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| 2. |
- Hammarlund, Emma U., 1971-, et al.
(författare)
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A sulfidic driver for the end-Ordovician mass extinction
- 2012
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Ingår i: Earth and Planetary Science Letters. - : Elsevier BV. - 0012-821X .- 1385-013X. ; 331, s. 128-139
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Tidskriftsartikel (refereegranskat)abstract
- The end-Ordovician extinction consisted of two discrete pulses, both linked, in various ways, to glaciation at the South Pole. The first phase, starting just below the Normalograptus extraordinarius Zone, particularly affected nektonic and planktonic species, while the second pulse, associated with the Normalograptus persculptus Zone, was less selective. Glacially induced cooling and oxygenation are two of many suggested kill mechanisms for the end-Ordovician extinction, but a general consensus is lacking. We have used geochemical redox indicators, such as iron speciation, molybdenum concentrations, pyrite framboid size distribution and sulfur isotopes to analyze the geochemistry in three key Hirnantian sections. These indicators reveal that reducing conditions were occasionally present at all three sites before the first pulse of the end-Ordovician extinction, and that these conditions expanded towards the second pulse. Even though the N. extraordinarius Zone appears to have been a time of oxygenated deposition, pyrite is significantly enriched in 34S in our sections as well as in sections reported from South China. This suggests a widespread reduction in marine sulfate concentrations, which we attribute to an increase in pyrite burial during the early Hirnantian. The S-isotope excursion coincides with a major positive carbon isotope excursion indicating elevated rates of organic carbon burial as well. We argue that euxinic conditions prevailed and intensified in the early Hirnantian oceans, and that a concomitant global sea level lowering pushed the chemocline deeper than the depositional setting of our sites. In the N. persculptus Zone, an interval associated with a major sea level rise, our redox indicators suggests that euxinic conditions, and ferruginous in some places, encroached onto the continental shelves. In our model, the expansion of euxinic conditions during the N. extraordinarius Zone was generated by a reorganization of nutrient cycling during sea level fall, and we argue, overall, that these dynamics in ocean chemistry played an important role for the end-Ordovician mass extinction. During the first pulse of the extinction, euxinia and a steepened oxygen gradient in the water column caused habitat loss for deep-water benthic and nektonic organisms. During the second pulse, the transgression of anoxic water onto the continental shelves caused extinction in shallower habitats.
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| 3. |
- Hammarlund, Emma U., et al.
(författare)
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The Sirius Passet Lagerstätte of North Greenland—A geochemical window on early Cambrian low-oxygen environments and ecosystems
- 2019
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Ingår i: Geobiology. - : Wiley. - 1472-4677. ; 17:1, s. 12-26
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Tidskriftsartikel (refereegranskat)abstract
- The early Cambrian Sirius Passet fauna of northernmost Greenland (Cambrian Series 2, Stage 3) contains exceptionally preserved soft tissues that provide an important window to early animal evolution, while the surrounding sediment holds critical data on the palaeodepositional water-column chemistry. The present study combines palaeontological data with a multiproxy geochemical approach based on samples collected in situ at high stratigraphic resolution from Sirius Passet. After careful consideration of chemical alterations during burial, our results demonstrate that fossil preservation and biodiversity show significant correlation with iron enrichments (FeHR/FeT), trace metal behaviour (V/Al), and changes in nitrogen cycling (δ15N). These data, together with Mo/Al and the preservation of organic carbon (TOC), are consistent with a water column that was transiently low in oxygen concentration, or even intermittently anoxic. When compared with the biogeochemical characteristics of modern oxygen minimum zones (OMZs), geochemical and palaeontological data collectively suggest that oxygen concentrations as low as 0.2–0.4 ml/L restricted bioturbation but not the development of a largely nektobenthic community of predators and scavengers. We envisage for the Sirius Passet biota a depositional setting where anoxic water column conditions developed and passed over the depositional site, possibly in association with sea-level change, and where this early Cambrian biota was established in conditions with very low oxygen.
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| 4. |
- Dahl, Tais W., et al.
(författare)
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Devonian rise in atmospheric oxygen correlated to the radiations of terrestrial plants and large predatory fish
- 2010
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 107:42, s. 17911-17915
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Tidskriftsartikel (refereegranskat)abstract
- The evolution of Earth's biota is intimately linked to the oxygenation of the oceans and atmosphere. We use the isotopic composition and concentration of molybdenum (Mo) in sedimentary rocks to explore this relationship. Our results indicate two episodes of global ocean oxygenation. The first coincides with the emergence of the Ediacaran fauna, including large, motile bilaterian animals, ca. 550-560 million year ago (Ma), reinforcing previous geochemical indications that Earth surface oxygenation facilitated this radiation. The second, perhaps larger, oxygenation took place around 400 Ma, well after the initial rise of animals and, therefore, suggesting that early metazoans evolved in a relatively low oxygen environment. This later oxygenation correlates with the diversification of vascular plants, which likely contributed to increased oxygenation through the enhanced burial of organic carbon in sediments. It also correlates with a pronounced radiation of large predatory fish, animals with high oxygen demand. We thereby couple the redox history of the atmosphere and oceans to major events in animal evolution.
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| 6. |
- El Albani, Abderrazak, et al.
(författare)
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Large colonial organisms with coordinated growth in oxygenated environments 2.1 Gyr ago
- 2010
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 466:7302, s. 100-104
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Tidskriftsartikel (refereegranskat)abstract
- The evidence for macroscopic life during the Palaeoproterozoic era (2.5-1.6 Gyr ago) is controversial(1-5). Except for the nearly 2-Gyr-old coil-shaped fossil Grypania spiralis(6,7), which may have been eukaryotic, evidence for morphological and taxonomic bio-diversification of macroorganisms only occurs towards the beginning of the Mesoproterozoic era (1.6-1.0 Gyr)(8). Here we report the discovery of centimetre-sized structures from the 2.1-Gyr-old black shales of the Palaeoproterozoic Francevillian B Formation in Gabon, which we interpret as highly organized and spatially discrete populations of colonial organisms. The structures are up to 12 cm in size and have characteristic shapes, with a simple but distinct ground pattern of flexible sheets and, usually, a permeating radial fabric. Geochemical analyses suggest that the sediments were deposited under an oxygenated water column. Carbon and sulphur isotopic data indicate that the structures were distinct biogenic objects, fossilized by pyritization early in the formation of the rock. The growth patterns deduced from the fossil morphologies suggest that the organisms showed cell-to-cell signalling and coordinated responses, as is commonly associated with multicellular organization(9). The Gabon fossils, occurring after the 2.45-2.32-Gyr increase in atmospheric oxygen concentration(10), may be seen as ancient representatives of multicellular life, which expanded so rapidly 1.5 Gyr later, in the Cambrian explosion.
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| 7. |
- Gangannagaripalli, J., et al.
(författare)
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A Standard Set of Value-Based Patient-Centered Outcomes and Measures of Overall Health in Adults
- 2022
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Ingår i: Patient-Patient Centered Outcomes Research. - : Springer Science and Business Media LLC. - 1178-1653 .- 1178-1661. ; 15:3, s. 341 - 351
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Tidskriftsartikel (refereegranskat)abstract
- Background The definition of population-specific outcomes is an essential precondition for the implementation of value-based health care. We developed a minimum standard outcome set for overall adult health (OAH) to facilitate the implementation of value-based health care in tracking, comparing, and improving overall health care outcomes of adults across multiple conditions, which would be of particular relevance for primary care and public health populations. Methods The International Consortium for Health Outcomes Measurement (ICHOM) convened an international panel (patients, clinicians, and topic experts). Following the development of a conceptual framework, a modified Delphi method (supported by public consultations) was implemented to identify, in sequence, the relevant domains, the best instruments for measuring them, the timing of measurement, and the relevant adjustment variables. Findings Outcomes were identified in relation to overall health status and the domains of physical, mental, and social health. Three instruments covering these domains were identified: PROMIS Scale v1.2-Global Health (10 items), WHO Wellbeing Index (5 items), and the WHO Disability Assessment Schedule 2.0 (12 items). Case-mix variables included a range of sociodemographic and biometric measures. Yearly measurement was proposed for all outcomes and most case-mix variables. Interpretation The ICHOM OAH Standard Set has been developed through consensus-based methods based on predefined criteria following high standards for the identification and selection of high-quality measures The involvements of a wide range of stakeholders supports the acceptability of the set, which is readily available for use and feasibility testing in clinical settings.
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| 8. |
- Haxen, Emma R., et al.
(författare)
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“Hypoxic” Silurian oceans suggest early animals thrived in a low-O2 world
- 2023
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Ingår i: Earth and Planetary Science Letters. - 0012-821X. ; 622
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Tidskriftsartikel (refereegranskat)abstract
- Atmospheric oxygen (O2) concentrations likely remained below modern levels until the Silurian–Devonian, as indicated by several recent studies. Yet, the background redox state of early Paleozoic oceans remains poorly constrained, hampering our understanding of the relationship between early animal evolution and O2. Here, we present a multi-proxy analysis of redox conditions in the Caledonian foreland basin to Baltica from the early to the mid-Silurian. Our results indicate that anoxic to severely hypoxic bottom waters dominated during deposition of the Silurian sediments cored in the Sommerodde-1 well (Bornholm, Denmark), and regional comparison suggests that these conditions persisted across the Baltoscandian foreland basin. Indeed, even during times of relative oxygenation, ichnological observations indicate that conditions were, at most, very weakly oxic. The results suggest that dissolved O2 was generally scarce in the bottom waters of the extensive Silurian seaway between Baltica and Avalonia, even between Paleozoic “Anoxic Events”. In light of delayed oxygenation of the atmosphere–hydrosphere system, it may be time to consider that early animals were adapted to “hypoxia” and thrived through ∼100 million years of low-O2 conditions after the Cambrian.
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| 9. |
- Hulth, Stefan, 1965, et al.
(författare)
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Nitrogen removal in marine environments: recent findings and future research challenges
- 2005
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Ingår i: Marine Chemistry. - : Elsevier BV. - 0304-4203. ; 94:1-4, s. 125-145
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Tidskriftsartikel (refereegranskat)abstract
- Respiratory reduction of nitrate (denitrification) is recognized as the most important process converting biologically available (fixed) nitrogen to N-2. In current N cycle models, a major proportion of global marine denitrification (50-70%) is assumed to take place on the sea floor, particularly in organic rich continental margin sediments. Recent observations indicate that present conceptual views of denitrification and pathways of nitrate reduction and N, formation are incomplete. Alternative N cycle pathways, particularly in sediments. include anaerobic ammonium oxidation to nitrite, nitrate and N-2 by Mn-oxides, and anaerobic ammonium oxidation coupled to nitrite reduction and subsequent N, mobilization. The discovery of new links and feedback mechanisms between the redox cycles of, e.g., C, N, S, Mn and Fe casts doubt on the present general understanding of the global N cycle. Recent models of the oceanic N budget indicate that total inputs are significantly smaller than estimated fixed N removal. The occurrence of alternative N reaction pathways further exacerbates the apparent imbalance as they introduce additional routes of N removal. In this contribution, we give a brief historical background of the conceptual understanding of N cycling in marine ecosystems, emphasizing pathways of aerobic and anaerobic N mineralization in marine sediments, and the implications of recently recognized metabolic pathways for N removal in marine environments. (c) 2004 Elsevier B.V. All rights reserved.
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| 10. |
- MacLennan, Steven, et al.
(författare)
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Systematic Review of Oncological Outcomes Following Surgical Management of Localised Renal Cancer
- 2012
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Ingår i: European Urology. - : Elsevier BV. - 0302-2838 .- 1873-7560. ; 61:5, s. 972-993
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Forskningsöversikt (refereegranskat)abstract
- Context: Renal cell carcinoma (RCC) accounts for 2-3% of adult malignancies. There remain uncertainties over the oncological outcomes for the surgical management of localised RCC. Objective: Systematically review relevant literature comparing oncological outcomes of surgical management of localised RCC (T1-2N0M0). Evidence acquisition: Relevant databases including Medline, Embase, and the Cochrane Library were searched up to October 2010, and an updated scoping search was performed up to January 2012. Randomised controlled trials (RCTs) or quasi-RCTs, prospective observational studies with controls, retrospective matched-pair studies, and comparative studies from well-defined registries/databases were included. The main outcomes were overall survival, cancer-specific survival, recurrence, and metastases. The Cochrane risk of bias tool was used to assess RCTs, and an extended version was used to assess nonrandomised studies (NRSs). The quality of evidence was assessed using Grading of Recommendations Assessment, Development, and Evaluation (GRADE). Evidence synthesis: A total of 4580 abstracts and 389 full-text articles were assessed. Thirty-four studies met the inclusion criteria (6 RCTs and 28 NRSs). Meta-analyses were planned but were deemed inappropriate due to data heterogeneity. There were high risks of bias and low-quality evidence across the evidence base. Open radical nephrectomy and open partial nephrectomy showed similar cancer-specific and overall survival, but when both open and laparoscopic approaches are considered together, the evidence showed improved survival for partial nephrectomy for tumours <= 4 cm. The overall evidence suggests either equivalent or better survival with partial nephrectomy. Laparoscopic radical nephrectomy offered equivalent survival to open radical nephrectomy, and all laparoscopic approaches achieved equivalent survival. Open and laparoscopic partial nephrectomy achieved equivalent survival. The issue of ipsilateral adrenalectomy or complete lymph node dissection with radical nephrectomy or partial nephrectomy remains unresolved. Conclusions: The evidence base suggests localised RCCs are best managed by nephron-sparing surgery where technically feasible. However, the current evidence base has significant limitations due to studies of low methodological quality marked by high risks of bias. (C) 2012 European Association of Urology. Published by Elsevier B. V. All rights reserved.
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