Palaeoecological Record Research Articles

A novel, continuous high-resolution palaeoecological record from central Italy suggests comparable land-use dynamics in Southern and Central Europe during the Neolithic

Although rare, temporally and taxonomically highly-resolved palaeoecological studies with high chronological precision are essential to perform detailed comparisons with precisely dated independent evidence such as archaeological findings, historical events, or palaeoclimatic data. Using a new highly-resolved and chronologically precise sedimentary record from Lago di Mezzano (central Italy), we reconstruct decadal-scale vegetation, species diversity, and fire dynamics, aiming to better understand the linkages between climate, land use, fire, and plant communities from the Neolithic to the Copper Age (c. 5100–3100 cal. BC). Closed, mixed beech-oak forests, including evergreen Quercus ilex, dominated the landscape around Lago di Mezzano during the Neolithic and were disturbed by repeated opening phases, with important implications for lake biogeochemistry and mixing regimes. This was in conjunction with increasing fire activity to promote agro-pastoral practices, as inferred from increasing charcoal, Cerealia type, Triticum type, Hordeum type, Plantago lanceolata type, and Urtica pollen. Fires, on their turn, augmented species diversity (richness and evenness). The comparison of the Mediterranean record from Lago di Mezzano with available continuous and high-precision submediterranean and cool-temperate palynological sequences suggests comparable land use pulses across Southern and Central European regions, most likely in connection with climate change. The outcomes of this study are not only of palaeoecological and archaeological interest; they may also help to improve projections of ecosystem dynamics under future global change.

A paleoecological context for forest distribution and restoration in Grootbos Nature Reserve, Agulhas Plain, South Africa

Grootbos Nature Reserve falls within the Cape Floristic Region of South Africa and comprises fynbos and forest vegetation elements, which exist as alternate stable states and are naturally maintained by feedbacks between vegetation, fire, topography and climate. The objective of this study was to investigate changes in forest extent in the Baviaansfontein valley in Grootbos Nature Reserve in order to understand whether current forest coverage was greater or lesser prior to colonial settlement. Incorporating paleoecology has the potential to define historical ranges of landscape variability that can guide forest restoration programs that are aligned to historical forest occurrence. Not all landscapes are suited for tree planting initiatives as they harbor indigenous open vegetation, which is of conservation value. Historical and palaeoecological information is especially valuable as tree planting initiatives and reforestation programs are becoming more popular. Here we present a combined palynological (pollen, spores, charcoal) and geochemical approach (X-ray fluorescence elemental ratios, Loss-on-ignition), to evaluate the historic extent and distribution of forest and fynbos vegetation for the past ~250 years at Baviaansfontein in the Grootbos Nature Reserve. The start of the record was dominated by pollen typical of asteraceous fynbos, with evidence of forest elements also present, though in low abundance. After 200 years (c.1750 CE–1950 CE) of increased input of micro- and macrocharcoal, the subsequent decline in charcoal indicates a decrease in fire occurrence. This decline coincides with increased input of forest pollen taxa, suggesting that fire suppression most likely triggered forest expansion and perhaps initiated the beginning of a biome boundary shift. The continued decline in fire promoted the development of the present-day proteoid fynbos type around ~1980 CE and was responsible for the replacement of the previously more asteraceous-dominated fynbos type. The results show that changes in fire occurrence have driven compositional changes over time within fynbos but also contributed to the expansion of forest at the expense of fynbos. Considering the palaeoecological record and the expected warmer climate with more fires, forest expansion at Baviaansfontein is not recommended. The proteoid-dominated fynbos biome might be similarly negatively affected by warmer climate and a shift to an asteraceous fynbos community could occur in the future.

Influence of flooding variability on the development of an Amazonian peatland

ABSTRACTPeat in the Pastaza–Marañón Foreland Basin (PMFB), northern Peru, forms beneath open wetlands, palm swamps, pole forests and seasonally flooded forests. These vegetation communities may represent different successional stages of peatlands, but the spatiotemporal patterns of peatland development in Amazonia are still poorly understood. We present a new geochemical and palaeoecological record spanning the last c. 4330 years from an open peatland (San Roque, core SAR_T3_03_B). Our results suggest the persistence of predominantly herbaceous vegetation communities at the core site since the start of peat accumulation (c. 3180 cal a bp). Micro‐X‐ray fluorescence core scanning provides evidence for episodes of fluvially derived minerogenic input and simultaneous increases in flood‐tolerant taxa relating to intervals of increased frequency and depth of riverine flooding. The establishment of Mauritia flexuosa palms from around 440 cal a bp coincided with a shift to lower flooding depth and frequency which continues to the present day. This study reveals the role of flooding variability in shaping peatland development and influencing vegetation succession in the PMFB, underlining the need to understand natural environmental variability for the conservation of these ecosystems due to their vital contributions to ecosystem services and carbon storage.

Spatially explicit, quantitative reconstruction of past vegetation based on pollen or charcoal data as a tool for autecology of trees

ContextThe determination of autecological preferences based on long-term vegetation dynamics is hampered by the lack of realistic estimates for past occurrence and abundance patterns. Palaeoecological record has still rather character of points than spatially continuous maps.ObjectivesTo infer long-term autecological preferences of trees from reconstructed vegetation. Compare reconstructions based on pollen and charcoals.MethodsWe employed to the regional training set of 58 sites the Extended Downscaling Approach (EDA) using nine topographic factors clustered in 8 habitat classes, data on pollen productivity estimates, fossil pollen, charcoal sequences from soil and archaeological contexts. Based on abundances and habitat preferences from the last 9 millennia, we calculated the autecological preferences of tree taxa, using multivariate statistics.ResultsThe significant spatiotemporal patterns between soil-charcoal and pollen-based EDA validated the reconstruction, the use of both records in the EDA, and the EDA model. One of the topographic indices—vertical distance to channel network—evidenced the following: the closest taxon to the groundwater is Picea; Abies, Betula, Pinus and Quercus have intermediate distances; Fagus grows far from the channel network and Corylus even further.ConclusionsThe EDA model linked past forest composition to realistic topography. Such a spatially explicit reconstruction produced by our new algorithm allows inferring the relationship between past plant communities and environmental variables. The long-term preferences of tree species to habitat characteristics match their current autecological demands. This might be a breakthrough in quantitative plant paleoecology.

New insights into the origin of buckwheat cultivation in southwestern China from pollen data.

Buckwheat is an important crop which originated in China and spread widely across Eurasia. However, exactly where in China domestication took place remains controversial. Archaeological and palynological records suggest a longer cultivation history of buckwheat in northern China than in southwestern China, but this conflicts with phylogenetic evidence implicating southwestern China as the centre of origin and diversity of buckwheat. We investigate alternative methodologies for inferring the occurrence of buckwheat cultivation and suggest that relative abundance could provide a reliable measure for distinguishing between wild and cultivated buckwheat in both present-day and fossil samples. Approximately 12 800-yr palaeoecological record shows that Fagopyrum pollen occurred only infrequently before the early Holocene. As southwestern China entered the early agricultural period, c. 8000-7000 yr ago, a slight increase in abundance of Fagopyrum pollen was observed. Approximately 4000 yr ago, concurrent with the Pu minority beginning to develop dry-land agriculture, the abundance of Fagopyrum pollen increased significantly, suggesting the cultivation of this crop. Fagopyrum pollen rose to a maximum value c. 1270 yr ago, suggesting an intensification of agricultural activity. These findings fill a gap in the Fagopyrum pollen record in southwestern China and provide new indications that early cultivation may have occurred in this region.

Impact of farming on African landscapes

As the continent with the deepest record of human history, the relationship between landscape formation and human subsistence practices is inseparable. The activities that constitute ‘farming’ are open for some matter of discussion, but essentially speak to the co-evolution of human, plant and animal reproductive systems along a continuum of interdependence. This process is ever evolving, but has resulted in the formation of landscapes in which anthropogenic processes characterize ecosystem functionality in nearly all biomes on the continent. Practices of cultivation, broadly conceptualized, across Africa are varied in the ways in which they have transformed ecological systems and landscapes. The use of fire as a landscape management tool dates to the Pleistocene, and penning of wild sheep to the early Holocene. The alteration of the landscape of fear by these types of human activities had fundamentally restructured trophic systems in Africa prior to the introduction of agriculture. However, the introduction of animal herding and intensive forms of plant cultivation by the middle Holocene correlated to even more significant ecological changes. The creation of agricultural landscapes has had a negative impact on biodiversity in some locations, whereas other some practices at different points in time have positively affected biodiversity. It is now recognized that humans have long influenced the evolution of landscapes wherever they live, but the current research focuses on where, when and how socio-ecological processes become coupled in the palaeoecological record.

A 1300-year multi-proxy palaeoecological record from the northwest Putorana Plateau (Russian Subarctic): environmental changes, vegetation dynamics and fire history

This paper presents a reconstruction of natural environmental dynamics, wildfires and vegetation change in northwest Putorana Plateau during the last 1300 years. The study area is a remote and poorly investigated region of subarctic Siberia, relatively untouched by human impacts, which offers a unique opportunity to examine natural environmental dynamics and climate-vegetation-fire relationships. The paleoenvironmental reconstructions are based on multi-proxy analysis of the Gervi peatland including pollen, plant macrofossil, testate amoebae and charcoal analysis, loss on ignition measurements and AMS radiocarbon dating. The results revealed the main phases of regional paleoenvironmental change: a warm period between 680 and 1200 C.E. (Common Era) corresponding to the Mediaeval Climate Anomaly (MCA), followed by climate cooling during the Little Ice Age (LIA, 1200–1850 C.E.) and subsequent centuries. Climate amelioration during the MCA led to afforestation of northwestern Putorana Plateau and an expansion of spruce extending 70 km northeast of its present geographical range. A quantitative water-table reconstruction was generated using a testate amoebae transfer function and suggested that relatively dry climate conditions during the MCA triggered high fire frequencies. The LIA appeared in the study area as a period of pronounced climate cooling and moderate moistening, which caused an extension of tundra vegetation and a dramatic decline of fire activity. Distinct environmental changes at the study site were detected since 1990 C.E., characterized by a high peat accumulation rate and rising water table. Since 1990 C.E., the macroscopic charcoal accumulation rate in the peat core increased abruptly, suggesting a recent increase in the fire frequency in the study region.

Intensification of ENSO frequency drives forest disturbance in the andes during the holocene

The biodiverse montane forests of the tropical Andes are today frequently disturbed by rainfall-driven mass movements which occur mostly during extreme El Niño events. Over the coming decades these events are projected to double under the 1.5 °C global warming scenario. The consequent increased rainfall and mass movement events likely present an elevated risk to millions of people living in the Andes. However, the impact of more frequent rainfall extremes remains unclear due to a lack of studies that directly link past changes in El Niño-Southern Oscillation (ENSO) frequency to forest and landscape disturbance patterns. Here, we present the first Holocene palaeoecological record from Laguna Pallcacocha, southern Ecuador, a key site for El Niño reconstructions. We demonstrate that for the past 10,000 years plant taxa indicative of recolonization – such as Alnus acuminata – covary with El Niño-induced flood layers in the lake. An amplified forest disturbance pattern is observed in the late Holocene, suggesting enhanced slope instability following deforestation. The temporal pattern is not explained by tree line fluctuations or human impact, while the latter does amplify the impact of ENSO on landscape disturbance. Spatial correlations between modern ENSO and precipitation are consistent with a regional comparison of Holocene records of landscape disturbance. Our results indicate that climate extremes, such as those associated with future intensification of El Niño, combined with ongoing land use change will increase the frequency of mass movements elevating risks for millions of people in the Andes.

Variations in modern pollen distribution in sediments from nearby upland lakes: implications for the interpretation of paleoecological data

To determine whether modern pollen content in sediments from upland lake systems reflects the factual regional and extra-local vegetation composition, we analysed twenty-five samples focusing on aspects such as pond size and morphology, relative position in the catchment, local vegetation, canopy configuration and seasonality of the water table. The average pollen percentages of all sediment samples studied allows a fairly good reconstruction of the main vegetation units in the area, but major differences between the average samples obtained in each sedimentary system, and also between some samples taken from the same system are found. The main factors explaining those differences are the size of the pond, its tree canopy and the seasonality of the water table, which strongly determines the Ericaceae and Pinus percentages. A high-resolution multiproxy palaeoecological record from a small upland lake is re-evaluated in light of the new experimental evidence, and it is concluded that the interpretation of the importance of heathland and pinewoods in the Late Glacial landscape using pollen data may be magnified by the transport of both pollen types through water flows and their accumulation in the basin. Furthermore, anomalous Pinus pollen peaks occur in dry periods when the water table remains low. The sediment can also be depleted of some high-buoyancy pollen types (tetrads and saccate) when the water level is high and effluents are active. These effects may also be important in fluvio-marine systems in which Ericaceae and Pinus pollen are often overrepresented.

Palaeoecological signals for Mesolithic land use in a Central European landscape?

ABSTRACTDuring the Early Holocene, climate was the major factor causing fires, but whether during the Mesolithic (~11.5–7.4 cal ka BP) people co‐shaped their environment by means of fire remains of debate. Few studies have tackled this question by linking high‐resolution multi‐proxy palaeoecological studies from near Mesolithic occupation sites. An Early Holocene sediment record from the Ammer Valley palaeo‐wetland in south‐west Germany was studied using pollen, micro‐ and macrocharcoal, and plant macroremains. Archaeological evidence from Early and Late Mesolithic sites of Rottenburg‐Siebenlinden allowed us to link this palaeoecological record with Mesolithic land use in the same catchment. Between 11.6 and 10.6 cal kabp,intensive wildfires reinforced the persistence of open and pioneer vegetation. A transition from a river‐dominated landscape towards a wetland with open stagnant waters at 10.6–9.5 cal ka bpmade the region attractive to hunter‐gatherers, providing various plant resources (incl. hazel). From 10.1 cal ka bponwards, Mesolithic communities may have shaped their environment by using fire as a tool to expand open areas, which were important for the implementation of their subsistence strategies. After 9.5 cal ka bp, human control over fires cannot be excluded as Mesolithic occupation phases chronologically coincide with frequent low‐intensity fires and vegetation disturbance.

Palaeoecological record of long Eemian series from Kozłów (Central Poland) with reference to palaeoclimatic and palaeohydrological interpretation

In this study, we present the full sequence of Eemian succession from the Kozłów palaeolake – one of the key sites for Eemian Interglacial in this part of Poland. In the paper, previous palynological and diatom assessments were supplemented by further pollen, Cladocera and macrofossil analysis. This enabled detailed reconstruction of a palaeolake functioning under changes of climate and other environmental conditions during MIS 5e. All identified alterations of trophy, depth and aquatic vegetation within the reservoir point to dynamic changes in early stages of lake functioning, relatively stable conditions in mid-Eemian and gradual lake shallowing starting from Caprinus phase. Thus, Kozlów palaeolake joins the noble group of sites with exceptionally well-recognized multi-proxy records of the Eemian Interglacial environment, and has the potential to become a benchmark for this part of Europe.

The Contribution of Kurī (Polynesian Dog) to the Ecological Impacts of the Human Settlement of Aotearoa New Zealand

The pre-human Aotearoa New Zealand fauna was dominated by avian and reptilian species. Prior to first human settlement by East Polynesian colonists, the top predators were two giant raptorial birds. Aside from humans themselves, colonisation also resulted in the simultaneous introduction of two novel mammalian predators into this naive ecosystem, the kiore (Pacific rat) and kurī (Polynesian dog). While the ecological impacts of kiore are relatively well understood, those of kurī are difficult to assess, and as such kurī have frequently been disregarded as having any meaningful impact on New Zealand’s biodiversity. Here we use the archaeological and palaeoecological record to reassess the potential impacts of kurī on this ecosystem. We argue that far from being confined to villages, kurī could have had a significant widespread but relatively localised impact on New Zealand’s avian, reptilian and marine mammal (seals and sea lions) fauna as a novel predator of medium-sized species. In this way, kurī potentially amplified the already significant impacts of Polynesian colonists and their descendants on New Zealand’s ecosystem, prior to European arrival. As such, kurī should be included in models of human impact in addition to over-hunting, environmental modification and predation by kiore.

Plant community responses to experimental climate manipulation in a Welsh ombrotrophic peatland and their palaeoenvironmental context.

We test whether vegetation community composition from a 10-year climate manipulation experiment on a Welsh peat bog resembles vegetation communities during periods of climate change inferred from a peat core. Experimentally warmed and combined warmed and droughted treatments drove significant increases in ericaceous shrubs but Sphagnum was unaffected. Similarly, Calluna vulgaris seeds increase during inferred warmer periods in the palaeoecological record. Experimental short-term episodic drought (four 4-week drought treatments) did not affect vegetation. Plant community composition has undergone several abrupt changes throughout the past c. 1500years, often in response to human disturbance. Only slight changes occurred during the Medieval Climate Anomaly (c. 950-1250 Common Era [CE]) in vegetation and hydrology, while abrupt changes occurred during the Little Ice Age (c. 1300-1850 CE) when water tables were highest, suggesting that these shifts were driven by changes in water table, modulated by climate. A period of water table drawdown c. 1800, synchronous with historical records of increased drainage, corresponds with the development of the present-day vegetation community. Modern analogues for fossil material, characterized by abundant Rhynchospora alba and Sphagnum pulchrum, are more common after this event. Vegetation changes due to climate inferred from the palaeo record differ from those observed in the experiments, possibly relating to differences in the importance of drivers of vegetation change over varying timescales. Whereas temperature is frequently identified as the dominant driver of plant community change in experiments, sustained changes in water table appear to be more important in the long-term record. We find evidence that recent climate change and other anthropogenic stressors (e.g. drainage, heavy metal and nitrogen pollution) may promote the development of novel plant communities without analogues in the fossil record. These communities may be poorer at sequestering carbon and may respond differently to future climate change.

Environmental change during the last glacial on an ancient land bridge of southeast Australia

AbstractAimThe Last Glacial Maximum (LGM) remains an enigmatic period in southeast Australia due to the limited spatial and temporal resolution of its palaeoclimatic records. A major feature of the LGM landscape was the existence of the Bassian Land Bridge, joining Tasmania with the mainland of Australia during periods of low sea level, and potentially facilitating increased biotic movement between these regions. To better understand biogeographical changes on the land bridge and in southeast Australia generally during the LGM, we present a 35 ka‐year palaeoecological record from one of the larger islands of Bass Strait.LocationBass Strait, southeast Australia.TaxonEucalyptus, Poaceae, Monotoca, Myriophyllum, Zygnemataceae, Botryococcus, Pediastrum.MethodsPollen, charcoal, and non‐pollen palynomorphs were analysed in a 1.75‐m sediment core from truwana/Cape Barren Island, Bass Strait, to reconstruct changes in vegetation, fire regimes and lake levels on the Bassian Land Bridge. Results were then compared to existing palaeoenvironmental studies in the region to develop a broader context of the prevailing land bridge environment and the potential influence on biotic dispersals in Australia during the last glacial period.ResultsResults suggest a major vegetation shift on the Bassian Land Bridge in response to the establishment of the LGM climate, with grassland expansion at the expense of woodland from ~29–11 ka. Floristic richness, biomass burned and lake levels also markedly decreased through this period, with the driest interval being ~25–18 ka. Dryland herbaceous taxa dispersed between the mainland and Tasmania when the landbridge was fully exposed.Main conclusionsIn agreement with previous studies, our results show that the dry grassland that dominated southeast Australia (and Southern Hemisphere mid‐latitude areas) during the LGM also extended across the Bassian Land Bridge. The prevailing environment on the land bridge is likely to have exerted a selective influence on biotic dispersals in Australia during glacial periods.

The European palaeoecological record of Swedish red-listed beetles

Recent global changes have triggered a biodiversity crisis. However, climate fluctuations have always influenced biodiversity and humans have affected species distributions since prehistoric times. Conservation palaeobiology is a developing field that aims to understand the long-term dynamics of such interactions by studying the geohistorical records in a conservation perspective. Case studies exist for vertebrates and plants, but insects have largely been overlooked so far. Here, we analysed the current red-listed beetle species (Coleoptera) in Sweden and investigated their occurrence and representation in the European Quaternary fossil record. Fossil data currently exist for one third of the Swedish red-listed beetle species. All the red-list conservation classes are represented in the fossil record, which may allow for comparative studies. We found significantly different representations in the fossil records among taxonomic groups and ecological traits, which may depend on the fossil depositional and sampling environments and variation in how difficult species are to identify. Species that are today associated with modern urban environments were mostly found in Quaternary sites with archaeological human settlements, reflecting early human-driven environmental change. Combining modern and fossil insect species data for biodiversity conservation needs to be undertaken with care, and attention paid to biases in both modern and palaeo-data. Nevertheless, this approach opens new opportunities for conservation biology by providing a millennial-scale perspective on biodiversity change, including consideration of the long-term dynamics of species range shifts, species invasions and regional extinctions under changing climates.

Mid-Holocene coastline reconstruction from geomorphological sea level indicators in the Tràng An World Heritage Site, Northern Vietnam

In this paper we present a high resolution palaeo coastline model for the isolated limestone massif of Tràng An, Ninh Bình province, Vietnam. The archaeological and palaeoecological record here comprise rich archives of human activity set within a landscape that was cyclically transformed between inland and archipelagic states under the influence of past sea level changes. These records have become informative proxies in the study of current sea level rise. Well-preserved notches along the vertical limestone cliffs within the study property reveal several phases of prolonged stable sea levels that likely pertain to the Mid-Holocene marine transgression 8 ka BP to 4 ka BP and allow for detailed coastline reconstructions for parts of the Red River Delta (RRD). The resulting coastline model facilitates a closer look at past human responses to landscape and environmental changes at local and individual site-level, which improves our understanding of past human adaptations to climate-change induced sea level rise. These data also stand to inform current coastal vulnerability assessments and climate change response models.

Settlement, landscape and land-use change at a Pictish Elite Centre: Assessing the palaeoecological record for economic continuity and social change at Rhynie in NE Scotland

The first millennium AD was a transformative period when many of the medieval kingdoms of Europe began to take shape, but despite recent advances in palaeoecological and archaeological research there remains a shortage of interdisciplinary collaborative research targeting this period. For some regions we know relatively little about the societies who lived during this formative period. This current investigation focusses on an early medieval elite centre near to Rhynie in NE Scotland; an important power-centre during the fourth–seventh centuries AD as evidenced by a remarkable series of Class I Pictish symbol stones, fortified enclosures at Cairn more, Tap o’ Noth and the Craw-Stane, as well as high status metal-working and a range of continental imports from the Craw-Stane enclosure. However, by the end of the seventh century AD, elite focus appears to have shifted elsewhere with the Craw-Stane and Cairn More enclosures all being abandoned. By combining paleoenvironmental analysis with available historical and archaeological archives this paper provides new insights into societal change during the first Millennium AD, with focus on the economic, social and environmental impacts caused by the rise and subsequent abandonment of elite nodes of power. A calibrated age of AD 260–415, near the base of the core, coincides with the earliest dates for the Craw-Stane complex and pre-dates the construction of the nearby Cairn More enclosure. The results provide a rare snapshot of the Late Roman Iron Age to Medieval environment of Northeast Scotland. This centre appears to have been supported by a rich agricultural landscape, with evidence of pastoral and arable farming, and potential metal working. One of the most significant findings of this study has revealed that despite abandonment of these elite enclosed sites by the seventh century AD, people continued to utilise the surrounding landscape and available resources right through until modern times.

Special feature: measuring components of ecological resilience in long-term ecological datasets.

Ecological resilience has become a focal concept in ecosystem management. Palaeoecological records (i.e. the sub-fossil remains preserved in sediments) are useful archives to address ecological resilience since they can be used to reconstruct long-term temporal variations in ecosystem properties. The special feature presented here includes nine new papers from members and associates of the PAGES EcoRe3 community. The papers build on previous work in palaeoecology to investigate, identify and compare components of ecosystem resilience on centennial to millennial timescales. There are four key messages that can be summarized from the findings of papers within the special feature: (i) multi-proxy studies reveal insights into the presence and mechanisms of alternative states; (ii) transitions between alternative states may not necessarily be abrupt; (iii) components of ecological resilience can be identified in long-term ecological data and (iv) the palaeoecological record can also provide insights into factors influencing the resilience of ecosystem functioning. Overall, these papers demonstrate the importance of using long-term ecological records for addressing questions related to the theoretical framework provided by ecological resilience.

The fast-acting \u201cpulse\u201d of Heinrich Stadial 3 in a mid-latitude boreal ecosystem

A 3800 year-long radiocarbon-dated and highly-resolved palaeoecological record from Lake Fimon (N-Italy) served to investigate the effects of potential teleconnections between North Atlantic and mid-to-low latitudes at the transition from Marine Isotope Stage (MIS) 3 to 2. Boreal ecosystems documented in the Fimon record reacted in a sensitive way to millennial and sub-millennial scale Northern Hemisphere atmospheric circulation patterns. The high median time-resolution of 58 years allows the identification of five abrupt event-boundaries (i.e., main forest expansion and decline excursions) synchronous with the sharp stadial/interstadial (GS/GI) transitions within dating uncertainties. During Heinrich Stadial 3 (HS 3) we reconstruct more open and dry conditions, compared to the other GS, with a dominant regional scale fire signal. Linkages between local fires and climate-driven fuel changes resulted in high-magnitude fire peaks close to GI/GS boundaries, even exacerbated by local peatland conditions. Finally, palaeoecological data from the HS 3 interval unveiled an internal variability suggesting a peak between 30,425 and 29,772 cal BP (2σ error) which matches more depleted δ18O values in alpine speleothems. We hypothesise that this signal, broadly resembling that of other mid-latitudes proxies, may be attributed to the southward shift of the Northern Hemisphere storm tracks and the associated delayed iceberg discharge events as documented during other HS.

Vegetation over the last glacial maximum at Girraween Lagoon, monsoonal northern Australia

AbstractNorthern Australia is a region where limited information exists on environments at the last glacial maximum (LGM). Girraween Lagoon is located on the central northern coast of Australia and is a site representative of regional tropical savanna woodlands. Girraween Lagoon remained a perennial waterbody throughout the LGM, and as a result retains a complete proxy record of last-glacial climate, vegetation and fire. This study combines independent palynological and geochemical analyses to demonstrate a dramatic reduction in both tree cover and woody richness, and an expansion of grassland, relative to current vegetation at the site. The process of tree decline was primarily controlled by the cool-dry glacial climate and CO2 effects, though more localised site characteristics restricted wetland-associated vegetation. Fire processes played less of a role in determining vegetation than during the Holocene and modern day, with reduced fire activity consistent with significantly lower biomass available to burn. Girraween Lagoon's unique and detailed palaeoecological record provides the opportunity to explore and assess modelling studies of vegetation distribution during the LGM, particularly where a number of different global vegetation and/or climate simulations are inconsistent for northern Australia, and at a range of resolutions.