The future response of the Antarctic ice sheet to rising temperatures remains highly uncertain. A useful period for assessing the sensitivity of Antarctica to warming is the Last Interglacial (LIG) ...(129 to 116 ky), which experienced warmer polar temperatures and higher global mean sea level (GMSL) (+6 to 9 m) relative to present day. LIG sea level cannot be fully explained by Greenland Ice Sheet melt (~2 m), ocean thermal expansion, and melting mountain glaciers (~1 m), suggesting substantial Antarctic mass loss was initiated by warming of Southern Ocean waters, resulting from a weakening Atlantic meridional overturning circulation in response to North Atlantic surface freshening. Here, we report a blue-ice record of ice sheet and environmental change from theWeddell Sea Embayment at the periphery of the marine-based West Antarctic Ice Sheet (WAIS), which is underlain by majormethane hydrate reserves. Constrained by awidespread volcanic horizon and supported by ancient microbial DNA analyses, we provide evidence for substantial mass loss across the Weddell Sea Embayment during the LIG, most likely driven by ocean warming and associated with destabilization of subglacial hydrates. Ice sheet modeling supports this interpretation and suggests that millennial-scale warming of the Southern Ocean could have triggered a multimeter rise in global sea levels. Our data indicate that Antarctica is highly vulnerable to projected increases in ocean temperatures and may drive ice–climate feedbacks that further amplify warming.
► High-resolution C and Sr isotope profile for the Ediacaran–Cambrian Xiaotan section. ► Large negative δ13C excursion below the first appearance of small shelly fossils. ► Positive δ13C excursion ...coincided with the first appearance of Watsonella crosbyi. ► 87Sr/86Sr decreased from 0.7086 to 0.7082 in Nemakit-Daldynian stage in this section. ► Decreased continental weathering and increased hydrothermal alteration in Fortunian Stage (∼16Myrs).
This study reports a high-resolution carbon and strontium isotope profile for the Ediacaran–Cambrian Xiaotan section, situated in northeastern Yunnan, South China. Xiaotan section represents a more distal setting than the more condensed Meishucun section in eastern Yunnan, and is, biostratigraphically and chemostratigraphically, the best constrained section on the Yangtze platform covering the Ediacaran–Cambrian interval. The carbonate carbon isotopic ratios of the late Ediacaran, upper Dengying Formation to the early Cambrian, Zhujiaqing Formation, exhibit a large negative excursion (N1, −12.2‰) in the Daibu Member, just below the first appearance of small shelly fossils (SSF) at the base of the Zhongyicun Member, and a sustained pre-‘Tommotian’ positive excursion (P4, δ13C up to +7.3‰) which coincides with the occurrence of the Heraultipegma yunnanensis (=Watsonella crosbyi) Assemblage SSF in the Dahai Member. Least altered strontium isotope ratios, based on sequential acid leaching of limestones as well as dolostones and phosphorites following rigid petrographic and geochemical selection, reveal a systematic decreasing trend from 0.7085–6 in the latest Ediacaran (Daibu Member) to about 0.7082–3 by the FAD of Watsonella crosbyi in China (Dahai Member). The carbon and strontium isotope features of the Xiaotan section can be correlated with those from sections in Morocco, Mongolia and Siberia, and confirm a decrease in seawater 87Sr/86Sr during Cambrian Stage 1 accompanied by C-isotope oscillations, which together may assist global stratigraphic correlation of the early Cambrian. As previously intimated by C-isotopes and biostratigraphy, this new Sr-isotope evidence confirms a depositional gap during the pre-Tommotian in the Aldan River area of SE Siberia. The decreasing trend of 87Sr/86Sr in the Cambrian Stage 1 marks a temporary (∼16Myrs) reversal of the overall increasing trend during the Ediacaran and Cambrian periods, and potentially records a short-term decrease in continental weathering within a prolonged interval of generally increasing weathering rates. Other factors, such as increased submarine hydrothermal alteration, ocean spreading rates and/or chemical weathering of volcanic provinces and young carbonate dissolution might also have affected this decrease in seawater 87Sr/86Sr.
The off-rift central volcano of Öræfajökull has very distinctive EM1-like isotopic compositions compared with other Icelandic lavas. New Pb–Nd–Sr isotopic data from Öræfajökull show strong ...correlations interpreted as a result of mixing. End-members are a depleted mantle source incorporating 0.5 % subduction-processed sediment and a mantle source with an isotopic signature similar to lavas of the Reykjanes Peninsula. Sr–Nd–Pb isotopic correlations of Icelandic Eastern Rift Zone (ERZ) lavas are almost completely distinct from those of the Reykjanes Peninsula and the Western Rift Zone (WRZ) and require a high-
207
Pb/
204
Pb, low-
143
Nd/
144
Nd end-member that resembles Öræfajökull compositions, which is very distinct from the enriched end-members suggested for the Reykjanes Peninsula and the WRZ. Given the similar depth and degree of melting at rift zones, variation in the observed enriched end-members between rift zones must indicate spatial variations in enriched mantle sources within the shallow mantle under Iceland rather than purely mixing of melts from a bi-lithological mantle. This is consistent with observations that the ERZ lavas erupted closest to Öræfajökull exhibit the most Öræfajökull-like isotopic compositions, implying that a homogenised Öræfajökull source with positive ∆
207
Pb is focused under the Öræfajökull centre and its associated flank zone. This then mixes laterally with the dominant negative-∆
207
Pb ERZ mantle source. Like Reykjanes Peninsula and WRZ lavas, the ERZ mantle source has strongly negative Δ
207
Pb and low K/Nb (<170), and these provide evidence for a recycled oceanic crust contribution. The range in
206
Pb/
204
Pb in mantle sources with negative Δ
207
Pb was probably generated by heterogeneity in
206
Pb/
204
Pb and
μ
in the recycled oceanic crust, which is the dominant source of incompatible elements in Icelandic lavas.
Objectives/Hypothesis
Evaluate and compare surgical outcomes of slide tracheoplasty for the treatment of congenital tracheal stenosis in children with and without pulmonary malformations.
Study ...Design
Retrospective chart review at a tertiary care pediatric medical center.
Methods
We identified patients with tracheal stenosis who underwent slide tracheoplasty from 2001 to 2014, and a subset of these patients who were diagnosed with congenital pulmonary malformations. Hospital course and preoperative and postoperative complications were recorded.
Results
One hundred thirty patients (18 with pulmonary malformations, 112 with normal pulmonary anatomy) were included. Pulmonary malformations included unilateral pulmonary agenesis (61%) and hypoplasia (39%). Children with pulmonary malformations had a greater median age compared to their normal lung anatomy counterparts. Preoperatively, patients with pulmonary malformations more frequently required preoperative mechanical ventilation (55.6% vs. 21.3%, P = .007), extracorporeal membrane oxygenation (ECMO) (11% vs. 0.9%, P = .05), and tracheostomy (22.2% vs. 3.6%, P = .01). Postoperatively, patients with pulmonary malformations more frequently required mechanical ventilation >48 hours (78% vs. 37%, P =.005) and ECMO use (11% vs. 0.9%, P = .05). Pulmonary malformation patients and children with normal anatomy did not differ in terms of postoperative tracheostomy (16.7% vs. 4.4%, P > .05), dehiscence (6% vs. 0%, P > .05%), restenosis (11% vs. 6%, P > .05) or postoperative figure 8 deformity (6% vs. 3%, P > .05). Mortality, however, was significantly increased (22.2% vs. 3.6%, P = .01) in children with pulmonary malformations.
Conclusions
Although slide tracheoplasty can be successfully performed in patients with abnormal pulmonary anatomy, surgeons and families should anticipate a more difficult postoperative course, with possible associated prolonged mechanical ventilation, ECMO use, and higher mortality than in children with tracheal stenosis alone.
Level of Evidence
4. Laryngoscope, 127:1283–1287, 2017
ABSTRACT
The significance of the southern Caucasus in understanding Pleistocene hominin expansions is well established. However, the palaeoenvironments in which Palaeolithic occupation of the region ...took place are presently poorly defined. The Hrazdan river valley, Armenian Highlands, contains a rich Palaeolithic record alongside Middle Pleistocene volcanic, fluvial and lacustrine strata, and thus offer exciting potential for palaeoenvironmental reconstruction. We present the first results of sedimentological, geochemical, tephrostratigraphical and biological (diatoms) study of the sequence of Bird Farm 1, located in the central part of the valley. These data show six phases of landscape development during the interval 440–200 ka. The sequence represents the first quantitative Pleistocene diatom record from the Armenian Highlands and the southern Caucasus, and indicates the persistence of a deep, stratified lacustrine system, with evidence for changing lake productivity that is tentatively linked to climate. Furthermore, major element chemical characterization of visible and crypto‐tephra horizons in the sequence enables the first stages of the development of a regional tephrostratigraphy. Together, the evidence from Bird Farm 1 demonstrates the importance of lacustrine archives in the region for palaeoenvironmental reconstruction and highlights the potential for linkages between archives on both a local and regional scale.
The Sólheimar ignimbrite was one of the largest eruptions from the Katla caldera (Iceland) and is important for tephra studies in the North Atlantic because of its possible linkage with the Vedde ...Ash, a compositionally bimodal tephra layer used for correlation of sedimentary records in the North Atlantic and Northern Europe. The composition of the Sólheimar ignimbrite extends from rhyolite to basaltic-icelandite, a trend that defines a coherent magma mixing line. Mixing is evident both in mingled textures seen in hand specimens and thin sections and as binary mixing trends in major and trace element and 87Sr/86Sr isotopes of the volcanic glasses. The Sólheimar rhyolite is slightly more radiogenic than the basaltic-icelandite in terms of Sr isotopes, which is inconsistent with generation of the rhyolite by fractionation of the basaltic-icelandite. Alternatively, the Sólheimar rhyolite may have been produced by partial melting of Icelandic crust. Major and trace element modelling indicates that partial melting of Icelandic tholeiite does not replicate the observed rhyolite composition, in particular K2O is significantly lower in the modelled melt. However, partial melting of Katla alkali basalt does produce a comparable melt. We suggest a two-stage model in which 30–40% melting of basalt generated a dacitic magma which underwent subsequent ∼30% fractionation of the observed phenocryst phases (feldspar, clinopyroxene, spinel and FeTi oxide) form rhyolite. The eruption of the Sólheimar ignimbrite was triggered by the intrusion of basaltic-icelandite magma, which mixed with resident rhyolite magma during eruption.
The Sólheimar ignimbrite has been linked to the Vedde Ash (Lacasse et al., 1995), a compositionally bimodal tephra layer used to link sedimentary records in the North Atlantic and Northern Europe. Despite the importance of the Vedde Ash in late Quaternary studies, its provenance remains equivocal. We demonstrate that Vedde rhyolite glasses share the same major and trace element chemistry as the Sólheimar rhyolite, carrying the implication that these deposits may be produced by the same eruption. However, the Sólheimar ignimbrite lacks the basaltic component that is sometimes associated with rhyolitic shards of the Vedde Ash at far distal locations, therefore this correlation cannot be confirmed.
► Geochemical profile across Early Cambrian black shale successions. ► Multiple redox-proxy approach. ► Weakly reducing conditions followed by upwelling sulphide-rich waters. ► Correlation of Ni–Mo ...ore layer on platform margin. ► Ni–Mo ore layer originates from two separate events.
The Xiaotan section, situated on the southwestern Yangtze Platform, South China, contains an unusually expanded sedimentary record, spanning the upper Neoproterozoic to the Cambrian and representing more than 40My of marine sedimentation. Three distinct black shale units of the Shiyantou and Yuanshan formations were analysed for redox-sensitive trace elements and iron speciation, in order to constrain the evolution of the marine environment during the Early Cambrian metazoan biodiversification on the southwestern Yangtze Platform. For comparison we also include black shale samples of the Shiyantou Fm. from the Meishucun section, samples from a previous study covering the Shiyantou and Yuanshan Fm. at Dapotuo near Chengjiang, and samples from the strongly condensed Early Cambrian Niutitang Fm. from the Zhongnan section situated on the platform margin. Th/U and FeHR/FeT ratios reveal that bottom waters on the southwestern Yangtze Platform were commonly anoxic and ferruginous into the Cambrian, but became oxic after deposition of the black shales of the lower Yuanshan Formation, which elsewhere contains the Chengjiang Biota. Average Mo/TOC ratios, used as an indicator of the size of the Mo reservoir, increase up-section, and together with generally increasing S/C ratios suggest a trend towards normal (Phanerozoic) marine conditions. A distinctive Ni peak within the upper Shiyantou Fm. at Xiaotan and maximum Mo concentrations at the base of the Yuanshan Fm. can be correlated to the Ni–Mo sulphide layer within the lower Niutitang Fm. and thus indicate two separate pulses of sedimentary-exhalative nickel enrichment and subsequent, redox controlled molybdenum accumulation. A strong decoupling of organic carbon and pyrite sulphur within both sections further suggests upwelling of H2S-rich waters onto the platform. We argue here for an opening of the depositional environment on the northwestern Yangtze Platform which led to the upwelling of sulphidic waters, ventilation of the seafloor and ultimately its colonisation by newly emergent animal groups during the ‘Cambrian Explosion’.
Accurately reconstructing the scale and timing of dynamic processes, such as Middle-Late Pleistocene explosive volcanism and rapid climatic changes, requires rigorous and independent chronological ...constraints. In this framework, the study of distal volcanic ash layers, or tephra, transported and deposited over wide regions during explosive volcanic eruptions, is increasingly being recognised as a fundamental chronostratigraphic tool for addressing these challenging issues. Here we present a high-resolution distal tephra record preserved in the lacustrine sedimentary succession of the Fucino Basin, central Italy. The investigated record spans the 430-365 ka time interval, covering the entirety of Marine Isotope Stage 11 (MIS 11), and provides important insights into peri-Tyrrhenian potassic explosive volcanism from sources located in central Italy against a backdrop of Mediterranean palaeooclimate records. The succession of ash fall events of this time interval is reconstructed through a detailed lithostratigraphic, geochemical and 40Ar/39Ar geochronological characterization of the deposits preserved as discrete layers in the Fucino F4-F5 sediment core. This work is complemented by similarly detailed characterization of selected proximal pyroclastic units from the peri-Tyrrhenian potassic volcanoes. Geochemical fingerprinting of the tephra deposits by means of their major, minor and trace elements and Sr isotope composition indicates that all the thirty-two investigated ash layers derived from the peri-Tyrrhenian potassic volcanoes. The stratigraphically continuous succession of the Fucino tephra layers allowed the development of a fully independent, 40Ar/39Ar age-constrained, Bayesian age-depth model for the investigated time interval. The age-model allows us to establish modelled ages for the tephra layers within the succession that are not directly dated. The resulting dated tephra record clearly reveals a highly time resolved and previously unparalelled chronicle of explosive activity from the Vulsini, Vico, Sabatini, Colli Albani and Roccamonfina volcanic complexes. Our study provides a benchmark and valuable geochemical and geochronological dataset to be used as a reference for any future development and application of the tephrostratigraphic methods across the central Mediterranean area both during the investigated 430-365 ka time interval, and deeper in time. This contribution underlines the importance of integrating proximal and distal sedimentary records to more accurately establish long-term and comprehensive volcanic eruption records.
New Guinea has acted as the boundary between the Australian and Pacific plates for hundreds of millions of years. Strike-slip movement and arc–continent collisions along this boundary during the ...Cenozoic have shuffled rocks of different age and composition in a series of terranes along the plate boundary making mapping them a considerable challenge. Here we report results of SrNd isotopic data obtained from rock samples from western New Guinea that are representative of the different terranes. These isotopic data reveal the crustal affinity of the terranes and we have used these data to map their spatial distribution. The isotopic data show three distinct crustal domains underlying western New Guinea; Palaeozic–Mesozoic Australian continental crust (87Sr/86Sr = 0.719594 to 0.710921; εNd = −13.85 to 1.373); thinned transitional crust intruded by Miocene–Pleistocene magmatic rocks (87Sr/86Sr = 0.706524 to 0.704019; εNd = 6.67 to 2.13); and accreted island arc crust (87Sr/86Sr = 0.704053 to 0.703759; εNd = 6.63 to 4.97). These data, together with crustal contamination models, indicate that the northern-most extent of Australian continental crust exists beneath the northern-most section of western New Guinea. We also combined our isotopic data with existing data across New Guinea and used these to develop an isotopic map that shows the position of the ancient Australian–Pacific Plate boundary, producing results that are also consistent with broad-scale seismic tomography imagery. Our findings provide a framework for mapping other plate boundaries, particularly ancient systems where only fragmentary data exist.
•We present new SrNd isotopic data for magmatic rocks from NW New Guinea.•Three different isotopic signatures can be linked to distinct crustal fragments.•Isotopic mapping reveals the extent of these fragments across a poorly exposed region.•We determine the northern-most extent of Australian continental crust.•These data will better inform new tectonic reconstructions of this convergent margin.
The iconic climate archive of Tenaghi Philippon (TP), NE Greece, allows the study of short-term palaeoclimatic and environmental change throughout the past 1.3 Ma. To provide high-quality age control ...for detailed palaeoclimate reconstructions based on the TP archive, (crypto)tephra studies of a peat core ‘TP-2005’ have been carried out for the 0–130 ka interval. The results show that the TP basin is ideally positioned to receive tephra fall from both the Italian and Aegean Arc volcanic provinces. Two visible tephra layers, the Santorini Cape Riva/Y-2 (c. 22 ka) and the Campanian Ignimbrite (CI)/Y-5 (c. 39.8 ka) tephras, and six primary cryptotephra layers, namely the early Holocene E1 tephra from the Aeolian Islands (c. 8.3 ka), the Campanian Y-3 (c. 29 ka) and X-6 tephras (c. 109.5 ka), as well as counterpart tephras TM-18-1d (c. 40.4 ka), TM-23-11 (c. 92.4 ka) and TM-33-1a (c. 116.7 ka) from the Lago Grande di Monticchio sequence (southern Italy), were identified along with repeatedly redeposited Y-2 and CI tephra material. Bayesian modelling of the ages of seven of the primary tephra layers, 60 radiocarbon measurements and 20 palynological control points have been applied to markedly improve the chronology of the TP archive. This revised chronology constrains the age of tephra TM-18-1d to 40.90–41.66 cal ka BP (95.4% range). Several tephra layers identified in the TP record form important isochrons for correlating this archive with other terrestrial (e.g., Lago Grande di Monticchio, Sulmona Basin and Lake Ohrid) and marine (e.g., Adriatic Sea core PRAD 1-2 and Aegean Sea core LC21) palaeoclimate records in the Mediterranean region.
•8 (crypto)tephras are identified in the MIS 1–5 peat record of Tenaghi Philippon.•Tephras have Italian and Aegean Arc provenances.•Most Italian tephras, including X-6, were found in their most distal sites.•The MIS 1–5 chronology of TP was improved by Bayesian modelling.
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