The Eocene–Oligocene transition (EOT) was a climate shift from a largely ice-free greenhouse world to an icehouse climate, involving the first major glaciation of Antarctica and global cooling occurring ∼ 34 million years ago (Ma) and lasting ∼ 790 kyr. The change is marked by a global shift in deep-sea δ18O representing a combination of deep-ocean cooling and growth in land ice volume. At the same time, multiple independent proxies for ocean tempera- ture indicate sea surface cooling, and major changes in global fauna and flora record a shift toward more cold-climate- adapted species. The two principal suggested explanations of this transition are a decline in atmospheric CO2 and changes to ocean gateways, while orbital forcing likely influenced the precise timing of the glaciation. Here we review and synthesise proxy evidence of palaeogeography, temperature, ice sheets, ocean circulation and CO2 change from the marine and terrestrial realms. Furthermore, we quantitatively com- pare proxy records of change to an ensemble of climate model simulations of temperature change across the EOT. The simulations compare three forcing mechanisms across the EOT: CO2 decrease, palaeogeographic changes and ice sheet growth. Our model ensemble results demonstrate the need for a global cooling mechanism beyond the imposition of an ice sheet or palaeogeographic changes. We find that CO2 forcing involving a large decrease in CO2 of ca. 40 % (∼ 325 ppm drop) provides the best fit to the available proxy evidence, with ice sheet and palaeogeographic changes play- ing a secondary role. While this large decrease is consistent with some CO2 proxy records (the extreme endmember of decrease), the positive feedback mechanisms on ice growth are so strong that a modest CO2 decrease beyond a critical threshold for ice sheet initiation is well capable of triggering rapid ice sheet growth. Thus, the amplitude of CO2 decrease signalled by our data–model comparison should be consid- ered an upper estimate and perhaps artificially large, not least because the current generation of climate models do not in- clude dynamic ice sheets and in some cases may be under- sensitive to CO2 forcing. The model ensemble also cannot exclude the possibility that palaeogeographic changes could have triggered a reduction in CO2.

A new temperature data portal will aid scientists in tracking and accessing paleoclimate data from the Miocene, a past warm climate interval and future climate analogue.

The presence of stomata is a diagnostic trait of all living and extinct land plants with the exception of liverworts. They are preserved widely in the fossil record from anatomically pristine stomatal complexes on permineralized and charcoalified stems of the earliest land plants dating back >400 million years to isolated guard cell pairs in Quaternary aged palynological samples. Detailed study of fossil stomatal complexes has been used to track the evolution of genome size and to reconstruct atmospheric composition, to circumscribe new species to science and to bring ancient landscapes to life by providing both habitat information and insights on fossil plant ecophysiological function and life-form. This review explores how fossil stomata can be used to advance our understanding of plant, environment and atmospheric evolution over the Phanerozoic. We compare the utility of qualitative (e.g. presence/absence of stomatal crypts) versus quantitative stomatal traits (e.g. amphistomaty ratio) in palaeoecological reconstructions. A case study on Triassic-Jurassic Ginkgoales is provided to highlight the methodological difficulty of teasing apart the effect of genome size, ploidy and environment on guard cell size evolution across mass extinction boundaries. We critique both empirical and mechanistic stomatal-based models for palaeo-CO₂ reconstruction and highlight some key limitations and advantages of both approaches. Finally we question if different stomatal developmental pathways have ecophysiological consequence for leaf gas exchange and ultimately the application of different stomatal-based CO₂ proxy methods. We conclude that most studies currently only capture a fraction of the potential invaluable information that can be gleaned from fossilized stomata and highlight future approaches to their study that better integrate across the disciplinary boundaries of palaeobotany, developmental biology, palaeoecology and plant physiology.

The end-Triassic event (ETE), a short global interval occurring at the end of the Triassic Period (~201.5 Ma), was characterized by climate change, environmental upheaval, as well as widespread extinctions in both the marine and terrestrial realms. It was associated with extensive perturbations of the carbon cycle, principally caused by the volcanic emplacement of the Central Atlantic Magmatic Province in relation to the break-up of Pangea. The correlated change in atmospheric CO2 concentrations (pCO2) can be reconstructed with the stomatal proxy, which utilizes the inverse relationship between stomatal densities of plant leaves (here stomatal index (SI), which is the percentage of stomata relative to epidermal cells) and pCO2. Fossilized Lepidopteris leaves are common and widespread in Triassic strata, thus offering great potential for high-resolution pCO2 reconstructions. A dataset of leaf cuticle specimens belonging to the seed fern species Lepidopteris ottonis from sedimentary successions in Skåne (Scania), southern Sweden, provided the possibility of pCO2 reconstruction at the onset of the ETE. Here, we tested the intra- and interleaf variability of L. ottonis SI, and estimated the pCO2 during the onset of the ETE. Our findings confirm L. ottonis as a valid proxy for palaeo-pCO2, also when using smaller leaf fragments. Importantly, the statistical analyses showed that the SI values of abaxial and adaxial cuticles are significantly different, providing a tool to distinguish between the two sides and select cuticles for analysis. Reconstructed pCO2 increased from ~1000 pre ETE to ~1300 ppm at the onset of the event, a significant increase of ~30% over a relatively short time period. The pCO2 recorded here is similar to previously published estimates, and strongly supports the observed pattern of elevated pCO2 at the onset of the ETE.

Climate change is likely to have altered the ecological functioning of past ecosystems, and is likely to alter functioning in the future; however, the magnitude and direction of such changes are difficult to predict. Here we use a deep-time case study to evaluate the impact of a well-constrained CO2-induced global warming event on the ecological functioning of dominant plant communities. We use leaf mass per area (LMA), a widely used trait in modern plant ecology, to infer the palaeoecological strategy of fossil plant taxa. We show that palaeo-LMA can be inferred from fossil leaf cuticles based on a tight relationship between LMA and cuticle thickness observed among extant gymnosperms. Application of this new palaeo-LMA proxy to fossil gymnosperms from East Greenland reveals significant shifts in the dominant ecological strategies of vegetation found across the Triassic–Jurassic transition. Late Triassic forests, dominated by low-LMA taxa with inferred high transpiration rates and short leaf lifespans, were replaced in the Early Jurassic by forests dominated by high-LMA taxa that were likely to have slower metabolic rates. We suggest that extreme CO2-induced global warming selected for taxa with high LMA associated with a stress-tolerant strategy and that adaptive plasticity in leaf functional traits such as LMA contributed to post-warming ecological success.

To improve future predictions of anthropogenic climate change, a better understanding of the relationship between global temperature and atmospheric concentrations of CO2 (pCO2), or climate sensitivity, is urgently required. Analyzing proxy data from climate change episodes in the past is necessary to achieve this goal, with certain geologic periods, such as the Miocene climatic optimum (MCO), a transient period of global warming with global temperatures up to ~7°C higher than today, increasingly viewed as good analogues to future climate under present emission scenarios. However, a problem remains that climate models cannot reproduce MCO temperatures with less than ~800 ppm pCO2, while most previously published proxies record pCO2 < 450 ppm. Here, we reconstructed MCO pCO2 with a multitaxon fossil leaf database from the well‐dated MCO Lagerstätte deposits of Clarkia, Idaho, USA, using four current methods of pCO2 reconstructions. The methods are principally based on either stomatal densities, carbon isotopes, or a combination of both—thus offering independent results. The total of six reconstructions mostly record pCO2 of ~450–550 ppm. Although slightly higher than previously reconstructed pCO2, the discrepancy with the ~800 ppm required by climate models remains. We conclude that climate sensitivity was heightened during MCO, indicating that highly elevated temperatures can occur at relatively moderate pCO2. Ever higher climate sensitivity with rising temperatures should be very seriously considered in future predictions of climate change.

Reliable reconstructions of atmospheric carbon dioxide concentrations (pCO2) are required at higher resolution than currently available to help resolve the relationship between mass extinctions and changes in palaeo-pCO2 levels. Such reconstructions are needed: 1, at a high temporal resolution for constraining the pre- and post-extinction atmospheres; and 2, at a sufficient spatial resolution to constrain potential inter-hemispheric differences. Here we estimate pCO2 based on fossil Lauraceae leaf cuticle specimens derived from three localities with strata spanning the latest Cretaceous to the mid-Paleocene, including a new Cretaceous–Paleogene boundary (K–Pg) locality, in New Zealand. We use two independent methods of stomatal density-based pCO2 reconstructions; a transfer function calibrated using herbarium material and the stomatal ratio method, producing three calibration sets. Our results based on the mean values of each of the three calibration methods indicate pCO2 ranging between ca. 460 and 650 ppm during the latest Cretaceous, falling precipitously to average values between ca. 360 and 430 ppm across the K–Pg boundary, and further to ca. 305–320 ppm in the mid-Paleocene. A ‘spike’ of extremely high pCO2 at the K–Pg could not be confirmed, but our results are, nonetheless, consistent with previously published pCO2 records from the Northern Hemisphere, and show that stomatal density worldwide was responding to significant changes in pCO2 across the K–Pg.

The Miocene epoch (23.03–5.33 Ma) was a time interval of global warmth, relative to today. Continental configurations and mountain topography transitioned toward modern conditions, and many flora and fauna evolved into the same taxa that exist today. Miocene climate was dynamic: long periods of early and late glaciation bracketed a ∼2 Myr greenhouse interval—the Miocene Climatic Optimum (MCO). Floras, faunas, ice sheets, precipitation, pCO2, and ocean and atmospheric circulation mostly (but not ubiquitously) covaried with these large changes in climate. With higher temperatures and moderately higher pCO2 (∼400–600 ppm), the MCO has been suggested as a particularly appropriate analog for future climate scenarios, and for assessing the predictive accuracy of numerical climate models—the same models that are used to simulate future climate. Yet, Miocene conditions have proved difficult to reconcile with models. This implies either missing positive feedbacks in the models, a lack of knowledge of past climate forcings, or the need for re-interpretation of proxies, which might mitigate the model-data discrepancy. Our understanding of Miocene climatic, biogeochemical, and oceanic changes on broad spatial and temporal scales is still developing. New records documenting the physical, chemical, and biotic aspects of the Earth system are emerging, and together provide a more comprehensive understanding of this important time interval. Here, we review the state-of-the-art in Miocene climate, ocean circulation, biogeochemical cycling, ice sheet dynamics, and biotic adaptation research as inferred through proxy observations and modeling studies.

Flood basalt volcanism has been implicated in several episodes of mass extinctions and environmental degradation in the geological past, including at the Triassic–Jurassic (Tr–J) transition, through global warming caused by massive outgassing of carbon dioxide. However, the patterns of biodiversity loss observed are complicated and sometimes difficult to reconcile with the effects of global warming alone. Recently, attention has turned to additional volcanic products as potential aggravating factors, in particular sulphur dioxide (SO₂). SO₂ acts both directly as a noxious environmental pollutant and indirectly through forming aerosols in the atmosphere, which may cause transient global dimming and cooling. Here, we present a range of morphological changes to fossil plant leaf cuticle surfaces of hundreds of Ginkgoales and Bennettitales specimens across the Tr–J boundary of East Greenland. Our results indicate that morphological structures of distorted cuticles near the Tr–J boundary are consistent with modern cuticle SO₂-caused damage and supported by recent leaf-shape SO₂ proxy results, thus identifying cuticle surface morphology as a potentially powerful proxy for SO₂. Recording the timing and duration of SO₂ emissions in the past may help distinguish between the driving agents responsible for mass extinction events and thus improve our understanding of the Earth System.

To understand Earth ́s climate variability and improve predictions of future climate change, studying past climates is an important avenue to explore. A previously published record of pCO2, across the Triassic–Jurassic boundary (TJB, ~201 Ma) of East Greenland, showed that Bennettitales (Anamozamites and Pterophyllum) responded in parallel to the empirically proven pCO2-responders Ginkgoales, reducing their stomatal densities by half across the TJB, indicating a transient doubling of pCO2. The abundance of fossil Bennettitales in Mesozoic strata and natural history museum collections worldwide offers enormous potential for further stomatal proxy pCO2 reconstructions, but a suitable nearest living equivalent (NLE) should ideally first be identified for this extinct plant group. Using specimens from herbarium collections, three species of cycads, historically considered the best NLE, were tested for pCO2 response, as well as two species of tree ferns, grown in experimental growth chambers. None responded to changes in pCO2, and were consequently rejected as NLEs. Finally, two species of ferns were selected from the literature, and produced very similar pCO2 compared to Ginkgoales. However, these understory ferns are not appropriate NLEs for Bennettitales due to differences in habitat and a distant evolutionary relationship. Future work should test additional plant groups, in particular seed plants such as basal angiosperms and Gnetales, for suitability as NLE for Bennettitales in pCO2 reconstructions, for example through biogeo- chemical fingerprinting using infrared microspectroscopy. Until an appropriate NLE is identified, Bennettitales pCO2 can be reconstructed based on cross-calibration of stomatal densities with those of co-occurring pCO2 responders, such as Ginkgoales.

To understand Earth ́s climate variability and improve predictions of future climate change, studying past climates is an important avenue to explore. A previously published record of pCO2, across the Triassic– Jurassic boundary (TJB, ~201 Ma) of East Greenland, showed that Bennettitales (Anamozamites and Pterophyllum) responded in parallel to the empirically proven pCO2-responders Ginkgoales, reducing their stomatal densities by half across the TJB, indicating a transient doubling of pCO2. The abundance of fossil Bennettitales in Mesozoic strata and natural history museum collections worldwide offers enormous potential for further stomatal proxy pCO2 reconstructions, but a suitable nearest living equivalent (NLE) should ideally first be identified for this extinct plant group. Using specimens from herbarium collections, three species of cycads, historically considered the best NLE, were tested for pCO2 response, as well as two species of tree ferns, grown in experimental growth chambers. None responded to changes in pCO2, and were consequently rejected as NLEs. Finally, two species of ferns were selected from the literature, and produced very similar pCO2 compared to Ginkgoales. However, these understory ferns are not appropriate NLEs for Bennettitales due to differences in habitat and a distant evolutionary relationship. Future work should test additional plant groups, in particular seed plants such as basal angiosperms and Gnetales, for suitability as NLE for Bennettitales in pCO2 reconstructions, for example through biogeo- chemical fingerprinting using infrared microspectroscopy. Until an appropriate NLE is identified, Bennettitales pCO2 can be reconstructed based on cross-calibration of stomatal densities with those of co-occurring pCO2 responders, such as Ginkgoales.

Waning annual seasonality is documented in an up to one-month advance in spring onset since the 1980’s in northern latitudes, perturbing ecosystems and socio-economic performance. Summer temperatures, in contrast, have been rising only recently, indicating an offset in seasonal warming. The limited time span of this observational data makes the asynchronous pattern difficult to quantify, hindering projections of intra-annual dynamics. We explore temporal phase relations of seasonal warming over the Late Pleniglacial/Bølling and the Younger Dryas/Holocene climate transitions that preceded present anthropogenic warming. We determine past spring onset and thermal properties from dwarf birch paleo-phenology. Reconstructed spring warming led maximum summer warming by about a century during both transitions. Long-term reconstruction of intra-annual temperature regimes provides the perspective required for seasonal response analysis. Our results document that multidecadal spring season warming precedes sudden summer temperature rise also during natural climate change. The rapidity of present seasonality changes, however, is unprecedented.

A fossil cave and associated sediments and fossil fauna located on the Greek island of Rhodes in the eastern Aegean Sea is reported here, and the depositional history discussed. The sediments were deposited during the late Pliocene, in the interstitial space between basement boulders of up to 1500 tons. The depositional history of the cave comprises eight stages. From initial flooding, the basin experienced a continuous transgression with sea-level rise in excess of 500 m, followed by a rapid, forced regression of similar magnitude. The recognition of a succession of fossil communities illustrates this transgression, with a seemingly abrupt shift from endolithic to epilithic biota dominance late in the transgressive cycle. The communities recording the increasing water depth from 0 to >150 m are: The Gatrochaenolithes torpedo (bivalve boring) and Entobia gonioides (sponge boring) ichnocoenosis, with peak distribution between 0 and 1 m water depth; the E. gonioides – E. magna ichnocoenosis, with 1–5 m depth peak distribution; the exclusive E. magna ichnocoenosis, with 5–40 m depth peak distribution; and the E. giganteaichnocoenosis, with a peak distribution approaching 150–200 m. Below this depth, an epilithic community without boring organisms takes over, characterized by the calcareous sponge Merliacf. normani, and the inarticulate brachiopod Novocrania turbinata. Simultaneously with the succession of the endo- and epilithic cave wall fossil communities, skeletal calcarenite accumulated on the cave floor; the erosional remnants of this sediment are insufficient to further expand the overall transgression–regression model.

The Ginkgoales, including the ‘living fossil’ Ginkgo biloba, are an important group for stomata-based palaeo-pCO2 reconstructions, with long evolutionary lineages and an extensive, abundant fossil record. The stomatal proxy for palaeo-pCO2 can improve our understanding of the exact relationship between pCO2 and temperatures – Earth's climate sensitivity: a key measure of global warming by pCO2. However, pCO2 records from future climate analogues in the past, such as the mid-Miocene Climatic Optimum, seemingly underestimate pCO2 – climate models cannot simulate the past temperatures with the only moderately elevated pCO2 reconstructed by proxies. Either climate sensitivity must have been elevated, which has implications for future climate forecasts, or proxies underestimate pCO2 due to additional environmental factors. Here we tested whether climate conditions impact stomatal parameters and thus pCO2 reconstruction on a large global database of G. biloba leaves from all continents except Antarctica, spanning 12 climate zones. We reconstructed ambient pCO2 using three stomatal proxy methods (stomatal ratio, transfer functions, Franks gas exchange model) and one stomata-independent isotope-based proxy for comparison (C3 proxy). We found that the stomatal proxy methods reconstructed ambient pCO2 reasonably well and uniformly, but that the C3 proxy underestimated pCO2. All the investigated stomatal parameters displayed an unexpectedly large variability, but no significant relationship with temperature, precipitation, or seasonality. Based on these results, the stomatal proxy is not influenced by climate and specifically does not systematically underestimate pCO2 under high temperatures. Climate sensitivity was likely instead elevated during past global warming episodes, an urgent consideration in climate forecasts for our rapidly warming Earth.

To improve future predictions of anthropogenic climate change, a better understanding of the relationship between global temperature and atmospheric concentrations of CO2 (pCO2), orclimate sensitivity, is urgently required. Analyzing proxy data from climate change episodesin the past is necessary to achieve this goal, with certain geologic periods, such as the midMiocene Climatic Optimum (MCO), a transient period of global warming with globaltemperatures up to ~7°C higher than today, increasingly viewed as good analogues to future climate under present emission scenarios. However, a problem remains that climate modelscannot reproduce MCO temperatures with less than ~800 ppm pCO2, while most previously published proxies record pCO2 <450 ppm. Here, we reconstructed MCO pCO2 with a multitaxon fossil leaf database from the well-dated MCO Lagerstätte deposits of Clarkia, Idaho,USA, using four current methods of pCO2 reconstructions. The methods are principally based on either stomatal densities, carbon isotopes, or a combination of both – thus offering independent results. The total of six reconstructions mostly record pCO2 of ~450–550 ppm. Although slightly higher than previously reconstructed pCO2, the discrepancy with the ~800 ppm required by climate models remains. We conclude that climate sensitivity was heightened during MCO, indicating that highly elevated temperatures can occur at relatively moderate pCO2. Ever higher climate sensitivity with rising temperatures should be very seriously considered in future predictions of climate change.

Reliable reconstructions of atmospheric carbon dioxide concentrations (pCO2) are required at higher resolution than currently available to help resolve the relationship between mass extinctions and changes in palaeo-pCO2 levels. Such reconstructions are needed: 1, at a high temporal resolution for constraining the pre- and post- extinction atmospheres; and 2, at a sufficient spatial resolution to constrain potential inter-hemispheric differ- ences. Here we estimate pCO2 based on fossil Lauraceae leaf cuticle specimens derived from three localities with strata spanning the latest Cretaceous to the mid-Paleocene, including a new Cretaceous–Paleogene bound- ary (K–Pg) locality, in New Zealand. We use two independent methods of stomatal density-based pCO2 recon- structions; a transfer function calibrated using herbarium material and the stomatal ratio method, producing three calibration sets. Our results based on the mean values of each of the three calibration methods indicate pCO2 ranging between ca. 460 and 650 ppm during the latest Cretaceous, falling precipitously to average values between ca. 360 and 430 ppm across the K–Pg boundary, and further to ca. 305–320 ppm in the mid-Paleocene. A ‘spike’ of extremely high pCO2 at the K–Pg could not be confirmed, but our results are, nonetheless, consistent with previously published pCO2 records from the Northern Hemisphere, and show that stomatal density world- wide was responding to significant changes in pCO2 across the K–Pg. 

The reorganisation of Earth's climate system from the Oligocene to the Miocene was influenced by complex interactions between Tethyan tectonics, orbital parameters, oceanographic changes, and carbon cycle feedbacks, with climate modelling indicating that pCO2 was an important factor. Oscillating episodes of climate change during the Oligocene–Miocene transition (OMT) have however been difficult to reconcile with existing pCO2 records. Here we present a new pCO2 record from the OMT into the early Miocene, reconstructed using the stomatal proxy method with a database of fossil Lauraceae leaves from New Zealand. The leaf database derives from three relatively well-dated sites located in the South Island of New Zealand; Foulden Maar, Mataura River and Grey Lake. Atmospheric pCO2 values were obtained based on four separate calibrations with three nearest living equivalents, using the stomatal ratio method as well as transfer functions. Our results, based on the mean values of each of the four calibrations, indicate pCO2 ranging ~582–732 ppm (average 650 ppm) at the OMT, falling precipitously to mean values of ~430–538ppm (average 492ppm) for the earliest Miocene and ~454–542 ppm (average 502 ppm) in the early Miocene. The much higher values of pCO2 at the OMT indicate that pCO played an important role in climate dynamics during this time, potentially including the abrupt ter- mination of glaciations. 

The reorganisation of Earth's climate system from the Oligocene to the Miocene was in fluenced by complex interactions between Tethyan tectonics, orbital parameters, oceanographic changes, and carbon cycle feedbacks, with climate modelling indicating that pCO2 was an important factor. Oscillating episodes of climate change during the Oligocene-Miocene transition (OMT) have however been difficult to reconcile with existing pCO2 records. Here we present a new pCO2 record from the OMT into the early Miocene, reconstructed using the stomatal proxy method with a database of fossil Lauraceae leaves from New Zealand. The leaf database derives from three relatively well-dated sites located in the South Island of New Zealand; Foulden Maar, Mataura River and Grey Lake. Atmospheric pCO2 values were obtained based on four separate calibrations with three nearest living equivalents, using the stomatal ratio method as well as transfer functions. Our results, based on the mean values of each of the four calibrations, indicate pCO2 ranging ~582–732 ppm (average 650 ppm) at the OMT, falling precipitously to mean values of ~430–538 ppm (average 492 ppm) for the earliest Miocene and ~454–542 ppm (average 502 ppm) in the early Miocene. The much higher values of pCO2 at the OMT indicate that pCO played an important role in climate dynamics during this time, potentially including the abrupt termination of glaciations.

Reducing the uncertainty in predictions of future climate change is one of today’s greatest scientific challenges, with many significant problems unsolved, including the relationship between pCO2 and global temperature. To better constrain these forecasts, it is meaningful to study past time intervals of global warmth, such as the Eocene (56.0–33.9 Ma), serving as climatic analogues for the future. Here we reconstructed pCO2 using the stomatal densities of a large fossil Lauraceae (laurel) leaf database from ten sites across the Eocene of Australia and New Zealand. We show that mostly moderate pCO2 levels of ∼450–600 ppm prevailed throughout the Eocene, levels that are considerably lower than the pCO2 forcing currently needed to recreate Eocene temperatures in climate models. Our data record significantly lower pCO2 than inferred from marine isotopes, but concur with previously published Northern Hemisphere Eocene stomatal proxy pCO2. We argue that the now globally consistent stomatal proxy pCO2 record for the Eocene is robust and that climate sensitivity was elevated and/or that additional climate forcings operated more powerfully than previously assumed.

Premise of research. Geochemical fingerprinting of fossil plants is a relatively new research field complementing morphological analyses and providing information for paleoenvironmental interpretations. Ginkgoales contains a single extant species but was diverse through the Mesozoic and is an excellent target for biochemical analyses.

Methodology. Cuticles derived from fresh and fallen autumn leaves of extant Ginkgo biloba and seven fossil gink- goalean leaf taxa, one seed fern taxon, and two taxa with bennettitalean affinity were analyzed by infrared (IR) microspec- troscopy at the D7 beamline in the MAX IV synchrotron laboratory, Sweden. The fossil material derives from Triassic and Jurassic successions of Greenland. Spectral data sets were compared and evaluated by hierarchical cluster analysis (HCA) and principal component analysis performed on vector-normalized, first-derivative IR absorption spectra.

Pivotal results. The IR absorption spectra of the fossil leaves all reveal signatures that clearly indicate the pres- ence of organic compounds. Spectra of the extant G. biloba leaves reveal the presence of aliphatic chains, aromatic and ester carbonyl functional groups from polymer cutin and other waxy compounds, and polysaccharides. Inter- estingly, both the extant autumn leaves and the fossil specimens reveal the presence of carboxyl/ketone molecules, suggesting that chemical alterations during the initial stages of decomposition are preserved through fossilization. Two major subclusters were identified through HCA of the fossil spectra.

Conclusions. Consistent chemical IR signatures, specific for each fossil taxon are present in cuticles, and suf- ficient molecular content is preserved in key regions to reflect the plants’ original chemical signatures. The alter- ations of the organic compounds are initiated as soon as the leaves are shed, with loss of proteins and increased ester and carboxyl/ketone compound production in the fallen leaves. We further show that the groupings of taxa reflect a combination of phylogeny and environmental conditions related to the end-Triassic event.

The Last Termination (19 000–11 000 a BP) with its rapid and distinct climate shifts provides a perfect laboratory to study the nature and regional impact of climate variability. The sedimentary succession from the ancient lake at Hässeldala Port in southern Sweden with its distinct Lateglacial/early Holocene stratigraphy (>14.1–9.5 cal. ka BP) is one of the few chronologically well-constrained, multi-proxy sites in Europe that capture a variety of local and regional climatic and environmental signals. Here we present Hässeldala's multi-proxy records (lithology, geochemistry, pollen, diatoms, chironomids, biomarkers, hydrogen isotopes) in a refined age model and place the observed changes in lake status, catchment vegetation, summer temperatures and hydroclimate in a wider regional context. Reconstructed mean July temperatures increased between c. 14.1 and c. 13.1 cal. ka BP and subsequently declined. This latter cooling coincided with drier hydroclimatic conditions that were probably associated with a freshening of the Nordic Seas and started a few hundred years before the onset of Greenland Stadial 1 (c. 12.9 cal. ka BP). Our proxies suggest a further shift towards colder and drier conditions as late as c. 12.7 cal. ka BP, which was followed by the establishment of a stadial climate regime (c. 12.5–11.8 cal. ka BP). The onset of warmer and wetter conditions preceded the Holocene warming over Greenland by c. 200 years. Hässeldala's proxies thus highlight the complexity of environmental and hydrological responses across abrupt climate transitions in northern Europe.