Simon Haberle

Post-glacial evolution of the Indo-Pacific Warm Pool and El Nino-Southern Oscillation

Recent research has revealed new insights into the temperature, size, and variability of the Indo-Pacific Warm Pool (IPWP) and the nature of the El Nino-Southern Oscillation (ENSO) since the Last Glacial Maximum (LGM). Sea surface temperature (SST) reconstructions from foraminiferal Mg/Ca, alkenone, and revised coral Sr/Ca palaeothermometry agree that SSTs in the IPWP during the LGM were similar to 3degreesC cooler than at present. In the central portion of the IPWF, the rapid post-glacial rise in SST led the deglaciation by similar to 3000 years to produce near-modern SSTs by the early Holocene. In contrast, further west and north, post-glacial shifts in SSTs in the South China and Sulu Seas are synchronous with abrupt climate changes in the North Atlantic. New evidence for the nature of the Little Ice Age in the tropics has been obtained from a 420-year record of coral Sr/Ca and 6180 from the Great Barrier Reef, Australia. This indicates that SSTs and salinity were higher in the 18th century than in the 20th century. The results suggest that the tropical Pacific played a role as a source region of water vapour during the global expansion of Little Ice Age glaciers. The onset of modern ENSO periodicities is identified by palaeo-ENSO records throughout the tropical Pacific region similar to 5000 years ago, with an abrupt increase in ENSO magnitude similar to 3000 years ago. Individual ENSO events recorded by corals reveal that the precipitation response to El Nino temperature anomalies was subdued in the mid-Holocene. The apparent non-linear onset of ENSO in the late Holocene appears to reflect abruptly enhanced interaction between the Southern Oscillation and the Pacific Intertropical Convergence Zone. Comparisons of precipitation variability recorded by Great Barrier Reef corals with ENSO indices for the last 350 years confirms that non-stationarity of ENSO teleconnections is a natural characteristic of modern climate

Holocene biomass burning and global dynamics of the carbon cycle

Fire regimes have changed during the Holocene due to changes in climate, vegetation, and in human practices. Here, we hypothesise that changes in fire regime may have affected the global CO2 concentration in the atmosphere through the Holocene. Our data are based on quantitative reconstructions of biomass burning deduced from stratified charcoal records from Europe, and South-, Central- and North America, and Oceania to test the fire-carbon release hypothesis. In Europe the significant increase of fire activity is dated approximately 6000 cal. yr ago. In north-eastern North America burning activity was greatest before 7500 years ago, very low between 7500-3000 years, and has been increasing since 3000 years ago. In tropical America, the pattern is more complex and apparently latitudinally zonal. Maximum burning occurred in the southern Amazon basin and in Central America during the middle Holocene, and during the last 2000 years in the northern Amazon basin. In Oceania, biomass burning has decreased since a maximum 5000 years ago. Biomass burning has broadly increased in the Northern and Southern hemispheres throughout the second half of the Holocene associated with changes in climate and human practices. Global fire indices parallel the increase of atmospheric CO2 concentration recorded in Antarctic ice cores. Future issues on carbon dynamics relatively to biomass burning are discussed to improve the quantitative reconstructions.

The aftermath of megafaunal extinction: Ecosystem transformation in Pleistocene Australia

Human Impact? Following the arrival of humans in Australia 40- to 50,000 years ago, many species of large vertebrates rapidly became extinct. By analyzing sediment cores from a site in northeastern Australia, Rule et al. (p. 1483; see the Perspective by McGlone) show that the extinction of the Australian megafauna caused important ecosystem shifts. Prominent among these were a shift from rainforest vegetation to sclerophyllous vegetation and a sustained increase in the incidence of fire. The cores also provide evidence of the cause of megafaunal extinction in Australia, ruling out climate and anthropogenic fire as possible causes while confirming that the extinctions closely followed human arrival. These findings show how landscapes sometimes have been fundamentally changed by the indirect effects of early humans—which underscores the impact that even prehistoric human societies had on natural systems. The extinction of megafauna 40,000 years ago after the arrival of humans led to major changes in vegetation and fire regimes. Giant vertebrates dominated many Pleistocene ecosystems. Many were herbivores, and their sudden extinction in prehistory could have had large ecological impacts. We used a high-resolution 130,000-year environmental record to help resolve the cause and reconstruct the ecological consequences of extinction of Australia’s megafauna. Our results suggest that human arrival rather than climate caused megafaunal extinction, which then triggered replacement of mixed rainforest by sclerophyll vegetation through a combination of direct effects on vegetation of relaxed herbivore pressure and increased fire in the landscape. This ecosystem shift was as large as any effect of climate change over the last glacial cycle, and indicates the magnitude of changes that may have followed megafaunal extinction elsewhere in the world.

Predictability of biomass burning in response to climate changes

Climate is an important control on biomass burning, but the sensitivity of fire to changes in temperature and moisture balance has not been quantified. We analyze sedimentary charcoal records to show that the changes in fire regime over the past 21,000 yrs are predictable from changes in regional climates. Analyses of paleo- fire data show that fire increases monotonically with changes in temperature and peaks at intermediate moisture levels, and that temperature is quantitatively the most important driver of changes in biomass burning over the past 21,000 yrs. Given that a similar relationship between climate drivers and fire emerges from analyses of the interannual variability in biomass burning shown by remote-sensing observations of month-by-month burnt area between 1996 and 2008, our results signal a serious cause for concern in the face of continuing global warming.

Effect of altitude on the carbon‐isotope composition of forest and grassland soils from Papua New Guinea

The carbon-isotope composition of both forest and grassland soils from Papua New Guinea exhibit predictable trends with increasing altitude. Soils under pure C3 vegetation (forests and alpine grasslands above 4000 m) show an increase in δ13C value with altitude paralleling the increase in δ13C value observed in plant leaves by Korner et al. [1988]. Grassland soils show a decrease in δ13C value above about 1000 m, from maximum values which are close to pure C4 values (−12 to −13‰ vs. PDB) to minimum values which are indistinguishable from pure C3 values at 3500–4000 m (∼−26‰). Within this general framework, several factors can influence the soil δ13C value at individual locations. In local forest settings, soil δ13C values will be influenced by the degree to which respired CO2 is re-utilized during photosynthesis, the proportions of leaf and wood litter, and the degree of decomposition. In grassland settings the primary factor controlling the observed δ13C variability at any specific altitude is the amount of nongrass C3 carbon present in the sample. It is also possible that other factors, such as moisture availability, may play some role in determining the proportions of C3 and C4 grasses at any given altitude, although further work would be required to substantiate such a link. The results provide a framework within which to more accurately constrain the carbon-isotope composition of terrestrial carbon pools and to interpret variations in the isotopic composition of riverine particulate organic carbon.

Late Quaternary vegetation change in the Tari Basin, Papua New Guinea

The changes in Late Quaternary vegetation at two sites in the Tari Basin, central highlands of New Guinea, are presented. Haeapugua basin (1650 m altitude) and Tugupugua basin (2300 m altitude) lie within the lower montane forest belt, where the climate is characterised by high relative humidity and low seasonality. Pollen analysis, mineral magnetics, carbonised particle analysis, and dating by radiocarbon and thermoluminescence techniques are employed to reconstruct the vegetation and sediment history. The sequences include fragmentary interglacial/interstadial records from before 50,000 yr B.P. and a continuous record from at least 28,000 yr B.P. to the present. The study shows that, prior to 21,000 yr B.P., vegetation in the basin was dominated by fluctuating proportions of tree taxa indicative of a forested environment. The montane forest taxon, Nothofagus, is important throughout the record, although other tree taxa, including Castanopsis, Myrtaceae, Dacrydium and Pandanus, attain dominance at different times under the influence of a range of environmental factors. The creation of an open environment around 21,000 yr B.P. is considered to be a consequence of the arrival of humans in the region. The late glacial transition, between 14,500 and 8500 yr B.P., is a period of climatic instability with landscape and vegetation adjustments proceeding at different rates across the highlands. Vegetational adjustments match modern ranges by about 8500 yr B.P., when swamp forest developed across the sites. At the lower altitude site there are indications of anthropogenic forest disturbance, associated with swamp forest clearance, commencing around 1700 yr B.P. and intensifying through to the present. Forest clearance is recorded only after 700 yr B.P. at the higher site, where agriculture was probably only sustainable after the introduction of sweet potato (Ipomoea batatas).

Environmental change in the Baliem Valley,* montane Irian Jaya, Republic of Indonesia

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New Evidence and Revised Interpretations of Early Agriculture in Highland New Guinea

This review of the evidence for early agriculture in New Guinea supported by new data from Kuk Swamp demonstrates that cultivation had begun there by at least 6950-6440 cal BP and probably much earlier. Contrary to previous ideas, the first farming in New Guinea was not owed to SouthEast Asia, but emerged independently in the Highlands. Indeed plants such as the banana were probably first domesticated in New Guinea and later diffused into the Asian continent.

Prehistoric human impact on rainforest biodiversity in highland New Guinea

In the highlands of New Guinea, the development of agriculture as an indigenous innovation during the Early Holocene is considered to have resulted in rapid loss of forest cover, a decrease in forest biodiversity and increased land degradation over thousands of years. But how important is human activity in shaping the diversity of vegetation communities over millennial time-scales? An evaluation of the change in biodiversity of forest habitats through the Late Glacial transition to the present in five palaeoecological sites from highland valleys, where intensive agriculture is practised today, is presented. A detailed analysis of the longest and most continuous record from Papua New Guinea is also presented using available biodiversity indices (palynological richness and biodiversity indicator taxa) as a means of identifying changes in diversity. The analysis shows that the collapse of key forest habitats in the highland valleys is evident during the Mid–Late Holocene. These changes are best explained by the adoption of new land management practices and altered disturbance regimes associated with agricultural activity, though climate change may also play a role. The implications of these findings for ecosystem conservation and sustainability of agriculture in New Guinea are discussed.

The Macroecology of Airborne Pollen in Australian and New Zealand Urban Areas

The composition and relative abundance of airborne pollen in urban areas of Australia and New Zealand are strongly influenced by geographical location, climate and land use. There is mounting evidence that the diversity and quality of airborne pollen is substantially modified by climate change and land-use yet there are insufficient data to project the future nature of these changes. Our study highlights the need for long-term aerobiological monitoring in Australian and New Zealand urban areas in a systematic, standardised, and sustained way, and provides a framework for targeting the most clinically significant taxa in terms of abundance, allergenic effects and public health burden.