Barry H. Lomax

Reconstruction of past vegetation underpins understanding of long-term ecosystem and societal change, helping to contextualise present-day patterns in biodiversity, ecosystem trajectories and effective landscape management practices against historical ecosystem states. This is particularly important in regions, such as southeastern Australia, where landscapes have been extensively shaped by long-term human activity including Indigenous fire management, creating cultural landscapes that can be difficult to identify through traditional palaeoecological techniques. Quantitative vegetation reconstruction models provide an opportunity to reconstruct these systems with greater precision but require robust validation with real-world data before application to past landscapes. Here, we present the first Southern Hemisphere application of the Extended Downscaling Approach (EDA), focussing on western Tasmania and southeastern Victoria. Using 86 modern pollen samples from moss and sedimentary records across seven study locations, we test whether the EDA reconstructs local-scale vegetation cover more accurately than uncorrected pollen percentages. By comparing EDA outputs with ground-surveyed vegetation cover, we find that the EDA reduces taxonomic representation biases, particularly for tree taxa. Across all study locations, EDA reconstructions differ from surveyed vegetation by <2.5% on average, compared with 4–9% for uncorrected pollen, while also showing higher Bray-Curtis similarity and Squared Chord Distance (SCD) values consistently below southeastern Australian analogue benchmarks. While this study does not assess the spatial outputs of the EDA, it demonstrates that the model can provide reliable local-scale vegetation reconstructions, supporting future spatial validation and Holocene applications within ancient cultural landscapes.

Current morphological palynological methods for taxonomic discrimination of wild Poaceae versus domesticated cereals result in high levels of uncertainty. This uncertainty complicates the use of pollen records when investigating changes in historical landscapes managed by communities since the first evidence of cereal cultivation. To improve taxonomic resolution in the Poaceae family, we applied a chemotaxonomic approach using pollen chemical traits measured by Fourier-transform infrared (FTIR) microspectroscopy. Predictive classifier models trained on the pollen-derived chemotaxonomic data of 22 modern grass taxa yielded an accuracy of 87.4%, indicating a strong taxonomic signal. Next, subfossil pollen from Nar Gölü, in Cappadocia, Türkiye, was classified according to the closest match from modern pollen chemistry reference library. Our study shows that such subfossil pollen classification, although challenging, is possible when the chemistry of the subfossils lies within the modern reference range, and therefore exhibit chemical signatures comparable to extant pollen. For this reason, novelty detection techniques were employed to distinguish subfossil spectra non-existent (novel) to the modern dataset and reject their classifications. This study represents the first attempt to use chemotaxonomy to classify subfossil pollen. We provide an assessment of the potential of such methods for future applications, such as palaeoecological research to classify cryptic pollen assemblages and further unpack ancient agricultural systems.

The Permian–Triassic mass extinction represents the most severe loss of biodiversity in Earth history and profoundly reorganized terrestrial ecosystems. On land, this crisis was followed by a marked floral turnover, with herbaceous lycophytes dominating Early Triassic vegetation. Here we show that these pioneer (so-called disaster) taxa that rapidly colonized stressed post-extinction environments, possessed specialized physiological traits that promoted survival under extreme conditions. Independent phylogenetic analyses show that Early Triassic lycophytes are closely related to modern Isoetales, a group characterized by exceptional ecophysiological flexibility. Their carbon isotope signatures resemble those of extant Isoetes that use crassulacean acid metabolism (CAM) photosynthesis, indicating a similar physiological strategy in deep time. Coupling these results with climate simulations suggests that CAM photosynthesis could have conferred a substantial advantage under Early Triassic super greenhouse conditions. Together, our findings identify CAM physiology as a potential mechanism enabling plant survival and ecosystem recovery following Earth’s largest mass extinction.

Elevated levels of surface ultraviolet-B (UV-B) irradiance can have a negative impact on different aspects of ecosystem functioning. Our understanding of spatial and temporal variations in surface UV-B in the past is limited, mainly due to the challenges of reconstructing and modelling surface UV-B prior to the instrumental record. Here, we reconstruct surface UV-B irradiance for the Southern South Island of New Zealand, on sub-decadal resolution over the past 60 years and during the Maunder Minimum, using Pinus and Prumnopitys taxifolia sporopollenin chemistry from the Lake Ohau sediment sequence. We show a statistically significant positive relationship between UV-absorbing compounds (UACs) recorded in both taxa. These results indicate that different taxa show similar trends in UAC production in response to short-term variations in UV-B radiation. We further observe strong anticorrelation between the Pinus record and total column ozone, and strong positive correlation with annually estimated erythemally weighted and surface UV-B in the area. This demonstrates that variations in ozone thickness and cloud cover are the main regulators on sub-decadal changes in surface level UV-B flux, rather than solar output. The strong correlations were not observed with the Prumnopitys taxifolia UAC data, which can be ascribed to a lack of high-resolution data for the distal areas where the pollen grains were sourced from rather than the taxon not responding to UV-B induced stress. These results are consistent with our sub-decadal observations over the Maunder Minimum, a period of lower solar activity. We found no evidence for the 11-year solar cycle or a relationship with TSI or UV-B for the UAC data spanning the Maunder Minimum. The lack of a relationship can be explained by population-level factors influencing the relationship, with presumably cloud cover being the most dominant factor. A comparison of broad trends shows that the mean UAC values during the Maunder Minimum are lower than those from the period just before and after. Mean values from the satellite era are lower than those of the Maunder Minimum, which can be explained by Maunder Minimum Prumnopitys taxifolia trees experiencing higher annual sunshine hours due to different source locations than those of the satellite era. The biochemical responses in both Pinus and Prumnopitys taxifolia recorded here show the potential for local to regional surface UV-B reconstructions using the UAC proxy over both short-term and long-term temporal resolutions.

Mutated pteridophyte spores occur abundantly in conjunction with the end-Triassic mass-extinction (ETME), ~201.6 million years ago, one of the ‘Big Five’ mass-extinction events of the past 500 million years. Based on high concentrations of sedimentary mercury (Hg) in beds that contain abundant mutated fern spore fossils, it has been hypothesized that volcanogenic Hg-emission from large-scale volcanism in the Central Atlantic Magmatic Province exerted stress on standing and pioneering vegetation, causing malfunctions in meiosis and the production of malformed pteridophyte spores. Here, we provide the first clear in vivo evidence for anomalously high Hg among the plants that survived and proliferated through the ETME using synchrotron X-ray fluorescence (XRF). Our analysis reveals highly enriched values of Hg within the fronds of the earliest Jurassic fern Phlebopteris angustiloba from southern Germany. Intriguingly, P. angustiloba, a member of the Matoniaceae, is recognized as the parent plant which produced malformed spores within the Deltoidospora-Concavisporites complex that are common in the same beds that contain the fossil fern leaves. Using XRF and X-ray absorption near edge structure (XANES) analyses, we made comparisons between the fossil fern leaves and those of extant ferns growing in high-mercury environments in Slovenia, Slovakia, and the Czech Republic. These comparisons suggest that ferns can tolerate elevated Hg-levels and bind it in their placentas with sulfurous compounds. Our combined analysis of extant and extinct ferns suggests that these traits may have evolved in response to past environments with high concentrations of toxic metals—like those caused by magmatically-triggered mass extinctions—during which metal-tolerant strategies would have greatly enhanced survivorship.

Two-hundred-million years ago, the emission of an estimated 100,000 Gt of CO2 during pulsed eruptions in the Central Atlantic Magmatic Province had dire consequences for the biosphere driving the end-Triassic mass-extinction (ETME). Palynological assemblages obtained from drill cores in Germany, Luxemburg, Denmark and the UK that span the extinction event exhibit a remarkable darkening of pollen and spores that is at odds with simple thermal maturation. Here, we investigate this latest Triassic “Dark Zone”, using the Palynomorph Darkening Index (PDI) obtained from trilete fern spores and Classopollis pollen. Coinciding with a collapse of forest communities and the spread of a fern-dominated pioneer vegetation, PDI reaches peak darkness in the Germanic Triletes Beds and equivalent strata elsewhere. Comparison of PDI records from fossil pollen and spores to the results of controlled heating experiments of modern Lycopodium spores indicates that latest Triassic darkening of palynomorphs was caused by surface fires carried in fern savannahs. Frequent wildfires were widespread in Europe during the ETME based on elevated levels of micro-charcoal and pyrolytic polycyclic aromatic hydrocarbons (PAHs) during the “Dark Zone”. Continental-scale wildfires during the end-Triassic mass-extinction suggests intense climate change-induced heat stress on vegetation contributed to the collapse of terrestrial ecosystems.

Two-hundred-million years ago, the emission of an estimated 100,000 Gt of CO2 during pulsed eruptions in the Central Atlantic Magmatic Province had dire consequences for the biosphere and resulted in the end-Triassic extinction. The exact causes for the extinction of organisms remain enigmatic, but a complex and drawn-out scenario is emerging that is in line with the pulsed activity in the CAMP. Palynological assemblages obtained from the immediate extinction interval from multiple locations exhibit a remarkable darkening of pollen and spores that is at odds with simple thermal maturation during burial. Here, we investigate this latest Triassic “dark zone”, using the Palynomorph Darkening Index (PDI) obtained from trilete fern spores in the Schandelah-1 core (North Germany) and Classopollis pollen in drill cores from Denmark (Stenlille-4), the United Kingdom (ICDP Prees-2), and Luxemburg (Elvange). Coinciding with a collapse of forest vegetation and the spread of a pioneer fern vegetation, the fern spores’ PDI reaches peak darkness in the uppermost Triletes Beds from Germany and equivalents elsewhere. This darkening event is mimicked in highest PDI values in Classopollis from the upper Lilstock Formation in the Prees-2 core and equivalent beds in the Elvange and Stenlille-4 cores. Controlled heating experiments of Lycopodium spores followed by PDI analyses suggest that latest Triassic darkening of palynomorphs is consistent with frequent surface fires carried in fern savannahs. The ensuing extreme soil erosion during wetter intervals resulted in mass removal of charred organic material in coastal sediments. The impact of continental-scale wildfires during the height of the end-Triassic mass-extinction suggests intense climate change exerting heat stress on vegetation as a major factor in the collapse of terrestrial ecosystems.

During the Permian-Triassic Mass Extinction (PTME) ~252Ma, diverse lowland forests were replaced by low diversity pioneer herbaceous lycopod communities that proceeded to dominate the Early and Middle Triassic landscape. The flourishing of Early-Middle Triassic herbaceous lycopods was coincident with data that suggests lethally warm surface temperatures (>40ºC) occurred across large regions of the planet. To explore how these plants were able to thrive during this interval of enhanced climatic stress, we collected data from over 400 fossil plant specimens from South China, supplemented by additional data from literature reviews from other regions and geological ages. Our studies on their morphology indicate that among all Phanerozoic lycopods the transitional Permian-Triassic genus Tomiostrobus (=Annalepis) has the closest morphological relationship with the recent lycopod Isoetes.Extant Isoetes are renowned for their flexibility with regard to the photosynthetic pathway they use and their capacity to absorb CO2 through their roots. To evaluate whether this photosynthetic flexibility was linked to their Early-Middle Triassic ecosystem dominance, we undertook carbon isotope and sedimentary facies analysis including plant taphonomy to test for the presence of the Crassulacean Acid Metabolism (CAM) photosynthetic pathway. Plants capable of CAM pathway growing in stressful environment typically have heavier isotopic signatures while show typical C3 plant signatures in hospitable environment. Our carbon isotope data shows that Permian Triassic Transition Tomiostrobus isotopic signature is on average ~2‰ less negative when compared to contemporary non lycophyte vegetation. Furthermore, the carbon isotope of the Middle Triassic lycopods ~1.07‰ heavier than the other plants, while Late Permian Lepidodendron exhibits a similar δ13C value with other contemporary plants. These findings suggest that CAM photosynthesis may have played a role in the dominance of the Triassic herbaceous lycopods. The dominance of CAM plants following the PTME has implications from an Earth Systems standpoint due to their diminished productivity and a lower capacity for biotic weathering, features that likely suppressed negative feedback loops important in driving climate stabilization during the ~5Ma PTME recovery phase.

Https://doi.org/10.1016/j.marpolbul.2023.115350 Introduction: X-ray Computed Tomography (CT) is a three-dimensional non-destructive imaging technique, which could in theory allow for the non-invasive identification of microplastics in-situ within sediment cores. In this study, the utility of CT was explored as a novel technique for the non-destructive analysis of microplastics in river sediments, forming part of a wider study investigating sources and sinks of microplastics in the river Thames estuary, UK. Methods: The technique was tested in three stages: (1) layered cores (for assessing detectability), (2) randomly spiked cores (simulating environmental samples), and (3) environmental samples (real-world examples). Layered and spiked cores were created using a stock of homogenised intertidal foreshore sediment collected from Purfleet on the Thames estuary. Each of the four cores for both types were spiked with a different plastic polymer to test the influence of plastic type on recoverability. They were also categorised as ‘large’ (~4 mm diameter) or ‘small’ microplastics (~125 μm diameter), to assess the impact of size on recoverability. For the environmental samples, two sediment gravity cores were used which had been extracted from a transect of Barking Creek (a tributary of the Thames) as part of the wider study. Results: When examined in layers within artificial cores, all microplastic types could be observed by CT imagery, with good contrast in X-ray attenuation against background sediments. The size and shape were reliably represented, allowing discrete particles to be classified using existing typology (Fig. 1). Differences in attenuation between polymer types suggested that it may be possible to uniquely identify different plastic polymers. Large microplastics were also detectable within spiked cores, having sufficient difference in attenuation to isolate individual microplastics (Fig. 2). Due to limitations on scan resolution, smaller microplastics could not be detected in spiked cores. Imaging of environmental samples revealed two distinct cores in terms of sediment structure, and a range of particle types were visible in the imagery of both (Fig. 3). It was not yet possible to confidently differentiate microplastic particles from others within these cores. Figure 1: Grayscale CT image slices of layered cores, annotated with image average gray level values for different particle types. Figure 2: False colour 3D reconstruction of polypropylene (left) and PET (right) spiked core scans, when suspected microplastics were isolated by a specified grayscale colour range and digitally coloured according to particle volume. Figure 3: CT image slices of environmental cores UT3C (top) and UT3F (bottom). Core UT3C was extracted from Barking Creek (London, UK) and spanned depths of 0-30 cm, while UT3F was from the adjacent saltmarsh, spanning depths of 30-60 cm. Conclusions: This study shows that microplastics can be detected in sediments using CT. As a highly complementary approach, it has potential to be used alongside established techniques to reveal additional information about the sediment structure. While further work is needed to make it a robust, reproducible screening technique for the direct investigation of microplastics in environmental samples, this is an important early step in the use of CT within the field.