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  • 1.
    Ampel, Linda
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kylander, Malin E.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Steinthorsdottir, Margret
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Wohlfarth, Barbara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Abrupt climate change and early lake development - the Lateglacial diatom flora at Hasseldala Port, southeastern Sweden2015In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 44, no 1, p. 94-102Article in journal (Refereed)
    Abstract [en]

    The fossil diatom record from the Hasseldala Port palaeolake, southeastern Sweden, offers an excellent opportunity to investigate how past climatic shifts influenced catchment conditions and early lake development. The record, dating to between 13900 and 11200 cal. a BP, covers a climatically dynamic period, starting with deglaciation followed by oscillations between warmer and colder climate states. The stratigraphical changes in the fossil diatom assemblages show a trend of less open-water taxa and a successively more complex periphytic community as the lake shallows and the aquatic habitat structure develops. A diatom-based reconstruction of lake water pH indicates a natural acidification trend early in the record from 13900 to 12500 cal. a BP. From 12500 cal. a BP, coincident with the start of climate cooling, to 11300 cal. a BP this trend is disrupted and lake waters become more alkaline. A cooler and drier climate most likely resulted in reduced soil organic matter build-up as well as more frozen ground that impeded hydrological flow and decreased the input of dissolved organic matter and organic acids into the lake system. This study demonstrates the importance of the hydrological system as a link between terrestrial and aquatic ecosystems during early lake ontogeny.

  • 2. Haworth, Matthew
    et al.
    Gallagher, Angela
    Sum, Elysia
    Hill-Donnelly, Marlene
    Steinthorsdottir, Margret
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mcelwain, Jennifer
    On the reconstruction of plant photosynthetic and stress physiology across the Triassic-Jurassic boundary2014In: Turkish Journal of Earth Sciences, ISSN 1300-0985, E-ISSN 1303-619X, Vol. 23, no 3, p. 321-329Article in journal (Refereed)
    Abstract [en]

    The Triassic-Jurassic boundary (TJB) coincides with major disruption to the carbon cycle and global warming as the Central Atlantic Magmatic Province developed. This resulted in both marine and terrestrial extinctions, with terrestrial plants thought to experience thermal stress as global temperatures and atmospheric CO2 levels rose. As plant compression fossils typically only preserve external morphological features, it has not been possible to reconstruct plant paleophysiology in order to elucidate the mechanisms underlying plant stress and extinction. Here we present a new approach allowing us to infer the photosynthetic performance and stress physiology of fossil plants, applied to fossil Ginkgoales across the TJB. We use correlations between the adaxial epidermal cell density of extant Ginkgo biloba and photosynthetic and protective stress physiology to infer the paleophysiological condition of Late Triassic-Early Jurassic-aged plants from Astartekloft, East Greenland. The density of fossil leaf adaxial epidermal cells indicates that photosynthetic performance of Ginkgoales became increasingly impaired towards the latter stages of the Triassic, before improving into the Early Jurassic. This is consistent with delta C-13 isotope values, paleo-[CO2] levels, and global mean temperatures, suggesting that photosynthetic performance was influenced by the prevailing environmental conditions during the TJB event. Dissipation of absorbed energy as heat would also have risen towards the boundary as plant stress increased, in order to protect the photosynthetic physiology. The increase in dissipation of energy as heat, associated with a reduction in convective heat loss due to reduced transpiration rates, would have exacerbated plant thermal stress at the TJB, thus contributing to sudden biodiversity loss and ecological change.

  • 3. Mays, Chris
    et al.
    Steinthorsdottir, Margret
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Stilwell, Jeffrey D.
    Climatic implications of Ginkgoites waarrensis Douglas emend. from the south polar Tupuangi flora, Late Cretaceous (Cenomanian), Chatham Islands2015In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 438, p. 308-326Article in journal (Refereed)
    Abstract [en]

    The flora of the Cenomanian-Turonian (ca. 96-90 Ma) Tupuangi Formation, Chatham Islands, New Zealand, was inhabiting a region well within the south polar circle (similar to 70-80 degrees S) during the early Late Cretaceous, an interval characterised by extreme global greenhouse conditions. The Tupuangi flora offers a unique perspective into an ecological and environmental setting which has no extant analogue, whilst providing proxies of polar palaeoclimatic conditions during a phase of extreme global warming. Ginkgoites waarrensis Douglas, 1965 (emended herein), a species known previously from a single occurrence in Australia, is an abundant element of the Tupuangi flora. Forty-five leaf samples from three localities are reported, and a systematic treatment of this species revealed a wide morphological range. In contrast to the exclusively riparian niche of more recent members of Ginkgoales, associated sedimentological and palaeoecological data suggest that this species had an ecological preference for regularly disturbed, coastal deltaic settings. Herein, we review the geographic and stratigraphic distributions of Cretaceous Gondwanan ginkgoalean leaf taxa. An increasing diversity of this group from the Early Cretaceous to the early Late Cretaceous supports a broader trend of floral provincialisation throughout this interval, most likely driven by concurrent global transgression and active tectonic extension across southern Gondwana. Carbon dioxide has been inferred as a primary proximate cause of the mid-Cretaceous global greenhouse. The leaf cuticles of Ginkgoites waarrensis were utilised to approximate atmospheric carbon dioxide (pCO(2)) during the Cenomanian. Stomatal index (SI) data were collected from ten specimens, and the stomatal ratio method yielded a semi-quantitative pCO(2) estimate of 1150-1350 ppmv, which is consistent with modelled and proxy estimates of the Cenomanian. The present study explores the inherent limitations of the transfer function method for estimating CO2 when applied to taxa with very low SI values, such as G. waarrensis. In addition to pCO(2), temperature and irradiance are identified as environmental variables which may have systematically promoted the low SI of G. waarrensis, but their combined influence is likely mitigated by the relatively high temperature of this region during the mid-Cretaceous and the high summer insolation at polar latitudes.

  • 4. McElwain, Jennifer C.
    et al.
    Steinthorsdottir, Margret
    Stockholm University, Faculty of Science, Department of Geological Sciences. Swedish Museum of Natural History, Sweden.
    Paleoecology, Ploidy, Paleoatmospheric Composition, and Developmental Biology: A Review of the Multiple Uses of Fossil Stomata2017In: Plant Physiology, ISSN 0032-0889, E-ISSN 1532-2548, Vol. 174, no 2, p. 650-664Article in journal (Refereed)
  • 5. Soh, W. K.
    et al.
    Wright, I. J.
    Bacon, K. L.
    Lenz, T. I.
    Steinthorsdottir, Margret
    Stockholm University, Faculty of Science, Department of Geological Sciences. Swedish Museum of Natural History, Sweden.
    Parnell, A. C.
    McElwain, J. C.
    Palaeo leaf economics reveal a shift in ecosystem function associated with the end-Triassic mass extinction event2017In: Nature Plants, ISSN 2055-026X, Vol. 3, no 8, article id 17104Article in journal (Refereed)
    Abstract [en]

    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 CO 2 -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.

  • 6.
    Steinthorsdottir, Margret
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Bacon, Karen L.
    Popa, Mihai E.
    Bochner, Laura
    Mcelwain, Jennifer C.
    BENNETTITALEAN LEAF CUTICLE FRAGMENTS (HERE ANOMOZAMITES AND PTEROPHYLLUM) CAN BE USED INTERCHANGEABLY IN STOMATAL FREQUENCY-BASED PALAEO-CO(2) RECONSTRUCTIONS2011In: Palaeontology, ISSN 0031-0239, E-ISSN 1475-4983, Vol. 54, p. 867-882Article in journal (Refereed)
    Abstract [en]

    Bennettites are an abundant and frequently well-preserved component of many Mesozoic fossil floras, often playing an important ecological role in flood plain vegetation communities. During a recent study focusing on stomatal indices of Triassic-Jurassic fossil plants, it became evident that the leaf fragments of two bennettite genera Anomozamites Schimper (1870) emend. Harris (1969) and Pterophyllum Brongniart (1825) display a significant overlap of leaf shape as well as cuticular characters. Owing to the preference of recognition of single taxa (ideally species) for the stomatal method, we use a database of 70 leaf fragments of Anomozamites and Pterophyllum compressions from five isotaphonomic Late Triassic sedimentary beds of Astartekloft in East Greenland to test whether leaf and cuticle fragments of the two genera can be separated using a range of quantitative and qualitative morphological and statistical analyses. None of the observed characters - including stomatal frequencies could be applied to separate the fragments of the two genera into well-defined groups. Our results therefore indicate that fragmented material and dispersed cuticles cannot be utilized to distinguish between Anomozamites or Pterophyllum at the genus level, but that instead these cuticle fragments may be used interchangeably as stomatal proxies. Classification of fossil leaves into either of these genera is thus only possible given adequate preservation of macro-morphology and is not possible based solely on cuticle morphology. We suggest that this large inter- and intra-generic morphological variation in both leaf and cuticle traits within Anomozamites and Pterophyllum may be related to the bennettites' role as understory plants, experiencing a range of micro-environmental conditions, perhaps depending mainly on sun exposure. Based on the results obtained in this study, we conclude that Anomozamites and Pterophyllum cuticle fragments can be employed interchangeably in palaeo [CO(2)] reconstructions based on the stomatal method, thus potentially annexing a plethora of bennettitalean fossil plant material as CO(2) proxies, including dispersed cuticles.

  • 7.
    Steinthorsdottir, Margret
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    de Boer, Agatha M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Oliver, Kevin I. C.
    Muschitiello, Francesco
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Blaauw, Maarten
    Reimer, Paula J.
    Wohlfarth, Barbara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Synchronous records of pCO(2) and Delta C-14 suggest rapid, ocean-derived pCO(2) fluctuations at the onset of Younger Dryas2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 99, p. 84-96Article in journal (Refereed)
    Abstract [en]

    Just before the onset of the Younger Dryas (YD) cold event, several stomatal proxy-based pCO(2) records have shown a sharp increase in atmospheric CO2 concentration (pCO(2)) of between ca 50 and 100 ppm, followed by a rapid decrease of similar or even larger magnitude. Here we compare one of these records, a high-resolution pCO(2) record from southern Sweden, with the IntCal13 record of radiocarbon (Delta C-14). The two records show broadly synchronous fluctuations at the YD onset. Specifically, the IntCal13 record documents decreasing Delta C-14 just before the YD onset when pCO(2) peaks, consistent with a source of old CO2 from the deep ocean. We propose that this fluctuation occurred due to a major ocean flushing event. The cause of the flushing event remains speculative but could be related to the hypothesis of the glacial ocean as a thermobaric capacitor. We confirm that the earth system can produce such large multi-decadal timescale fluctuations in pCO(2) through simulating an artificial ocean flushing event with the GENIE Earth System Model. We suggest that sharp transitions of pCO(2) may have remained undetected so far in ice cores due to inter-firn gas exchange and time-averaging. The stomatal proxy record is a powerful complement to the ice core records for the study of rapid climate change.

  • 8.
    Steinthorsdottir, Margret
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    de Boer, Agatha M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Oliver, Kevin I. C.
    Muschitiello, Francesco
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Blaauw, Maarten
    Wohlfarth, Barbara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Response to: Comment on Synchronous records of pCO(2) and Delta C-14 suggest rapid, ocean-derived pCO(2) fluctuations at the onset of Younger Dryas (Steinthorsdottir et al., 2014, Quaternary Science Reviews 99, 84-96)2015In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 107, p. 270-273Article in journal (Refereed)
  • 9.
    Steinthorsdottir, Margret
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Swedish Museum of Natural History, Sweden.
    Elliott-Kingston, Caroline
    Bacon, Karen L.
    Cuticle surfaces of fossil plants as a potential proxy for volcanic SO2 emissions: observations from the Triassic-Jurassic transition of East Greenland2018In: Palaeobiodiversity and Palaeoenvironments, ISSN 1867-1594, E-ISSN 1867-1608, Vol. 98, no 1, p. 49-69Article in journal (Refereed)
    Abstract [en]

    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.

  • 10.
    Steinthorsdottir, Margret
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Swedish Museum of Natural History, Sweden.
    Håkansson, Eckart
    ENDO- AND EPILITHIC FAUNAL SUCCESSION IN A PLIOCENE-PLEISTOCENE CAVE ON RHODES, GREECE: RECORD OF A TRANSGRESSION2017In: Palaeontology, ISSN 0031-0239, E-ISSN 1475-4983, Vol. 60, no 5, p. 663-681Article in journal (Refereed)
    Abstract [en]

    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. gigantea ichnocoenosis, with a peak distribution approaching 150-200 m. Below this depth, an epilithic community without boring organisms takes over, characterized by the calcareous sponge Merlia cf. 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.

  • 11.
    Steinthorsdottir, Margret
    et al.
    School of Biology and Environmental Science, University College Dublin.
    Ian Woodward, F.
    Surlyk, F.
    McElwain, J. C.
    Deep-time evidence of a link between elevated CO 2 concentrations and perturbations in the hydrological cycle via drop in plant transpiration2012In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 40, no 9, p. 815-818Article in journal (Refereed)
    Abstract [en]

    The physiological effects of high CO 2 concentrations, i.e., [CO 2], on plant stomatal responses may be of major importance in understanding the consequences of climate change, by causing increases in runoff through suppression of plant transpiration. Radiative forcing by high [CO 2] has been the main consideration in models of global change to the exclusion of plant physiological forcing, but this potentially underestimates the effects on the hydrological cycle, and the consequences for ecosystems. We tested the physiological responses of fossil plants from the Triassic-Jurassic boundary transition (Tr-J) succession of East Greenland. This interval marks a major high CO 2-driven environmental upheaval, with faunal mass extinctions and significant floral turnover. Our results show that both stomatal size (expressed in fossil material as SL, the length of the stomatal complex opening) and stomatal density (SD, the number of stomata per mm 2) decreased significantly during the Tr-J. We estimate, using a leaf gas-exchange model, that the decreases in SD and SL resulted in a 50%-60% drop in stomatal and canopy transpiration at the Tr-J. We also present new field evidence indicating simultaneous increases in runoff and erosion rates. We propose that the consequences of sto- matal responses to elevated [CO 2] may lead to locally increased runoff and erosion, and may link terrestrial and marine biodiversity loss via the hydrological cycle. © 2012 Geological Society of America.

  • 12.
    Steinthorsdottir, Margret
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jeram, Andrew J.
    McElwain, Jennifer C.
    Extremely elevated CO(2) concentrations at the Triassic/Jurassic boundary2011In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 308, no 3-4, p. 418-432Article in journal (Refereed)
    Abstract [en]

    Although progress has been made in recent years in reconstructing the environmental conditions at the Triassic/Jurassic Boundary (TJB), published records of atmospheric CO(2) concentrations have been of low resolution and/or based on multi-taxon estimates. This is addressed here by reconstructing CO(2) concentrations across the TJB using stomatal frequencies of four phylogenetically and ecologically distinct plant groups from two depositionally, geographically and taphonomically separate boundary sections in East Greenland and Northern Ireland, with stomatal proxy methods and regression analysis. The resulting CO(2) records then are compared with an additional existing TJB record from a geological section in Sweden. The final results indicate that pre-TJB (Rhaetian), the CO(2) concentration was approximately 1000 ppm, that it started to rise steeply pre-boundary and had doubled to around 2000-2500 ppm at the TJB. The CO(2) concentration then remained elevated for some time post-boundary, before returning to pre-TJB levels in the Hettangian. These results are in very good accordance with published C-isotope, fire and leaf dissection records, and clearly indicate steeply rising and lingering CO(2) concentration at the TJB.

  • 13.
    Steinthorsdottir, Margret
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Porter, Amanda S.
    Holohan, Aidan
    Kunzmann, Lutz
    Collinson, Margaret
    McElwain, Jennifer C.
    Fossil plant stomata indicate decreasing atmospheric CO2 prior to the Eocene-Oligocene boundary2016In: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 12, no 2, p. 439-454Article in journal (Refereed)
    Abstract [en]

    A unique stratigraphic sequence of fossil leaves of Eotrigonobalanus furcinervis (extinct trees of the beech family, Fagaceae) from central Germany has been used to derive an atmospheric pCO(2) record with multiple data points spanning the late middle to late Eocene, two sampling levels which may be earliest Oligocene, and two samples from later in the Oligocene. Using the inverse relationship between the density of stomata and pCO(2), we show that pCO(2) decreased continuously from the late middle to late Eocene, reaching a relatively stable low value before the end of the Eocene. Based on the subsequent records, pCO(2) in parts of the Oligocene was similar to latest Eocene values. These results suggest that a decrease in pCO(2) preceded the large shift in marine oxygen isotope records that characterizes the Eocene-Oligocene transition and that when a certain threshold of pCO(2) change was crossed, the cumulative effects of this and other factors resulted in rapid temperature decline, ice build up on Antarctica and hence a change of climate mode.

  • 14.
    Steinthorsdottir, Margret
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Tosolini, Anne-Marie P.
    Mcelwain, Jennifer C.
    EVIDENCE FOR INSECT AND ANNELID ACTIVITY ACROSS THE TRIASSIC-JURASSIC TRANSITION OF EAST GREENLAND2015In: Palaios, ISSN 0883-1351, E-ISSN 1938-5323, Vol. 30, no 8, p. 597-607Article in journal (Refereed)
    Abstract [en]

    During a study of macroflora from the Astartekloft locality in Jameson Land, East Greenland, endophytic insect ovipositions (egg traces) belonging to ichnogenus Paleoovoidus were recorded for the first time in ginkgoalean (Ginkgoites, Sphenobaiera, and Baiera) fossil leaves across the Triassic-Jurassic (Tr-J) transition (ca. 200 Ma). The ovipositions may have been produced by insects in the order Odonata (dragonflies and damselflies) and are relatively more abundant before than after the Tr-J transition, possibly reflecting changes in plant-insect association. Fossil clitellate annelid (leech) cocoons were also discovered in a macerated sample from a single bed within the Tr-J transition. The cocoons belong to two species: Dictyothylakos pesslerae and Pilothylakos pilosus, extending the range of the latter genus from the Early Cretaceous to the Early Jurassic. This new evidence suggests that the ecosystem and food webs were profoundly affected by the environmental degradation surrounding the end-Triassic event (ETE), which was marked by faunal mass extinctions and floral turnover. Invertebrate ichno- and body fossils may add significantly to paleoenvironmental information provided by plant fossil assemblages, and therefore a protocol for recording evidence of invertebrate activity in paleobotanical research is suggested, including analyzing a standardized number of specimens for fossil traces and bulk maceration for discovery of invertebrate body fossils. More well-designed studies on Mesozoic plant-invertebrate associations are needed and will provide deeper knowledge about the structure and evolution of complex ecosystems.

  • 15.
    Steinthorsdottir, Margret
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Vajda, V.
    Early Jurassic (late Pliensbachian) CO2 concentrations based on stomatal analysis of fossil conifer leaves from eastern Australia2015In: Gondwana Research, ISSN 1342-937X, E-ISSN 1878-0571, Vol. 27, no 3, p. 932-939Article in journal (Refereed)
    Abstract [en]

    The stomatal index (a measure of stomatal density) of an extinct Australian Early Jurassic araucariacean conifer species, Allocladus helgei Jansson, is used to reconstruct the atmospheric carbon dioxide concentration (pCO(2)) in the Early Jurassic. The fossil leaves are preserved in a single bed, palynologically dated to late Pliensbachian (similar to 185-183 Mya). Atmospheric pCO(2) is estimated from the ratios between the stomatal index of A. helgei and the stomatal indices of three modern analogs (nearest living equivalent plants). CO2 concentration in the range of similar to 750-975 ppm was calibrated from the fossil material, with a best-estimated mean of similar to 900 ppm. The new average pCO(2) determined for the late Pliensbachian is thus similar to, although similar to 10% lower, than previously inferred minimum concentrations of similar to 1000, based on data from the Northern Hemisphere, but may help constrain pCO(2) during this period. Our results are the first pCO(2) estimates produced using Jurassic leaves from the Southern Hemisphere and show that i) paleo-atmospheric pCO(2) estimates are consistent at a global scale, though more investigations of Southern Hemisphere material are required, and ii) the stomatal proxy method can now be used without the context of relative change in pCO(2) when applying the correct methodology.

  • 16.
    Steinthorsdottir, Margret
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Vajda, Vivi
    Pole, Mike
    Global trends of pCO(2) across the Cretaceous-Paleogene boundary supported by the first Southern Hemisphere stomatal proxy-based pCO(2) reconstruction2016In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 464, p. 143-152Article in journal (Refereed)
    Abstract [en]

    Reliable reconstructions of atmospheric carbon dioxide concentrations (pCO(2)) are required at higher resolution than currently available to help resolve the relationship between mass extinctions and changes in palaeo-pCO(2) 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 pCO(2) 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 pCO(2) 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 pCO(2) 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 pCO(2) at the K-Pg could not be confirmed, but our results are, nonetheless, consistent with previously published pCO(2) records from the Northern Hemisphere, and show that stomatal density worldwide was responding to significant changes in pCO(2) across the K-Pg.

  • 17.
    Steinthorsdottir, Margret
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Wohlfarth, Barbara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kylander, Malin E.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Blaauw, Maarten
    Reimer, Paula J.
    Stomatal proxy record of CO2 concentrations from the last termination suggests an important role for CO2 at climate change transitions2013In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 68, p. 43-58Article in journal (Refereed)
    Abstract [en]

    A new stomatal proxy-based record of CO2 concentrations ([CO2]), based on Betula nana (dwarf birch) leaves from the Hasseldala Port sedimentary sequence in south-eastern Sweden, is presented. The record is of high chronological resolution and spans most of Greenland Interstadial 1 (GI-1a to 1c, Allerod pollen zone), Greenland Stadial 1 (GS-1, Younger Dryas pollen zone) and the very beginning of the Holocene (Preboreal pollen zone). The record clearly demonstrates that i) [CO2] were significantly higher than usually reported for the Last Termination and ii) the overall pattern of CO2 evolution through the studied time period is fairly dynamic, with significant abrupt fluctuations in [CO2] when the climate moved from interstadial to stadial state and vice versa. A new loss-on-ignition chemical record (used here as a proxy for temperature) lends independent support to the Hasseldala Port [CO2] record. The large-amplitude fluctuations around the climate change transitions may indicate unstable climates and that tipping-point situations were involved in Last Termination climate evolution. The scenario presented here is in contrast to [CO2] records reconstructed from air bubbles trapped in ice, which indicate lower concentrations and a gradual, linear increase of [CO2] through time. The prevalent explanation for the main climate forcer during the Last Termination being ocean circulation patterns needs to re-examined, and a larger role for atmospheric [CO2] considered.

  • 18.
    Wohlfarth, Barbara
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Muschitiello, Francesco
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Andersson, August
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Kylander, Malin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Smittenberg, Rienk H.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Steinthorsdottir, Margret
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Watson, Jenny
    Whitehouse, Nicola J.
    Hasseldala-a key site for Last Termination climate events in northern Europe2017In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 46, no 2, p. 143-161Article in journal (Refereed)
    Abstract [en]

    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 Hasseldala 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 Hasseldala'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. Hasseldala's proxies thus highlight the complexity of environmental and hydrological responses across abrupt climate transitions in northern Europe.

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