A. Peter Kershaw

Evolution of late pleistocene and holocene climates in the circum-south pacific land areas

Paleovegetation maps were reconstructed based on a network of pollen records from Australia, New Zealand, and southern South America for 18 000, 12000, 9000, 6000, and 3000 BP and interpreted in terms of paleoclimatic patterns. These patterns permitted us to speculate on past atmospheric circulation in the South Pacific and the underlying forcing missing line mechanisms. During full glacial times, with vastly extended Australasian land area and circum-Antarctic ice-shelves, arid and cold conditions characterized all circum-South Pacific land areas, except for a narrow band in southern South America (43° to 45°S) that might have been even wetter and moister than today. This implies that ridging at subtropical and mid-latitudes must have been greatly increased and that the storm tracks were located farther south than today. At 12000 BP when precipitation had increased in southern Australia, New Zealand, and the mid-latitudes of South America, ridging was probably still as strong as before but had shifted into the eastern Pacific, leading to weaker westerlies in the western Pacific and more southerly located westerlies in the eastern Pacific. At 9000 BP when, except for northernmost Australia, precipitation reached near modern levels, the south Pacific ridges and the westerlies must have weakened. Because of the continuing land connection between New Guinea and Australia, and reduced seasonality, the monsoon pattern had still not developed. By 6000 BP, moisture levels in Australia and New Zealand reached their maximum, indicating that the monsoon pattern had become established. Ridging in the South Pacific was probably weaker than today, and the seasonal shift of the westerlies was stronger than before. By 3000 BP essentially modern conditions had been achieved, characterized by patterns of high seasonal variability.

Millennial and orbital variations of El Nino/Southern Oscillation and high-latitude climate in the last glacial period

The El Niño/Southern Oscillation (ENSO) phenomenon is believed to have operated continuously over the last glacial–interglacial cycle. ENSO variability has been suggested to be linked to millennial-scale oscillations in North Atlantic climate during that time, but the proposals disagree on whether increased frequency of El Niño events, the warm phase of ENSO, was linked to North Atlantic warm or cold periods. Here we present a high-resolution record of surface moisture, based on the degree of peat humification and the ratio of sedges to grass, from northern Queensland, Australia, covering the past 45,000 yr. We observe millennial-scale dry periods, indicating periods of frequent El Niño events (summer precipitation declines in El Niño years in northeastern Australia). We find that these dry periods are correlated to the Dansgaard–Oeschger events—millennial-scale warm events in the North Atlantic climate record—although no direct atmospheric connection from the North Atlantic to our site can be invoked. Additionally, we find climatic cycles at a semiprecessional timescale (∼11,900 yr). We suggest that climate variations in the tropical Pacific Ocean on millennial as well as orbital timescales, which determined precipitation in northeastern Australia, also exerted an influence on North Atlantic climate through atmospheric and oceanic teleconnections.

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

Environmental change in Greater Australia

Australia, a dry island continent in mid latitude, spans from tropical to cold temperate regions; long isolation has given it its own flora and fauna. Environmental changes in the late Quaternary have had their own and special courses in the continent and its several regions. The role of fires set by people is an important issue in the changing ‘natural’ landscape.

Climate and vegetation in southeastern Australia respond to Southern Hemisphere insolation forcing in the late Pliocene–early Pleistocene

Terrestrial climate responses to orbital forcing during the late Pliocene–early Pleistocene are poorly understood, particularly in the Southern Hemisphere, but are important for determination of the timing of regional climate evolution early in the history of the glaciated Quaternary world. We present a pollen record from southeastern Australia that shows marked cyclic change over some 280,000 yr straddling the Pliocene-Pleistocene boundary. Rainforest communities responded to climate forcing primarily within the precession and eccentricity bands, suggesting that major vegetation changes were driven directly by summer insolation, rather than by obliquity-dominated glacial cycles.

The relationship between modern pollen samples and environment in the humid tropics region of northeastern Australia

Abstract Pollen samples from moss polsters and litter were taken from 14 floristically-describes rainforest and marginal rainforest sites considered to cover a large range of existing environmental variation. One hundred and forty pollen types were identified of which only a small number could be related to parent species. However, a number of pollen types had systematic representation in relation to major environmental parameters, and pattern analyses revealed marked similarities in spatial distributions of sites based on pollen and species data. Site ordination demonstrated high correlation between pollen variation and annual and seasonal attributes of climate as well as soil fertility indicating the potential for refining palaeoenvironmental reconstructions from pollen diagrams produced from the region.

The last glacial cycle from Wyelangta, the Otway region of Victoria, Australia

Abstract This paper presents the first long Quaternary palynological record from the Otway region of Victoria, an area which is biogeographically important in that it is an outlier of the southeastern highlands containing distinctive forest vegetation with great similarities to the island of Tasmania. The record is derived from a small remnant patch of cool temperate rainforest dominated by Nothofagus cunninghamii surrounded by tall open eucalypt forest. Three clear phases are identified: an older rainforest phase dated to beyond 40,000 years BP which probably represents the latter part of Oxygen Isotope Stage 5; a phase of more open vegetation which covers at least part of the last glacial period; and a younger rainforest phase of Holocene age. The record is significant in providing refinements to late Quaternary climatic estimates from southeastern Australia utilising the climatic profiles of key rainforest taxa, and in indicating the likely presence and nature of a glacial rainforest ‘refugium’. The occurrence of a major rain forest tree, Phyllocladus, during the early forest phase and of the subalpine taxon Gunnera, during the last glacial period, taxa now restricted to Tasmania, demonstrates an even greater biogeographic link to this island in the recent past. Their extinction on the mainland is consistent with the general demise of cool temperate taxa with close Gondwanan affinities on the Australian mainland through the Late Cenozoic period. Their late disappearance contributes to the growing list of mainland extinctions of ancient and geographically interesting taxa adding weight to the proposal that Aboriginal burning has had a substantial impact on the Australian landscape during the last glacial cycle.

The contributions of uranium/thorium and marine palynology to the dating of the Lake Wangoom pollen record, western plains of Victoria, Australia

Abstract An extended pollen record from Lake Wangoom provides clear evidence for two climatic cycles incorporating three major effective precipitation peaks. The existing radiocarbon dates and age estimates derived from uranium/thorium dating and correlation with the pollen sequence from an isotopically-dated marine record presented here provide conflicting chronologies for these cycles. The radiocarbon dates indicate the youngest and middle precipitation peaks correspond, respectively, to the Holocene and the last major interstadial (oxygen isotope stage 3). By extrapolation, the oldest peak correlates most closely with substage 5c. Uranium/thorium disequilibrium dates suggest both the middle and oldest precipitation peaks occur within the isotope stage 5 complex, the middle phase corresponding with an interstadial and the oldest with the height of the Last Interglacial. The most reliable chronology, at least for the later cycle, is considered to be provided by comparison with the pollen record from a marine core with an oxygen isotope sequence from offshore Victoria. This record indicates that the last time precipitation levels attained those of the Holocene was during the Last Interglacial period and suggests that the Wangoom record extends back to the penultimate interglacial of isotope stage 7.

Environmental and cultural change on the Mt Eccles lava-flow landscapes of southwest Victoria, Australia

The Gunditjmara people developed a socio-economic system based on the modification of wetland ecosystems associated with the Mt Eccles lava flow primarily for sustainable production and management of the highly nutritious shortfin eel (Anguilla australis). This paper examines the environmental history of these landscapes since their inception about 30 000 years ago, through palaeoecological analysis of sediment cores from associated lakes and swamps, in order to contribute to an understanding of the causes and timing of cultural transformation. Two records cover the whole of the 30 000 year history of the landscape while two others provide evidence of change within the Holocene. A great deal of variation within the landscape is revealed, both temporally and spatially, with opportunities for human exploitation through the whole recorded period. Although most features of the records can be explained by natural landscape development and climate change, some human modification can be suggested from around the Pleistocene—Holocene transition while more obvious indications of management relating to eel aquaculture are evident from about 4000 cal. yr BP that appear to include adaptations to the onset of a drier and more variable climate. The study has implications for the explanation of intensification of settlement in Australia more generally within the mid to late Holocene.

Evolution and History of Mediterranean Vegetation Types in Australia

Mediterranean climates in Australia occur in the southwest and in near coastal South Austalia and adjacent western Victoria. Most of these regions support species-rich sclerophyllous heaths, with or without scattered tree cover, and eucalypt woodland with herbaceous understory. Despite wide taxonomic differences the regions show strong physiological and structural analogues with vegetation in other mediterranean regions.