggradational seismic geometry. Proc. ODP, Sci Results 133, 315–326. Gentilli, J., 1972. Australian Climatic Patterns. Nelson, Melbourne.

21

Grimm, E.C., 1987. CONISS: a FORTRAN 77 program for stratigraphically constrained cluster analysis by the method of incremental sum of squares. Comput. Geol. 13, 13–35. Grimm, E.C., 2004. TGView Version 2.0.2. Illinois State Museum, Springfield, IL, USA. Grindrod, J., Moss, P.T., van der Kaars, S., 1999. Late Quaternary cycles of mangrove development and decline on the north Australian continental shelf. J. Quat. Sci. 14, 465–470. Grindrod, J., Moss, P.T., van der Kaars, S., 2002. Late Quaternary mangrove pollen records from the continental shelf and deep ocean cores in the north Australian region in Bridging Wallace's Lines— the environmental and cultural history and dynamics of the SEAsian-Australian Region. In: Kershaw, A.P., David, B., Tapper, T., Penny, D., Brown, J. (Eds.), Adv. Geoecol., vol. 34. Cantena Verl., Reiskirchen, Germany, pp. 119–148. Hooghiemstra, H., Stalling, H., Agwu, C.O.C., Dupont, L.M., 1992. Vegetational and climatic change at the northern fringe of the Sahara 250,000–5000 years BP: evidence from 4 marine pollen records located between Portugal and the Canary Islands. Rev. Palaeobot. Palynol. 74, 1–53. Hopkins, M.S., Ash, J., Graham, A.W., Head, J., Hewett, R.K., 1993. Charcoal evidence of the spatial extent of the Eucalyptus woodland expansions and rainforest contractions in north Queensland during the late Pleistocene. J. Biogeogr. 20, 357–372. Isern, A.R., McKenzie, J.A., Feary, D.A., 1996. The role of sea-surface temperature as a control on carbonate platform development in the western Coral Sea. Palaeogeogr. Palaeoclimatol. Palaeoecol. 124, 247–272. Jahns, S., Hüls, M., Sarnthein, M., 1998. Vegetation and climate history of west equatorial Africa based on a marine pollen record off Liberia (site GIK 16776) covering the last 400,000 years. Rev. Palaeobot. Palynol. 102, 277–288. Kershaw, A.P., 1986. The last two glacial–interglacial cycle from northeastern Australia: implication for climate change and Aboriginal burning. Nature 322, 47–49. Kershaw, A.P., 1994. Pleistocene vegetation of the humid tropics of northeastern Queensland, Australia. Palaeogeogr. Palaeoclimatol. Palaeoecol. 109, 399–412. Kershaw, A.P., Bulman, D., 1994. The relationship between modern pollen samples and environment in the humid tropics region of northeastern Australia. Rev. Palaeobot. Palynol. 83, 83–96. Kershaw, A.P., McKenzie, G.M., McMinn, A., 1993. A Quaternary vegetation history of northeastern Queensland from pollen analysis of ODP site 820. Proc. Ocean Drill. Program Sci. Results 133, 107–114. Kershaw, A.P., van der Kaars, S., Moss, P.T., 2003a. Late Quaternary Milankovitch-scale climate change and variability and its impacts on monsoonal Australia. Mar. Geol. 201, 81–95. Kershaw, A.P., Moss, P.T., van der Kaars, S., 2003b. Causes and consequences of long-term climatic variability on the Australian continent. Freshwater Biol. 48, 1274–1283. Kershaw, A.P., Moss, P.T., Wild, R., 2005. Patterns and causes of vegetation change in the Australian Wet Tropics region over the last 10 million years. In: Bermingham, E., Dick, C., Moritz, C. (Eds.), Tropical Rainforests: Past, Present and Future. The University of Chicago Press, Chicago, pp. 374–400. Kershaw, A.P., van der Kaars, S., Moss, P., Opdyke, B., Guichard, F., Rule, S., Turney, C., 2006. Environmental change and the arrival of people in the Australian region. Before Farming [online] http:// www.waspress.co.uk/journals/beforefarming//journal_20061/, 2006/1 article 2. Kershaw, A.P., Bretherton, S.C., van der Kaars, S., 2007. A complete pollen record of the last 230 ka from Lynch's Crater, northeastern

22

P.T. Moss, A.P. Kershaw / Palaeogeography, Palaeoclimatology, Palaeoecology 251 (2007) 4–22

Australia. Palaeogeogr. Palaeoclimatol. Palaeoecol. 251, 23–45 (this volume). Lawrence, K.T., Herbert, T.D., 2005. Late Quaternary sea-surface temperatures in the western Coral Sea: implications for the growth of the Australian Great Barrier Reef. Geology 33 (8), 677–680. Lezine, A.-M., 1991. West African Paleoclimates during the last climatic cycle inferred from an Atlantic deep-sea pollen record. Quat. Res. 35, 456–463. Lezine, A.-M., Casanova, J., 1991. Correlated oceanic and continental records demonstrate past climate and hydrology of North Africa (0–140 ka). Geology 19, 307–310. Moss, P.T. 1999. Late Quaternary environments of the humid tropics of northeastern Australia. unpublished PhD Thesis, Monash University, Australia. Moss, P.T., Kershaw, A.P., 2000. The last glacial cycle from the humid tropics of northeastern Australia: comparison of a terrestrial and marine record. Palaeogeogr. Palaeoclimatol. Palaeoecol. 155, 155–176. Moss, P.T., Grindrod, J., Kershaw, A.P., 2005. Fluvial and marine pollen transport in the humid tropics of Northeastern Australia. Rev. Palaeobot. Palynol. 134, 55–69. Peerdeman, F.M., Davies, P.J., Chivas, A.R., 1993. The stable oxygen isotope signal in shallow-water, upper-slope sediments off the Great Barrier Reef (Hole 820A). Proc. Ocean Drill. Program Sci. Results 133, 163–173. Shackleton, N.J., Chapman, M., Sánchez Goñi, M.F., Pailler, D., Lancelot, Y., 2002. The classic marine isotope substage 5e. Quat. Res. 58, 14–16. Sniderman, J.M.K., Pillans, B., O'Sullivan, P.B., Kershaw, A.P., 2007. Climate and vegetation in southeastern Australia respond to southern hemisphere insolation forcing in the Late Pliocene–Early Pleistocene. Geology 35, 41–44.

Shi, N., Schneider, R.R., Beug, H.-J., Dupont, L.M., 2001. Southeast trade wind variations during the last 135 kyr: evidence from pollen spectra in eastern South Atlantic sediments. Earth Planet. Sci. Lett. 187, 311–321. Tracey, J.G., 1982. The Vegetation of the Humid Tropical Region of North Queensland. CSIRO, Melbourne, Australia. Turney, C.S.M, Kershaw, A.P., Moss, P., Bird, M.I., Fifield, L.K., Cresswell, R.G., Santos, G.M., Di Tada, M.L., Hausladen, P.A., Youping, Z., 2001. Redating the onset of burning at Lynch's Crater (North Queensland): implications for human settlement in Australia. J. Quat. Sci. 16, 767–771. Tzedakis, P.C., Andrieu, V., de Beaulieu, H.-L., Crowhurst, S., Follieri, M., Hooghiemstra, H., Magri, D., Reille, M., Sadori, L., Shackleton, N.J., Wijmstra, T.A., 1997. Comparison of terrestrial and marine records of changing climate of the last 500,000 years. Earth Planet. Sci. Lett. 150, 171–176. Tzedakis, P.C., Roucoux, K.H., de Abreu, L., Shackleton, N.J., 2004. The duration of forest stages in Southern Europe and interglacial climate variability. Science 306, 2231–2235. Van Campo, E., Duplessy, J.C., Rossignol-Strick, M., 1982. Climatic conditions deduced from a 150-kyr oxygen isotope−pollen record from the Arabian Sea. Nature 296, 56–59. van der Kaars, W.A., 1991. Palynology of eastern Indonesian marine piston-cores: a late Quaternary vegetational and climatic record for Australasia. Palaeogeogr. Palaeoclimatol. Palaeoecol. 85, 239–302. Wang, X., van der Kaars, S., Kershaw, A.P., Bird, M., Jansen, F., 1999. A record of fire, vegetation and climate through the last three glacial cycles from Lombok Ridge core G6-4, eastern Indian Ocean, Indonesia. Palaeogeogr. Palaeoclimatol. Palaeoecol. 147, 241–256. Webster, J.M., Davies, P.J., 2003. Coral variation in two deep drill cores: significance for the Pleistocene development of the Great Barrier Reef. Sediment. Geol. 159, 61–80.