The ‘suitcase hypothesis’: Can entrainment of meroplankton by eddies provide a pathway for gene flow between Madagascar and KwaZulu-Natal,South Africa?     

S Ockhuis  JA Huggett  G Gouws  C Sparks 《African Journal of Marine Science》2017,39(4):435-451

Similarities in the marine fauna found off the coasts of southern Madagascar and KwaZulu-Natal Province (KZN), South Africa, led to the development of the ‘suitcase project,’ with the aim of establishing whether eddies that form off southern Madagascar may package and transport biological material across the Mozambique Channel, facilitating connectivity and gene flow. Meroplankton (larval stages of fishes and benthic invertebrates) were collected on the Madagascan shelf and along a transect through a cyclonic eddy in the Mozambique Channel. The samples were analysed using microscopy and DNA barcoding, seeking to identify species known to be common to both the southeast coast of Madagascar and the east coast of South Africa and thereby to reveal potential indicators of connectivity between these regions. The greatest zooplankton biovolume in the upper 200 m occurred on the shelf, followed by in the western part of the eddy and in the region outside the eddy to the west, and was lowest in the region outside the eddy to the east. The meroplankton were dominated by taxa of coastal origin and these were also most abundant on the shelf and in the western part of the eddy, with the lowest abundances in the region outside the eddy to the east. The findings show greater zooplankton biovolumes and larval abundances and the presence of reef-associated larval assemblages on the Madagascan shelf and along the transect through the cyclonic eddy, providing support for the suitcase hypothesis that planktonic organisms are entrained within eddies as they propagate south-westwards of the Madagascan shelf.  相似文献   

Determination of physical and radiant meteor properties using PFISR interferometry measurements of head echoes     

Jonathan J. Sparks  Diego Janches  Michael J. Nicolls  Craig Heinselman 《Journal of Atmospheric and Solar》2010,72(16):1221-1230

Over the past decade, High Power and Large Aperture (HPLA) radars have been widely utilized for the study of sub-millimeter extraterrestrial particles via the detection of the meteor head-echo. These observations have been a successful tool in the study of the sporadic meteor background, however, they have been limited by the lack of precise knowledge of the particle's location within the radar beam and its absolute trajectory and velocity. This limitation prevents for example the accurate determination of the meteors radiant and orbit. Interferometry measurements of the head-echo has been proven to be a detection technique that satisfies this need. Unfortunately very few radars are capable of performing them. We have developed a methodology which takes advantage of the multi-receiving capabilities of the 450 MHz Poker Flat Incoherent Scatter Radar (PFISR) enabling us to utilize the phased array of crossed-dipoles as an interferometer. This new PFISR capability allows us to determine the instantaneous position of meteors within the radar beam. This enables us to determine absolute velocities and ultimately meteor radiant and orbit around the Sun. In this work, we present initial results from 9 h of observations during which 142 particles were individually detected by the three different receiving channels simultaneously. For these meteors absolute velocities were obtained and meteor dynamical, physical and radiant properties were derived.  相似文献   

Professional conduct of scientists during volcanic crises   总被引：1，自引：0，他引：1  

IAVCEI Subcommittee for Crisis Protocols: Chris Newhall · Shigeo Aramaki · Franco Barberi · Russell Blong · Marta Calvache · Jean-Louis Cheminee · Raymundo Punongbayan · Claus Siebe · Tom Simkin · Stephen Sparks · Wimpy Tjetjep  Chris Newhall 《Bulletin of Volcanology》1999,60(5):323-334

Stress during volcanic crises is high, and any friction between scientists can distract seriously from both humanitarian and scientific effort. Friction can arise, for example, if team members do not share all of their data, if differences in scientific interpretation erupt into public controversy, or if one scientist begins work on a prime research topic while a colleague with longer-standing investment is still busy with public safety work. Some problems arise within existing scientific teams; others are brought on by visiting scientists. Friction can also arise between volcanologists and public officials. Two general measures may avert or reduce friction: (a) National volcanologic surveys and other scientific groups that advise civil authorities in times of volcanic crisis should prepare, in advance of crises, a written plan that details crisis team policies, procedures, leadership and other roles of team members, and other matters pertinent to crisis conduct. A copy of this plan should be given to all current and prospective team members. (b) Each participant in a crisis team should examine his or her own actions and contribution to the crisis effort. A personal checklist is provided to aid this examination. Questions fall generally in two categories: Are my presence and actions for the public good? Are my words and actions collegial, i.e., courteous, respectful, and fair? Numerous specific solutions to common crisis problems are also offered. Among these suggestions are: (a) choose scientific team leaders primarily for their leadership skills; (b) speak publicly with a single scientific voice, especially when forecasts, warnings, or scientific disagreements are involved; (c) if you are a would-be visitor, inquire from the primary scientific team whether your help would be welcomed, and, in general, proceed only if the reply is genuinely positive; (d) in publications, personnel evaluations, and funding, reward rather than discourage teamwork. Models are available from the fields of particle physics and human genetics, among others.  相似文献   

A global analysis of cities’ geosocial temporal signatures for points of interest hours of operation     

Kevin Sparks  Gautam Thakur  Amol Pasarkar  Marie Urban 《International journal of geographical information science》2020,34(4):759-776

ABSTRACT

The temporal nature of humans interaction with Points of Interest (POIs) in cities can differ depending on place type and regional location. Times when many people are likely to visit restaurants (place type) in Italy, may differ from times when many people are likely to visit restaurants in Lebanon (i.e. regional differences). Geosocial data are a powerful resource to model these temporal differences in cities, as traditional methods used to study cross-cultural differences do not scale to a global level. As cities continue to grow in population and economic development, research identifying the social and geophysical (e.g., climate) factors that influence city function remains important and incomplete. In this work, we take a quantitative approach, applying dynamic time warping and hierarchical clustering on temporal signatures to model geosocial temporal patterns for Retail and Restaurant Facebook POIs hours of operation for more than 100 cities in 90 countries around the world. Results show cities’ temporal patterns cluster to reflect the cultural region they represent. Furthermore, temporal patterns are influenced by a mix of social and geophysical factors. Trends in the data suggest social factors influence unique drops in temporal signatures, and geophysical factors influence when daily temporal patterns start and finish.  相似文献   

Emplacement temperatures of pyroclastic and volcaniclastic deposits in kimberlite pipes in southern Africa     

Giovanni Fontana  Conall Mac Niocaill  Richard J. Brown  R. Stephen J. Sparks  Matthew Field 《Bulletin of Volcanology》2011,73(8):1063-1083

Palaeomagnetic techniques for estimating the emplacement temperatures of volcanic deposits have been applied to pyroclastic and volcaniclastic deposits in kimberlite pipes in southern Africa. Lithic clasts were sampled from a variety of lithofacies from three pipes for which the internal geology is well constrained (the Cretaceous A/K1 pipe, Orapa Mine, Botswana, and the Cambrian K1 and K2 pipes, Venetia Mine, South Africa). The sampled deposits included massive and layered vent-filling breccias with varying abundances of lithic inclusions, layered crater-filling pyroclastic deposits, talus breccias and volcaniclastic breccias. Basalt lithic clasts in the layered and massive vent-filling pyroclastic deposits in the A/K1 pipe at Orapa were emplaced at >570°C, in the pyroclastic crater-filling deposits at 200–440°C and in crater-filling talus breccias and volcaniclastic breccias at <180°C. The results from the K1 and K2 pipes at Venetia suggest emplacement temperatures for the vent-filling breccias of 260°C to >560°C, although the interpretation of these results is hampered by the presence of Mesozoic magnetic overprints. These temperatures are comparable to the estimated emplacement temperatures of other kimberlite deposits and fall within the proposed stability field for common interstitial matrix mineral assemblages within vent-filling volcaniclastic kimberlites. The temperatures are also comparable to those obtained for pyroclastic deposits in other, silicic, volcanic systems. Because the lithic content of the studied deposits is 10–30%, the initial bulk temperature of the pyroclastic mixture of cold lithic clasts and juvenile kimberlite magma could have been 300–400°C hotter than the palaeomagnetic estimates. Together with the discovery of welded and agglutinated juvenile pyroclasts in some pyroclastic kimberlites, the palaeomagnetic results indicate that there are examples of kimberlites where phreatomagmatism did not play a major role in the generation of the pyroclastic deposits. This study indicates that palaeomagnetic methods can successfully distinguish differences in the emplacement temperatures of different kimberlite facies.  相似文献   

The volatile content of hypabyssal kimberlite magmas: some constraints from experiments on natural rock compositions   总被引：1，自引：0，他引：1  

Richard A. Brooker  R. Stephen J. Sparks  Janine L. Kavanagh  Matthew Field 《Bulletin of Volcanology》2011,73(8):959-981

Kimberlites are volatile rich magmas that ascend from deep in the mantle at high velocities, then as they reach a ‘root zone’ at 1–3 km in depth they either discharge explosively through to the surface or stall to form dykes and sills. Understanding this eruptive behaviour is difficult due to a lack of data on volatile solubility, particularly at conditions where the magmas enter the ‘root zone’ (∼30–80 MPa). In this study, we perform experiments on some putative primary kimberlite magma compositions to assess the amount of CO₂ and H₂O retained if these compositions represent magma as it enters the root zone. At the conditions investigated (100–200 MPa and 1,275–1,100°C) the results suggest that none of these particular kimberlite compositions reproduce a magma that can retain the observed high volatile content when intruded at these pressures (∼4–8 km). In our experiments, the low volatile retention is due to a combination of factors including a high proportion of solid phases, none of which are volatile-bearing, and inadequate volatile solubilities in the subordinate amounts of melt present. Modelled solubilities also suggest that the dissolved volatile contents remain too low even at super-liquidus temperatures (i.e. 100% melt). For water, the higher values observed in natural rocks can be explained by the addition of H₂O associated with ubiquitous post-emplacement serpentinization. The high CO₂ contents in hypabyssal rocks are unlikely to be related to alteration. We suggest that most kimberlites originally had lower SiO₂ contents and as such may have been ‘transitional’ between silicate and carbonate melts. This results in both higher CO₂ solubilities and lower liquidus temperatures. For such compositions, it is possible that both CO₂ and water solubility may first decrease and then increase as magmas decompress and crystallize. Such unusual behaviour can help explain why kimberlite magmas can be very explosive or form shallow hypabyssal intrusions.  相似文献   

An application of Bayesian spatial statistical methods to the study of racial and poverty segregation and infant mortality rates in the US     

P. Johnelle Sparks  Corey S. Sparks  Joseph J. A. Campbell 《GeoJournal》2013,78(2):389-405

The infant mortality rate is a fundamental measure of population health used internationally. In the United States, the infant mortality rate is higher than what would be expected for a country of its affluence. We present an analysis of US county infant mortality rates using modern Bayesian spatial statistical methodologies. Our key predictors in our statistical analysis are residential racial and poverty segregation, measured by the dissimilarity, interaction and spatial proximity indexes. We use both Exploratory Spatial Data Analysis methods and Hierarchical Bayesian spatial regression models to examine the influences of these segregation measures on the infant mortality rate for each county, net of income inequality, degree of rurality and relative socioeconomic deprivation. The spatial measures of racial segregation suggest that when blacks live in close proximity to each other, this tends to increase the infant mortality rate. The results for poverty segregation suggest the same pattern, when poor populations live in close proximity to one another this is generally detrimental to the county infant mortality rate. However, interaction between blacks and whites and poor and non-poor residents of an area is protective for infant mortality.  相似文献   

A review of: “Geothermal systems”     

Herbert E. Huppert  R. Stephen  J. Sparks 《地球物理与天体物理流体动力学》2013,107(3-4):327-329

Abstract

By John W. Elder. Academic Press, 1981. 508 pp. ($20.60) (ISBN 0 12 236450.3).  相似文献   

Non-explosive,constructional evolution of the ice-filled caldera at Volcán Sollipulli,Chile     

J. S. Gilbert  M. V. Stasiuk  S. J. Lane  C. R. Adam  M. D. Murphy  R. S. J. Sparks  J. A. Naranjo 《Bulletin of Volcanology》1996,58(1):67-83

 A radar and gravity survey of the ice-filled caldera at Volcán Sollipulli, Chile, indicates that the intra-caldera ice has a thickness of up to 650 m in its central part and that the caldera harbours a minimum of 6 km³ of ice. Reconnaissance geological observations show that the volcano has erupted compositions ranging from olivine basalt to dacite and have identified five distinct volcanic units in the caldera walls. Pre- or syn-caldera collapse deposits (the Sharkfin pyroclastic unit) comprise a sequence which evolved from subglacial to subaerial facies. Post-caldera collapse products, which crop out along 17 of the 20 km length of the caldera wall, were erupted almost exclusively along the caldera margins in the presence of a large body of intra-caldera ice. The Alpehué crater, formed by an explosive eruption between 2960 and 2780 a. BP, in the southwest part of the caldera is shown to post date formation of the caldera. Sollipulli lacks voluminous silicic pyroclastic rocks associated with caldera formation and the collapse structure does not appear to be a consequence of a large-magnitude explosive eruption. Instead, lateral magma movement at depth resulting in emptying of the magma chamber may have generated the caldera. The radar and gravity data show that the central part of the caldera floor is flat but, within a few hundred metres of the caldera walls, the floor has a stepped topography with relatively low-density rock bodies beneath the ice in this region. This, coupled with the fact that most of the post-caldera eruptions have taken place along the caldera walls, implies that the caldera has been substantially modified by subglacial marginal eruptions. Sollipulli caldera has evolved from a collapse to a constructional feature with intra-caldera ice playing a major role. The post-caldera eruptions have resulted in an increase in height of the walls and concomitant deepening of the caldera with time. Received: 12 June 1995 / Accepted: 7 December 1995  相似文献   

Degassing during magma ascent in the Mule Creek vent (USA)   总被引：1，自引：1，他引：1  

Mark V. Stasiuk  Jenni Barclay  Michael R. Carroll  Claude Jaupart  James C. Ratté  R. Stephen J. Sparks  Stephen R. Tait 《Bulletin of Volcanology》1996,58(2-3):117-130

 The structures and textures of the rhyolite in the Mule Creek vent (New Mexico, USA) indicate mechanisms by which volatiles escape from silicic magma during eruption. The vent outcrop is a 300-m-high canyon wall comprising a section through the top of a feeder conduit, vent and the base of an extrusive lava dome. Field relations show that eruption began with an explosive phase and ended with lava extrusion. Analyses of glass inclusions in quartz phenocrysts from the lava indicate that the magma had a pre-eruptive dissolved water content of 2.5–3.0 wt% and, during eruption, the magma would have been water-saturated over the vertical extent of the present outcrop. However, the vesicularity of the rhyolite is substantially lower than that predicted from closed-system models of vesiculation under equilibrium conditions. At a given elevation in the vent, the volume fraction of primary vesicles in the rhyolite increases from zero close to the vent margin to values of 20–40 vol.% in the central part. In the centre the vesicularity increases upward from approximately 20 vol.% at 300 m below the canyon rim to approximately 40 vol.% at 200 m, above which it shows little increase. To account for the discrepancy between observed vesicularity and measured water content, we conclude that gas escaped during ascent, probably beginning at depths greater than exposed, by flow through the vesicular magma. Gas escape was most efficient near the vent margin, and we postulate that this is due both to the slow ascent of magma there, giving the most time for gas to escape, and to shear, favouring bubble coalescence. Such shear-related permeability in erupting magma is supported by the preserved distribution of textures and vesicularity in the rhyolite: Vesicles are flattened and overlapping near the dense margins and become progressively more isolated and less deformed toward the porous centre. Local zones have textures which suggest the coalescence of bubbles to form permeable, collapsing foams, implying the former existence of channels for gas migration. Local channelling of gas into the country rocks is suggested by the presence of sub-horizontal syn-eruptive rhyolitic tuffisite veins which depart from the vent margin and invade the adjacent country rock. In the central part of the vent, similar local channelling of gas is indicated by steep syn-eruption tuffisite veins which cut the rhyolite itself. We conclude that the suppression of explosive eruption resulted from gas separation from the ascending magma and vent structure by shear-related porous flow and channelling of gas through tuffisite veins. These mechanisms of gas loss may be responsible for the commonly observed transition from explosive to effusive behaviour during the eruption of silicic magma. Received: 24 May 1995 / Accepted: 13 March 1996  相似文献