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  • 1. Dunk, M.
    et al.
    Strachan, R. A.
    Cutts, K. A.
    Lasalle, S.
    Storey, C. D.
    Burns, I. M.
    Whitehouse, Martin J.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Fowler, M.
    Moreira, H.
    Dunlop, J.
    Pereira, I.
    Evidence for a late Cambrian juvenile arc and a buried suture within the Laurentian Caledonides of Scotland: Comparisons with hyperextended Iapetan margins in the Appalachian Mountains (North America) and Norway2019Inngår i: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 47, nr 8, s. 734-738Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Uranium-lead (U-Pb) zircon dating establishes a late Cambrian (Drumian) protolith age of 503 ± 2 Ma for a trondhjemitic gneiss of the calc-alkaline Strathy Complex, northern Scottish Caledonides. Positive εHf and εNd values from trondhjemitic gneisses and co-magmatic amphibolites, respectively, and an absence of any inheritance in zircon populations support published geochemistry that indicates a juvenile origin distal from Laurentia. In order to account for its present location within a stack of Laurentia-derived thrust sheets, we interpret the complex as allochthonous and located along a buried suture. We propose that a microcontinental ribbon was detached from Laurentia during late Neoproterozoic to Cambrian rifting; the intervening oceanic tract closed by subduction during the late Cambrian and formed a juvenile arc, the protolith of the Strathy Complex. The microcontinental ribbon was reattached to Laurentia during the Grampian orogeny, which transported the Strathy Complex as a tectonic slice within a nappe stack. Peak metamorphic conditions for the Strathy Complex arc (650–700 °C, 0.6–0.75 GPa) are intermediate in pressure between those published previously for Grampian mineral assemblages in structurally overlying low-pressure migmatites (670–750 °C, <0.4 GPa) that we deduce to have been derived from an adjacent backarc basin, and structurally underlying upper amphibolite rocks (650–700 °C, 1.1–1.2 GPa) that we interpret to represent the partially subducted Laurentian margin. This scenario compares with that of the northern Appalachian Mountains and Norway where microcontinental blocks are interpreted to have their origins in detachment from passive margins of the Iapetus Ocean during Cambrian rifting and to have been re-amalgamated during Caledonian orogenesis.

  • 2. Ge, Rongfeng
    et al.
    Wilde, Simon
    Nemchin, Alexander
    Whitehouse, Martin
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Bellucci, Jeremy
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Erickson, Timmons
    Frew, Adam
    Thern, Eric
    A 4463 Ma apparent zircon age from the Jack Hills (Western Australia) resulting from ancient Pb mobilization2018Inngår i: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 46, nr 4, s. 303-306Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hadean (≥4.0 Ga) zircon grains provide the only direct record of the first half-billion years of Earth’s history. Determining accurate and precise crystallization ages of these ancient zircons is a prerequisite for any interpretation of crustal evolution, surface environment, and geodynamics on the early Earth, but this may be compromised by mobilization of radiogenic Pb due to subsequent thermal overprinting. Here we report a detrital zircon from the Jack Hills (Western Australia) with 4486–4425 Ma concordant ion microprobe ages that yield a concordia age of 4463 ± 17 Ma (2σ), the oldest zircon age recorded from Earth. However, scanning ion imaging reveals that this >4.4 Ga apparent age resulted from incorporation of micrometer-scale patches of unsupported radiogenic Pb with extremely high 207Pb/206Pb ratios and >4.5 Ga 207Pb/206Pb ages. Isotopic modeling demonstrates that these patches likely resulted from redistribution of radiogenic Pb in a ca. 4.3 Ga zircon during a ca. 3.8 Ga or older event. This highlights that even a concordia age can be spurious and should be carefully evaluated before being interpreted as the crystallization age of ancient zircon.

  • 3.
    Kenny, Gavin
    et al.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Karlsson, Andreas
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Schmieder, Martin
    Whitehouse, Martin
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Nemchin, Alexander
    Bellucci, Jeremy
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Recrystallization and chemical changes in apatite in response to hypervelocity impact2020Inngår i: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 48, nr 1, s. 19-23Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Despite the wide utility of apatite, Ca5(PO4)3(F,Cl,OH), in the geosciences, including tracing volatile abundances on the Moon and Mars, little is known about how the mineral responds to the extreme temperatures and pressures associated with hypervelocity impacts. To address this deficiency, we here present the first microstructural analysis and chemical mapping of shocked apatite from a terrestrial impact crater. Apatite grains from the Paasselkä impact structure, Finland, display intragrain crystal-plastic deformation as well as pervasive recrystallization—the first such report in terrestrial apatite. A partially recrystallized grain offers the opportunity to investigate the effect of shock recrystallization on the chemical composition of apatite. The recrystallized portion of the fluorapatite grain is depleted in Mg and Fe relative to the remnant non-recrystallized domain. Strikingly, the recrystallized region alone hosts inclusions of (Mg,Fe)2(PO4)F, wagnerite or a polymorph thereof. These are interpreted to be a product of phase separation during recrystallization and to be related to the reduced abundances of certain elements in the recrystallized domain. The shock-induced recrystallization of apatite, which we show to be related to changes in the mineral’s chemical composition, is not always readily visible in traditional imaging techniques (such as backscattered electron imaging of polished interior surfaces), thus highlighting the need for correlated microstructural, chemical, and isotopic studies of phosphates. This is particularly relevant for extraterrestrial phosphates that may have been exposed to impacts, and we urge the consideration of microstructural data in the interpretation of the primary or secondary nature of elemental abundances and isotopic compositions.

    Fulltekst tilgjengelig fra 2021-01-01 12:00
  • 4.
    Kenny, G.G.
    et al.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Whitehouse, Martin J.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Balz, B.S
    Differentiated impact melt sheets may be a potential source of Hadean detrital zircon.2016Inngår i: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 44, s. 431-434Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Constraining the origin and history of very ancient detrital zircons has unique potential for furthering our knowledge of Earth’s very early crust and Hadean geodynamics. Previous applications of the Ti-in-zircon thermometer to >4 Ga zircons have identified a population with relatively low crystallization temperatures () of ~685 °C. This could possibly indicate wet minimum-melting conditions producing granitic melts, implying very different Hadean terrestrial geology from other rocky planets. Here we report the first comprehensive ion microprobe study of zircons from a transect through the differentiated Sudbury impact melt sheet. The new zircon Ti contents and corresponding  fully overlap with those of the Hadean zircon population. Previous studies, which measured Ti in impact melt sheet zircons did not find this wide range because they analyzed samples only from a restricted portion of the melt sheet and because they used laser ablation analyses that can overestimate true Ti content. It is important to note that internal differentiation of the impact melt is likely a prerequisite for the observed low  in zircons from the most evolved rocks. On Earth, melt sheet

  • 5.
    Kenny, G.G.
    et al.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Whitehouse, Martin J.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Kamber, B.S.
    Differentiated impact melt sheets may be a potential source of Hadean detrital zircon: Reply2016Inngår i: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 44, artikkel-id e399Artikkel i tidsskrift (Fagfellevurdert)
  • 6.
    Kiel, Steffen
    Naturhistoriska riksmuseet, Enheten för paleobiologi.
    Using network analysis to trace the evolution of biogeography through geologic time: A case study2017Inngår i: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 45, s. 711-714Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The biogeographic distribution of organisms has continuously changed through Earth’s

    history as plate tectonics changed the configurations of land masses, ocean basins, and climate

    zones. Yet, methods to investigate this dynamic through geologic time are limited. Here,

    network analysis is used to explore and to visualize the biogeographic history of brachiopods

    through the entire Triassic period. Many previously recognized biogeographic provinces are

    found, and in addition, the stratigraphic ranges of these provinces were identified. Provinces

    in the Tethys Ocean show the lowest degree of connectedness, which can be linked to higher

    evolutionary rates in this tropical ocean basin and possibly also to higher habitat heterogeneity.

    Stratigraphically, the Tethyan provinces are separated largely along the boundaries of

    the Early, Middle, and Late Triassic. This suggests that the events resulting in faunal changes

    among the index fossils used to define these sub-periods also affected the brachiopods. However,

    through the ~50 m.y. of the Triassic period, geographic proximity played a greater role

    in producing faunal similarity than proximity in geologic age. Thus network analysis is a

    viable tool to better understand the dynamic evolution of biogeography through geologic time.

  • 7.
    Kiel, Steffen
    et al.
    Naturhistoriska riksmuseet, Enheten för paleobiologi.
    Krystyn, Leopold
    Department of Palaeontology, Vienna University, 1090 Vienna, Austria.
    Demirtaş, Ferdi
    Department of Geological Engineering, Akdeniz University, 07058 Antalya, Turkey.
    Koşun, Erdal
    Department of Geological Engineering, Akdeniz University, 07058 Antalya, Turkey.
    Peckmann, Jörn
    Institute for Geology, Universität Hamburg, 20146 Hamburg, Germany.
    Late Triassic mollusk-dominated hydrocarbon-seep deposits from Turkey2017Inngår i: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 44, s. 751-754Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Deep-sea hydrothermal vents and hydrocarbon seeps host unique ecosystems relying on geochemical energy rather than photosynthesis. Whereas the fossil and evolutionary history of these ecosystems is increasingly well known from the Cretaceous onward, their earlier history remains poorly understood and brachiopods are considered to have played a dominant role during the Paleozoic and Mesozoic. Here we report five new hydrocarbon-seep deposits from the Upper Triassic Kasımlar shales in southern Turkey. The pyritiferous seep limestones predominantly consist of 13C-depleted micrite with δ13C values as low as −10.4‰, and contain only sparse 13C-depleted rim cement (δ13C as low as −12.0‰), interpreted to result from the recrystallization of banded and botryoidal crystal aggregates of fibrous cement. The geologic ages of the studied seep deposits were determined as late Carnian and early Norian using conodonts. The associated fauna is dominated by modiomorphid and anomalodesmatan bivalves, and also includes a diversity of gastropods and the dimerelloid brachiopod Halorella. These faunal assemblages allow a comparison between seep faunas from the two major Triassic ocean basins—the present assemblages being from Tethys, and the only previously known examples being from eastern Panthalassa—and indicate that a cosmopolitan, seep-restricted fauna as in the present-day oceans has existed since the Late Triassic. With almost 20 species, the seep fauna of the Kasımlar shales approaches the diversity of Cretaceous to present-day seep faunas, further emphasizing the ecological similarity of seep faunas since the early Mesozoic. Our findings also highlight that brachiopods and bivalves had a more complex history of coexistence at seeps than currently appreciated.

  • 8.
    Mays, Chris
    et al.
    Naturhistoriska riksmuseet, Enheten för paleobiologi. Monash University.
    Cantrill, David
    Royal Botanic Gardens Victoria, Private Bag 2000, South Yarra, VIC 3141, Australia.
    Bevitt, Joseph J.
    Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW 2234, Australia.
    Polar wildfires and conifer serotiny during the Cretaceous globalhothouse2017Inngår i: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 45, nr 12, s. 1119-1122Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Several highly effective fire-adaptive traits first evolved among modern plants duringthe mid-Cretaceous, in response to the widespread wildfires promoted by anomalously highatmospheric oxygen (O2) and extreme temperatures. Serotiny, or long-term canopy seedstorage, is a fire-adaptive strategy common among plants living in fire-prone areas today,but evidence of this strategy has been lacking from the fossil record. Deposits of abundantfossil charcoal from sedimentary successions of the Chatham Islands, New Zealand, recordwildfires in the south polar regions (75°–80°S) during the mid-Cretaceous (ca. 99–90 Ma).Newly discovered fossil conifer reproductive structures were consistently associated withthese charcoal-rich deposits. The morphology and internal anatomy as revealed by neutrontomography exhibit a range of serotiny-associated characters. Numerous related fossils fromsimilar, contemporaneous deposits of the Northern Hemisphere suggest that serotiny was akey adaptive strategy during the high-fire world of the Cretaceous.

  • 9. Olierook, Hugo K.H.
    et al.
    merle, Renaud E.
    Naturhistoriska riksmuseet.
    Jourdan, Fred
    Sircombe, Keith
    Fraser, Geoff
    Timms, Nicholas E.
    Nelson, Gabriel
    Dadd, Kelsie A.
    Kellerson, Laurent
    Borissova, Irina
    Age and geochemistry of magmatism on the oceanic Wallaby Plateau and implications for the opening of the Indian Ocean2015Inngår i: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 43, nr 11, s. 971-974Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The temporal relationship between tectonic and volcanic activity on passive continental margins immediately before and after the initiation of mid-ocean ridge spreading is poorly understood because of the scarcity of volcanic samples on which to perform isotope geochronology. We present the first accurate geochronological constraints from a suite of volcanic and volcaniclastic rocks dredged from the 70,000 km2 submerged Wallaby Plateau situated on the Western Australian passive margin. Plagioclase 40Ar/39Ar and zircon U-Pb sensitive high-resolution ion microprobe ages indicate that a portion of the plateau formed at ca. 124 Ma. These ages are at least 6 m.y. younger than the oldest oceanic crust in adjacent abyssal plains (minimum = 130 Ma). Geochemical data indicate that the Wallaby Plateau volcanic samples are enriched tholeiitic basalt, similar to continental flood basalts, including the spatially and temporally proximal Bunbury Basalt in southwestern Australia. Thus, the Wallaby Plateau volcanism could be regarded as a (small) flood basalt event on the order of 104–105 km3. We suggest that magma could not erupt prior to 124 Ma because of the lack of space adjacent to the plateau. Eruption was made possible at 124 Ma via the opening of the Indian Ocean during the breakup of Greater India and Australia along the Wallaby-Zenith Fracture Zone. The scale of volcanism and the temporal proximity to breakup challenges the prevailing theory that the Western Australian margin formed as a volcanic passive margin. Given that the volume of volcanism is too small for typical flood basalts associated with volcanic passive margins, we suggest that the two end members, magma-poor and volcanic passive margins, should rather be treated as a continuum.

  • 10.
    Petersson, Andreas
    Naturhistoriska riksmuseet, Enheten för geovetenskap. University of Western Australia.
    A Yilgarn seed to the Pilbara Craton (Australia)? Evidence from inherited zircons2019Inngår i: Geology, ISSN 0091-7613, E-ISSN 1943-2682, ISSN 0091-7613, Vol. 47, nr 11, s. 1098-1102Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Knowledge of the age and compositional architecture of Archean cratonic lithosphere is critical for models of geodynamics and continental growth on early Earth, but can be difficult to unravel from the exposed geology. We report the occurrence of numerous >3.7 Ga zircon crystals in 3.45 Ga rhyolites of the eastern Pilbara Craton (Western Australia), which preserve evidence for an Eoarchean meta-igneous component in the deep Pilbara crust. This inherited zircon population shares similar and distinctive age and Hf-O isotope characteristics with the oldest gneissic components of the Yilgarn Craton ∼500 km farther south, suggesting a common ca. 3.75 Ga felsic crustal nucleus to these two Archean granite-greenstone terranes. We infer a pivotal role for such ‘seeds’ in facilitating the growth and persistence of Archean continental lithosphere.

  • 11.
    Qu, Yuangao
    et al.
    Institute of Deep-Sea Science and Engineering, Chinese Academy of Sciences.
    McLoughlin, Nicola
    Rhodes University.
    van Zuilen, Mark A.
    Sorbonne Paris Cité.
    Whitehouse, Martin
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Engdahl, Anders
    MAX IV Laboratory, Lund University.
    Vajda, Vivi
    Naturhistoriska riksmuseet, Enheten för paleobiologi. Department of Geology, Lund University, Sweden.
    Evidence for molecular structural variations in the cytoarchitectures of a Jurassic plant2019Inngår i: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 47, s. 325-329Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

     

    In this study, we investigate the molecular structural characteristics of organic remains in various cellular organelles from a 180 Ma Jurassic royal fern belonging to the Osmundaceae family of ferns, and compare their carbon isotopic compositions to a now-living species of royal fern (Osmunda regalis). We discovered molecular structural variations indicated by Raman and infrared spectral parameters obtained from various fossilized cellular organelles. The organic remains preserved in the chromosomes and cell nuclei show marked structural heterogeneities compared to the cell walls during different stages of the cell cycle. The fossil and extant fern have similar δ13C values obtained from bulk samples, supporting evolutionary stasis in this plant lineage and an unchanged metabolic pathway of carbon assimilation since the Jurassic. The organic remains in the cellular organelles of the fossil seem to be less heterogeneous than those in the extant fern, likely due to the preferential preservation of certain cellular compounds during fossilization. Taphonomic processes appear to have diminished the subcellular isotopic heterogeneities. Our research sheds light on the functioning of ancient plant cellular organelles during mitosis, provides insights to the taphonomic processes operating at molecular and isotopic levels, and shows the practicability of in situ techniques in studying the evolution and behaviors of ancient cells.

  • 12.
    Renne, Paul R
    et al.
    Berkeley Geochronology Center, Berkeley, California 94709, USA.
    Arenillas, Ignacio
    Departamento de Ciencias de la Tierra, and Instituto Universitario de Investigación en Ciencias Ambientales de Aragón, Universidad de Zaragoza, E-50009 Zaragoza, Spain.
    Arz, José A.
    Departamento de Ciencias de la Tierra, and Instituto Universitario de Investigación en Ciencias Ambientales de Aragón, Universidad de Zaragoza, E-50009 Zaragoza, Spain.
    Vajda, Vivi
    Naturhistoriska riksmuseet, Enheten för paleobiologi. Department of Geology, Lund University, Sweden.
    Gilabert, Vicente
    Departamento de Ciencias de la Tierra, and Instituto Universitario de Investigación en Ciencias Ambientales de Aragón, Universidad de Zaragoza, E-50009 Zaragoza, Spain.
    Bermúdez, Hermann D
    Grupo de Investigación Paleoexplorer, St. George, Vermont 05495, USA.
    Multi-proxy record of the Chicxulub impact at the Cretaceous-Paleogene boundary from Gorgonilla Island, Colombia2018Inngår i: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 46, s. 547-550Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A 40 m stratigraphic section at Gorgonilla Island, Colombia, provides a unique deepmarine, low-latitude, Southern Hemisphere record of events related to the end-Cretaceous Chicxulub impact and the global Cretaceous/Paleogene boundary (KPB). The KPB is marked by a 20-mm-thick, densely packed spherule bed as defined by planktic foraminifera, in contrast to complex relationships found in high-energy, impact-proximal sites in the Gulf of Mexico and Caribbean basins. The absence of basal Danian foraminiferal Zone P0 may indicate a possible hiatus of <10 ka immediately above the spherule bed, but is most probably an artifact of deposition below the calcite compensation depth as suggested by the nearly complete absence of calcareous fossils for 20 m below the Zone Pα. A weighted mean 40Ar/39Ar age of 66.051 ± 0.031 Ma for 25 fresh glassy spherules unequivocally establishes both their derivation from Chicxulub, and the association between the impact and the KPB. The spherule bed, and Maastrichtian strata below it, display soft-sediment deformation features consistent with strong seismic motion, suggesting that seismic activity in the immediate aftermath of the Chicxulub impact continued for weeks. We discovered a fern-spike immediately above the spherule bed, representing the first record of this pioneer vegetation from the South American continent, and from a low-latitude (tropical) environment.

  • 13. Smit, Matthijs
    et al.
    Ratschbacher, Lothar
    Kooijman, Ellen
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Stearns, Michael
    Early evolution of the Pamir deep crust from Lu-Hf and U-Pb geochronology and garnet thermometry2014Inngår i: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 42, nr 12, s. 1047-1050Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Determining early orogenic processes within the Pamir-Tibet orogen represents a critical step toward constructing a comprehensive model on the tectonic evolution of the region. Here we investigate the timing and cause of prograde metamorphism of Cenozoic metamorphic rocks from the Pamir plateau through Lu-Hf geochronology, U-Pb rutile thermochronology, and garnet thermometry. Regional prograde metamorphism and heating to 750–830 °C, as constrained by thermometry, occurred between 37 and 27 Ma. Prograde growth of garnet first occurred in the South Pamir and spread to the Central Pamir during the following 10 m.y. The early metamorphism is attributed to high mantle heat flow following the ca. 45 Ma break-off of the Indian slab south of the Pamir. Our investigation confirms a long-lived thermal history of the Pamir deep crust before the Miocene, and provides a causal link between break-off, enhanced mantle heat flow, and prograde heating of the subduction hanging wall.

  • 14.
    Steinthorsdottir, Margret
    et al.
    Naturhistoriska riksmuseet, Enheten för paleobiologi. Bolin Centre for Climate Research, Stockholm University.
    Vajda, Vivi
    Naturhistoriska riksmuseet, Enheten för paleobiologi. Department of Geology, Lund University, Sweden.
    Pole, Mike
    3Queensland Herbarium, Brisbane Botanic Gardens.
    Holdgate, Guy
    4School of Earth Sciences, University of Melbourne.
    Moderate levels of Eocene pCO2 indicated by Southern Hemisphere fossil plant stomata2019Inngår i: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 47, s. 914-918Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    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.

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