Sander van der Kaars

Late Quaternary climates of the Australian arid zone: a review

Abstract Aridity in Australia has generally been associated with glacial intervals of the last few glacial cycles. The causes and nature of aridity varied from north to south over the continent. In northern and central Australia, reduced monsoon rain in global cold stages caused lakes and rivers to dry, vegetation to become more sparse, sand dunes to become active, and dust advection to increase. While the monsoon is correlated with warmer global temperatures and high sea levels overall, the exact timing of the greatest development of the monsoon in Stage 5 remains uncertain. In southeastern Australia, the proxy records give a less clear picture. While vegetation seems to have been more sparse in cold stages and sand dune activity and dust flux consequently greater, records of runoff in rivers and lakes have mixed or opposite behaviour to northern or central Australia. The nature of aridity in southeastern Australia is not analogous to conditions anywhere on the continent today. Greatly reduced temperatures over the central and southern interior, greater influence of snow and periglaciation on runoff, high groundwater tables, lower rainfall and reduced atmospheric carbon dioxide levels may all have contributed to and interacted to produce the reconstructed picture of a cold, sparsely vegetated arid landscape with large rivers and perennial lakes. The largest changes in circulation patterns over the glacial cycle probably occurred in the location and/or intensity of summer tropical convergence in northern Australia. Over southern Australia, changes to the temperature and humidity of the westerly circulation have been more significant than the small fluctuations in latitude of the sub-tropical high pressure ridge.

History of vegetation and habitat change in the Austral-Asian region

Over 1000 marine and terrestrial pollen diagrams and Some hundreds of vertebrate faunal sequences have been studied in the Austral-Asian region bisected by the PEPII transect, from the Russian arctic extending south through east Asia, Indochina, southern Asia, insular Southeast Asia (Sunda), Melanesia, Australasia (Sahul) and the western south Pacific. The majority of these records are Holocene but sufficient data exist to allow the reconstruction of the changing biomes over at least the past 200,000 years. The PEPII transect is free of the effects of large northern ice caps yet exhibits vegetational change in glacial cycles of a similar scale to North America. Major processes that can be discerned are the response of tropical forests in both lowlands and uplands to glacial cycles, the expansion of humid vegetation at the Pleistocene-Holocene transition and the change in faunal and vegetational controls as humans occupy the region. There is evidence for major changes in the intensity of monsoon and El Nino-Southern oscillation variability both on glacial-interglacial and longer time scales with much of the region experiencing a long-term trend towards more variable and/or drier climatic conditions. Temperature variation is most marked in high latitudes and high altitudes with precipitation providing the major climate control in lower latitude, lowland areas. At least some boundary shifts may be the response of vegetation to changing CO2 levels in the atmosphere. Numerous questions of detail remain, however, and current resolution is too coarse to examine the degree of synchroneity of millennial scale change along the transect

A Late Quaternary palaeoecological record from the Banda Sea, Indonesia: patterns of vegetation, climate and biomass burning in Indonesia and northern Australia

Abstract Palynological, charcoal, elemental carbon and elemental carbon stable isotope analyses on Banda Sea core SHI-9014 provide a detailed regional vegetation, fire and climate history for the Banda Sea area (eastern Indonesia and northern Australia) through the last 170–180,000 years. Reliable chronostratigraphic control is provided by a detailed oxygen isotope record and, in the younger part of the sequence, by radiocarbon dates. The results indicate that during the last two glacial periods (particularly stages 6, 4, and 2) drier climates prevailed in both eastern Indonesia and northern Australia and lower montane forests dominated by Fagaceae expanded, indicating cooler climatic condition in eastern Indonesia. High charcoal and elemental carbon values suggest increased burning during these periods. Expansion of tropical lowland rainforests, humid mid and upper montane forests, fern and woodland cover occurred in the interglacial periods (stage 5 and the Holocene), indicating warm and humid conditions. The Banda Sea record indicates that before 37,000 yr B.P. Dipterocarpaceae formed an important part of the tropical lowland vegetation of eastern Indonesia. Its subsequent demise coincides with an increase in disturbance pollen indicators, the replacement of Eucalyptus woodlands and open forests by open grassland vegetation and higher burning levels. It is likely that these changes relate to an increase in human impact on the landscape.

Late Quaternary palaeoecology, palynology and palaeolimnology of a tropical lowland swamp: Rawa Danau, West-Java, Indonesia

Abstract Sedimentological, limnological and palynological analyses of a sediment core from a lowland site in West-Java, Indonesia, provide a detailed palaeoenvironmental record for the Late Glacial and the Holocene. The record suggests open vegetation under inferred drier climatic conditions for the Late Glacial. However, there is no unequivocal evidence for cooler conditions at this time. The onset of the Holocene coincides with a change to more humid climatic conditions, with the development of a fern-rich closed forest vegetation type. Dramatic changes in diatom community composition provide a striking record of habitat change associated with lake shallowing, but this process appears to be a result of basin in-filling rather than variations in precipitation/evaporation balance associated with climatic fluctuations. Evidence for human impact on the vegetation development is restricted to the last few hundred years.

A Late Quaternary pollen record from deep-sea core Fr10/95, GC17 offshore Cape Range Peninsula, northwestern Western Australia

Abstract Pollen and charcoal analysis on marine sediment core Fr10/95, GC-17 provides a record of vegetation, fire and climate change for the last 100 ka, with a hiatus from 64 to 46 ka, for the Cape Range Peninsula, Western Australia. Our results indicate significantly drier conditions and reduced summer rain after 46 ka compared with 100–64 ka. Periods of maximum summer rain occurred at 100, 80 and 70 ka. Vegetation changed from open Eucalyptus woodlands rich in grasses to open Eucalyptus and Gyrostemon shrublands rich in Chenopodiaceae/Amaranthaceae and Asteraceae Tubuliflorae, in the period from 46 to 40 ka. The charcoal record does not suggest human involvement in this vegetation change. The period from 14 to 3 ka was wetter with heavier summer rain compared to today, probably as a result of higher sea-surface temperatures. Increased strength of the Leeuwin Current during the last 5000 years is suggested by the presence of Pteridophyta spores derived from Indonesia.

Late Quaternary cycles of mangrove development and decline on the north Australian continental shelf

Mangrove communities in the Australian tropics presently occur as narrow belts of vegetation in estuaries and on sheltered, muddy coasts. Palynological data from continental shelf and deep-sea cores indicate a long-term cyclical component of mangrove development and decline at a regional scale, which can be linked to specific phases of late Quaternary sealevel change. Extensive mangrove development, relative to today, occurs during periods of marine transgression, whereas very diminished mangrove occurs during marine regressions and during rarer periods of relative sea-level stability. Episodes of flourishing mangrove cannot be linked to phases of humid climate, as has been suggested in studies elsewhere. Rather, the cycle of expansion and decline of mangrove communities on a grand scale is explained in terms of contrasting physiographic settings characteristic of continental-shelf coasts during transgressive and regressive phases, in particular by the existence, or lack, of well-developed tidal estuaries. Copyright (C) 1999 John Wiley & Sons, Ltd.

Pollen distribution in marine sediments from the south-eastern Indonesian waters

Abstract Pollen analysis on box core sediments from the south-eastern Indonesian waters provide information on trends in pollen transport and on pollen distribution in the marine surface sediments. Pollen and, at a lower rate, Pteridophyta spore concentration values tend to decrease with increasing distance from the shoreline. As a result, Pteridophyta percentages tend to increase with increasing distance from the shoreline. Mangrove pollen shows very little export from its distribution area, while pollen from the mid-upper montane group shows a substantial export from its onshore distribution area. In general, despite the complex nature of vegetation patterns and pollen transport in this region, the onshore distribution of individual taxa and major vegetation types is well reflected in the pollen distribution in the marine sediments.

Vegetation and climate change in West-Java, Indonesia during the last 135,000 years

Abstract Sedimentological and palynological analyses of two sediment cores from the intramontane Bandung basin (Java, Indonesia) provide the first palaeoclimatic record for the Indonesian region covering the last 135,000 years. Our data indicate anomalously dry conditions for the penultimate glacial and very warm and humid conditions during the last interglacial. During the last glacial period, fresh water swamp forests of the Bandung plain were replaced by open swamp vegetation, dominated by grasses and sedges, indicating a change to considerably drier climatic conditions, possibly as a consequence of lower sea levels at the onset of glacial conditions. For the Last Glacial Maximum, temperatures 4–7°C lower than at present are recorded.

Pollen distribution in marine surface sediments offshore Western Australia

We have examined the pollen content in sediments from the top of 38 cores taken offshore Western Australia (WA). Water depth for these cores ranges between 81 and 4090 m. All samples are used to plot maps of total pollen and total Pteridophyta spore concentration. Only the 26 core tops that yielded sufficient pollen grains (>35) are used in the present study to plot percentage maps for individual pollen taxa, including that of the genus Pinus (recently introduced to Australia). Five major bioclimatic zones are recognised by the distribution of pollen assemblages offshore WA. These are related to the amount and seasonality of rainfall and vegetation distribution on land. They reflect: (1) the open Eucalyptus forests and woodlands of northern WA with high and summer rainfall; (2) the open Eucalyptus woodlands with Acacia and grasslands of northwestern WA with lower (400–600 mm) and summer rainfall; (3) the open Acacia shrublands with grasses and grasslands of northwestern WA with low (300–400 mm) and summer rainfall; (4) the open Acacia shrublands of central WA with low (<300 mm) and summer as well as winter rainfall; and (5) the open Eucalyptus forests and mixed shrublands of southwestern WA with lower (300–600 mm) and winter rainfall. The influence of Indonesian-derived waters via surficial currents such as the Leeuwin Current is recognised by the presence of Pteridophyta spores in the sediments at northern sites.

A Review of the use of Non-Pollen Palynomorphs in Palaeoecology with Examples from Australia

Records of the past climate and vegetation of Australia are frequently constructed using data generated from the analysis of pollen and pteridophyte spores alone, or in association with sedimentology. We demonstrate that the organic residue prepared for pollen analysis yields other organic-walled microfossils that can be used to provide additional and independent palaeoenvironmental information. These non-pollen palynomorphs (NPP) include microscopic remains of algae, cyanobacteria, fungi, insects, other invertebrates and cormophytes. Our study of the NPP from two Late Quaternary lake records from western Victoria, Australia, provided additional information on water quality, salinity, depth, temperature and nutrient levels to the general environmental interpretation derived from pollen data. From a review of the ecological preferences of taxa, and comparison of the NPP results with pollen and spore curves from the lake records, ecological indicator values were derived. The study confirms the utility of NPP in enhancing environmental reconstructions in Australia, and encourages their routine examination in palynological studies.