Subaqueous pyroclastic flows and ignimbrites: an assessment

An assessment of the literature on subaqueous pyroclastic flows and their deposits shows that the term pyroclastic flow is frequently used loosely to describe primary, hot gas-rich pyroclastic flows, mass-flows which resulted from the transformation of gassupported flows into water-supported ones, and secondary mass-flows carrying redeposited pyroclastic debris. Based on subaerial pyroclastic flows, the term pyroclastic flow should be restricted to demonstrably hot, gas-rich mass-flows of pyroclastic debris. Using this definition, very few examples of subaqueous pyroclastic deposits with evidence for hot emplacement and of having been wholly submerged have been described. In the majority of these cases, the evidence for a hot state of emplacement and for the subaqueous nature of the host depositional environment is inadequate. The only unequivocal cases of hot pyroclastic flow deposits with adequate supporting evidence are the Ordovician nearshore, shallow marine ignimbrites of Ireland and Wales, and Miocene ignimbrites of southwest Japan, resulting from the passage of subaerially erupted pyroclastic flows into shallow water. Other possible examples are near-vent dense clast deposits in the Donzurobo Formation of Japan, possible submarine intra-caldera ponded ignimbrite successions in California and Wales, and near-vent pumiceous deposits of Ramsay Island, Wales. All other purported cases are either clearly the result of water-supported mass-flow transportation and deposition (debris avalanches, debris flows, turbidity currents), or lack adequate supporting evidence regarding the heat state or the palaeoenvironment. Only the shallow marine ignimbrites of Ireland and Wales show adequate evidence of welding, but even these could have been nearly wholly exposed above sea-level when welding occurred. We conclude that when pyroclastic flows enter water they are generally disrupted explosively and/or ingest water and transform into water-supported mass-flows, and we suggest the various scenarios in which this occurs. There is no evidence to suggest that welding in wholly subaqueous environments is common.     

Climate benefits of changing diet

Climate change mitigation policies tend to focus on the energy sector, while the livestock sector receives surprisingly little attention, despite the fact that it accounts for 18% of the greenhouse gas emissions and for 80% of total anthropogenic land use. From a dietary perspective, new insights in the adverse health effects of beef and pork have lead to a revision of meat consumption recommendations. Here, we explored the potential impact of dietary changes on achieving ambitious climate stabilization levels. By using an integrated assessment model, we found a global food transition to less meat, or even a complete switch to plant-based protein food to have a dramatic effect on land use. Up to 2,700 Mha of pasture and 100 Mha of cropland could be abandoned, resulting in a large carbon uptake from regrowing vegetation. Additionally, methane and nitrous oxide emission would be reduced substantially. A global transition to a low meat-diet as recommended for health reasons would reduce the mitigation costs to achieve a 450 ppm CO₂-eq. stabilisation target by about 50% in 2050 compared to the reference case. Dietary changes could therefore not only create substantial benefits for human health and global land use, but can also play an important role in future climate change mitigation policies.     

Global patterns of dissolved inorganic and particulate nitrogen inputs to coastal systems: Recent conditions and future projections

We examine the global distribution of dissolved inorganic nitrogen (DIN) and particulate nitrogen (PN) export to coastal systems and the effect of human activities and natural processes on that export. The analysis is based on DIN and PN models that were combined with spatially explicit global databases. The model results indicate the widely uneven geographic distribution of human activities and rates of nitrogen input to coastal systems at the watershed, latitudinal, and regional-continental scales. Future projections in a business-as-usual scenario indicate that DIN export rates increase from approximately 21 Tg N yr⁻¹ in 1990 to 47 Tg N yr⁻¹ by 2050. Increased DIN inputs to coastal systems in most world regions are predicted by 2050. The largest increases are predicted for Southern and Eastern Asia, associated with predicted large increases in population, increased fertilizer use to grow food to meet the dietary demands of that population, and increased industrialization. Results of an alternative scenario for North America and Europe in 2050 indicate that reductions in the human consumption of animal protein could reduce fertilizer use and result in substantial decreases in DIN export rates by rivers. In another scenario for 2050, future air pollution control in Europe that would reduce atmospheric deposition of nitrogen oxides in watersheds is predicted to decrease DIN export by rivers, particularly from Baltic and North Atlantic watersheds. Results of a newly developed global PN river export model indicate that total global PN and DIN export by rivers in 1990 are similar, even though the global distribution of the two differ considerably.     

Nutrient load estimates for Manila Bay,Philippines using population data

A major source of nutrient load to periodically hypoxic Manila Bay is the urban nutrient waste water flow from humans and industries to surface water. In Manila alone, the population density is as high as 19,137 people/km². A model based on a global point source model by Morée et al. (2013) was used to estimate the contribution of the population to nitrogen and phosphorus emissions which was then used in a water transport model to estimate the nitrogen (N) and phosphorus (P) loads to Manila Bay. Seven scenarios for 2050 were tested, with varying degrees and amounts for extent of sewage treatment, and population growth rates were also included. In scenario 1, the sewage connection and treatment remains the same as 2010; in scenario 2, sewage connection is improved but the treatment is the same; in scenario 3, the sewage connection as well as treatment is improved (70% tertiary); and in scenario 4, a more realistic situation of 70% primary treatment achieved with 100% connection to pipes is tested. Scenarios 5, 6, and 7 have the same parameters as 1, 2, and 3 respectively, but with the population growth rate per province reduced to half of what was used in 1, 2, and 3. In all scenarios, a significant increase in N and P loads was observed (varying from 27% to 469% relative to 2010 values). This was found even in scenario 3 where 70% of the waste water undergoes tertiary treatment which removes 80% N and 90% P. However, the lowest increase in N and P load into the bay was achieved in scenarios 5 to 7 where population growth rate is reduced to half of 2010 values. The results suggest that aside from improving sewage treatment, the continued increase of the human population in Manila at current growth rates will be an important determinant of N and P load into Manila Bay.

     

断裂引起的应变量计算方法

本文介绍了断裂引起的应变量计算方法。断裂作用可导致连续应变和非连续应变。连续应变与断裂位移,断裂长度比值及断裂面上有效应力成正相关关系。影响非连续应变的因素有：断裂几何形态、断裂的旋转性、断裂规模。已经提出三种断裂旋转机制：刚性旋转,垂直剪切和斜向剪切。对于这三种机制,我们分别建立了断裂非连续应变的计算公式。这些公式与断裂的旋转角度和位移大小相关。刚性旋转时,断块内部没有任何塑性变形,因此地层的长度没有变化。它引起的非连续应变最小。垂直剪切作用使断块内地层变形,但水平方向的地层长度不变。推算的公式表明,对于相同的原始数据,它引起的非连续应变比刚性旋转机制引起的非连续应变大。斜向剪切也使断块内地层变形,但水平方向的长度也不变。在同等条件下,它引起的非连续应变比垂直剪切机制引起的非连续应变大。     

On the ecology of meiofauna in an organically polluted estuarine mudflat

The structure, distribution and seasonal changes of the benthic meiofauna in an organically polluted, tidal, brackish-water mudflat in the Ems-Dollart estuary were analysed. Towards the outfall of polluted fresh water, macrofauna disappeared, numbers of meiofauna increased but the diversity of the meiofauna decreased. In the area surrounding the outfall the numbers and biomass of nematodes and oligochaetes increased rapidly in spring and remained high until autumn (c. 13 × 10⁶ individuals m⁻²; c. 2gCm⁻²). The benthic fauna comprised small numbers of species, dominated by a few fast-growing diatom-feeding nematodes (Eudiplogaster pararmatus and Dichromadora geophila) and oligochaetes (Amphichaeta sannio and Paranais litoralis). Eudiplogaster pararmatus exhibits brood care and it tolerates low salinities. Dichromadora geophila which is oviparous, behaved similarly regarding tolerances, life cycle and feeding but this species was less successful than Eudiplogaster in colonizing the mudflats near the outfall. The success of the two naidid oligochaete species results from their method of reproduction by means of binary fission.Most organisms fed on benthic diatoms. In spite of intensive mineralization in the mudflat, only one bacteria-feeding organism was found in abundance (the nematode Leptolaimus papilliger). The absence of macrofaunal organisms, e.g. Nereis diversicolor, is probably also responsible for the development of high densities of meiofauna in the upper sediment layers of the mudflats in the vicinity of the outfall.The heavy load of organic waste entering the Dollart reduced the diversity within the benthic ecosystem, but nevertheless a simple system remained, based on the recurrent reoxidation of the sediment surface.     

On the pre-supernova parameters of the Hercules X-1 system

On the assumption that, at the moment of the supernova explosion, the presently nondegenerate companion of Her X-1 was a Main-Sequence star with polytropic indexn=3, it is found that the effects of impact and ablation cannot have removed more than about 10% of its pre-supernova mass. A remnant mass for a neutron star of 1.4M was adopted. The effects of impact and ablation were calculated in the manner given by Wheeleret al. (1975). Depending on the ejection velocity of the SN shell, it is found that with a pre-SN mass of 2.2M (i.e., the maximum possible value) for the non-degenerate component, the initial binary period was in the range 2–4 days.     

Submillimeter Studies of Prestellar Cores and Protostars: Probing the Initial Conditions for Protostellar Collapse

Improving our understanding of the earliest stages of star formation is crucial to gain insight into the origin of stellar masses, multiple systems, and protoplanetary disks. We discuss recent advances made in this area, thanks to submillimeter mapping observations with large single-dish telescopes and interferometers. Although ambipolar diffusion appears to be too slow cores, there is nevertheless good evidence that the gravitational collapse of isolated protostellar cores is strongly magnetically controlled. We also argue that the beginning of protostellar collapse is much more violent in cluster-forming clouds than in regions of distributed star formation.