| 1. |
- Ao, Hong, et al.
(författare)
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Orbital climate variability on the northeastern Tibetan Plateau across the Eocene-Oligocene transition
- 2020
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- The first major build-up of Antarctic glaciation occurred in two consecutive stages across the Eocene-Oligocene transition (EOT): the EOT-1 cooling event at similar to 34.1-33.9Ma and the Oi-1 glaciation event at similar to 33.8-33.6Ma. Detailed orbital-scale terrestrial environmental responses to these events remain poorly known. Here we present magnetic and geochemical climate records from the northeastern Tibetan Plateau margin that are dated precisely from similar to 35.5 to 31Ma by combined magneto- and astro-chronology. These records suggest a hydroclimate transition at similar to 33.7Ma from eccentricity dominated cycles to oscillations paced by a combination of eccentricity, obliquity, and precession, and confirm that major Asian aridification and cooling occurred at Oi-1. We conclude that this terrestrial orbital response transition coincided with a similar transition in the marine benthic delta O-18 record for global ice volume and deep-sea temperature variations. The dramatic reorganization of the Asian climate system coincident with Oi-1 was, thus, a response to coeval atmospheric CO2 decline and continental-scale Antarctic glaciation. Marine records indicate a greenhouse to icehouse climate transition at similar to 34 million years ago, but how the climate changed within continental interiors at this time is less well known. Here, the authors show an orbital climate response shift with aridification on the northeastern Tibetan Plateau during this time.
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| 2. |
- Barbolini, Natasha, 1985-
(författare)
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Bringing science communication skills into the university classroom and back out again : What do palaeoscience educators think?
- 2022
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Ingår i: Frontiers in Education. - : Frontiers Media SA. - 2504-284X. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- University-level pedagogy and public science communication both have the same broad goal: to facilitate the sharing of knowledge and understanding from a specialist or expert, to a non-specialist group. Recent research has emphasised the need for there to be a two-way transfer or dialogue of ideas between these fields, but collaboration thus far is rare, particularly at the tertiary education level. Performing science outreach is mostly a voluntary service for academics, and institutions provide little in the way of support, training or recognition. Here I explore the potential for a positive feedback loop between science communication and higher-education pedagogy in the palaeosciences. A synthesis of best practises in science outreach is drawn from the literature and related to pedagogical concepts and findings. The resulting congruences suggest enormous potential for ‘cross-pollination' of ideas between the fields. However, in-depth one-on-one interviews and focus groups with palaeoscience educators, as well as an online survey, indicate that this potential remains largely untapped in the palaeosciences community. While respondents could identify certain skills as being integral to success in science communication, they did not appear to realise that the same skills, when applied in the classroom, could contribute towards key challenges in higher education today, including the stimulation of student engagement and motivation, the accommodation of an increasingly diverse student body, the anticipation of common student misconceptions in science, and the improvement of pedagogical models of delivery. Another emergent theme was that being a good science communicator was “much simpler” than being a good teacher, conflicting with evidence-based pedagogical and outreach research. While many palaeoscientists did express strong commitments to science communication, they had previous experience of time constraints and conflicts with other academic responsibilities. Therefore, both palaeoscientists and their institutions would benefit from viewing science communication as a valuable and formally rewardable activity within the scholarship of sharing knowledge, which also contributes to other aspects of a successful academic career.
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| 3. |
- Barbolini, Natasha, et al.
(författare)
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Cenozoic evolution of the steppe-desert biome in Central Asia
- 2020
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Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 6:41
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Forskningsöversikt (refereegranskat)abstract
- The origins and development of the arid and highly seasonal steppe-desert biome in Central Asia, the largest of its kind in the world, remain largely unconstrained by existing records. It is unclear how Cenozoic climatic, geological, and biological forces, acting at diverse spatial and temporal scales, shaped Central Asian ecosystems through time. Our synthesis shows that the Central Asian steppe-desert has existed since at least Eocene times but experienced no less than two regime shifts, one at the Eocene-Oligocene Transition and one in the mid-Miocene. These shifts separated three successive stable states, each characterized by unique floral and faunal structures. Past responses to disturbance in the Asian steppe-desert imply that modern ecosystems are unlikely to recover their present structures and diversity if forced into a new regime. This is of concern for Asian steppes today, which are being modified for human use and lost to desertification at unprecedented rates.
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| 4. |
- Cavalcante, Larissa Lopes, et al.
(författare)
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Analysis of fossil plant cuticles using vibrational spectroscopy: A new preparation protocol
- 2023
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Ingår i: Review of Palaeobotany and Palynology. - : Elsevier. - 0034-6667 .- 1879-0615. ; 316
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Tidskriftsartikel (refereegranskat)abstract
- Analyses for organic “fingerprints” on fossilized plant cuticles and pollen hold valuable chemotaxonomic and palaeoclimatic information, and are thus becoming more utilized by palaeobotanists. Plant cuticle and pollen composition are generally analyzed after standard treatments with several chemical reagents for mineral and mesophyll removal. However, the potential alterations on the fossil composition caused by the different cleaning reagents used are still poorly understood. We tested the effects of commonly used palaeobotanical processing methods on the spectra of fossilized cuticles from successions of Late Triassic to Early Jurassic age, including the gymnosperms Lepidopteris, Ginkgoites, Podozamites, Ptilozamites and Pterophyllum astartense. Our study shows that standard chemical processing caused chemical alterations that might lead to erroneous interpretation of the infrared (IR) spectra. The difference in pH caused by HCl induces changes in the proportion between the two bands at ~1720 and 1600 cm 1 (carboxylate and C-C stretch of aromatic compounds) indicating that the band at ~1610 cm 1 at least partially corresponds to carboxylate instead of C-C stretch of aromatic compounds. Interestingly, despite being used in high concentration, HF did not cause changes in the chemical composition of the cuticles. The most alarming changes were caused by the use of Schulze ’s solution, which resulted in the addition of both NO2 and (O)NO2 compounds in the cuticle. Consequently, a new protocol using H2CO3, HF, and H2O2 for preparing fossil plant cuticles aimed for chemical analyses is proposed, which provides an effective substitute to the conventional methods. In particular, a less aggressive and more sustainable alternative to Schulze’s solution is shown to be hydrogen peroxide, which causes only minor alteration of the fossil cuticle ’s chemical composition. Future work should carefully follow protocols, having in mind the impacts of different solutions used to treat leaves and other palaeobotanical material such as palynomorphs with aims to enable the direct comparison of spectra obtained in different studies.
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| 5. |
- Licht, Alexis, et al.
(författare)
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Decline of soil respiration in northeastern Tibet through the transition into the Oligocene icehouse
- 2020
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Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182 .- 1872-616X. ; 560
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Tidskriftsartikel (refereegranskat)abstract
- Soil respiration (Rs), the production of carbon dioxide in soils, increases dramatically from deserts to forested ecosystems. Rs values thus provide a potential tool to identify past ecosystems if recorded in sedimentary archives. Here, we propose a quantitative method to reconstruct past Rs values from paleosols. This method reverses the soil paleobarometer, a proxy that estimates past atmospheric CO2 concentration values (CO2atm) from paleosols while considering a narrow range of variation for Rs. We use past CO2atm values from marine proxies to reconstruct soil respiration from a 20 million year-long isotopic record from northeastern Tibet covering the transition from the Eocene greenhouse to the Oligocene icehouse. We show that Rs dropped at least 4-fold through the transition into the Oligocene icehouse, marking the spread of boreal desert-steppes of Central Asia. We show that increasing aridity and the decline of monsoonal rainfall, in parallel with global cooling, caused the fall of soil respiration. These highly dynamic Rs emphasize the need for a systematic screening of paleosol isotopic data before using the soil paleobarometer to reconstruct CO2atm.
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| 6. |
- Meijer, Niels, et al.
(författare)
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Loess-Like Dust Appearance at 40 Ma in Central China
- 2021
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Ingår i: Paleoceanography and Paleoclimatology. - 2572-4517 .- 2572-4525. ; 36:3
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Tidskriftsartikel (refereegranskat)abstract
- Asian mineral dust has been studied extensively for its role in affecting regional-to global-scale climate and for its deposits, which enable reconstructing Asian atmospheric circulation in the past. However, the timing and origin of the dust deposits remain debated. Numerous loess records have been reported across the Asian continent with ages varying from the Miocene to the Eocene and linked to various mechanisms including global cooling, Tibetan Plateau uplift and retreat of the inland proto-Paratethys Sea. Here, we study the Eocene terrestrial mudrocks of the Xining Basin in central China and use nonparametric end-member analysis of grain-size distributions to identify a loess-like dust component appearing in the record at 40 Ma. This is coeval with the onset of high-latitude orbital cycles and a shift to predominant steppe-desert vegetation as recognized by previous studies in the same record. Furthermore, we derive wind directions from eolian dune deposits which suggest northwesterly winds, similar to the modern-day winter monsoon which is driven by a high pressure system developing over Siberia. We propose that the observed shifts at 40 Ma reflect the onset of the Siberian High interacting with westerly derived moisture at obliquity timescales and promoting dust storms and aridification in central China. The timing suggests that the onset may have been triggered by increased continentality due to the retreating proto-Paratethys Sea.
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| 7. |
- Steinthorsdottir, Margret, et al.
(författare)
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The Miocene : the Future of the Past
- 2021
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Ingår i: Paleoceanography and Paleoclimatology. - : American Geophysical Union (AGU). - 2572-4517 .- 2572-4525. ; 36:4
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Tidskriftsartikel (refereegranskat)abstract
- The Miocene epoch (23.03–5.33 Ma) was a time interval of global warmth, relative to today. Continental configurations and mountain topography transitioned towards 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 analogue 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 modelling studies.
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| 8. |
- Tardif, Delphine, et al.
(författare)
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Orbital variations as a major driver of climate and biome distribution during the greenhouse to icehouse transition
- 2021
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Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 7:43
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Tidskriftsartikel (refereegranskat)abstract
- Recent studies suggest increasing sensitivity to orbital variations across the Eocene-Oligocene greenhouse to icehouse climate transition. However, climate simulations and paleoenvironmental studies mostly provide snapshots of the past climate, therefore overlooking the role of this short-term variability in driving major environmental changes and possibly biasing model-data comparisons. We address this problem by performing numerical simulations describing the end-members of eccentricity, obliquity, and precession. The orbitally induced biome variability obtained in our simulations allows to reconcile previous apparent mismatch between models and paleobotanical compilations. We show that precession-driven intermittent monsoon-like climate may have taken place during the Eocene, resulting in biomes shifting from shrubland to tropical forest in the intertropical convergence zone migration region. Our Oligocene simulations suggest that, along with decreased pCO2, orbital variations crucially modulated major faunal dispersal events around the EOT such as the Grande Coupure by creating and fragmenting the biome corridors along several key land bridges.
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| 9. |
- Woutersen, A., et al.
(författare)
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The evolutionary history of the Central Asian steppe-desert taxon Nitraria (Nitrariaceae) as revealed by integration of fossil pollen morphology and molecular data
- 2023
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Ingår i: Botanical Journal of the Linnean Society. - : Oxford University Press (OUP). - 0024-4074 .- 1095-8339. ; 202:2, s. 195-214
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Tidskriftsartikel (refereegranskat)abstract
- The transition from a greenhouse to an icehouse world at the Eocene-Oligocene Transition (EOT) coincided with a large decrease of pollen from the steppe-adapted genus Nitraria. This genus, now common along the Mediterranean coast, Asia and Australia, has a proposed coastal origin and a geographically widespread fossil record. Here we investigated the evolution, taxonomic diversity and morphological disparity of Nitraria throughout the Cenozoic by integrating extant taxa and fossil palynological morphotypes into a unified phylogenetic framework based on both DNA sequences and pollen morphological data. We present the oldest fossil pollen grain of Nitraria, at least 53 Myr old. This fossil was found in Central Asian deposits, providing new evidence for its origin in this area. We found that the EOT is an evolutionary bottleneck for Nitraria, coinciding with retreat of the proto-Paratethys Sea, a major global cooling event and a turnover in Central Asian steppe vegetation. We infer the crown age of modern Nitraria spp. to be significantly younger (Miocene) than previously estimated (Palaeocene). The diversity trajectory of Nitraria inferred from extant-only taxa differs markedly from one that also considers extinct taxa. Our study demonstrates it is therefore critical to apply an integrative approach to fully understand the plant evolutionary history of Nitrariaceae.
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| 10. |
- Yuan, Qin, et al.
(författare)
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Aridification signatures from fossil pollen indicate a drying climate in east-central Tibet during the late Eocene
- 2020
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Ingår i: Climate of the Past. - Vienna : European Geosciences Union (EGU). - 1744-9588 .- 1814-9332 .- 1814-9324. ; 16, s. 2255-2273
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Tidskriftsartikel (refereegranskat)abstract
- Central Asia experienced a number of significant elevational and climatic changes during the Cenozoic, but much remains to be understood regarding the timing and driving mechanisms of these changes as well as their influence on ancient ecosystems. Here, we describe the palaeoecology and palaeoclimate of a new section from the Nangqian Basin in Tibet, north-western China, dated as Bartonian (41.2–37.8 Ma; late Eocene) based on our palynological analyses. Located on the east-central part of what is today the Tibetan Plateau, this section is excellently placed for better understanding the palaeoecological history of Tibet following the Indo-Asian collision. Our new palynological record reveals that a strongly seasonal steppe–desert ecosystem characterized by drought-tolerant shrubs, diverse ferns, and an underlying component of broad-leaved forests existed in east-central Tibet during the Eocene, influenced by a southern monsoon. A transient warming event, possibly the middle Eocene climatic optimum (MECO; 40 Ma), is reflected in our record by a temporary increase in regional tropical taxa and a concurrent decrease in steppe–desert vegetation. In the late Eocene, a drying signature in the palynological record is linked to proto-Paratethys Sea retreat, which caused widespread long-term aridification across the region. To better distinguish between local climatic variation and farther-reaching drivers of Central Asian palaeoclimate and elevation, we correlated key palynological sections across the Tibetan Plateau by means of established radioisotopic ages and biostratigraphy. This new palynozonation illustrates both intra- and inter-basinal floral response to Qinghai–Tibetan uplift and global climate change during the Paleogene, and it provides a framework for the age assignment of future palynological studies in Central Asia. Our work highlights the ongoing challenge of integrating various deep time records for the purpose of reconstructing palaeoelevation, indicating that a multi-proxy approach is vital for unravelling the complex uplift history of Tibet and its resulting influence on Asian climate.
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