The Main Ethiopian Rift (MER) has developed during the 18 Ma‐Recent separation of the Nubian and Somalian plates. Extension in its central and northern sectors is associated with seismic activity and ...active magma intrusion, primarily within the rift, where shallow (<5 km) seismicity along magmatic centers is commonly caused by fluid flow through open fractures in hydrothermal systems. However, the extent to which similar magmatic rifting persists into the southern MER is unknown. Using data from a temporary network of five seismograph stations, we analyze patterns of seismicity and crustal structure in the Abaya region of the southern MER. Magnitudes range from 0.9 to 4.0; earthquake depths are 0–30 km. VP/VS ratios of ∼1.69, estimated from Wadati diagram analysis, corroborate bulk‐crustal VP/VS ratios determined via teleseismic P‐to‐S receiver function H‐κ stacking and reveal a relative lack of mafic intrusion compared to the MER rift sectors to the north. There is a clear association of seismicity with the western border fault system of the MER everywhere in our study area, but earthquake depths are shallow near Duguna volcano, implying a shallowed geothermal gradient associated with rift valley silicic magmatism. This part of the MER is thus interpreted best as a young magmatic system that locally impacts the geothermal gradient but that has not yet significantly modified continental crustal composition via rift‐axial magmatic rifting.
Plain Language Summary
The East African Rift in Ethiopia captures the transition from continental rifting in the south to incipient seafloor spreading in the north. A consensus has emerged over the past two decades that a significant proportion of extension in the Ethiopian rift is accommodated by magma intrusion, not faulting and plate stretching. However, in the southernmost, least mature, part of the rift, sub‐surface geophysical constraints are lacking, meaning where/how magmatic extension occurs is unknown. Using a new network of seismograph stations in the Lake Abaya region of the southern Main Ethiopian Rift, we constrain crustal thickness and the first earthquake catalog for the southern Main Ethiopian Rift. Earthquakes are mostly located along the western margin of the rift and persist to lower crustal depths. Only near the Duguna volcano are earthquakes confined to the upper crust, implying magmatic modification of the crust due to magmatic extension is not yet established in this rift sector.
Key Points
New seismograph network constraints seismicity and crustal structure in the southern Main Ethiopian Rift (MER)
Clear association of seismicity with the western border fault system, not in‐rift faults associated with the magmatic extension
Wadati diagram analysis and low receiver function‐derived bulk crustal VP/VS ratios reveal the southern MER is a magma‐poor rift sector
•We measured the CO2 and C balances of an intensively managed pasture in New Zealand.•Averaged over 4 years, the site was a sink for both CO2 (165gCm−2y−1), and total C (61gCm−2y−1).•Climatic ...conditions and farm management both had large impacts on CO2 and total C budgets.•Global data compilation revealed C sequestration generally increased with increasing NEP.
We estimated the net ecosystem carbon (C) balance (NECB) of a temperate pasture in the North Island of New Zealand for four years (2008–2011). The pasture was intensively managed with addition of fertiliser and year-round rotational grazing by dairy cows. Climatic conditions and management practices had a large impact on CO2 exchange, with a severe drought in one year and cultivation in another both causing large short-term (∼3 months) net losses of CO2–C (100–200gCm−2). However, CO2 was regained later in both of these years so that on annual timescales, the site was a CO2 sink or CO2 neutral. Management practices such as effluent application and harvesting silage also influenced non-CO2–C fluxes, and had a large impact on annual NECB. Despite these major environmental or management perturbations, both NEP and NECB were relatively constant on annual timescales. It is likely that this apparent resilience of the CO2 and C balance to perturbations was at least partly attributable to the relatively warm temperatures, also in winter, providing good growing conditions year-round (in the absence of major perturbations such as moisture stress). In several instances, the farmer’s decisions aimed at maintaining a constant milk yield between years also appeared to contribute to a relatively stable C balance.
Averaged over the full four-year study period, the site was a net sink for both CO2 (NEP=165±51gCm−2y−1), and total C (NECB=61±53gCm−2y−1) after non-CO2–C fluxes were accounted for. Annual NEP and NECB values were similar to results collated from other managed temperate grasslands on mineral soils globally, for which average NEP and NECB were 188±44gCm−2y−1 and 44±33gCm−2y−1, respectively. In the global dataset, we noted a general trend for increased C sequestration with increasing NEP, suggesting that it may be possible to meet the dual goal of increased pasture production (thus milk, meat and fiber production) and increasing soil C storage in managed temperate grasslands. Identification of management practices that increase C storage while maintaining or enhancing pasture production requires more standardised reporting between NECB studies, and experiments involving side-by-side comparison of treatment and control plots.
•We measured CO2 losses following cultivation of pasture for 3 cultivation events.•Short-term CO2 losses (<43 days) ranged between 3.9 and 7.8gCm−2d−1.•Rates of CO2 loss were generally higher than ...reported for other permanent pastures.•Net C loss from cultivated pasture (accounting for lost photosynthetic input) was up to 406gCm−2.•Rates of CO2 loss showed a strong positive relationship with soil moisture content.
It is well known that frequent cultivation of cropped soils leads to increased soil respiration and loss of soil carbon (C). In contrast, little is known about the impact of occasional cultivation of permanent grasslands on soil C and CO2 dynamics. Occasional cultivation of pastures is common if a pasture is part of an arable-ley rotation, or as part of pasture renewal.
Here we report on the CO2 balance following three cultivation events of temperate permanent pasture in New Zealand. For two experiments, one during a drought during late summer/autumn 2008 and one under moist soil conditions in spring 2008, CO2 losses following cultivation were measured using the closed chamber technique. During the spring 2008 experiment, two soils with different clay mineralogy and drainage were studied. During a third cultivation event in autumn 2010 CO2 exchange was measured using eddy covariance.
Measured short-term respiratory losses following cultivation across the three experiments ranged from 151 to 329gCm−2 over 39 to 43 days. Rates of CO2 loss measured during non-drought conditions were generally higher than those previously reported from studies in Europe and North America, presumably because of generally high soil temperatures, non-limiting moisture conditions and high organic carbon availability at our study site. The ‘net impact of cultivation’ (taking into account both direct respiratory losses of CO2 and the lack of photosynthetic carbon input following cultivation) across the three experiments ranged between 77 and 406gCm−2 over 39–43 days. Both direct CO2 respiratory losses and the net impact of cultivation appeared highly dependent on soil moisture status, with lowest losses measured during a severe drought and highest losses measured in spring when ample moisture was present. Rates of respiratory CO2 losses did not decrease over the duration of our experiments (39–43 days).
Our results suggest that when aiming to reduce C losses resulting from cultivation of permanent grassland, it is preferable to cultivate when conditions for soil microbial activity and photosynthesis are sub-optimal; for our study site this meant in autumn instead of spring because of lower soil moisture availability. We also recommend minimising the duration of the period between spraying the old sward and establishment of the new sward or crop.
Spin‐up of UK Earth System Model 1 (UKESM1) for CMIP6 Yool, A.; Palmiéri, J.; Jones, C. G. ...
Journal of advances in modeling earth systems,
August 2020, 2020-08-00, 20200801, 2020-08-01, Letnik:
12, Številka:
8
Journal Article
Recenzirano
Odprti dostop
For simulations intended to study the influence of anthropogenic forcing on climate, temporal stability of the Earth's natural heat, freshwater, and biogeochemical budgets is critical. Achieving such ...coupled model equilibration is scientifically and computationally challenging. We describe the protocol used to spin‐up the UK Earth system model (UKESM1) with respect to preindustrial forcing for use in the sixth Coupled Model Intercomparison Project (CMIP6). Due to the high computational cost of UKESM1's atmospheric model, especially when running with interactive full chemistry and aerosols, spin‐up primarily used parallel configurations using only ocean/land components. For the ocean, the resulting spin‐up permitted the carbon and heat contents of the ocean's full volume to approach equilibrium over 5,000 years. On land, a spin‐up of 1,000 years brought UKESM1's dynamic vegetation and soil carbon reservoirs toward near‐equilibrium. The end‐states of these parallel ocean‐ and land‐only phases then initialized a multicentennial period of spin‐up with the full Earth system model, prior to this simulation continuing as the UKESM1 CMIP6 preindustrial control (piControl). The realism of the fully coupled spin‐up was assessed for a range of ocean and land properties, as was the degree of equilibration for key variables. Lessons drawn include the importance of consistent interface physics across ocean‐ and land‐only models and the coupled (parent) model, the extreme simulation duration required to approach equilibration targets, and the occurrence of significant regional land carbon drifts despite global‐scale equilibration. Overall, the UKESM1 spin‐up underscores the expense involved and argues in favor of future development of more efficient spin‐up techniques.
Plain Language Summary
Earth system models (ESMs) are an important tool for understandingz the Earth and for projecting how climate change may affect natural and human systems. For simulations of ESMs to separate anthropogenic influences on climate from the background state, the stability of the unperturbed system is critical. However, achieving this equilibrium is both scientifically and computationally challenging. Here, we describe how this was achieved for one such model, UKESM1, for the sixth Coupled Model Intercomparison Project (CMIP6). Due to the cost of the full model, especially when running with atmospheric chemistry and aerosols, much of UKESM1's spin‐up to equilibrium made use of ocean‐ and land‐only configurations. Millennial‐scale spin‐up phases of these component‐only models were used to initialize a final centennial‐scale phase of the full model to reach preindustrial equilibrium targets. The stability and realism of UKESM1's spun‐up state was then evaluated across a broad range of properties. A number of lessons were drawn from this spin‐up including the extreme simulation duration required to reach equilibrium. A key conclusion is the importance of developing efficient techniques to spin‐up ESMs.
Key Points
Earth system components and spin‐up protocol of UKESM1 for CMIP6 outlined
Ocean‐only (5,000 years) and land‐only (1,000 years) phases used prior to fully coupled finalizing of spin‐up (500 year)
Evaluation of spin‐up protocol presented, including cross‐component validation of piControl state and drift
Given the mucosal transmission of HIV-1, we compared whether a mucosal vaccine could induce mucosal cytotoxic T lymphocytes (CTLs) and protect rhesus macaques against mucosal infection with ...simian/human immunodeficiency virus (SHIV) more effectively than the same vaccine given subcutaneously. Here we show that mucosal CTLs specific for simian immunodeficiency virus can be induced by intrarectal immunization of macaques with a synthetic-peptide vaccine incorporating the LT(R192G) adjuvant. This response correlated with the level of T-helper response. After intrarectal challenge with pathogenic SHIV-Ku2, viral titers were eliminated more completely (to undetectable levels) both in blood and intestine, a major reservoir for virus replication, in intrarectally immunized animals than in subcutaneously immunized or control macaques. Moreover, CD4+ T cells were better preserved. Thus, induction of CTLs in the intestinal mucosa, a key site of virus replication, with a mucosal AIDS vaccine ameliorates infection by SHIV in non-human primates.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
6.
Electron diffraction of tilted perovskites Reaney, Ian M.; Woodward, David I.
Acta crystallographica. Section B, Structural science,
August 2005, Letnik:
61, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Simulations of electron diffraction patterns for each of the known perovskite tilt systems have been performed. The conditions for the appearance of superlattice reflections arising from rotations of ...the octahedra are modified to take into account the effects of different tilt systems for kinematical diffraction. The use of selected‐area electron diffraction as a tool for perovskite structure determination is reviewed and examples are included.
An electron diffraction study performed on thin sections of CaxSr1 xTiO3 ceramics with compositions x = 0.2 and 0.5 has revealed diffraction patterns that are inconsistent with currently accepted ...space group symmetries. Here, the data are presented and alternative models suggested. It is proposed that CaxSr1 xTiO3 has the space group C 2/m at x = 0.2 and the space group P 21/m across the range 0.2 < x < 0.6. The sequence of phases across the solid solution is therefore proposed to be
We describe the HadGEM2 family of climate configurations of the Met Office Unified Model, MetUM. The concept of a model "family" comprises a range of specific model configurations incorporating ...different levels of complexity but with a common physical framework. The HadGEM2 family of configurations includes atmosphere and ocean components, with and without a vertical extension to include a well-resolved stratosphere, and an Earth-System (ES) component which includes dynamic vegetation, ocean biology and atmospheric chemistry. The HadGEM2 physical model includes improvements designed to address specific systematic errors encountered in the previous climate configuration, HadGEM1, namely Northern Hemisphere continental temperature biases and tropical sea surface temperature biases and poor variability. Targeting these biases was crucial in order that the ES configuration could represent important biogeochemical climate feedbacks. Detailed descriptions and evaluations of particular HadGEM2 family members are included in a number of other publications, and the discussion here is limited to a summary of the overall performance using a set of model metrics which compare the way in which the various configurations simulate present-day climate and its variability.
Abstract
Background
Dialysate sodium (DNa) prescription policy differs between haemodialysis (HD) units, and the optimal DNa remains uncertain. We sought to summarize the evidence on the agreement ...between prescribed and delivered DNa, and whether the relationship varied according to prescribed DNa.
Methods
We searched MEDLINE and PubMed from inception to 26 February 2020 for studies reporting measured and prescribed DNa. We analysed results reported in aggregate with random-effects meta-analysis. We analysed results reported by individual sample, using mixed-effects Bland–Altman analysis and linear regression. Pre-specified subgroup analyses included method of sodium measurement, dialysis machine manufacturer and proportioning method.
Results
Seven studies, representing 908 dialysate samples from 10 HD facilities (range 16–133 samples), were identified. All but one were single-centre studies. Studies were of low to moderate quality. Overall, there was no statistically significant difference between measured and prescribed DNa {mean difference = 0.73 mmol/L 95% confidence interval (CI) −1.12 to 2.58; P = 0.44} but variability across studies was substantial (I2 = 99.3%). Among individually reported samples (n = 295), measured DNa was higher than prescribed DNa by 1.96 mmol/L (95% CI 0.23–3.69) and the 95% limits of agreement ranged from −3.97 to 7.88 mmol/L. Regression analysis confirmed a strong relationship between prescribed and measured DNa, with a slope close to 1:1 (β = 1.16, 95% CI 1.06–1.27; P < 0.0001).
Conclusions
A limited number of studies suggest that, on average, prescribed and measured DNa are similar. However, between- and within-study differences were large. Further consideration of the precision of delivered DNa is required to inform rational prescribing.
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